MCQ Questions for Class 8 Science: Ch 10 Reaching the Age of Adolescence
1. The chemical substances which are secreted from endocrine glands are called
(a) puberty
(b) hormones
(c) estrogen
(d) adolescence
► (b) hormones
2. How many pairs of Chromosomes are found in nuclei of their cells?
(a) 22 pairs
(b) 23 pairs
(c) 24 pairs
(d) 25 pairs
► (b) 23 pairs
3. Which of the following will occur in females at puberty?
(a) Ovulation
(b) Enlargement of breasts
(c) Broadening of hips
(d) All of these
► (d) All of these
4. Puberty ends when an adolescent reaches
(a) Reproductive maturity
(b) Physical maturity
(c) Birth maturity
(d) Growth maturity
► (a) Reproductive maturity
5. The menstrual cycle stops in a women at about 50 years old. The woman is said to have reached
(a) puberty.
(b) menopause.
(c) menarche.
(d) adolescence.
► (b) menopause.
6. Which of the following does not take place during the final stage of the menstrual cycle?
(a) Further thickening of the uterine lining.
(b) Repair and growth of the uterine lining.
(c) Ovulation.
(d) Both (B) and (C)
► (c) Ovulation.
7. Which one is another terms for teenage is
(a) Maturity
(b) Puberty
(c) Adolescence
(d) Thyroid
► (c) Adolescence
8. Larynx is called
(a) Voice Box
(b) Music Box
(c) Respiratory organ
(d) None of these
► (a) Voice Box
9. Glands without ducts
(a) Mammary gland
(b) Exocrine gland
(c) Endocrine glands
(d) Pancreatic gland
► (c) Endocrine glands
10. Sebaceous gland is also known as
(a) Pancreatic gland
(b) Oil gland
(c) Sweat gland
(d) Mater gland
► (b) Oil gland
11. Thyroxine is produced by
(a) Pituitary gland
(b) Adrenal gland
(c) Thyroid gland
(d) Testes
► (c) Thyroid gland
12. In girls, secondary sexual characteristics develop between
(a) 9 and 11 years.
(b) 11 and 14 years.
(c) 15 and 18 years.
(d) 19 and 21 years.
► (b) 11 and 14 years.
13. Adolescence begins around the age of
(a) 18 years
(b) 13 years
(c) 25 years
(d) 11 years
► (d) 11 years
14. The most clearly visible change during puberty is the
(a) Sudden change of hip size
(b) Sudden formation of breast
(c) Slow growth of head
(d) Sudden increase in height
► (d) Sudden increase in height
15. Initially girls grow _____ than boys.
(a) Faster
(b) Slower
(c) Both of these
(d) None of these
► (a) Faster
16. In general, boys have a Low pitch voice while the girls have
(a) Low pitch voice
(b) Hoarse voice
(c) Deep voice
(d) High pitch voice
► (d) High pitch voice
17. Progesterone level falls during
(a) Menopause
(b) Lactation
(c) Gestation
(d) Menstruation
► (a) Menopause
18. Which among the boys and girls puberty starts earlier?
(a) Any one
(b) Boys
(c) Girls
(d) Both together
► (c) Girls
19. Incomplete development of male secondary sexual characteristics is caused due to deficiency in?
(a) Estrogen.
(b) Progesterone.
(c) Adrenaline.
(d) Testosterone.
► (d) Testosterone.
20. Which of the following is NOT a secondary sexual characteristic feature of girls?
(a) The enlargement of breasts.
(b) The deepening of voice.
(c) The menstruation begins.
(d) The growth of hair at armpit.
► (b) The deepening of voice.
21. Deficiency of which hormone cause diabetes?
(a) Insulin
(b) Estrogen
(c) Testosterone
(d) Thyroxin
► (a) Insulin
22. Puberty age in females is
(a) 10 to 12 years
(b) 12 to 14 years
(c) 8 to 10 years
(d) More than 14 years.
► (a) 10 to 12 years
23. Menstrual cycle is controlled by
(a) Time duration
(b) Physical activity
(c) Food habit
(d) Hormones
► (d) Hormones
24. The right meals for adolescents consist of
(a) Chips, noodles, coke
(b) Rice, noodles and burger
(c) Chapatti, dal, vegetable
(d) Vegetable cutlets, chips and lemon drink
► (c) Chapatti, dal, vegetable
25. Which chromosomes determine the sex of an individual?
(a) Autosomes
(b) Allosomes
(c) Plasmid
(d) Giant chromosomes
► (b) Allosomes
26. Which of the following statements is true?
(a) Boys reach puberty at an earlier age than girls.
(b) Girls reach puberty earlier than boys.
(c) At the end of rapid growth, girls are normally heavier than boys.
(d) Between the age of 4 to 12, girls grow faster than boys.
► (b) Girls reach puberty earlier than boys.
Class 8 Science Chapter 10 Extra Questions and Answers Reaching the Age of Adolescence
Extra Questions for Class 8 Science Chapter 10 Reaching the Age of Adolescence with Answers Solutions
Reaching the Age of Adolescence Class 8 Extra Questions Very Short Answer Type
Question 1. What is Adam’s apple? Answer: The protruding part of the throat in males is called Adam’s apple.
Question 2. Name the hormone in female that is produced by ovaries and helps in development of mammary glands. Answer: Estrogen
Question 3. Whose height grow faster initially boys or girls? Answer: Girls
Question 4. Name a gland which transports secretions through ducts. Answer: Sweat glands/salivary glands/ oil gland (any one).
Question 5. What is puberty? Answer: The age at which boys and girls become capable of reproduction.
