In This Post we are providing Chapter-5 PRINCIPLE OF INHERITANCE AND VARIATION NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON PRINCIPLE OF INHERITANCE AND VARIATION
1. A woman with O blood group marries a man with AB blood group (i) work out all the possible phenotypes and genotypes of the progeny. (ii) Discuss the kind of dominance in the parents and the progeny in this case. Ans. (i) Blood group AB has alleles as IA, IB and O group has ii which on cross gives the both blood groups A and B while the genotype of progeny will be IAi and IBi. (ii) IA and IB are equally dominant (co-dominant). In multiple allelism, the gene I exists in 3 allelic forms, IA, IB and i.
2. Explain the cause of Klinefelters syndrome. Give any four symptoms shown by sufferer of this syndrome. Ans. Cause : Presence of an extra chromosome in male i.e., XXY. Symptoms : Development of breast, Female type pubic hair pattern, poor beard growth, under developed testes and tall stature with Feminized physique.
3. In Mendels breeding experiment on garden pea, the offspring of F2 generation are obtained in the ratio of 25% pure yellow pod, 50% hybrid green pods and 25% green pods State (i) which pod colour is dominant (ii) The Phenotypes of the individuals of F1 generation. (iii) Workout the cross. Ans. (i) Green pod colour is dominant (ii) Green pod colour Phenotypic ratio 3 : 1 Genotypic ratio 1 : 2 : 1
4. In Antirrhinum majus a plant with red flowers was crossed with a plant with white flowers. Work out all the possible genotypes & phenotypes of F1 & F2 generations comment on the pattern of inheritance in this case? Ans. The inheritance of flower colour in snapdragon or Antirrhinum majus is an example of incomplete dominance. When a cross was made between a red flowered plant & a white flowered plant, the F1hybrid was pink i-e-an intermediate between red & white which means that both red & white are incompletely dominant. When F1 individuals was self – pollinated, the F2 generation consists of red, pink & white flower appears in ratio 1:2:1 respectively.
5. A red eyed male fruitfly is crossed with white eyed female fruitfly. Work out the possible genotype & phenotype of F1 & F2 generation. Comment on the pattern of inheritance in this cross? Ans. When a red eyed is crossed with white eyed female fruitfly, offspring will have both white eyed male & red eyed female in 1:1 ration in F1 generation. In F2 generation, 50% females will be red – eyed & 50% will be white eyed, similarly, in males 50% will be red eyed & 50% will be white eyed. This result indicates that in sex-linked genes, males transmit their sex-linked characters to their grandson through their daughter; such type of inheritance is called criss-cross inheritance –
6. A man with AB blood group marries a woman with O group blood. (i) Work out all the possible phenotypes & genotypes of the progeny. (ii) Discuss the kind of domination in parents & progeny in this case? Ans. (i) Half the progeny will have blood group A with genotype IA IO & half the progeny will have blood group B with genotype IB IO. (ii) IA & IB both the genes are dominant over IO gene hence progeny shows either blood group A or B while in parents since both the dominant genes are present together man will have blood group AB & this phenomena is called co-dominance.
7. In an cross made between a hybrid tall & red plant (TtRr) with dwarf & white flower (ttrr). What will be the genotype of plants in F1 generation? Ans.
8. In dogs, barking trait is dominant over silent trait & erect ears are dominant over drooping ears. What is the expected phenotypic ratio of offspring when dogs heterozygous for both the traits are crossed? Ans. Ration :- Barking & erect = 9 Barking & drooping =3 Silent & erect = 3 Silent & drooping =1 Phenotypic ratio = 9 : 3 : 3 : 1
9. Differentiate between dominance, co-dominance & Incomplete dominance with one example each. Ans. (i) Dominance :- When a cross is made between true – breeding tall pea plant & true – breeding dwarf pea plant, all the plants in F1 generation are tall this sows that tall character is dominant over dwarf (ii) Co-dominance :- If the two equally dominant genes are present together, both of them will be equally expressed, this phenomena is called co-dominance eg alleles of blood group IA & IB ore dominant over IO but when both the alleles are present together, both of them will equally express & forms a phenotype AB. (iii) In complete dominance :- When a cross is made between two characters of which none of them is completely dominant then an intermediate character develops in the progeny eg. when a cross is made between red flower & white flower in snapdragon flower an intermediate pink colour appears in the progeny
10. A dihybrid heterozygous tall & yellow pea plant was crossed with double recessive plant. (i) What type of cross is this? (ii) Work out the genotype & phenotype of progeny (iii) What principle of Mendel is illustrated through result of this cross? Ans. (i) Test cross. (ii) (iii) Principle of Independent Assortment – Acc to which, in the inheritance of contrasting characters the factors of each pair of character segregate independently of the factors of the other pair of characters.Search for:
In This Post we are providing Chapter-4 REPRODUCTIVE HEALTH NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON REPRODUCTIVE HEALTH
Question 1. Define population. What are the aims of the population study?
Answer: The population is defined as the total number of individuals of a species present in a particular area. The members of a population have some common characteristics, share a common gene pool, and are capable of interbreeding among themselves to produce fertile offsprings. Aims of Population Study. An alarming rise in the human population has created many serious problems. Therefore, population education has been introduced into the school and college curricula.
Population education is aimed at making the students aware of the:
consequences of uncontrolled population growth such as environmental pollution, depletion of natural resources, extinction of species, etc ;
benefits of lowering population growth rate to the biosphere ;
advantages of a small family to humans ;
growth, distribution, and density of population ;
relation of population to the standards of life.
Question 2. Define birth rate, death rate, and fertility rate.
Answer: 1. Birth or natality rate: It is generally expressed as the number of births per 1,000 individuals of a population per year. It increases the population size (total number of individuals of a population) and population density.
The national average birth rate in India is about 28.6 per 1,000 per year. Among Indian states, Kerala has the lowest birth rate of 18 per 1,000, while U.P. has the highest of 34.8 per 1,000. 2. Death or mortality rate: It is the opposite of the natality rate. It is commonly expressed as the number of deaths per 1,000 individuals of a population per year. 3. Fertility rate: It is the number of live births per unit time per unit number of fertile females. Fertility Rate h
Question 3. What is family planning? List the ways of family planning:
Answer: Family planning: The main objective of family planning or family welfare program is to prevent the fertilization of the ovum by the male sperm and stop the increase in population growth by various methods, such as contraceptives, intrauterine devices, vasectomy, and tubectomy. The contraceptives (Anirudh) for males and intra-uterine devices, loop for females are used to avoid pregnancy.
Vasectomy is the method of sterilizing males by surgical operation of sperm duct or vas deferens. Tubectomy is the method of sterilizing females by the surgical operation of fallopian tubes. Whatever the method employed, it must take care of the health of the persons concerned.
Because of the family planning methods, the birth rate in India is reduced to some extent. The government gives incentives to those who adopt family planning.
Ways of family planning:
Late marriage for young persons.
Increase in the sources of recreation so as to divert the attention from sex.
The couple should not mate between 8-18th days from the start of the menstrual cycle.
Use of contraceptives.
Sterilization.
Use of drugs.
Abortion.
Restrict the family to two children.
Question 4. Suggest the various measures of population control:
Answer: Population control: Population explosion can be checked by two methods-population education and birth control.
A. Population education: The knowledge about the relationship of population size and the availability of resources for the welfare of the society is called population education.
The students should be convinced about the relationship between overpopulation and unemployment.
The citizens should be told how the large size of the population is eating away the resources of the state and the reasons for the limited availability of healthcare, education facilities, and other welfare schemes.
People should be made aware of how a large number of children eat away the meager resources of the family with nothing left for bad days, how large families rely on indebtedness to meet emergencies, how child bread earners do not improve the conditions of the family, how uneducated children remain a burden on the society, etc. They should be convinced that a small family can live comfortably even with meager resources.
B. Birth control:
Mass media of communication. Radio, television, newspapers, magazines, hoardings, and posters should be employed to spread the message of family planning and birth control and its advantages. The future of mankind depends on the stabilization of the human population at a level that ensures basic necessities of life, employment, and happiness,
The law about marriageable age should be widely published and strictly enforced (21 years for boys and 18 years for girls). In developed countries, women marry at the age of 25-35 years.
As far as possible, stress should be laid on raising the social status of women. Women having higher social status prefer smaller families. Such women generally marry late.
Remove the superstitions and wrong beliefs in the society about a higher number of children being God’s gift connected with earthly or heavenly prosperity.
Question 5. What is amniocentesis? Write its procedure and significance:
Answer: Amniocentesis is a fetal sex determination test based upon the chromosomal pattern in the amniotic fluid surrounding the developing embryo. It should be legally banned throughout the country as such a ban shall check increasing female foeticide cases and maintain a normal sex ratio in the country.
Procedure:
The fetus bathes in the amniotic fluid that fills the amniotic cavity. At an early stage of pregnancy (14th or 15th week), the location of the fetus and placenta is determined by sonography (use of high-frequency sound waves).
Then a small amount of amniotic fluid is drawn by passing a special surgical syringe needle through the abdominal wall and uterine wall into the amniotic sac containing the amniotic fluid.
Celts that have sloughed from the fetus’s skin or respiratory tract into the fluid are thus sucked into the syringe.
Significance:
These cells can be examined for chromosomal abnormalities, such as Down’s syndrome, Klinefelter’s syndrome, Turner’s syndrome, etc resulting from non-disjunction during cell division.
The cells can also be cultured and in about a fortnight enough cells become available for test. The cells and fluid are also tested for metabolic disorders such as phenylketonuria, sickle-cell anemia, etc.
Question 6. Write a note on test-tube babies:
Answer: Test-Tube Babies: In some women normal conception is not possible because of blocked oviducts or spermicidal secretions in the vagina or the low sperm count of the husband. In such cases, her ovum is removed, fertilized by her husband’s sperm in a laboratory dish, checked that development has begun, and a morula (up to 32 cell stage) replaced or implanted in her uterus.
The entire operation is carried out under sterilized conditions. With proper medical care, she will give birth to a normal child on the completion of gestation. The baby produced in this manner (conceived out of and nursed in the uterus) is called a test-tube baby. The baby is not reared in the test tube. A scientific term for this procedure is in vitro (“in glass”) fertilization
The success rate of the technique is less than 20%. To increase the chances of success, the prospective mother is given fertility drugs which cause many ovarian follicles to mature at the same time. This releases many eggs simultaneously, thereby increasing the chances of success.
Question 7. Reproductive and Child Healthcare (RCH) programs are currently in operation. One of the major tasks of these programs is to create awareness amongst people about the wide range of reproduction-related aspects. This is important and essential for building a reproductive health society. 1. “Providing sex education in schools is one of the ways to meet this goal.” Give four points in support of your opinion regarding this statement.
Answer: Sex education is important in schools: (a) to provide the right information about myths and misconceptions. (b) to create awareness about reproduction. (c) to provide knowledge about the growth of reproductive organs and sexually transmitted diseases (STDs) (d) to guide the students about social evils such as sex abuse, sex-related crimes, etc.
(ii) List any two indicators that indicate a reproductively healthysociety. Answer: Indicators about a reproductively healthy society. (a) Low infant mortality rate (IMR) (b) Low maternal mortality rate (MMR)
Increased number of couples with small families.
Better detection and cure of STDs.
Question 8. Give a brief account of Assisted Reproductive Technologies (ART).
Answer: Where corrective treatments are not available, there are special techniques called Assisted Reproductive Technologies (ART) to help the couple produce children; they are as follows: 1. Test-Tube baby programs: (a) In this method, ovum from the wife or a donor female and the sperms from the husband or a donor is allowed to fuse under simulated conditions (as that of the body) in the laboratory; it is called in vitro fertilization (IVF).
2. The zygote or early embryo is transferred into the uterus or fallopian tube for further development; this process is called Embryo Transfer (ET) and can be done in the following ways: (a) The zygote or embryo up to eight blastomeres is transferred into the fallopian tube; it is called Zygote Intra Fallopian Transfer (ZIFT). (b) Embryos with more than eight blastomeres are transferred into the uterus. It is called Intrauterine Transfer (IUT).
3. Gamete Intra Fallopian Transfer (GIFT): This method involves the transfer of an ovum collected from a donor female into another female, who cannot produce ova, but can provide suitable conditions for fertilization and further development of the fetus up to parturition.
4. Intra Cytoplasmic Sperm Injection (ICSI): In this method, the sperm is directly injected into the ovum to form an embryo in the laboratory, and then embryo transfer is carried out.