Question 6. What are hormones? Answer: The chemical substances produced by endocrine glands are called hormones.
Question 7. How long is a woman’s reproductive life lasts? Answer: Menarche to menopause.
Question 8. Name the female hormone. Answer: Estrogen
Question 9. Which gland is called master gland? Answer: Pituitary gland
Question 10. What is a balanced diet? Answer: The meal that includes all nutrients is called a balanced diet.
Question 11. What is menstruation? Answer: Extrusion of uterus lining and blood along with the unfertilised egg from the vagina is called menstruation.
Question 12. What is menarche? Answer: The first menstrual flow begins at puberty and is termed as menarche.
Question 13. What is menopause? Answer: Stoppage of menstruation is called menopause.
Question 14. What causes goitre? Answer: Deficiency of thyroxine hormone.
Question 15. Which gland secretes thyroxine? Answer: Thyroid gland
Question 16. What are chromosomes? Answer: The thread-like structures in the nucleus are called chromosomes.
Question 17. How many chromosomes are present in human cell? Answer: 23 pairs or 46 chromosomes.
Question 18. How many sex chromosomes are there in human cell? Answer: Two, i.e., one pair.
Question 19. Which hormone is necessary for normal growth of a person? Answer: Growth hormone.
Question 20. Which gland secretes insulin? Answer: Pancreas
Question 21. What causes diabetes? Answer: Deficiency of insulin.
Question 22. Name the chromosome present in a female. Answer: X chromosome
Question 23. Name the chromosome present in a male. Answer: X and Y chromosomes
Question 24. Which chromosome does the unfertilised egg contain? Answer: X chromosome
Question 25. Which hormone balances the proportion of salts in the blood? Answer: Adrenaline
Question 26. What decides the sex of an unborn child? Answer: Sex chromosome of father.
Question 27. Name the glands other than the pituitary gland. Answer: Thyroid, pancreas and adrenals.
Question 28. When does the puberty ends? Answer: Puberty ends when an adolescent reaches reproductive maturity.
Question 29. Do the boys and girls undergo same physical changes at puberty? Answer: No
Question 30. Why do we need to have a balanced diet? Answer: To keep the body healthy.
MCQ Questions for Class 8 Science: Ch 8 Cell Structure and Functions
1.Which of the following cells can change its shape
(a) White blood cell
(b) Egg cell
(c) Red blood cell
(d) All of the above
► (a) White blood cell
2. What are pseudopodia?
(a) Eye of amoeba
(b) False feet of amoeba
(c) Heart of amoeba
(d) Vacuole of amoeba
► (b) False feet of amoeba
3. Vacuoles of plant cells are
(a) permanent
(b) semi-permanent
(c) temporary
(d) impermeable
► (a) permanent
4. Tissue is a
(a) Group of organs
(b) Group of cells
(c) Group of tissues
(d) Group of organisms
► (b) Group of cells
5. Which of the following is a saclike structure that store food, wastes and water?
(a) Lysosomes
(b) Centrosomes
(c) Chromosomes
(d) Vacuoles
► (d) Vacuoles
6. Which of the following is absent in an animal cell?
(a) Cytoplasm
(b) Nucleus
(c) Cell membrane
(d) Cell wall
► (d) Cell wall
7. Which of the following given below is in the ascending order of the number of nuclei present in cells?
(a) Paramoecium, brain cell, RBC of mammals.
(b) RBC of mammals, brain cell, paramoecium.
(c) Brain cell, RBC of mammals, paramoecium.
(d) All of these
► (b) RBC of mammals, brain cell, paramoecium.
8. Power house of the cell is :
(a) mitochondria
(b) chloroplast
(c) ribosome
(d) nucleus
► (a) mitochondria
9. Which of the following tissues include blood cell?
(a) Epithelial tissue
(b) Muscle tissue
(c) Connective tissue
(d) Nervous tissue
► (c) Connective tissue
10. Which type of tissues support, defend and store food in animals?
(a) Epithelial
(b) Connective
(c) Nervous
(d) Muscular
► (b) Connective
11. Membrane of nucleus is porous so it :
(a) allows movement of chromosomes out of nucleus
(b) allows exchange of cell organelles
(c) allows transport of specific proteins
(d) allows leakage of genes into cytoplasm
► (c) allows transport of specific proteins
12. Thread like structures present inside nucleus are :
(a) chromosomes
(b) ribosomes
(c) lysosomes
(d) all of them
► (a) chromosomes
13. Identify the statement which is true for cells.
(a) Cells can be easily seen with naked eyes.
(b) Insect’s egg is not a cell.
(c) A single cell can perform all the functions in a unicellular organism.
(d) The size and shape of cells is uniform in multicellular organisms
► (c) A single cell can perform all the functions in a unicellular organism.
14. Cell wall of bacteria contains :
(a) phospholipid
(b) ribonucleic acid
(c) peptidoglycan
(d) deoxyribonucleic acid
► (c) peptidoglycan
15. If your father has brown eyes, you may also have brown eyes. If your mother has curly hair, you might also end up having curly hair. This transfer of characteristics is due to the transfer of ______.
(a) Mitochondria
(b) Chromosomes
(c) Lysosomes
(d) Chloroplasts
► (b) Chromosomes
16. Which of the following is the control room of the cell?
(a) Nucleus
(b) Protoplasm
(c) Chloroplast
(d) Ribosome
► (a) Nucleus
17. Which of the following is a locomotory organelle in protozoa ?
(a) pseudocoelom
(b) tentacles
(c) flagella
(d) all of them
► (c) flagella
18. Which of the following components is/ are present in the nervous system?
(a) Brain
(b) Spinal cord
(c) Cranial and spinal nerves
(d) All of these
► (d) All of these
19. Cell membrane is also called:
(a) cell wall
(b) nucleolus
(c) cytoplasm
(d) Plasma membrane
► (d) Plasma membrane
20. The power house of cell is called
(a) Cell wall
(b) Mitochondria
(c) Ribosomes
(d) Nucleus
► (b) Mitochondria
21. Which of the following statements is/are the functions of golgi apparatus?
(a) Transporting proteins that are to be released from the cell
(b) Packaging proteins into vesicles.
(c) Altering or modifying proteins.
(d) All of these
► (b) Packaging proteins into vesicles.
22. Single celled organisms are called
(a) Unicellular
(b) Multicellular
(c) Both of these
(d) None of these
► (a) Unicellular
23. The plastid responsible for fruit colour is :
(a) chromoplast
(b) amyloplast
(c) chloroplast
(d) leucoplast
► (a) chromoplast
24. Cell is discovered by
(a) Robert Brown
(b) Robert Hooke
(c) John Mendal
(d) Charles Darwin
► (b) Robert Hooke
25. Which of the following is selectively permeable?
(a) cell membrane
(b) cell wall
(c) plasmid membrane
(d) capsule
► (a) cell membrane
Class 8 Science Chapter 8 Extra Questions and Answers Cell Structure and Functions
Extra Questions for Class 8 Science Chapter 8 Cell Structure and Functions with Answers Solutions
Cell Structure and Functions Class 8 Extra Questions Very Short Answer Type
Question 1. What is the basic, functional and structural unit of life? Answer: Cell
Question 2. Which cell does not have nucleus? Answer: Red blood cell
Question 3. What is the name of the organism which can be seen only with the help of microscope? Answer: Microorganisms
Question 4. What are the organisms which are composed of many cells packed together called? Answer: Multicellular organisms
Question 5. What is the name of the power house of the cell? Answer: Mitochondria
Question 6. Name one example of prokaryotic cell. Answer: Blue-green algae
Question 7. Amoeba and Paramecium belong to which category of organisms? Answer: Unicellular
Question 8. Which instrument is used to observe cells? Answer: Micrbscope
Question 9. Why we do not sense any pain when we cut nails and hair? Answer: Nails and hair are made up of dead cells.
Question 10. What is the name of living substance present in cell? Answer: Protoplasm
Question 11. What is the other name of cell membrane? Answer: Plasma membrane
Question 12. What is the name of thread-like structure present in nucleoplasm? Answer: Chromatin
Question 13. What is the name of cell which has a well-defined nucleus? Answer: Eukaryotic cell
Question 14. Name the two types of cell. Answer: Prokaryotic cells and eukaryotic cells.
Cell Structure and Functions Class 8 Extra Questions Short Answer Type
Question 1. What is the function of cell wall? Answer: Cell wall is a tough, rigid layer that surrounds some types of cells (plants and some bacterial cells). The major function of the cell wall is to provide rigidity, tensile strength, structural support, protection against mechanical stress and infection.
Question 2. Name the parts of the nucleus and state its function. Answer: Nucleus consists of three main parts nuclear membrane, nucleoplasm and nucleolus. Nucleus plays an important role during cell division. It also controls the activities of the cell.
Question 3. What is an organ? Answer: The structure that contains more than one type of tissues and is visible to the naked eyes are called organs.
Question 4. What do you mean by unicellular and multicellular organisms? Answer: Organisms which consists of only one cell are called unicellular organisms while the organisms made up of more than one cell are called multicellular organisms.
Question 5. Give a brief description of nucleus. Answer: Nucleus is a dense round body found in the centre of an animal cell and mostly on the periphery of the plant cell. The nucleus controls all the activities in a cell.
h
Question 6. Name the following: (i) Controls the function of a cell. (ii) Selectively allows things to get in and out of the cell. (iii) Transfer characters from parents to offsprings. Answer: (i) Nucleus (ii) Cell membrane (iii) Genes
Question 7. What is nucleolus? Answer: A spherical body present at the centre of the nucleus is called the nucleolus.
Question 8. What is endoplasmic reticulum? Answer: It is the system of complex folded network of membranous tubes which connects nuclear membrane with the plasma membrane. They allow movement of substances within the cell.
Question 9. What are cell organelles? Answer: The tiny components present in the cytoplasm are called cell organelles.
Question 10. What is cell membrane? Answer: The thin and delicate membrane surrounding the cell cytoplasm is called cell membrane.
MCQ Questions for Class 8 Science: Ch 7 Conservation of Plants and Animals
1. Ill effect of deforestation is it
(a) Increases temperature of earth
(b) Increases pollution level
(c) Increases CO2 level of atmosphere
(d) All of the above
► (d) All of the above
2. Which of the following is an abiotic component? (a) Cow (b) Grass (c) Temperature (d) Bacteria ► (c) Temperature
3. The place of living of an organism in environment is called:
(a) Home
(b) Resort
(c) Habitat
(d) Reservoir
► (c) Habitat
4. The species which are at the verge of the extinction are called:
(a) Endemic
(b) Extinct
(c) Endangered
(d) None of these
► (c) Endangered
5. Which of the following are the effects of the mismanagement of timber logging?
(a) Floods
(b) Soil erosion
(c) Aforestation
(d) Both (A) and (B)
► (d) Both (A) and (B)
6. Which of the following is/are caused due to uncontrolled deforestation?
(a) The destruction of habitats
(b) Landslides
(c) Floods
(d) All of these
► (d) All of these
7. Deforestation takes place:
(a) Only by human activities
(b) Only by natural reasons.