5. Artificial insemination: (a) In this method, the semen collected from the husband or a healthy donor is artificially introduced into the vagina or into the uterus (intrauterine insemination). (b) This method is used in cases where infertility is due to the inability of the male partner to inseminate the female or due to very low sperm counts in the ejaculates.
Question 9. It is commonly observed that parents feel embarrassed to discuss freely with their adolescent children about sexuality and reproduction. The result of this parental inhibition is that the children go astray sometimes. (i) Explain the reasons that you feel are behind such embarrassment amongst some parents to freely discuss such issues with their growing children.
Answer: Parents feel embarrassed because of the following reasons: (a) Indian society is not that broad-minded. So parents feel shy talking openly about these matters to their children. (b) Improper communication and age gap are the reasons behind such embarrassment.
(ii) By taking one example of a local plant and animal, how would you help these parents to overcome such inhibitions about reproduction and sexuality? Answer: Parents can take the example of China rose to explain the process of sexual reproduction. They can also take an example of the male honeybee and orchid Ophrys flower.
It is evident that sexual attraction is a natural phenomenon. The honeybee is attracted to an Ophrys flower and assumes its one petal as its female partner and pseudo copulate with it. So it is a natural phenomenon and parents should talk regarding this matter to their children.
Question 10. (a) Explain one application of each one of the following: (A) Amniocentesis:
Answer:
Detection of a genetic disorder
Detection of chromosomal disorder
Sex determination
Karyotyping (used for detecting chromosomal aberrations)
(B) Lactational amenorrhea: Answer: It is a kind of natural contraception to prevent pregnancy. When the women breastfeed regularly her menstrual cycle stops for some period and thus can’t have a baby.
(C) ZIFT: Answer: Application of ZIFT (Zygote Intrafallopian Transfer)- In vitro fertilization, the zygote or early embryos at eight blastomeres stage are transferred to the fallopian tale to complete its further development inside the body of the mother. Hence this method is very helpful for infertile couples.
(b) Prepare a poster for the school program depicting the objectives of the “Reproductive and Child Health Care Programme”. Answer: Reproductive and Child Health Care:
Objectives of RCH:
Creating awareness about various reproduction-related problems.
Providing facilities and support for building up a reproductively healthy society.
Providing audio-visual and print, media support, to various government and non-government organizations.
Educating the people and providing the right information to save them from myths and misconceptions.
Providing proper education regarding reproductive organs, adolescence and related changes, safe and hygienic sexual practices.
Providing information regarding the danger of sexually transmitted diseases, AIDS, etc.
Awareness regarding that gender selection and detection is punishable.
Example – Hum do hamare do, Beti bachao beti padhao, Do boond zindasi ke etc.
In This Post we are providing Chapter-3 HUMAN REPRODUCTION NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON HUMAN REPRODUCTION
1. Differentiate between spermatogenesis and oogenesis. Ans.
Spermatogenesis
Oogenesis
1. It occurs inside the testes.
1. It occurs inside the ovary.
2. All the stages are completed inside the testes.
2. Majority occurs inside the ovary but last stages occur in the oviduct.
3. Spermatogonia develop from the germinal epithelium lining in the seminiferous tubules.
3. Oogonia develop from the germinal epithelium overlying the ovary.
4. All spermatogonia give rise to spermatocytes.
4. Only few oogonia give rise to oocytes.
5. Primary spermatocytes divide by meiosis I to give rise to two secondary spematocytes
5. Primary oocyte undergoes meiosis I to give rise to one secondary oocyte and a polar body.
6. Secondary spermatocyte divides by meiosisII to give rise to two spermatids.
6. Secondary oocyte divides by meiosisII to form the ovum and the second polar body.
7. Each spermatid differentiates into spermatozoan or sperm.
7. No differentiation is required after meiosisII.
8. The sperms formed are motile.
8. The ovum or egg is non- motile.
2. ‘A fertilized egg is the blue print of future development’. Explain Ans. The sperm carries the genetic information from the father in form of 23 chromosomes (including the male sex chromosome X or Y) while the egg bears the genetic information from the mother (including the female sex chromosome X). Thus during fertilization the fusion of the male and the female gametes produce new genetic combination which introduces variation in the progeny. The zygote or the fertilized egg contain the genetic information which accordingly controls the development of the embryo.
3. Briefly describe the stages of spermatogenesis in human? Ans. Spermatogenesis consists of two phases:- I. FORMATIDN OF SPERMATIDS :- It further consist of 3 phases
Multiplication phase :- undifferentiated germ cells undergo repeated division to produce sperm mother cell or spermatogonia.
Growth phase :- Spermatogonia increase in volume & is now called PRIMARY SPERMATOCYTES.
Maturation phase: – primary spermatocyte undergoes meiosis I to produce small size haploid secondary spermatocyte secondary spermatocyte divides by meiosis – II & forms haploid Spermatids.
II.FORMATION OF SPERMS :- The tramsformation or differentiation of spermatids into spermatozoa or sperm is called spermiogenesis & occurs under the influence of FSH
4. Describe the hormonal control of human male reproduction system with the help of a flow chart & highlight the inhibitory & stimulatory directions in it? Ans. i) Spermatogenesis is initiated due to an increase in the secretion of Gonadotropin releasing hormone from hypothalamus at the age of puberty.
The increased levels of GnRH act on anterior pituitary& stimulate the secretion of two gonadotropins i-e. leuteinizing hormone (LH) & follicle stimulating hormone (FSH)
LH acts on leydig cells & stimulate them to secrete testosterone
FSH acts on sertoli cells & stimulate secretion of some factors help in spermiogenesis
5. A sperm has just fertilized a human egg in the fallopian tube. Trace the events that the fertilized eggs will undergoes upto implantation of blastocyst in the uterus. Ans. 1. CLEAVAGE :-Fertilized egg starts dividing lay specific mitotic divisions called cleavage. The zygotes undergoes mitotic division in the isthmus of oviduct to form daughter cell the cells formed as a result of cleavage called blastomere 2. BLASTOCYST :- 3-4 days after fertilization, the morula twins into large mass of cells called blastocyst Outer peripheral cells enlarge & flatten further & form trophoblast. Trophoblast cells secretes a fluid into interior & form a cavity called blastocoel. The embryonic stage with blastocoels is called blastula.
6. Where oogenesis does takes place. Describe the stages of this process? Ans. The process of formation & maturation of ovum is called oogenesis. It takes place in ovary & is initiated during embryonic development of female foetus. It consists of 3 phases :–
Multiplication phase :- The primordial germ cells divide by meiosis to produce oogonia. These oogonia divide lay repeated mitotic divisions forming clusters. In each cluster only one of them enters into growth phase & is called primary oocyte.
Growth phase :- Growth phase occurs only after attainment of puberty. It involves – increase in size of oocyte to many folds & synthesis of you.
Maturation phase :- The first division is meiotic as a result two haploid (n) cells are produced. In this division, cytobinesis is unequal, large daughter cell with almost all cytoplasm is called secondary oocyte & smaller me with less cytoplasm is called polar body. The secondary oocyte then undergoes second meiotic division to form an ovum & second polar body.
7. Ans. (i) ’D’ Spermatids = undergo spermiogenesis (ii) ‘A’= Spermatogonium; B = Primary spermatocyte (iii) ‘B’ = Diploid E = Haploid (iv) ‘F’ = Sertoli cells – Nutrition to germ cells (v) Mitosis in Cell ‘A’, Meiosis in cell ‘B’
8. Explain the development of human embryo with diagrams. Ans. The Fusion of the sperm and the egg in humans result into formation of the diploid structure called zygote. The zygote starts dividing mitotically as it moves through the oviduct into the uterus to form 2,4,8,16 daughter cells called blastomeres. The stage is called morula. The Morula divides further and differentiates into blastocysts. The outer layer of blastomeres called trophoblast gets attached to the endometrial layer of the uterus. The uterine wall divides and encloses the blastocysts and this is referred to as implantation. The inner layer of blastomeres in the blastocysts gives rise to the embryo.
9. What is menstruation? What are the specific actions of FSH, LH, estrogen & progesterone in menstrual cycle? Ans. During menstrual phase of menstrual cycle which starts on 28th day the endometrial lining of female genital tract break down due to lack of progesterone As a result bleeding occurs. This monthly flow of blood is caller menstruation. During menstrual cycles, the various changes occurs in the ovary under the influence of various hormones :-
Menstrual phase :- The levels of hormones LH ,FDH estrogen & progesterone is very less which results in breakdown of endometrial lining of uterus.
Follicular phase :- In this phase , the levels of pituitary hormones FSH & LH increases which causes ovarian hormone estrogen to release,. FSH controls the follicular phase , it stimulates the growth of follicles. Both FSH & LH reach their peak level in middle of cycle (14th day)
OVULATORY PHASE :- The level of LH hormones reaches its peak (called LH swing) induces the ruptures of mature Graffian follicle & there by release of ovum
Luteal phase :- The LH & FSH hormones begins to decline. After ovulation, the follicle becomes to ruptures & is transformed into corpus Luteum which secretes large quantities of progesterone
10. A woman has conceived & implantation has occurred within her uterus. Discuss the sequence of changes up to parturition which will take place within her body under the influence of various hormones. Ans. The following changes takes place in the body of women after implantation :-
The trophoblast differentiates into two layers outer layer secretes enzymes to dissolve the endometrium of uterus.
The inner layer grows out as finger – like projections called chorionic villi into uterine stoma. The chorionic villi & the uterine tissue become inter digitated to form structural & functional unit called placenta.
Placenta secretes hormones like HCG, HPL , estrogen & progesterone that are necessary to maintain pregnancy
Umbilical cord, the structure that connects the placenta with the foetus is formed.
Simultaneously, inner cell mass differentiates into outer layer called ectoderm & inner layer called endoderm. & a middle layer called mesoderm appears between ectoderm & endoderm.
The primary germ layers give rise to all the tissues & organs of the adults e.g. after one month heart is formed & after second month digits & limbs are formed.
By the end of ninth month of pregnancy, foetus is completely developed & is ready for delivery.
During parturition, ovary secretes a hormone called relaxin that facilitates parturition which softens the connective tissue. Mild contraction called foetal ejection reflex is induced. This triggers release of oxytocin from posterior pituitary. Oxytocin induces stronger leads to expulsion of baby from uterus, through birth canal.
In This Post we are providing Chapter-1 REPRODUCTION IN ORGANISM NCERT MOST IMPORTANT QUESTIONS for Class 112BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON REPRODUCTION IN ORGANISM
Question 1. Define: (i) juvenile phase,
Answer: Juvenile phase. The period of growth in the life of organisms before they start reproducing sexually and attain a level of maturity is called juvenile phase. It is followed by the reproductive phase.
(ii) reproductive phase Answer: Reproductive phase. The period of active reproductive behaviour, when the organisms show marked morphological and physiological changes is called reproductive phase. It is followed by senescence phase.
(iii) senescence phase. Answer: Senescence phase. The period when the reproductive phase ends and concomitant changes occur in the body such as slowing of metabolism is called senescence phase. It is followed by death.
Question 2. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Answer: 1. Differences between asexual reproduction and sexual reproduction.
Asexual Reproduction
Sexual Reproduction
1. The process involves only one cell or one parent.
1. This process involves two cells or gametes belonging to either the same or different parents.
2. The whole body of the parent may act as a reproductive unit or it can be a single cell or a bud.
2. The reproductive unit is called gamete which is unicellular and haploid.
3. The offspring are genetically similar to the parent.
3. The offspring differ from the parents.
4. Only mitotic division takes place.
4. Meiosis and mitosis both take place.
5. No formation of sex organs.
5. Formation of sex organs is essential.
6. No evolutionary significance.
6. It introduces variation; hence it is of evolutionary significance.
2. Vegetative reproduction is also considered a type of asexual reproduction because it does not involve meiotic division and there is no formation and fusion of gametes.
Question 3. How does an encysted Amoeba reproduce on the return of favourable conditions?
Answer: Multiple fission in encysted Amoeba:
Amoeba withdraws pseudopodia and secretes a cyst wall around itself. This phenomenon is called encystation.
Amoeba divides by multiple fission.
It produces a large number of pseudo- conidiospores.
The cyst wall breakdown.
The spores are liberated and settle down on suitable substrates and grow as amoebae. This process is also called sporulation.
Question 4. Discuss the advantages and disadvantages of asexual reproduction.
Answer: Advantages of asexual reproduction:
It involves simple mitotic division in single-parent and it may produce a large number of young ones.
Young ones produced by asexual methods are genetically similar to the parent.
It helps in the dispersal of offspring to far off places.