(c) Both of these
(d) None of these
► (c) Both of these
8. Our biosphere is made up of various ecosystems. All ecosystems are:
(a) inter related
(b) inter connected
(c) intraspecific
(d) both inter connected & inter related
► (d) both inter connected & inter related
9. What is the variety of life and the diversity of genes, species and ecosystems of a region and their inter connectedness called?
(a) Biosphere
(b) Biodiversity
(c) Bioconservation
(d) Biocommunity
► (b) Biodiversity
10. Species is a group of population capable of :
(a) interequilibrium
(b) interfeeding
(c) intercommunication
(d) interbreeding
► (d) interbreeding
11. A place in environment where an organism lives is ________
(a) Home
(b) Resort
(c) Habitat
(d) Reservoir
► (c) Habitat
12. Finest teak of India is obtained from :
(a) Forests of Kaziranga national park
(b) Forests of Satpura
(c) Sunderbans
(d) Forests of Kanha national park
► (b) Forests of Satpura
13. Which of the following is/are advantage(s) of forests?
(a) Forests provide us with oxygen.
(b) They protect soil and provide habitat to a large number of animals.
(c) They help in bringing good rainfall in neighboring areas.
(d) All of these
► (d) All of these
14. Cutting of a forest at a large scale is called:
(a) Deforestation
(b) Reforestation.
(c) Afforestation
(d) All of these.
► (a) Deforestation
15. Those species which exist in small numbers are called:
(a) extinct species
(b) rare species
(c) few species
(d) indeterminate species
► (b) rare species
16. Which of the following are the uses of IUCN Red List?
(a) Developing awareness about the importance of threatened biodiversity
(b) Identification and documentation of endangered species
(c) Providing a global index of the decline of biodiversity
(d) All of these
► (d) All of these
17. Fauna indicates for
(a) Plants
(b) Animals
(c) Both plants and animals
(d) None of these
► (b) Animals
18. The growing of more and more plants is called:
(a) Deforestation
(b) Reforestation
(c) Both of these
(d) None of these
► (b) Reforestation
19. Term biodiversity was coined by:
(a) Haeckal
(b) Wilson
(c) Stanley
(d) Diener
► (b) Wilson
20. A sustainable functional unit of biosphere is called:
(a) Ecology
(b) Ecomodem
(c) Ecosystem
(d) Ecomism
► (c) Ecosystem
21. Which of the following are living resources in nature?
(a) Flora
(b) Fauna
(c) Soil
(d) Both (A) and (B)
► (d) Both (A) and (B)
22. Which of the following shows a modern technology measure that helps preserve and conserve the environment?
(a) The practising crop rotation
(b) The recycling of paper, plastics and metal cans
(c) Using machines in agricultural industry
(d) Converting industrial wastes into biogas
► (b) The recycling of paper, plastics and metal cans
23. The first reserve forest of India is :
(a) Jim Corbett national park
(b) Sunderbans
(c) Satpura national park
(d) Eastern Ghats
► (c) Satpura national park
24. What is the main aim of conserving living organisms?
(a) To increase the world’s population of organisms
(b) To prevent the extinction of endangered species
(c) To help the students of botany and zoology
(d) To help in ecotourism
► (b) To prevent the extinction of endangered species
25. The variety of animals, plants and microbes found in a particular area constitutes that area
(a) Biostatistics
(b) Biomagnification
(c) Biovariety
(d) Biodiversity
► (d) Biodiversity
26. Biotic components of an ecosystem does not include :
(a) Minerals
(b) Mammals
(c) Mosses
(d) Microbes
► (a) Minerals
Class 8 Science Chapter 7 Extra Questions and Answers Conservation of Plants and Animal
Extra Questions for Class 8 Science Chapter 7 Conservation of Plants and Animal with Answers Solutions
Conservation of Plants and Animal Class 8 Extra Questions Very Short Answer Type
Question 1. What is sanctuary? Answer: An area where animals are protected from any disturbance to them and their habitat is called a – sanctuary.
Question 2. Name the major threat to the survival of organism. Answer: Deforestation
Question 3. Write the names of some parks and sanctuaries. Answer: Dudhwa National Park, Bharatpur Bird Sanctuary, Kaziranga National Park, Nelapattu Bird Sanctuary, etc.
Question 4. Write two natural causes of deforestation. Answer:
Severe droughts
Forest fires
Question 5. Give examples of flora. Answer: Teak, sal, mango, jamun, arjun, etc.
Question 6. Give examples of fauna. Answer: Elephant, tiger, wild bear, etc.
Question 7. Name two endemic fauna. Answer: Giant squirrel, bison
Question 8. Name some forest products. Answer: Paper, wood, timber, vegetables, fruits, rubber, etc.
Question 9. What is the name of the reserved land used to protect biodiversity? Answer: Biosphere Reserve
Question 10. Name the first Reserve Forest of India. Answer: Satpura National Park
Question 11. Name products obtained from animals for which they are hunted. Answer: Skin, fur, horn, eggs, flesh, etc.
Question 12. Does soil erosion affect the fertility of soil? Answer: Yes
Question 13. List the names of some migratory birds. Answer:
Siberian crane
Bar-headed goose
Arctic tern
Surkhab
Question 14. Write the names of some extinct animals. Answer: Dodo, dinosaurs, mammoth, etc.
Question 15. When was Project Tiger launched? Answer: April 1,1973
Question 16. How many rock shelters are there in Pachmarhi Biosphere Reserve? Answer: 55
Question 17. Name two wildlife sanctuaries present in Pachmarhi Biosphere Reserve. Answer: Pachmarhi, Bori
Question 18. What is the plantation of new plants called? Answer: Reforestation
Question 19. What is a zoo? Answer: A place where animals receive protection is called a zoo.
Question 20. Name one reason owing to which birds migrate. Answer: For breeding
Conservation of Plants and Animals Class 8 Extra Questions Short Answer Type
Question 1. What do you mean by deforestation? Answer: The cutting of trees on a large scale is called deforestation.
Question 2. Define national park. Answer: A national park is an area reserved for wildlife where they can freely use the habitats and natural resources.
Question 3. What are flora? Answer: The plant species found in a particular area are called flora.
Question 4. What are fauna? Answer: The animal species found in a particular area are called fauna.
Question 5. What do you mean by species? Answer: Species is a group of population which are capable of interbreeding.
Question 6. What is Satpura Tiger Reserve? Answer: It is a Project Tiger which was launched by the government in the country to protect the tigers.
Question 7. What are endangered animals? Answer: The animals whose numbers are diminishing to such a level that they might face extinction are known as ‘endangered animals.’
Question 8. Define ‘Red Data Book.’ Answer: A book that keeps records of all the endangered plant and animal species is called a Red Data Book.
Question 9. Define migratory birds. Answer: The birds which cover long distances to reach another land for some reasons are known as migratory birds.
Question 10. Mention the causes of deforestation. Answer: The cause of deforestation could be:
Forest fires
Building houses, factories
Severe droughts
Using wood for some purposes
Human encroachment and procuring land for cultivation
Question 11. What do you mean by desertification? Answer: The conversion of fertile land into deserts is called desertification.
Question 12. What is biodiversity? Answer: The diversity of plant and animal life in a particular habitat (or in the world as a whole) is called bio-diversity.
Question 13. Define biosphere. Answer: Biosphere is that part of the earth in which living organisms exist or which supports biological diver-sity.
Question 14. Define endemic species. Answer: The species of plants and animals which are found exclusively in a particular area are called endemic species.
Question 15. Explain the term ecosystem. Answer: Ecosystem is a system formed by the interaction of a community of organisms with their physical environment.
MCQ Questions for Class 8 Science: Ch 6 Combustion and Flame
1. Fuel may be
(a) Solid only
(b) Solid,Liquid or gas
(c) Liquid only
(d) Gas only
► (b) Solid,Liquid or gas
2. Which of the following has the characteristics of a good fuel?
(a) Coke
(b) Butane
(c) Coal
(d) Kerosene
► (b) Butane
3. Combustion is a _____ chemical reaction:
(a) volatile
(b) exothermic
(c) endothermic
(d) none of the above
► (b) exothermic
4. The substances which give heat and light after combustion are called
(a) flame
(b) fuel
(c) combustion
(d) none of these
► (b) fuel
5. Cutting trees at large scale leads to :
(a) deforestation
(b) afforestation
(c) reforestation
(d) both deforestation & afforestation
► (a) deforestation
6. What kind of reaction is combustion?
(a) Reduction
(b) Redox
(c) Substitution
(d) Oxidation
► (d) Oxidation
7. Substance that burns in oxygen to produce heat and light is called :
(a) renewable
(b) non combustible
(c) combustible
(d) limitless
► (c) combustible
8. If a glass plate/slide is held into the luminous part of candle flame we see a circular blackish ring that represents:
(a) unburnt carbon particles
(b) formation of coal
(c) burnt carbon particles
(d) Both burnt carbon particles & formation of coal
► (a) unburnt carbon particles
9. Burning of LPG is an example of :
(a) slow combustion
(b) spontaneous combustion
(c) Both slow combustion & spontaneous combustion
(d) rapid combustion
► (d) rapid combustion
10. SI unit of the calorific value of a fuel is :-
(a) KJ/kg
(b) KW/kg
(c) N/kg
(d) KJ/g
► (a) KJ/kg
11. Burning of charcoal in a closed room will produce
(a) carbon dioxide
(b) nitrogen dioxide
(c) carbon monoxide
(d) all of these
► (c) carbon monoxide
12. Which of the following is an example of rapid combustion?
(a) Candle
(b) Cracker
(c) White phosphorus
(d) Sulphur
► (a) Candle
13. The gas which supports combustion of coal is :
(a) carbon dioxide
(b) oxygen
(c) nitrogen
(d) hydrogen
► (b) oxygen
14. Amount of heat energy produced on complete combustion of 1kg of fuel is called :
(a) energy value
(b) combustion value
(c) heat value
(d) calorific value
► (d) calorific value
15. Combustion is a
(a) chemical process
(b) physical process
(c) both of these processes
(d) none of these processes
► (a) chemical process
16. A material that burns is one that can combine quickly with :
(a) hydrogen
(b) oxygen
(c) carbon
(d) water
► (b) oxygen
17. Water works as a fire extinguisher by removing :-
(a) source of combustible substance
(b) heat
(c) oxygen
(d) both oxygen & heat
► (d) both oxygen & heat
18. What is the lowest temperature at which a substance starts burning called?
(a) Minimum temperature
(b) Maximum temperature
(c) Boiling temperature
(d) Ignition temperature
► (d) Ignition temperature
19. It is dangerous to extinguish fire caused by an electric short circuit with the use of :
(a) sand
(b) carbon dioxide
(c) water
(d) carbon monoxide
► (c) water
20. Substance that does not burn in air is :
(a) sand
(b) kerosene
(c) wood
(d) diesel
► (a) sand
21. No external heat is required to start :
(a) simultaneous combustion
(b) spontaneous combustion
(c) splendid combustion
(d) spreading fire combustion
► (b) spontaneous combustion
22. CNG and LPG are the examples of
(a) solid fuels
(b) liquid fuels
(c) gaseous fuels
(d) they are not fuels
► (c) gaseous fuels
23. Which of the following is a non- combustible substance?
(a) Coke
(b) Diamond
(c) Coal
(d) Wood
► (b) Diamond
24. The products of combustion are
(a) carbon dioxide and water
(b) oxygen and water
(c) only carbon dioxide
(d) only oxygen
► (a) carbon dioxide and water
Class 8 Science Chapter 6 Extra Questions and Answers Combustion and Flame
Extra Questions for Class 8 Science Chapter 6 Combustion and Flame with Answers Solutions
Combustion and Flame Class 8 Extra Questions Very Short Answer Type
Question 1. Name the most common fuel used in homes. Answer: Liquefied Petroleum Gas. (LPG)
Question 2. Name the most common fire extinguisher. Answer: Water
Question 3. What are the states in which a fuel may exist? Answer: A fual may exist in solid, liquid or gaseous state.
Question 4. ame any two combustible substances. Answer: Charcoal, wood
Question 5. Does magnesium produce heat and light during its combustion? Answer: Yes, it does.
Question 6. What acts as a fuel for our body? Answer: Food
Question 7. Give two examples of non-combustible substances. Answer: Water, sand
Question 8. How are heat and light produced in the sun? Answer: In the sun, heat and light are produced by nuclear reactions.
Question 9. Where were matchsticks first used? Answer: Egypt
Question 10. What are the three essential requirements for combustion? Answer: Fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature).
Question 11. What is the ignition temperature of phosphorus? Answer: 25°C
Question 12. What is the colour of an LPG flame? Answer: Blue
Question 13. What type of process is combustion? Answer: A chemical process
Question 14. Name an ideal fuel. Answer: Compressed Natural Gas (CNG)
Question 15. What is the composition of the head of a matchstick? Answer: Antimony trisulphide and potassium chlorate.
Question 16. Which part of a flame does a goldsmith blow for melting gold and silver? Answer: The goldsmith blows the outermost zone of a flame for melting gold and silver.
Question 17. What is the unit for expressing the calorific value of a fuel? Answer: Kilojoules per kilogram (kJ/kg)
Question 18. Comparing the calorific values of coal and petrol, state which fuel is better. Answer: The calorific value of coal is about 25,000 – 33,000 kJ/kg, whereas that of petrol is 45,000 kJ/kg. Hence, petrol is better tuel.
Question 19. What is deforestation? Answer: The cutting down of trees on a large scale is termed as deforestation.
Question 20. Give any two examples of carbon fuels. Answer: Coal, petroleum
Combustion and Flame Class 8 Extra Questions Short Answer Type
Question 1. What does magnesium burn to form? Answer: Magnesium burns to form magnesium oxide and produces heat and light.
Question 2. What does coal produce during its combustion? Answer: Coal produces carbon dioxide, heat and light during its combustion.
Question 3. What is combustion? Answer: Combustion is a chemical process in which a substance reacts with oxygen to give off heat.
Question 4. Define the ignition temperature of a fuel. Answer: The lowest temperature at which a fuel catches fire is called its ignition temperature.
Question 5. How does a matchstick catch fire? Answer: By rubbing a matchstick against a rough surface (friction), it attains its ignition temperature and thus catches fire.
Question 6. Why is sodium kept immersed in kerosene? Answer: Sodium has very low ignition temperature, i.e., it catches fire on coming in contact with air, so it is kept in kerosene.
Question 7. What are combustible and non-combustible substances? Answer: Substances which undergo combustion are said to be combustible, whereas non-combustible substances are those which don’t burn.
Question 8. What are inflammable substances? Give examples. Answer: The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances; e.g., LPG, petrol, alcohol, etc.
Question 9. What is rapid combustion? Answer: When a substance burns instantly and produces a huge amount of heat and light, the combustion is called rapid combustion; e.g., the instant burning of LPG in a gas stove.
Question 10. Define spontaneous combustion. Answer: A type of combustion in which the substance suddenly catches fire without the supply of heat or friction externally is called spontaneous combustion; e.g., forest fires.
Question 11. Define explosion. Answer: A type of combustion during which a huge amount of heat and light is evolved with a boom, along with the production of gas, is known as explosion; e.g., the exploding of fireworks, i.e., crackers, etc.
Question 12. What is flame? Answer: Flame is a region where the burning or combustion of gaseous substances take place.
Question 13. Define fuel. Answer: Those substances which provide energy on burning are called ‘fuels’; e.g., coal, petroleum, LPG, etc.
Question 14. Give two examples each of solid fuels, liquid fuels and gaseous fuels. Answer:
Solid fuels – Wood, cow dung, etc.
Liquid fuels – Kerosene, petrol, etc.
Gaseous fuels – Hydrogen, methane, etc.
Question 15. Give two examples of fuels that are used to generate electricity. Answer: Two examples of fuels that are used to generate electricity are petrochemicals and coal.
Question 16. Define calorific value. Answer: The amount of heat produced on burning one kilogram of fuel completely is called its calorific value.
Question 17. 60 kg of fuel was completely burnt for an experiment. The amount of heat energy was found to be 1,80,000 kJ. Calculate the calorific value of the fuel. Answer: Amount of fuel burnt = 60 kg Amount of heat produced = 1,80,000 kJ ∴ Calorific value of the fuel is 3,000 kJ/kg.