Disadvantages of asexual reproduction.
The young ones thus produced do not possess much capacity to adapt rapidly to the environmental changes taking place in quick succession.
No genetic recombination occurs; thus no variation occurs.
Question 5. Discuss the advantages and disadvantages of sexual reproduction.
Answer: Advantages of sexual reproduction:
Genetic recombination, interaction, etc. take place which causes variations in the offspring, thus also form raw materials for evolution.
The offspring adapt more comfortably and quickly to the change in environmental conditions and have better chances of survival.
Disadvantages of sexual reproduction. Usually, two parents of opposite sexes are required (except in hermaphrodite).
Question 6. List various methods of natural vegetative propagation. Give examples:
Answer:
Vegetative propagation by stems, e.g.Grasses, Turmeric, Onion, Colocasia, Potato, Gladiolus and Crocus.
Vegetative propagation by roots, e.g. Murraya sp., Albizzia Lebbac, Dalbergia sissoo, Tuberous roots of sweet potato, Asparagus, Tapioca, Dahlia and Yams (Dioscorea).
Vegetative propagation from reproductive organs. Flower buds of century plant (Agave sp.) develop into bulbils.
Question 7. Define external fertilisation. Mention its disadvantages:
Answer: The fertilisation in which the fusion of gametes occurs outside the body of the female in an external medium, i.e. water, is called external fertilisation.
Examples. Bony fishes, amphibians, etc. Organisms that exhibit external fertilisation show great synchrony between the sexes in order to liberate the gametes at the same time.
Disadvantages of external fertilisation:
A large number of gametes are produced to ensure fertilisation, thus there is wastage.
The offspring formed are extremely vulnerable to predators, thus threatening their survival up to adulthood.
Question 8. Explain the process of budding in yeast.
Answer: Budding in yeast. It is a common type of vegetative reproduction. In a medium which is abundantly supplied with sugar, yeast cytoplasm forms a bud-like outgrowth. The growth soon enlarges and a part of the nucleus protrudes into the bud and breaks off. The bud then begins to grow and then separates from the mother cell. Often it will itself form a bud before it breaks away, and straight or branched chains are produced.
Thus, as a result, branched or unbranched chains of cells called pseudo my cilium are produced. The cells are loosely held together. Sooner or later they become independent.
Question 9. Describe the importance of vegetative propagation.
Answer: Merits of vegetative propagation:
Plants produced by vegetative propagation are genetically similar and constitute a uniform population called a clone.
Plants with reduced power of sexual reproduction, long dormant period of seed, poor viability, etc. are multiplied by vegetative methods.
Some fruit trees like banana and pineapple do not produce viable seeds. So these are propagated by only vegetative methods.
It is a more rapid and easier method of propagation.
Good characters are preserved by vegetative propagation.
Some plants such as doob grass (Cynodon dactylon) which produce only a small quantity of seed are mostly propagated by vegetative propagation.
Grafting helps in getting an economically important plant having useful characteristics of two different individuals in a short time.
Question 10. Write a note on sexuality in plants. Or Coconut palm is monoecious while date palm is dioecious. Why are they called so?
Answer: Sexuality in organisms: Sexual reproduction in organisms generally involves the coming together of gametes from two different individuals. But this is not always true.
Sexuality in Plants: Plants may have both male and female reproductive structures in the same plant (bisexual) or on different plants (unisexual). In several fungi and plants, terms such as homothallic and monoecious are used to denote the bisexual condition, and heterothallic and dioecious are used to describe the unisexual condition.
In flowering plants, the unisexual male flower is staminate, i.e. bearing stamens, while the female is pistillate or bearing pistils. In some flowering plants, both male and female flowers may be present on the same individual (monoecious) or on separate individuals (dioecious). Some examples of monoecious plants are cucurbits and coconuts and dioecious plants are papaya and date palm.
In This Post we are providing Chapter-2 SEXUAL REPRODUCTION IN FLOWERING PLANTS NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON SEXUAL REPRODUCTION IN FLOWERING PLANTS
1. Trace the development of microsporocyte into mature pollen grains. Ans. i) When the anther is young, the microsporangium contains compactly arranged homogenous cells forming the Sporogeneous tissues.
Every cell of the sporogenous tissue is a potential Pollen mother cell (PMC) & give rise to microspore tetrad or Pollen grains.
But Some of them forego this Potential & become differentiated into pollen or microspore mother cell (MMC)
Each microspore mother cell undergoes meiosis to form a cluster of four haploid cells called microspore tetrad.
As the anther matures, microspores dissociate from tetrad & develop into pollen grains.
The nucleus of microspore undergoes mitosis to form large vegetative cell & small generative cell. They develop a two layered wall – outer exine made up of sporopollenin & inner intine made up of cellulose & pectin. Usually Pollen grains are liberated at two celled stage.
2. i) Explain the structure of a maize grain with the help of a diagram ii) Why cannot we use the term maize seeds for maize grains? Ans. (i) In grass family ( eg. Maize ) fruit is single seeded where pericarp & seed coat are fused together to form the husk. Just below husk, there is a layer of cells called aleurone layer, with stores proteins. There is a large endosperm that stores starch. The embryo lies on one side of endosperm & consists of a single cotyledon called scutellum & embryonal axis. The region of embryonal axis that points down ward from point of attachment of cotyledons is radicle & is covered by protective sheath called coleorhiza. The region of embryonal axis that points upward from point of attachment of cotyledon is plumule, it is covered by foliaceous sheath called coleoptite (ii) We cannot use the term seeds for maize grain because seed is not completely developed from embryo but retains a part of endosperm.
3. Trace the development of megasporocyte into mature ovule. Ans. i. A single Megaspore mother cell is differentiated in the micropylar region of nucleus of an ovule & undergoes meiosis & forms a cluster of haploid cells called megaspore tetrad. Of these, soon three degenerates & only one megaspore becomes functional ii. Functional megaspore enlarges to form embryo sac. Its nucleus undergoes mitotic division & two nuclei move to opposite poles forming 2-nucleate embryo Sac. iii. Two successive mitotic divisions in each of these two nuclei results in formation of 8-nucleate embryo sac. iv. Three cells are grouped together at micropylar end to form egg apparatus. consisting of two synergids & a female egg cell . v. Three cells are grouped together at the chalazal end, they are called antipodal cells. vi. The remaining two nuclei are called Polar nuclei, they move to centre of embryo sac & fuse to form Secondary nucleus. Thus a typical angiospermic embryo sac is 8-nucleate 7-celled
4. “Incompatibility is the natural barrier in fusion of gamete”. Justify this statement. Ans. Pollen grains of a plant species cannot germinate on stigma of other unrelated species because both the species are incompatible & process is called pollen – pistil incompatibility. In many angiospermic plants, it is seen that pollen grains germinate on stigma of unrelated species but male gametes produced in pollen tube cannot fertilize egg. This is called gametic incompatibility Self incompatibility can be achieved by any of the following ways :-
Pollen Stigma interaction: – In this phenomenon, pollen grains fails to germinate on Stigma because of incompatibility.
Pollen tube style interaction: – In this phenomena, pollen grains become able to germinate on stigma & pollen tube penetrate stigmatic surface but due to incompatibility growth of pollen tube within stigma & style is inhibited.
Pollen – ovule interaction: – pollen tube successfully pierces & grows within style & its growth is inhibited at micropyle of ovule.
5. How dose pollination takes place in salivia. List any four adaptations required for such type of pollination. Ans. In salivia, entomophily or pollination lay insects occurs. The flowers of salivia are bilipped. Its upper lip consists of two petals & lower lip consists of three petals. The lower lip functions as sitting pad for insects. In normal conditions, the connective remains upright. When insect enters the tube of corolla towards nectar sitting on lower lip, it pushes sterile anther lobe which automatically brings about fertile anther to touch the back of insects gets the blow of fertile lobe. Pollen grains are dusted on back feather & legs of insects. ADAPTAIONS EOR ENTOMOPHILY :-
Flowers are brightly coloured.
Flowers possess nectar glands.
pollen grains are usually sticky & spiny
flowers are large – sized & stout
6. Explain the formation of an embryo sac with diagrams. Ans.
The functional megaspore grows in size.
The nucleus divides mitotically to form two nuclei which move to opposite poles.
Each nucleus at the poles undergoes two mitotic divisions to form four nuclei in each pole or a total of 8 nuclei.
two nuclei from each pole move to the centre to form the polar nuclei.
the other nuclei, three at each pole get surrounded by bit of cytoplasm to form cells.
the female gametophyte or the embryo sac thus has 7 cells and eight nuclei.
7. Explain the development of embryo in a dicotyledonous plant with neatly labeled diagrams. Ans. The embryo develops at the micropylar end where the zygote is located. The zygote starts developing only after certain amount of endosperm is formed to assure nutrition to the embryo. The zygote divides mitotically to form various stages including pro- embryo, globular, heart shaped and finally the mature embryo
8.Describe the post-fertilization changes taking place in a flowering plant? Ans. The major events taking place in a flowering plant after fertilization:- (i) DEVELOPMENT OF ENDOSPERM:- Endosperm development proceeds embryo development . The most common method of endosperm development is nuclear type where triploid endosperm (PEN) undergoes repeated mitotic divisions without cytokinesis – Subsequently cell wall formation occurs from periphery & endosperm store food materials which is later used up by embryo. (ii) DEVELOPMENT OF EMBRYO :- The zygote divides lay mitosis to for a pro-embryo first . Later development results in formation of globular & heart shaped embryo & that ultimately become horseshoe – shaped embryo with one or more cotyledons. In dicot embryo, the portion of embryonal axis about the level of attachment is epicotyl & it terminates into plumule while portion of embryonal axis below the level of attachment is hypocotyl & terminates into radicle.
9.Trace the events that would take place in flower from the time of Pollen grain of species fall on stigma up To completion of fertilization. Ans. GERMINATION OF POLLEN GRAINS ON STIGMA The pollen grains absorb fluid present on stigma & swell up. The exine ruptures at the place of germ pore & intine comes out in the form of tube with its internal contents. This small tubular structure is called pollen tube & process is called pollen germination. ii) Entry of pollen tube into Ovule: – The entry of pollen tube into ovule occurs through micropyle or chalaza or through lateral sides of ovule. Only one pollen tube enters inside the embryo sac of an ovule. Normal two synergids are destroyed while entry of pollen tube into embryo sac. iii) Discharge of Mate Gametes :- After enter of pollen tube both the male gametes discharged into embryo sac by either forming two pores into pollen tube & each male gamete is discharged through every pore or sometime pollen tube may burst & release the male gametes into embryo sac. iv) Fertilization:- The fusion of first male gamete (n) with egg (n) is called fertilization. It results in formation of a diploid zygote (2n). The second male gamete fuses with secondary nucleus (2n) to form triploid endosperm nucleus (3n). This fusion between second male gamete & secondary nuclei is triple fusion. Since process of fertilization occurs twice. It is called double fertilization.
10. i)Why is zygotes dominant for sometime in fertilized ovule. ii) What is polyembryony? Give an example. iii) In fruits, what is formed from following parts :- a) Ovary wall b) Outer integument c) Inner integument d) zygote e) primary endosperm f) Ovary g) Nucellus Ans.(i) Zygote remain dominant for sometime in a fertilized ovule because embryo develops after formation of endosperm therefore zygote wants for formation of endosperm which supplies food material for developing embryo (ii) The presence of more than one embryo in a seed is called polyembryony eg. Sometimes more than one embryo is formed within an embryo sac either by cleavage or splitting of egg, synergid, antipodal or endosperm. (iii) In fruits, the following is formed from given parts:-
In This Post we are providing Chapter-22 CHEMICAL COORDINATION AND INTEGRATION NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON CHEMICAL COORDINATION AND INTEGRATION
Question 1. What hormones are secreted by the posterior pituitary gland? What function do they serve? Where are these hormones actually produced? How these hormones are transported to the region from which they are released? Answer: 1. Vasopressin: Released from the axon terminals of hypothalamic neurons into the blood in the posterior lobe of the pituitary. It reduces the volume of urine by increasing the reabsorption of water from the urine, collecting tubules, and collection ducts in the kidney, hence called Antidiuretic hormone.
2. Oxytocin: It is released from the axon terminals of hypothalamic neurons into the blood in the posterior lobe of the pituitary due to the distension of the uterus by the full-term fetus.
It helps in childbirth. It is also known as milk ejection hormone.
Question 2. What are the examples of antagonistic hormones associated with basal metabolism? How does each pair function? Answer: Para hormone (PTH) and thyroid hormone calcitonin act agonistically to regulate the calcium phosphorous balance in the blood. The release of parathormone increases the blood calcium to normal by drawing calcium from the bones into the plasma, by increasing calcium absorption in the digestive tract, and by reducing loss of calcium in the urine. It lowers calcium-phosphorus balance and is necessary for the growth of bones and teeth.
Calcium is vital for blood clotting, muscle tone, and for normal nervous activity. It is also needed for the activities of many enzymes.
Question 3. What two hormones are produced by the adrenal medulla? What non-hormonal function do they serve? Answer: The hormone Adrenaline and Nor-adrenaline are secreted by the adrenal medulla. Function: These hormones act on organs and tissues supplied by sympathetic fibers and produce effects like those of sympathetic stimulation.
Question 4. From what chemical compounds are ail steroid hormones derived? Mention at least two examples of steroidal hormones. Answer: The adrenal cortex is the outer layer of the adrenal gland. It secretes steroidal hormones. Examples, Glucocorticoids, and mineralocorticoids.
The adrenal cortex produces steroid hormones through the modification of cholesterol.
Question 5. In general, how the steroid hormones affect changes in their target cells? Answer: Steroid hormones have minor differences, the various hormones have strikingly different functions. They bind to different receptors in the target cell and affect sets of chemical reactions.
Cortical steroids can be grouped into three functional categories.
Mineralocorticoids: They regulate saltwater balance through their effect on kidney and blood pressure.
Glucocorticoids: They regulate carbohydrate, protein, and lipid metabolism.
Ganado corticoids: It is a sex hormone and helps chemically and functionally to the sex.
Question 6. What hormones are produced when the body’s blood glucose levels drop below normal? How do these hormones act to return the level to normal? What hormone is produced when the body’s blood glucose levels become elevated? How does this hormone act to return the level to normal? Answer: B-cells secrete insulin. T-cells secrete somatostatin.
These two hormones regulate the level of glucose in the blood:
When the blood glucose level becomes excessive, insulin acts on the three target tissues: liver, muscle, and adipose cells. Insulin causes the liver to take up glucose and convert it into glycogen and fat. It facilitates the liver to take up glucose in the muscle and adipose cells causing the levels of the glucose in the blood lowered.
Somatostatin: acts as a paracrine, to inhibit the secretion of glycogen and insulin, decreases secretion, mortality, and absorption in the digestive tract.
Question 7. What is diabetes? What is the ultimate hormonal deficiency in these diseases? How does this affect an individual’s ability to use glucose? What are some possible treatments for adult-onset diabetes? Answer: Diabetes mellitus is a group of disorders that lead to an increase in the level of glucose in the blood. The deficiency of insulin hormone causes diabetes mellitus.
In this disease, the patient cannot use or store glucose. Thus, glucose accumulates in the blood from where it is excreted by kidneys in die urine.
Glucose increases the osmotic pressure of urine, causing loss of water from the body in urine. This produces excessive thirst. Degradation of fats increases, producing ketone bodies such as acetoacetate and acetone. Blood cholesterol rises, injuries may change into gangrenes. Healing power is ^ impaired leading to the damage of tissues.
A diabetic person has blurred vision and is weak, tired, irritable, nauseated, and underweight. In extreme cases, the patient may pass into a coma and die.
Treatment: Administration of insulin gives relief by lowering blood glucose levels. Diabetes caused by insufficient insulin production is called Insulin-dependent diabetes. Diabetes due to a person’s ability to use insulin is termed as insulin ) independent diabetes. It is more common than insulin-dependent diabetes. Diabetes mellitus may also be caused by the failure of insulin to move glucose from the blood into the cells for storage or consumption.
This is due to the defective insulin receptors or cell surfaces, starving the cells of glucose, or to an abnormality in pancreatic protein amylin, which regulates insulin’s activity.
Question 8. What are thyroids? Describe the disorders of thyroids hormones. Answer: The thyroid gland is situated in the neck close to the trachea in human beings. It consists of two elongated oval lobes joined together by a narrow band called ISTHMUS. It highly vascular organ and contains many- spherical or oval sac-like follicles.
Cells of the follicle secrete jelly-like semi-fluid called Colloid of Thyroid stored in the lumen of the follicle. This contains iodinated forms of an amino acid called THYRONINE. When required, two thyroid hormones, THYROXINE, and TRIIODOTHYRONINE are released from the colloid to the blood. (a) and (b) Thyroid gland
Disorders:
Failure of the thyroid from infancy or childhood causes a disease called cretinism. In it, there is slow body growth and mental development. There is also a low metabolic rate.
The deficiency of thyroid hormones in adults produces Myxedema. The patient shows a puffy appearance and lacks intelligence, lateness, and initiative. There is also a low metabolic rate.
The deficiency of iodine produces enlargement of thyroids causing Iodine Deficiency to Goitre.
Some thyroid enlargement is accompanied by a bulging of the eyeball. The disease is called Grave’s Disease or Exophthalami Goitre. The excessive amount of thyroid is secreted. ,
Question 9. Give an account of the primary male sex organ in man and mention briefly the functions of the hormone testosterone. Answer: The testis is the primary sex organ. There are pair of tests. Each testis is covered by a thick connective tissue sheath, Tunica Albuginea. Both testes normally remain suspended in a pouch called Scrotum outside the abdominal cavity. Each testis consists of many small and highly convoluted tubules, called seminiferous tubules, constituting its spermatogenic tissue.
Cells lining the tubules give rise to spermatozoa, which are released into the lumen of the tubule. These are present groups of polyhedral cells.
Interstitial cells of Leydig in the connective tissue around the seminiferous tubules. This constitutes the endocrine tissue of the testis. These cells secrete Testosterone into the blood. Somniferous tubules unite to form a large number of straight tubules, which open into irregular cavities in the posterior part of the testis. The vasa efferentia arise from these cavities and conduct spermatozoa out from the testis.
Functions of Testosterone:
It stimulates the growth and development of male secondary sex organs (prostate, seminal vesicles, and penis).
It stimulates and maintains the normal function of secondary sex organs in reproduction.
It also stimulates and maintains the development of external male characters such as beards, mustaches, and low-pitch male voices in males and combs and wattles in cock.
It also stimulates the formation of sperms in the testes.
It promotes the growth of many body tissues including bones and muscles.
T.S. of testis of an adult man
Question 10. Distinguish between (a) Follicle-stimulating hormone and luteinizing hormone. Answer: Follicle-stimulating hormone and luteinizing hormone:
Stimulating hormone (FSH)
Luteinizing hormone
(i) It stimulates the testes in the male to produce sperms.
(i) It stimulates the testes to secrete the male sex hormone.
(ii) It stimulates the ovaries in the female to produce ova.
(ii) It stimulates the ovaries to secrete the female sex hormone- progesterone.
(b) Somatostatin and somatomedin Answer: Somatostatin and somatomedin:
Somatostatin
Somatomedin
(i) It is secreted by the anterior lobe of the pituitary.
(i) It is secreted by the hypothalamus.
(ii) It stimulates body growth
(ii) It inhibits the secretion of the growth hormone from the anterior pituitary.
(c) Vasopressin and Oxytocin Answer: Vasopressin and Oxytocin:
Vasopressin
Oxytocin
(i) Vasopressin is released from the axon terminal of hypothalamic neurons into the blood in the posterior lobe of the pituitary due to the rise in blood osmotic pressure caused by the loss of water from the body.
(i) Oxytocin is released from the axon terminals of hypothalamic neurons into the blood in the posterior lobe of the pituitary due to distension of the uterus by the full-term fetus or due to the sucking of the breast by an infant.
(ii) It reduces the volume of urine by increasing the reabsorption of water from the urine in the distal convoluted tubules, collecting tubules, and collection ducts in the kidney, hence called Antidiuretic Hormone (ADH).
(ii) It helps in childbirth by causing uterine contractions at the end of pregnancy, hence called birth hormones.
(iii) It increases arterial blood pressure by causing constriction or narrowing of arterioles.
(iii) It causes the contractions of the mammary gland and muscles that help in the flow of stored milk from the mammary gland to the mouth of the sucking infant, hence called milk ejection hormone.
(d) Estrogen and progesterone Answer: Estrogens and Progesterone:
Estrogens
Progesterone
(i) These are secreted by the cells of maturing Grrafian follicle.
(i) Corpus luteum and placenta secrete progesterone.
(ii) Estrogen stimulates growth, maturation, and functions of female secondary sex organs at puberty.
(ii) Progesterone brings about most of the pregnancy changes such as uterine growth, attach¬ment of the embryo to the uterine wall, placenta formation.
(iii) These also develop and maintain external female sex characters like the high pitch female voice and the female pattern of body hair distribution.
(iii) No such action.
(e) Glucocorticoids and mineralcorticoids Answer: Glucocorticoids and Mineralocorticoids:
Glucocorticoids
Mineralocorticoids
(i) Glucocorticoids such as cortisols regulate the metabolism of carbohydrates, fats, and proteins.
(i) Mineralocorticoids such as Aldosterones regulate the metabolism of sodium and potassium.
(ii) These are secreted from the middle cellular layer (ZONA Fasciculate) of the adrenal cortex
(f) Diabetes mellitus and diabetes insipidus Answer: Diabetes mellitus and Diabetes insipidus:
Diabetes mellitus
Diabetes insipidus
(i) It is due to failure of insulin secretion.
(i) It is due to the failure of secretion of vasopressin.
(ii) The blood sugar is abnormally high and the glucose appears in the urine.
(ii) The blood sugar is normal and no glucose appears in the urine.
(iii) There are high blood cholesterol and ketone body formation.
(iii) There is no such phenomenon.
(g) Exophthalamia goiter and iodine deficiency goiter Answer: Exophthalmic Goitre and Iodine Deficiency goiter:
Exophthalmic Goitre
Iodine Deficiency goiter
(i) It is accompanied by a bulging of eyeballs, i.e., exophthalmos.
(i) It is accompanied by cretinism in children and myxedema in adults.
(ii) The thyroid is overactive and secretes an excessive amount of thyroid hormones.
(ii) The dietary deficiency of iodine causes the deficiency of thyroid hormones.
(h) Cretinism and dwarfism. Answer: Cretinism and dwarfism:
Cretinism
Dwarfism
(i) It is due to over secretion of so gonadotropin from childhood.
(i) It is due to the failure of secretion of somatotropin from an early age.
(ii) There is an abnormal elongation of all long bones.
(ii) There is stoppage of growth of long bones and of the body prematurely making the patient dwarf
In This Post we are providing Chapter-21 NEURAL CONTROL AND CORDINATION NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON NEURAL CONTROL AND CORDINATION
Question 1:
Briefly describe the structure of the following:
Brain (b) Eye (c) Ear
ANSWER:
(A)Brain: Brain is the main coordinating centre of the body. It is a part of nervous system that controls and monitors every organ of the body. It is well protected by cranial meninges that are made up of an outer layer called dura mater, a thin middle layer called arachnoid, and an inner layer called pia mater.
It is divided into three regions − forebrain, midbrain, and hindbrain.
Forebrain: It is the main thinking part of the brain. It consists of cerebrum, thalamus, and hypothalamus.
(a) Cerebrum:
Cerebrum is the largest part of the brain and constitutes about four-fifth of its weight. Cerebrum is divided into two cerebral hemispheres by a deep longitudinal cerebral fissure. These hemispheres are joined by a tract of nerve fibre known as corpus callosum. The cerebral hemispheres are covered by a layer of cells known as cerebral cortex or grey matter. Cerebrum has sensory regions known as association areas that receive sensory impulses from various receptors as well as from motor regions that control the movement of various muscles. The innermost part of cerebrum gives an opaque white appearance to the layer and is known as the white matter.
(b) Thalamus:
Thalamus is the main centre of coordination for sensory and motor signalling. It is wrapped by cerebrum.
(c) Hypothalamus:
It lies at the base of thalamus and contains a number of centres that regulate body temperature and the urge for eating and drinking. Some regions of cerebrum, along with hypothalamus, are involved in the regulation of sexual behaviour and expression of emotional reactions such as excitement, pleasure, fear, etc.
Midbrain:
It is located between the thalamus region of the forebrain and pons region of hindbrain. The dorsal surface of midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina. A canal known as cerebral aqueduct passes through the midbrain. Midbrain is concerned with the sense of sight and hearing.
Hindbrain:
It consists of three regions − pons, cerebellum, and medulla oblongata.
(a) Pons is a band of nerve fibre that lies between medulla oblongata and midbrain. It connects the lateral parts of cerebellar hemisphere together.