Question 18. Define dark zone of a flame. Answer: The innermost zone of a flame around the wick is called its dark zone. It is the least hottest zone comparatively to other.
Question 19. Name the colours of the flames of following substances: Barium, arsenic, sodium, magnesium Answer:
Name of the substance
Colour of its flame
Barium
Pale/Apple green
Arsenic
Blue
Sodium
Yellow
Magnesium
White
Question 20. Mention any three characteristics of a good fuel. Answer: Any three characteristics of a good fuel are following:
It has high calorific value.
It is very easy to transport.
It is cheap, affordable and economic.
Question 21. What is global warming? Answer: An increase in the average temperature of the earth’s atmosphere, especially a sustained increase that causes climatic changes, is termed as ‘global warming’.
MCQ Questions for Class 8 Science: Ch 5 Coal and Petroleum
1. Coal, Petroleum and natural gas are examples of
(a) Exhaustible Natural Resources
(b) Inexhaustible Natural Resources
(c) Expensive Resources
(d) None of the above
► (a) Exhaustible Natural Resources
2. What is the common name of petroleum?
(a) Black gold
(b) Yellow gold
(c) Green gold
(d) Blue gold
► (a) Black gold
3. By which of the given processes is coal formed?
(a) Carbonization
(b) Distillation
(c) Vaporization
(d) Evaporation
► (a) Carbonization
4. What does natural gas mainly consist of?
(a) C2H6
(b) CH4
(c) C3H8
(d) C4H10
► (b) CH4
5. When an oil well is drilled through rocks, which of the following comes out first? (a) Coal gas (b) Marsh gas (c) Natural gas (d) Carbon dioxide ► (c) Natural gas
6. Natural gas is a _____ resource :
(a) non renewable
(b) living
(c) renewable
(d) all the above
► (a) non renewable
7. What does gobar gas produced from animal and plant waste contain?
(a) Ethane
(b) Methane
(c) Propane
(d) Acetylene
► (b) Methane
8. What is the underlying principle based on which fractional distillation is carried out?
(a) Different densities of each fraction
(b) Different molecular weights of each fraction
(c) Different boiling points of each fraction
(d) Different melting points of each fraction
► (c) Different boiling points of each fraction
9. Where does natural gas occur?
(a) Above petroleum oil
(b) Below petroleum oil
(c) Along with petroleum oil
(d) Inside volcanic mountains
► (a) Above petroleum oil
10. A What are the most common sources of energy used in automobiles?
(a) Wood and coal
(b) Petroleum and diesel
(c) LPG and cow dung
(d) Natural gas and coal
► (b) Petroleum and diesel
11. When heated in air, coal burns to produce :
(a) Carbonates
(b) Carbon dioxide gas
(c) Oxygen gas
(d) Chlorofluorocarbons
► (b) Carbon dioxide gas
12. The purest form of carbon is
(a) Coal
(b) Charcoal
(c) Coke
(d) All of these
► (c) Coke
13. Coke is used to manufacture :
(a) coal tar
(b) producer gas
(c) natural gas
(d) biogas
► (b) producer gas
14. Coke is obtained from :
(a) destructive distillation of petroleum
(b) refining of coal
(c) destructive distillation of coal
(d) refining of petroleum
► (c) destructive distillation of coal
15. Fossil fuels are :
(a) renewable resource
(b) formed naturally
(c) formed artificially
(d) non combustible
► (b) formed naturally
16. At the petroleum refinery, crude oil mixture is :
(a) ultrafiltered
(b) filtered
(c) both filtered & ultrafiltered
(d) fractionated
► (d) fractionated
17. When coal burns in air then
(a) Carbon dioxide is formed
(b) Sulphur dioxide is formed
(c) Carbon monoxide is formed
(d) Hydrogen gas is formed
► (a) Carbon dioxide is formed
18. Where is kerosene mainly used?
(a) In laying down roads.
(b) As fuel in jet engines.
(c) In making water proof materials.
(d) In furnaces of industries.
► (b) As fuel in jet engines.
19. Coal was formed during :
(a) Devonian period
(b) Carboniferous period
(c) Silurian period
(d) Carbonian period
► (b) Carboniferous period
20. Coal is classified according to:
(a) its carbon content
(b) time taken in its formation
(c) layer of earth surface it is found
(d) its non carbon content
► (a) its carbon content
21. In fractional distillation of petroleum, where do the vapours with highest boiling point condense?
(a) In the upper-most portion
(b) In the lower-most portion
(c) In the middle portion
(d) Cannot be said
► (b) In the lower-most portion
22. Type of coal that can serve as good heating fuel for domestic purpose is :
(a) bituminous
(b) bauxite
(c) anthracite
(d) lignite
► (c) anthracite
23. Coal gas can be obtained from :
(a) burning coke with petroleum
(b) coal beds & destructive distillation of coal
(c) only fractional distillation of coal
(d) only destructive distillation of coal
► (b) coal beds & destructive distillation of coal
24. By what process is petroleum refined?
(a) Fractional distillation
(b) Destructive distillation
(c) Distillation
(d) All of the above
► (a) Fractional distillation
25. The youngest form of coal is:
(a) litter
(b) peat
(c) anthracite
(d) lignite
► (b) peat
26. PCRA stands for
(a) Public Conservations Research Association
(b) Petroleum Conservation Research Association
(c) Public Council of Research Association
(d) Partial Counting of Remaining Amendment
► (b) Petroleum Conservation Research Association
Class 8 Science Chapter 5 Extra Questions and Answers Coal and Petroleum
Extra Questions for Class 8 Science Chapter 5 Coal and Petroleum with Answers Solutions
Coal and Petroleum Class 8 Extra Questions Very Short Answer Type
Question 1. Name some renewable sources of energy. Answer: Water, wind, solar.