(b) Cerebellum is a large and well developed part of hindbrain. It is located below the posterior sides of cerebral hemispheres and above medulla oblongata. It is responsible for maintaining posture and equilibrium of the body.
(c) Medulla oblongata is the posterior and simplest part of the brain. It is located beneath the cerebellum. Its lower end extends in the form of spinal cord and leaves the skull through foramen magnum.
(B) Eye: Eyes are spherical structures that consist of three layers.
(a) The outer layer is composed of sclera and cornea.
(i) Sclera is an opaque tissue that is usually known as white of the eye. It is composed of a dense connective tissue.
(ii) Cornea is a transparent anterior portion of eye that lacks blood vessels and is nourished by lymph from the nearby area. It is slightly bulged forward and helps in focusing light rays with the help of lens.
(b) The middle layer of eye is vascular in nature and contains choroid, ciliary body, and iris.
(i) Choroid lies next to the sclera and contains numerous blood vessels that provide nutrients and oxygen to the retina and other tissues.
(ii) Ciliary body: The choroid layer is thin over posterior region and gets thickened in the anterior portion to form ciliary body. It contains blood vessels, ciliary muscles, and ciliary processes.
(iii) Iris: At the junction of sclera and cornea, the ciliary body continues forward to form thin coloured partition called iris. It is the visible coloured portion of eye.
The eye contains a transparent, biconvex, and elastic structure just behind the iris. It is known as lens. The lens is held in position by suspensory ligaments attached to the ciliary body. The lens divides the eye ball into two chambers – an anterior aqueous and posterior vitreous chamber.
(c) The innermost nervous coat of eye contains retina. Retina is the innermost layer. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types – rod cells and cone cells.
(a) Rod cells –The rods contain the rhodopsin pigment (visual purple) that is highly sensitive to dim light. It is responsible for twilight vision.
(b) Cone cells –The cones contain the iodopsin pigment (visual violet) and are highly sensitive to high intensity light. They are responsible for daylight and colour visions.
The innermost ganglionic cells give rise to optic nerve fibre that forms optic nerve in each eye and is connected with the brain.
(C) Ear: Ear is the sense organ for hearing and equilibrium. It consists of three portions – external ear, middle ear, and internal ear.
1. External ear:
It consists of pinna, external auditory meatus, and a tympanic membrane.
(a) Pinna is a sensitive structure that collects and directs the vibrations into the ear to produce sound.
(b) External auditory meatus is a tubular passage supported by cartilage in external ear.
(c) Tympanic membrane is a thin membrane that lies close to the auditory canal. It separates the middle ear from external ear.
2.Middle ear:
It is an air-filled tympanic cavity that is connected with pharynx through eustachian tube. Eustachian tube helps to equalize air pressure in both sides of tympanic membrane. The middle ear contains a flexible chain of three middle bones called ear ossicles. The three ear ossicles are malleus, incus, and stapes that are attached to each other.
3.Internal ear:
It is also known as labyrinth. Labyrinth is divided into bony labyrinth and a membranous labyrinth. Bony labyrinth is filled with perilymph while membranous labyrinth is filled with endolymph. Membranous labyrinth is divided into 2 parts.
(a) Vestibular apparatus
Vestibular apparatus is a central sac-like part that is divided into utriculus and sacculus. A special group of sensory cells called macula are present in sacculus and utriculus.
Vestibular apparatus also contains three semi-circular canals. The lower end of each semi-circular canal contains a projecting ridge called crista ampularis. Each ampulla has a group of sensory cells called crista. Crista and macula are responsible for maintaining the balance of body and posture.
(b) Cochlea:
Cochlea is a long and coiled outgrowth of sacculus. It is the main hearing organ. Cochlea consists of three membranes. The organ of corti, a hearing organ, is located on the basilar membrane that has hair cells.
Question 2:
Compare the following:
(a) Central neural system (CNS) and Peripheral neural system (PNS)
(b) Resting potential and action potential
(c) Choroid and retina
ANSWER:
(a) Central neural system (CNS) and Peripheral neural system (PNS)
Central neural system
Peripheral neural system
1.
It is the main coordinating centre of the body.
1.
It is not the main coordinating centre of the body.
2.
It includes brain and spinal cord.
2.
It includes cranial and spinal nerves that connect central nervous system to different parts of the body.
(b) Resting potential and action potential
Resting potential
Action potential
1.
It is the potential difference across the nerve fibre when there is no conduction of nerve impulse.
1.
It is the potential difference across nerve fibre when there is conduction of nerve impulse.
2.
The membrane is more permeable to K+ ions than to Na+ ions.
2.
The membrane is more permeable to Na+ ions than to K+ ions.
(c) Choroid and retina
Choroid
Retina
1.
Choroid is the middle vascular layer of eye.
1.
Retina is the innermost nervous coat of eye.
2.
It contains numerous blood vessels that provide nutrients and oxygen to retina and other tissues.
2.
It contains photoreceptor cells, rods and cones that are associated with twilight and colour vision respectively.
Question 3:
Explain the following processes:
(a) Polarisation of the membrane of a nerve fibre
(b) Depolarisation of the membrane of a nerve fibre
(c) Conduction of a nerve impulse along a nerve fibre
(d) Transmission of a nerve impulse across a chemical synapse
ANSWER:
(a) Polarisation of the membrane of a nerve fibre
During resting condition, the concentration of K+ ions is more inside the axoplasm while the concentration of Na+ ions is more outside the axoplasm. As a result, the potassium ions move faster from inside to outside as compared to sodium ions. Therefore, the membrane becomes positively charged outside and negatively charged inside. This is known as polarization of membrane or polarized nerve.
(b) Depolarisation of the membrane of a nerve fibre
When an electrical stimulus is given to a nerve fibre, an action potential is generated. The membrane becomes permeable to sodium ions than to potassium ions. This results into positive charge inside and negative charge outside the nerve fibre. Hence, the membrane is said to be depolarized.
(c) Conduction of a nerve impulse along a nerve fibre
There are two types of nerve fibres – myelinated and non-myelinated. In myelinated nerve fibre, the action potential is conducted from node to node in jumping manner. This is because the myelinated nerve fibre is coated with myelin sheath. The myelin sheath is impermeable to ions. As a result, the ionic exchange and depolarisation of nerve fibre is not possible along the whole length of nerve fibre. It takes place only at some point, known as nodes of Ranvier, whereas in non-myelinated nerve fibre, the ionic exchange and depolarization of nerve fibre takes place along the whole length of the nerve fibre. Because of this ionic exchange, the depolarized area becomes repolarised and the next polarized area becomes depolarized.
(d) Transmission of a nerve impulse across a chemical synapse
Synapse is a small gap that occurs between the last portion of the axon of one neuron and the dendrite of next neuron. When an impulse reaches at the end plate of axon, vesicles consisting of chemical substance or neurotransmitter, such as acetylcholine, fuse with the plasma membrane. This chemical moves across the cleft and attaches to chemo-receptors present on the membrane of the dendrite of next neuron. This binding of chemical with chemo-receptors leads to the depolarization of membrane and generates a nerve impulse across nerve fibre.
The chemical, acetylcholine, is inactivated by enzyme acetylcholinestrase. The enzyme is present in the post synaptic membrane of the dendrite.
It hydrolyses acetylcholine and this allows the membrane to repolarise.
The neural system provides rapid coordination among the organs of the body. This coordination is in the form of electric impulses and is quick and short lived. All the physiological processes in the body are closed linked and dependent upon each other. For example, during exercise, our body requires more oxygen and food. Hence, the breathing rate increases automatically and the heart beats faster. This leads to a faster supply of oxygenated blood to the muscles. Moreover, the cellular functions require regulation continuously. These functions are carried out by the hormones. Hence, the neural system along with the endocrine system control and coordinate the physiological processes.
(b) Forebrain
It is the main thinking part of the brain. It consists of cerebrum, thalamus, and hypothalamus.
(i) Cerebrum:
Cerebrum is the largest part of the brain and constitutes about four-fifth of its weight. Cerebrum is divided into two cerebral hemispheres by a deep longitudinal cerebral fissure. These hemispheres are joined by a tract of nerve fibres known as corpus callosum. The cerebral hemispheres are covered by a layer of cells known as cerebral cortex or grey matter. Cerebrum has sensory regions known as association areas that receive sensory impulses from various receptors as well as from motor regions that control the movement of various muscles. The innermost part of cerebrum gives an opaque white appearance to the layer and is known as the white matter.
(ii) Thalamus:
Thalamus is the main centre of coordination for sensory and motor signalling. It is wrapped by cerebrum.
(iii) Hypothalamus:
It lies at the base of thalamus and contains a number of centres that regulate body temperature and the urge for eating and drinking. Some regions of cerebrum, along with hypothalamus, are involved in the regulation of sexual behaviour and expression of emotional reactions such as excitement, pleasure, fear, etc.
(c) Midbrain
It is located between the thalamus region of the forebrain and pons region of hindbrain. The dorsal surface of midbrain consists of superior and inferior corpora bigemina and four round lobes called corpora quadrigemina. A canal known as cerebral aqueduct passes through the midbrain. Midbrain is concerned with the sense of sight and hearing.
(d) Hindbrain
It consists of three regions – pons, cerebellum, and medulla oblongata.
(i) Pons is a band of nerve fibres that lies between medulla oblongata and midbrain. It connects the lateral parts of cerebellar hemisphere together.
(ii) Cerebellum is a large and well developed part of hindbrain. It is located below the posterior sides of cerebral hemispheres and above the medulla oblongata. It is responsible for maintaining posture and equilibrium of the body.
(iii) Medulla oblongata is the posterior and simplest part of the brain. It is located beneath the cerebellum. Its lower end extends in the form of spinal cord and leaves the skull through foramen magnum.
(e) Retina
Retina is the innermost layer. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. The receptor cells present in the retina are of two types – rod cells and cone cells.
(i) Rod cells –The rods contain rhodopsin pigment (visual purple), which is highly sensitive to dim light. It is responsible for twilight vision.
(ii) Cone cells –The cones contain iodopsin pigment (visual violet) and are highly sensitive to high intensity light. They are responsible for daylight and colour visions.
The innermost ganglionic cells give rise to optic nerve fibre that forms optic nerve in each eye and is connected with the brain. In this region, the photoreceptor cells are absent. Hence, it is known as the blind spot. At the posterior part, lateral to blind spot, there is a pigmented spot called macula lutea. This spot has a shallow depression at its middle known as fovea. Fovea has only cone cells. They are devoid of rod cells. Hence, it is the place of most distinct vision.
(f) Ear ossicles
The middle ear contains a flexible chain of three middle bones called ear ossicles. The three ear ossicles are as follows.
(i) Malleus
(ii) Incus
(iii) Stapes
The malleus is attached to tympanic membrane on one side and to incus on the other side. The incus is connected with stapes. Stapes, in turn, are attached with an oval membrane, fenestra ovalis, of internal ear. The ear ossicles act as a lever that transmits sound waves from external ear to internal ear.
(g)Cochlea
Cochlea is a long, coiled outgrowth of sacculus. It is the main hearing organ. The cochlea forms three chambers.
(i) Upper − scala vestibule
(ii) Middle − scala media
(iii) Lower − scale tympani
The floor of the scala media is basilar membrane while its roof is Reissner’s membrane. Reissner’s membrane gives out a projection called tectorial membrane. The organ of corti, a hearing organ, is located on the basilar membrane. Organ of corti contains receptor hair cells. The upper scala vestibule and lower scala tympani contain perilymph.
(h) Organ of corti
Organ of corti is the hearing organ. It is located on the basilar membrane that contains hair cells. Hair cells act as auditory receptors. They are present on the internal side of organ of corti.
(i) Synapse
Synapse is a junction between the axon terminal of one neuron and the dendrite of next neuron. It is separated by a small gap known as synaptic cleft.
There are two types of synapses.
(a) Electrical synapse
(b) Chemical synapse
In electrical synapses, the pre and post synaptic neurons lie in close proximity to each other. Hence, the impulse can move directly from one neuron to another across the synapse. This represents a faster method of impulse transmission.
In chemical synapses, the pre and post synaptic neurons are not in close proximity. They are separated by a synaptic cleft. The transmission of nerve impulses is carried out by chemicals such as neurotransmitters.
Question 6:
Give a brief account of:
(a) Mechanism of synaptic transmission
(b) Mechanism of vision
(c) Mechanism of hearing
ANSWER:
(a) Mechanism of synaptic transmission
Synapse is a junction between two neurons. It is present between the axon terminal of one neuron and the dendrite of next neuron separated by a cleft.
There are two ways of synaptic transmission.
(1) Chemical transmission
(2) Electrical transmission
1. Chemical transmission – When a nerve impulse reaches the end plate of axon, it releases a neurotransmitter (acetylcholine) across the synaptic cleft. This chemical is synthesized in cell body of the neuron and is transported to the axon terminal. The acetylcholine diffuses across the cleft and binds to the receptors present on the membrane of next neuron. This causes depolarization of membrane and initiates an action potential.
2. Electrical transmission – In this type of transmission, an electric current is formed in the neuron. This electric current generates an action potential and leads to transmission of nerve impulse across the nerve fibre. This represents a faster method of nerve conduction than the chemical method of transmission.
(b)Mechanism of vision
Retina is the innermost layer of eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. A photoreceptor cell is composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through cornea, it leads to the dissociation of retinal from opsin protein. This changes the structure of opsin. As the structure of opsin changes, the permeability of membrane changes, generating a potential difference in the cells. This generates an action potential in the ganglionic cells and is transmitted to the visual cortex of the brain via optic nerves. In the cortex region of brain, the impulses are analysed and image is formed on the retina.
(c)Mechanism of hearing
The pinna of the external region collects the sound waves and directs it towards ear drum or external auditory canal. These waves strike the tympanic membrane and vibrations are created. Then, these vibrations are transmitted to the oval window, fenestra ovalis, through three ear ossicles, named as malleus, incus, and stapes. These ear ossicles act as lever and transmit the sound waves to internal ear. These vibrations from fenestra ovalis are transmitted into cochlear fluid. This generates sound waves in the lymph. The formation of waves generates a ripple in the basilar membrane. This movement bends the sensory hair cells present on the organ of corti against tectorial membrane. As a result of this, sound waves are converted into nerve impulses. These impulses are then carried to auditory cortex of brain via auditory nerves. In cerebral cortex of brain, the impulses are analysed and sound is recognized.
Question 7:
Answer briefly:
(a) How do you perceive the colour of an object?
(b) Which part of our body helps us in maintaining the body balance?
(c) How does the eye regulate the amount of light that falls on the retina?
ANSWER:
(a) Photoreceptors are cells that are sensitive to light. They are of two types – rods and cones. These are present in the retina. Cones help in distinguishing colours. There are three types of cone cells – those responding to green light, those responding to blue light, and those responding to red light. These cells are stimulated by different lights, from different sources. The combinations of the signals generated help us see the different colours.
(b) Vestibular apparatus is located in the internal ear, above the cochlea and helps in maintaining body balance. Crista and macula are the sensory spots of the vestibular apparatus controlling dynamic equilibrium.
(c) Pupil is the small aperture in the iris that regulates the amount of light entering the eye. Cornea, aqueous humour, lens, and vitreous humour act together and refract light rays, focussing them onto the photoreceptor cells of the retina.
Question 8:
Explain the following:
(a) Role of Na+ in the generation of action potential.
(b) Mechanism of generation of light-induced impulse in the retina.
(c) Mechanism through which a sound produces a nerve impulse in the
inner ear.
ANSWER:
(a) Sodium ions play an important role in the generation of action potential. When a nerve fibre is stimulated, the membrane potential decreases. The membrane becomes more permeable to Na+ ions than to K+ ions. As a result, Na+ diffuses from the outside to the inside of the membrane. This causes the inside of the membrane to become positively-charged, while the outer membrane gains a negatively charge. This reversal of polarity across the membrane is known as depolarisation. The rapid inflow of Na+ ions causes the membrane potential to increase, thereby generating an action potential.
(b) Retina is the innermost layer of the eye. It contains three layers of cells – inner ganglion cells, middle bipolar cells, and outermost photoreceptor cells. Photoreceptor cells are composed of a protein called opsin and an aldehyde of vitamin A called retinal. When light rays are focused on the retina through the cornea, retinal gets dissociated from opsin. As a result, the structure of opsin gets changed. This in turn causes the permeability of the membrane to change, thereby generating a potential difference in the cells. Consequently, an action potential is generated in the ganglion cells and is transmitted to the visual cortex of the brain via the optic nerves. In the cortex region of the brain, the impulses are analysed and the image is formed on the retina.
(c) The pinna of the external ear collects the sound waves and directs them to the tympanic membrane (ear drum) via the external auditory canal. The ear drum then vibrates the sound waves and conducts them to the internal ear through the ear ossicles. The ear ossicles increase the intensity of the sound waves. These vibrating sound waves are conducted through the oval window to the fluid in the cochlea. Consequently, a movement is created in the lymph. This movement produces vibrations in the basilar membrane, which in turn stimulate the auditory hair cells. These cells generate a nerve impulse, conducting it to the auditory cortex of the brain via afferent fibres. The auditory cortex region interprets the nerve impulse and sound is recognised.
Question 9:
Differentiate between:
(a) Myelinated and non-myelinated axons
(b) Dendrites and axons
(c) Rods and cones
(d) Thalamus and Hypothalamus
(e) Cerebrum and Cerebellum
ANSWER:
(a) Myelinated and non-myelinated axons
Myelinated axons
Non-myelinated axons
1.
Transmission of nerve impulse is faster
1.
Transmission of nerve impulse is slower
2.
Myelinated axon has a myelin sheath.
2.
Myelin sheath is absent
3.
Node of Ranvier is present between adjacent myelin sheaths.
3.
Node of Ranvier is absent
4.
Found in the brain, the spinal cord, the cranial and spinal nerves
4.
Found in autonomous and somatic neural systems
5.
Schwann cells are observed inside the myelin sheath
5.
Schwann cells are not observed inside the myelin sheath
(b) Dendrites and axons
Dendrites
Axons
1.
Dendrite is a small projection arising from the neuron. It conducts the nerve impulse toward the cell body.
1.
Axon is a single, long projection that conducts the nerve impulse away from cell body to the next neuron.
2.
Nissl’s granules are present in dendrites.
2.
Nissl’s granules are absent from axons.
3.
Dendrites are always non-myelinated.
3.
Axons can be myelinated or non-myelinated.
(c) Rods and cones
Rods
Cones
1.
Rods help in twilight vision.
1.
Cones help in colour vision.
2.
They have visual purple pigment called rhodopsin.
2.
They have visual violet pigment called iodopsin.
3.
Rods are the photoreceptor cells of the retina that are sensitive to dim light.
3.
Cones are the photoreceptor cells of the retina that are sensitive to bright light.
(d) Thalamus and Hypothalamus
Thalamus
Hypothalamus
Thalamus is the part of the forebrain that receives nerve impulses of pain, temperature, touch, etc., and conducts them to the cerebral hemisphere.
Hypothalamus is the part of the forebrain that controls involuntary functions such as hunger, thirst, sweating, sleep, fatigue, sexual desire, temperature regulation, etc.
(e) Cerebrum and Cerebellum
Cerebrum
Cerebellum
It is the part of the forebrain that controls voluntary functions. It is the place where intelligence, will power, memory, etc., reside.
It is the part of the hindbrain that controls voluntary functions and controls the equilibrium.
Question 10:
Answer the following:
(a) Which part of the ear determines the pitch of a sound?
(b) Which part of the human brain is the most developed?
(c) Which part of our central neural system acts as a master clock?
ANSWER:
(a) Cochlea determines the pitch of a sound.
(b) Forebrain is largest and the most developed part of the human brain.
(c) Hypothalamus acts as a master clock in the human body.
In This Post we are providing Chapter- 20 LOCOMOTION AND MOVEMENT NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON LOCOMOTION AND MOVEMENT
Question 1:
Draw the diagram of a sarcomere of skeletal muscle showing different regions.
ANSWER:
The diagrammatic representation of a sarcomere is as follows:
Question 2:
Define sliding filament theory of muscle contraction.
ANSWER:
The sliding filament theory explains the process of muscle contraction during which the thin filaments slide over the thick filaments, which shortens the myofibril.
Each muscle fibre has an alternate light and dark band, which contains a special contractile protein, called actin and myosin respectively. Actin is a thin contractile protein present in the light band and is known as the I-band, whereas myosin is a thick contractile protein present in the dark band and is known as the A-band. There is an elastic fibre called z line that bisects each I-band. The thin filament is firmly anchored to the z line. The central part of the thick filament that is not overlapped by the thin filament is known as the H-zone.
During muscle contraction, the myosin heads or cross bridges come in close contact with the thin filaments. As a result, the thin filaments are pulled towards the middle of the sarcomere. The Z line attached to the actin filaments is also pulled leading to the shortening of the sarcomere. Hence, the length of the band remains constant as its original length and the I-band shortens and the H-zone disappears.
Question 3:
Describe the important steps in muscle contraction.
ANSWER:
During skeletal muscle contraction, the thick filament slides over the thin filament by a repeated binding and releases myosin along the filament. This whole process occurs in a sequential manner.
Step 1: Muscle contraction is initiated by signals that travel along the axon and reach the neuromuscular junction or motor end plate. Neuromuscular junction is a junction between a neuron and the sarcolemma of the muscle fibre. As a result, Acetylcholine (a neurotransmitter) is released into the synaptic cleft by generating an action potential in sarcolemma.
Step 2: The generation of this action potential releases calcium ions from the sarcoplasmic reticulum in the sarcoplasm.
Step 3: The increased calcium ions in the sarcoplasm leads to the activation of actin sites. Calcium ions bind to the troponin on actin filaments and remove the tropomyosin, wrapped around actin filaments. Hence, active actin sites are exposed and this allows myosin heads to attach to this site.
Step 4: In this stage, the myosin head attaches to the exposed site of actin and forms cross bridges by utilizing energy from ATP hydrolysis. The actin filaments are pulled. As a result, the H-zone reduces. It is at this stage that the contraction of the muscle occurs.
Step 5: After muscle contraction, the myosin head pulls the actin filament and releases ADP along with inorganic phosphate. ATP molecules bind and detach myosin and the cross bridges are broken.
Stage 6: This process of formation and breaking down of cross bridges continues until there is a drop in the stimulus, which causes an increase in calcium. As a result, the concentration of calcium ions decreases, thereby masking the actin filaments and leading to muscle relaxation.
Question 4:
Write true or false. If false change the statement so that it is true.
(a) Actin is present in thin filament
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.
ANSWER:
(a) Answer: True
(b)Answer: False
H -zone of striated muscle fibre is the central part of the thick filament that is not overlapped by the thin filament.
(c) Answer: True
(d)Answer: False
There are 12 pairs of ribs in a man.
(e) Answer: True
Question 5:
Write the difference between:
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
ANSWER:
(a) Actin and Myosin
Actin
Myosin
1
Actin is a thin contractile protein.
1
Myosin is a thick contractile protein.
2.
It is present in light bands and is called an isotropic band.
2
It is present in dark bands and is called an anisotropic band.
(b) Red and White muscles
Red muscle fibre
White muscle fibre
1
Red muscle fibres are thin and smaller in size.
1
White muscle fibres are thick and larger in size.
2
They are red in colour as they contain large amounts of myoglobin.
2
They are white in colour as they contain small amounts of myoglobin
3
They contain numerous mitochondria.
3
They contain less number of mitochondria.
4
They carry out slow and sustained contractions for a long period.
4
They carry out fast work for short duration.
5
They provide energy by aerobic respiration.
5
They provide energy by anaerobic respiration.
(c) Pectoral and Pelvic girdle
Pectoral girdle
Pelvic girdle
1
It is a skeletal support from where the forelimbs of vertebrates are attached.
1
It is a skeletal support form where the hind limbs of vertebrates are attached.
2
It is composed of twoBones namely, clavicle or collar bones and scapula or shoulder bone.
2
It is composed of three bones, upper ileum, inner pubic, and ischium.
Question 6:
Match Column I with Column II :
Column I
Column II
(a)
Smooth muscle
(i)
Myoglobin
(b)
Tropomyosin
(ii)
Thin filament
(c)
Red muscle
(iii)
Sutures
(d)
Skull
(iv)
Involuntary
ANSWER:
Column I
Column II
(a)
Smooth muscle
(iv)
Involuntary
(b)
Tropomyosin
(ii)
Thin filament
(c)
Red muscle
(i)
Myoglobin
(d)
Skull
(iii)
Sutures
Question 7:
What are the different types of movements exhibited by the cells of human body?
ANSWER:
Movement is a characteristic feature of living organisms. The different types of movement exhibited by cells of the human body are:
Amoeboid movement: Leucocytes present in the blood show amoeboid movement. During tissue damage, these blood cells move from the circulatory system towards the injury site to initiate an immune response.
Ciliary movement: Reproductive cells such as sperms and ova show ciliary movement. The passage of ova through the fallopian tube towards the uterus is facilitated by this movement.
Muscular movement: Muscle cells show muscular movement.
Question 8:
How do you distinguish between a skeletal muscle and a cardiac muscle?
ANSWER:
Skeletalmuscle
Cardiac muscle
1.
The cells of skeletal muscles are unbranched.
1.
The cells of cardiac muscles are branched.
2.
Intercalated disks are absent.
2.
The cells are joined with one another by intercalated disks that help in coordination or synchronization of the heart beat.
3.
Alternate light and dark bands are present.
3.
Faint bands are present.
4.
They are voluntary muscles.
4.
They are involuntary muscles.
5.
They contract rapidly and get fatigued in a short span of time.
5.
They contract rapidly but do not get fatigued easily.
6.
They are present in body parts such as the legs, tongue, hands, etc.
6.
These muscles are present in the heart and control the contraction and relaxation of the heart.
Question 9:
Name the type of joint between the following:-
(a) atlas/axis
(b) carpal/metacarpal of thumb
(c) between phalanges
(d) femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle
ANSWER:
(a) atlas/axis: Pivotal joint
(b) carpal/metacarpal of thumb: Saddle joint
(c) between phalanges: Hinge joint
(d) femur/acetabulum: Ball and socket joint
(e) between cranial bones: Fibrous joint
(f) between pubic bones in the pelvic girdle: Cartilaginous joint
Question 10:
Fill in the blank spaces:
(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________.
(d) In a muscle fibre Ca++ is stored in __________
(e) __________ and __________ pairs of ribs are called floating ribs.
(f) The human cranium is made of __________ bones.
ANSWER:
(a) All mammals (except a few) have cervical vertebra.
(b) The number of phalanges in each limb of a human is.
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins, namely and.
In This Post we are providing Chapter-19 EXCRETORY PRODUCTS AND THEIR ELIMINATION NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON EXCRETORY PRODUCTS AND THEIR ELIMINATION
Question 1. State the importance of counter-current systems in renal functioning.
Answer: Vasa rectal is responsible for the concentration of urine. The vase rectal is in the form of loops. Therefore, the blood flows in the opposite directions in two limbs of each vasa Fecta; the blood entering its descending limb comes into close contact with the outgoing blood in the ascending limb. This is called a Counter-Current System. The two limbs of the loops of Henle form another Counter-Current System.
Importance: The counter-current system significantly contributes to concentrating urine in mammals.
Question 2. Describe the hormonal feedback circuits in controlling renal functions.
Answer: Two important hormonal control of the kidney function by negative feedback circuits can be identified: 1. Control by Antidiuretic Hormone ADH: ADH produced in the hypothalamus of the brain and released into the blood from the pituitary gland, enhances fluid retention by making the kidneys reabsorb more water. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the osmolarity of the blood.
The osmoreceptors cells also promote thirst. Drinking reduces the osmolarity of the blood which inhibits the secretion of ADB, thereby completing the feedback circuit.
2. Control by Juxtaglomerular Apparatus (JGH): It operates a multihormonal Renin-Angiotensin-Aldosterone System (RAAS). JGA responds to decrease the blood pressure and release enzyme renin into the blood. In the blood, the enzyme initiates chemical reactions that convert a plasma protein called angiotensinogen to a peptide called angiotensin II which works as a hormone.
Angiotensin II increases blood pressure and stimulates the adrenal gland to release aldosterone, a hormone. This leads to an increase in blood volume and pressure completing the feed¬back circuit by supporting the release of renin.
Still another hormone, a peptide called Atrial Natriuretic Factor ANF), opposes the regulation by RAAS.
Thus, ADH, the RAAS, and ANF provide an elaborate system of checks and balance that regulate the kidney functioning to control body fluid, osmolarity, salt concentration, blood pressure, and blood volume.
Question 3. State the normal and abnormal constituents of human urine.
Answer: Urine is a pale yellow colored slightly acidic watery fluid.
Abnormal Urine: Various metabolic errors of kidney malfunctioning changes the composition of urine.
Proteinuria: Excess of protein level.
Albuminuria: The presence of albumin, usually occurs in nephritis.
Glycosuria: Presence of glucose in urea as in case of diabetes mellitus.
Ketonuria: Presence of abnormally high ketone bodies.
Hematuria: Presence of blood or blood cells in urine.
hemoglobinuria: Presence of hemoglobin in urine.
Uremia: Presence of excess urea.
Normal Urine: Normal urine is slightly heavier than water. It gives an aromatic odor due to the presence of volatile, bad-smelling organic substances, the ruined water, organic and inorganic materials are the main constituents of normal urine.
The other nitrogenous constituents of normal urine are ammonia, uric acid, hippuric acid, and creatinine.
Non-nitrogenous substances are vitamin C, oxalic acid, phenolic substances. In inorganic substances, sodium chloride is the principal mineral salt in the urine.
Question 4. State the role of skin and lungs in excretion.
Answer: Role of Skin: Human skin possesses glands for secreting sweat and sebum (from the sebaceous gland). Sweat contains NaCl, lactic acid, urea, amino acids, and glucose. The volume of sweat various negligible to 14 L a day. The principal function of sweat is the evaporative cooling of the body surface.
Sebum is a waxy protective secretion to keep the skin oily and this secretion eliminates some lipids, such as waxes, sterols, other hydrocarbons, and fatty acids. Integument in many animals is excreting ammonia into the surrounding by diffusion.
Role of lungs in excretion: Human lungs eliminate around 18L of CO2 per day and about 400 ml of water in normal resting conditions. Water loss via lungs is small in hot humid climates and large in cold dry climates. The rate of ventilation and ventilation pattern also affects the water loss through the lungs. Different volatile materials are also readily eliminated through the lungs.
Question 5. Briefly state the mechanism of urine formation in the human kidney.
Answer: Three main processes are involved in urine formation 1. Glomerular filtration: Kidneys filter the equivalent of blood volume every 4 – 5 minutes. Filtration slits are formed by the assemblages of fine cellular processes of podocytes (foot cells). The process of ultra-filtration depends upon two main factors, first the net hydrostatic pressure difference between the lumen of the capillary and the lumen of the Bowman’s capsule favor filtration.
The glomerular ultrafiltrate contains essentially all the constituents of the blood except for blood corpuscles and plasma proteins. Nearly 15% – 25% of the water and salutes are removed from the plasma that flows through the glomerulus. The glomerular filtration rate is about 125 ml min1 or about 180 L day-1 in human kidneys.
2. Two important intrinsic mechanisms provide autoregulation of glomerular filtration rate. (a) Myogenic mechanism: Increase in blood pressure will tend to stretch the efferent arteriole, which would increase the blood flow to the glomerulus. The diameter of the arteriole is reduced, increasing the resistance to flow. This myogenic mechanism thus reduced variations inflow to the glomerulus in case of fluctuations in blood pressure.
(b) Juxtaglomerular apparatus (JGA): This specialized cellular apparatus is located where the distal convoluted tubule passes close to the Bowman’s capsule between the afferent and efferent arterioles. JGA cells secrete substances like renin that modulate blood pressure and renal blood flow and GFR are regulated.
Myogenic and juxtaglomerular mechanisms work together to autoregulate the GFR over a wide range of blood pressure. In addition to these extrinsic neural control also regulates the filtration rate.
3. Tubular re-absorption: The selective transport of substances across the epithelium of the excretory tubule from the ultrafiltrate to the interstitial fluid is called re-absorption. Nearly all the sugar, vitamins, organic substances (nutrients), and most of the water are reabsorbed.
4. Tubular secretion: It is a very selective process involving both passive and active transport. The filtrate travel through the nephron, substances that are transported across the epithelium from the surrounding interstitial fluid and join it. The net effect of renal secretion is the addition of plasma solutes to the filtrate within the tubule.
Question 6. Explain the following: (a) Skin functions as an accessory excretory organ.
Answer: The skin retains some excretory role in many animals. Human skin possesses two glands for secreting fluid on its surface. These are; sweat from sweat glands and sebum from sebaceous glands.
(b) Mammals can eliminate hypotonic and hypertonic urine according to body needs. Answer: When the animal takes a large quantity of water the kidneys excrete a very high amount of hypotonic urine. At the same time when the animal takes a small number of water kidneys to excrete a very high amount of hypertonic urine.
At the same time when the animal takes a small number of water kidneys to excrete a small amount of hypertonic urine, as kidneys need to conserve water. In this way, the osmotic concentration of blood is maintained by the kidneys. This flexibility of kidney nephrons is highly observed in mammals.
Hypotonic urine removes excess water from the body in order to raise the osmotic concentration of the blood to normal. Excess of water in body fluids generally lowers the osmotic pressure of blood and increases the volume of blood. This increase in the volume of blood raises the blood pressure and hydrostatic pressure which increases the rate of ultrafiltration. In this way, a large amount of hypotonic urine is produced in order to bring the volume of fluids to normal.
(c) Micturition is a reflex process but is under some voluntary control. Answer: It is the process of passing out urine. Nephrons produce urine and drain. When enough urine collects in the bladder the distension of its walls raises enough pressure which generates a spontaneous nervous activity under the stimulation of the sympathetic and parasympathetic nervous system. This nervous stimulation causes the smooth muscles on the urinary bladder to rise too high to control.
Similarly, micturition can voluntarily be initiated even before enough urine has accumulated in the bladder. Backflow of the urine into the ureters from the urinary bladder is prevented because the terminal part of each ureter passes through the bladder and gets closed as soon as the contraction of the bladder occurs.
(d) Mammals are ureotelic, but birds are uricotelic. Answer: Mammals are ureotelic animals as they eliminate nitrogen mainly urea. It is very soluble in water and needs a considerable amount of water for its elimination. Mammals can thus form hypertonic urine which they excrete. While the birds cannot excrete urine as hypertonic since nitrogen occurs mainly in the form of uric acid. The uric acid is insoluble in water and does not require much water for its elimination.
Question 7. Describe the functional anatomy of a human nephron.
Answer: Nephrons are structural and functional units of each kidney to form the urine. Each nephron is fine; microscopic highly coiled tubular structure differentiated into malpighian body and the renal tubule. The malpighian body comprises a large double-walled cup-shaped structure the Bowman’s capsule present in the renal cortex. It is lined by thin, semipermeable epithelial cells, the podocytes. Bowman’s capsule receives the blood supply through a branch of the renal artery.
The afferent arteriole forms a fine capillary network in the form of glomerules with high hydrostatic pressure. The lumen between two layers of Bowman’s capsule is continuous with the lumen of the tubule. The Bowman’s capsule and the glomerulus together form a globular body, the Malpighian body or the renal capsules.
The capillaries forming the glomerulus at the exit of Bowman’s capsule unite to form a narrow efferent arteriole which breaks up into a peritubular network of capillaries with low hydrostatic pressure.
The renal tubule is a long highly coiled tubular structure differentiated into proximal convoluted tubule (PCT) Henle’s loop, distal convoluted tubule (DCT). The U-shaped loop-like structure, descending and ascending from the renal tubule is called Henle’s loop.
Collecting tubules of several nephrons open into a wider duct called the collecting duct. A number of collecting ducts unite with each other in the medulla to form the ducts of Bellini, which drains down the urine into the ureter from each kidney to be stored in the urinary bladder.
The efferent arteriole emerges out from the glomerules breaks up into a peritubular capillary network around the renal tubule in the cortex. These capillaries also form a thin-walled, straight capillary the vasa recta. The vasa recta help in retaining the reabsorbed ions and urea in medullary interstitial fluid to maintain high osmotic pressure in kidneys.
Glomerular filtrate undergoes tubular reabsorption and tubular secretion for the formation of urine. (See diagram opposite page) Uriniferous tubules Or nephron of the kidney
Question 8. Describe the gross anatomical features of the human kidney with a suitable diagram.
Answer: Kidney: Kidney is chocolate brown, bean-shaped, large-sized about 10 cm long and 5 – 7 cm broad, 3 – 4cm thick flattened, metamorphic. The weight of each kidney is 150 to 170 gm. They are situated against the back wall of the abdominal cavity, just below the diaphragm, between the 12th thoracic and 3rd lumbar vertebrae.
The outer margin is convex. The inner concave presents a longitudinal opening called the hilum. The renal artery and renal vein respectively enter and leave the kidney through its hilum.
The two kidneys are slightly asymmetrical in position because the right kidney is slightly at a lower level than the left. Kidneys are held in position by a mass of adipose tissue called Renal fat. These rest against the abdominal muscles. Each kidney is covered on the ventral side by the peritoneum and is thus retroperitoneal in nature.
Surrounding the kidneys and the renal fat is a sheath of fibro elastic tissue known as renal fascia or capsule. They protect the kidney. The renal fat forms a shock-absorbing cushion. The renal fascia fixes the kidney to the abdominal wall. Longitudinal section (Diagrammatic of Kidney)
Question 9. (a)What is the role of the liver in excretion in mammals?
Answer: Role of liver in excretion: The liver changes ammonia into urea which is less toxic than ammonia. Urea is eliminated from the body by the kidneys through urine.
The liver is the principal organ of excretion of cholesterol, bile pigments (bilirubin and biliverdin) some vitamins, drugs, and inactivated products of steroid hormones. The liver excretes these substances in the bile which carries them to the small intestine. Ultimately, these substances get eliminated along with feces.
(b) What are the diseases associated with the urinary system? Answer: Diseases associated with the urinary system: 1. Polynephritis: It is a bacterial infection, which causes inflammation of renal pelvic nephrons and medullary tissues of the kidney. It affects the counter-current mechanism. Its main symptoms are frequent and painful urination, fever, and pain in the lumbar region.
2. Uremia: It causes the presence of a high concentration of urea, uric acid, creatinine, etc, in the blood due to some bacterial infection or some obstruction in the passage of the urinary system. Urea poisons the cells. It is not passed in the urine and accumulates in the blood.
3. Renal stones: When uric acid precipitates and accumulates in the nephrons of kidneys in the form of renal stones or when calcium phosphates and oxalates accumulate in the nephrons of the kidneys in the form of renal stones. It causes blockage or frequent painful urination along with blood in the urine. Renal stone causes severe colic pain starting in the back and radiating down to the front of the thigh or vulva or testicle on that side.
4. Glomerulonephritis: It is characterized by the inflammation of Glomeruliduct, some injury to the kidney, abnormal allergic reaction, or by some streptococci bacteria infection. Proteins and red blood corpuscles become filtered into the glomerular filtrate. It may lead to kidney failure in severe infection.
5. Oedema: It is characterized by the increased volume of interstitial fluid mainly caused by retention of excess Na+ ions which in turn causes water retention. Blood pressure increases dining edema.
Question 10. Write a short account on hemodialysis.
Answer: In case of renal failure, an artificial kidney is used for removing excess urea from the blood of the patient by a process called hemodialysis. Blood is taken out from the artery of the patient, cooled to 0°C, mixed with an anticoagulant such as heparin, and then pumped into the apparatus called artificial kidney. In this apparatus, blood flows through channels Working of artificial kidneys for hemodialysis
bounded by cellophane membrane. The membrane is impermeable to macromolecules but permeable to small solutes. The membrane separates the blood flowing inside the channels from a dialyzing fluid flowing outside the membrane. The wastes like urea, uric acid, and creatinine diffuse from the blood to the dialyzing fluid across the cellophane membrane.
Thus the blood is considerably cleared of nitrogenous waste products without losing plasma proteins. Such a processor separation of macromolecules from small solute particles with the help of a permeable membrane is called dialysis. The blood coming out of the artificial kidney is warmed to body temperature, mixed with an Antiheparin to restore its normal coagulability, and returned to a vein of the patient.
Hemodialysis saves and prolongs the life of many uremic patients.
In This Post we are providing Chapter-18 BODY FLUIDS AND CIRCULATION NCERT MOST IMPORTANT QUESTIONS for Class 11 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter.
NCERTMOST IMPORTANT QUESTIONS ON BODY FLUIDS AND CIRCULATION
Question 1:
Name the components of the formed elements in the bloodand mention one major function of each of them.
ANSWER:
The component elements in the blood are:
(1) Erythrocytes:
They are the most abundant cells and contain the red pigment called haemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced continuously in some parts of the body such as the marrow of long bones, ribs, etc. There are about 4 – 6 million RBCs per cubic millimetre of blood.
(2) Leukocytes
Leucocytes are colourless cells. These cells do not contain haemoglobin. They are the largest cells of the body and are divided into two main categories.
(a) Granulocytes
These leucocytes have granules in their cytoplasm and include neutrophils, eosinophils, and basophiles. Neutrophils are phagocytic cells that protect the body against various infecting agents. Eosinophils are associated with allergic reactions, while basophiles are involved in inflammatory responses.
(b) Agranulocytes
Lymphocytes and monocytes are agranulocytes. Lymphocytes generate immune responses against infecting agents, while monocytes are phagocytic in nature.
(3) Platelets
Platelets are small irregular bodies present in blood. They contain essential chemicals that help in clotting. The main function of platelets is to promote clotting.
Question 2:
What is the importance of plasma proteins?
ANSWER:
Plasma is the colourless fluid of blood which helps in the transport of food, CO2, waste products, and salts. It constitutes about 55% of blood. About 6.8% of the plasma is constituted by proteins such as fibrinogens, globulins, and albumins.
Fibrinogen is a plasma glycoprotein synthesised by the liver. It plays a role in the clotting of blood.
Globulin is a major protein of the plasma. It protects the body against infecting agents.
Albumin is a major protein of the plasma. It helps in maintaining the fluid volume within the vascular space.
Question 3:
Match column I with column II:
Column I
Column II
(a)
Eosinophils
(i)
Coagulation
(b)
RBC
(ii)
Universal Recipient
(c)
AB Group
(iii)
Resist Infections
(d)
Platelets
(iv)
Contraction of Heart
(e)
Systole
(v)
Gas transport
ANSWER:
Column I
Column II
(a)
Eosinophils
(iii)
Resist infections
(b)
RBC
(v)
Gas transport
(c)
AB Group
(ii)
Universal Recipient
(d)
Platelets
(i)
Coagulation
(e)
Systole
(iv)
Contraction of heart
Question 4:
Why do we consider blood as a connective tissue?
ANSWER:
Connective tissues have cells scattered throughout an extra-cellular matrix. They connect different body systems. Blood is considered as a type of connective tissue because of two reasons.
(i) Like the other connective tissues, blood is mesodermal in origin.
(ii) It connects the body systems, transports oxygen and nutrients to all the parts of the body, and removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.
Question 5:
What is the difference between lymph and blood?
ANSWER:
Lymph
Blood
1.
It is a colourless fluid that does not contain RBCs.
1.
It is a red-coloured fluid that contains RBCs.
2.
It contains plasma and lesser number of WBCs and platelets.
2.
It contains plasma, RBCs, WBCs, and platelets.
3.
It helps in body defence and is a part of the immune system.
3.
It is associated with the circulation of oxygen and carbon dioxide.
4.
Its plasma lacks proteins.
4.
Its plasma has proteins, calcium, and phosphorus.
5.
It transports nutrients from the tissue cells to the blood, through lymphatic vessels.
5.
It transports nutrients and oxygen from one organ to another.
6.
The flow of lymph is slow.
6.
The flow of blood in the blood vessels is fast.
Question 6:
What is meant by double circulation? What is its significance?
ANSWER:
Double circulation is a process during which blood passes twice through the heart during one complete cycle. This type of circulation is found in amphibians, reptiles, birds, and mammals. However, it is more prominent in birds and mammals as in them the heart is completely divided into four chambers – the right atrium, the right ventricle, the left atrium, and the left ventricle.
The movement of blood in an organism is divided into two parts:
(i) Systemic circulation
(ii) Pulmonary circulation
Systemic circulation involves the movement of oxygenated blood from the left ventricle of the heart to the aorta. It is then carried by blood through a network of arteries, arterioles, and capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules, veins, and vena cava, and is emptied into the left auricle.
Pulmonary circulation involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery, which then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium.
Hence, in double circulation, blood has to pass alternately through the lungs and the tissues.
Significance of double circulation:
The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells. Blood is circulated to the body tissues through systemic circulation and to the lungs through pulmonary circulation.
Question 7:
Write the differences between:
(a) Blood and Lymph
(b) Open and Closed system of circulation
(c) Systole and Diastole
(d) P-wave and T-wave
ANSWER:
(a)Blood and lymph
Blood
Lymph
1.
Blood is a red-coloured fluid that contains RBCs.
1.
Lymph is a colourless fluid that lacks RBCs.
2.
It contains plasma, RBCs, WBCs, and platelets. It also contains proteins.
2.
It contains plasma and lesser number of WBCs and platelets. It lacks proteins.
3.
Blood transports nutrients and oxygen from one organ to another.
3.
Lymph plays a role in the defensive system of the body. It is a part of the immune system.
(b)Open and closed systems of circulation
Open system of circulation
Closed system of circulation
1.
In this system, blood is pumped by the heart, through large vessels, into body cavities called sinuses.
1.
In this system, blood is pumped by the heart, through a closed network of vessels.
2.
The body tissues are in direct contact with blood.
2.
The body tissues are not in direct contact with blood.
3.
Blood flows at low pressure. Hence, it is a slower and less efficient system of circulation.
3.
Blood flows at high pressure. Hence, it is a faster and more efficient system of circulation.
4.
The flow of blood is not regulated through the tissues and organs.
4.
The flow of blood can be regulated by valves.
5.
This system is present in arthropods and molluscs.
5.
This system is present in annelids, echinoderms, and vertebrates.
(c)Systole and diastole
Systole
Diastole
1.
It is the contraction of the heart chambers to drive blood into the aorta and the pulmonary artery.
1.
It is the relaxation of the heart chambers between two contractions. During diastole, the chambers are filled with blood.
2.
Systole decreases the volume of the heart chambers and forces the blood out of them.
2.
Diastole brings the heart chambers back into their original sizes to receive more blood.
(d)P-wave and T-wave
P-wave
T-wave
1.
In an electrocardiogram (ECG), the P-wave indicates the activation of the SA node.
1.
In an electrocardiogram (ECG), the T-wave represents ventricular relaxation.
2.
During this phase, the impulse of contraction is generated by the SA node, causing atrial depolarisation.
2.
During this phase, the ventricles relax and return to their normal state.
3.
It is of atrial origin.
3.
It is of ventricular origin.
Question 8:
Describe the evolutionary change in the pattern of heart among the vertebrates.
ANSWER:
All vertebrates possess a heart – a hollow muscular organ composed of cardiac muscle fibres. The function of the heart is to pump oxygen to all parts of the body. The evolution of the heart is based on the separation of oxygenated blood from deoxygenated blood for efficient oxygen transport.
In fishes, the heart was like a hollow tube. This evolved into the four-chambered heart in mammals.
Piscean heart Fish has only two chambers in its heart – one auricle and one ventricle. Since both the auricle and the ventricle remain undivided, only deoxygenated blood passes through it. The deoxygenated blood enters the gills for oxygenation from the ventricle. It has additional chambers such as sinus venosus and conus arteriosus.
Amphibian heart Amphibians, such as frogs, have three-chambered hearts, with two auricles and one ventricle. The auricle is divided into a right and a left chamber by an inter-auricular septum, while the ventricle remains undivided. Additional chambers such as sinus venosus and conus arteriosus are also present. The oxygenated blood from the lungs enters the left auricle and simultaneously, the deoxygenated blood from the body enters the right auricle. Both these auricles empty into the ventricle, wherein the oxygenated and deoxygenated blood get mixed to some extent.
Reptilian heart Reptiles have incomplete four-chambered hearts, except for crocodiles, alligators, and gharials. They have only one accessory chamber called sinus venosus. The reptilian heart also shows mixed blood circulation.
Avian and mammalian hearts They have two pairs of chambers for separating oxygenated and deoxygenated bloods. The heart is divided into four chambers. The upper two chambers are called atria and the lower two chambers are called ventricles. The chambers are separated by a muscular wall that prevents the mixing of the blood rich in oxygen with the blood rich in carbon dioxide.
Question 9:
Why do we call our heart myogenic?
ANSWER:
In the human heart, contraction is initiated by a special modified heart muscle known as sinoatrial node. It is located in the right atrium. The SA node has the inherent power of generating a wave of contraction and controlling the heart beat. Hence, it is known as the pacemaker. Since the heart beat is initiated by the SA node and the impulse of contraction originates in the heart itself, the human heart is termed myogenic. The hearts of vertebrates and molluscs are also myogenic.
Question 10:
Sino-atrial node is called the pacemaker of our heart. Why?
ANSWER:
The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemaker of the human body.
h
cervical vertebra.
.
and
.
.
And 
pairs of ribs are called floating ribs.
bones.