Question 2. Give some examples of fossil fuels. Answer: Coal, petroleum, natural gas.
Question 3. Name the elements present in coal. Answer: Carbon, oxygen and sulphur.
Question 4. Which are the two main techniques of mining? Answer: Surface mining and underground mining.
Question 5. List four varieties of coal. Answer: Peat, lignite, bituminous, anthracite.
Question 6. Name the process of conversion of wood into coal. Answer: Carbonisation
Question 7. Mention the temperature at which destructive distillation is done. Answer: 1000°C
Question 8. When the crude oil is referred to be ‘sweet’? Answer: If the sulphur content is low.
Question 9. Name the process of conversion of kerogen into gaseous hydrocarbons. Answer: Catagenesis
Question 10. Name the country which is the leading producer of petroleum. Answer: Saudi Arabia
Question 11. Name the gas that occurs over petroleum in reservoirs deep inside the earth. Answer: Natural gas
Question 12. Expand PCRA. Answer: Petroleum Conservation Research Association.
Question 13. Name two fractions of petroleum which are used as fuel. Answer: Petrol and diesel
Question 14. What kind of pollution is caused by the burning of fossil fuels? Answer: Air pollution
Question 15. Write the full form of LPG. Answer: Liquefied Petroleum Gas.
Question 16. Which gas is produced when coal is burnt in air? Answer: Carbon dioxide
Question 17. Can we use all our natural resources forever? Answer: No
Question 18. What is the purest form of carbon? Answer: Coke
Question 19. Where and when was the first oil well drilled? Answer: Pennsylvania, USA in 1859.
Question 20. Name the places where natural gas is found in our country. Answer: Tripura, Rajasthan, Krishna Godavari Delta, Maharashtra, etc.
Coal and Petroleum Class 8 Extra Questions Short Answer Type
Question 1. What is fuel? Answer: Anything that burns to produce energy in an efficient manner is called a fuel.
Question 2. Define fossil fuels. Give examples. Answer: Natural fuels that are made up by burial of living organisms under deep down the earth for over a long period of time, are called fossil fuels. For example, coal, petroleum, natural gas.
Question 3. What is coal? Write its two uses. Answer: Coal is a hard, black combustible substance that mainly contains carbon. Uses:
It is used as a fuel in homes and industry.
It is used as a fuel at Thermal Power Plants for generating electricity.
Question 4. Give a brief description about peat. Answer: Peat is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel. Its carbon content is 20 – 25%.
Question 5. Name three constituents of petroleum and write their uses also. Answer: The three constituents of petroleum are: (a) petrol (b) paraffin wax (c) diesel Uses: (a) Petrol: It is used as a motor fuel and for dry cleaning. (b) Paraffin wax: It is used for making ointments, candles, vaseline, etc. (c) Diesel: It is used as a fuel for heavy motor vehicles and electric generators.
Question 6. Explain about coal tar. Answer: It is produced when the gases are evolved due to heating of coal in water. It is a black-coloured, thick, viscous liquid. It has a pungent smell. It is itself a mixture of many compounds. We can get benzene, toluene, napthalene, phenol, etc., from coal tar.
Question 7. Name two products that you obtain from the destructive distillation of coal. What is the residue left in’ this process? Give one main use of this residue. Answer: The two important products obtained from the destructive distillation of coal are: Coal gas and coal tar. The residue left in this process is coke. Coke is used mainly as a reducing agent in the extraction of metals.
Question 8. Where do we get coal and how is it formed? Answer: We get coal deep in the earth’s crust in coal mines. It is formed by the slow decomposition of dead trees and other vegetable matter buried deep under the earth’s crust under high pressure and temperature.
Question 9. Define the term ‘petrochemicals’. Answer: Petrochemicals are the substances obtained from petroleum and natural gas. They are used in the manufacture of detergents, fibres, polythene, etc.
Question 10. What is CNG? What are its uses? Answer: CNG is short form of Compressed Natural Gas. Natural gas is stored under high pressure as CNG. CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel.
Coal and Petroleum Class 8 Extra Questions Long Answer Type
Question 1. Explain about the varieties of coal. Answer: Depending upon the amount of carbon content, coal may be of four types:
Peat: This is the most inferior and softest form of coal. Its carbon content is very low. It has a large amount of moisture and is not much suitable to be used as fuel.
Lignite: Lignite is comparatively harder than peat, but still is very soft. Its carbon content is more than that of peat.
Bituminous: Its carbon content is higher, as it is free from moisture and other impurities.
Anthracite: This is the highest grade coal. This is also known as hard coal. It has maximum amount of carbon. It produces a very little smoke.
Question 2. The burning of fossil fuels causes air pollution. Explain. Answer: The burning of fossil fuels causes a lot of air pollution.
The burning of coal produces gases like carbon dioxide, carbon monoxide, sulphur dioxide, etc., which can lead to undesirable changes in climate due to increase greenhouse effect.
The major air pollutants produced by the burning of petrol in automobiles are carbon monoxide, sulphur dioxide, unbumt hydrocarbons, etc. These pollutants are harmful for human beings and living organisms which causes breathing problems and skin diseases.
Question 3. Write a short note on petroleum. Answer: Petroleum is the liquid form of fuel. It is also known as crude oil and found trapped between the layers of impervious rocks under the ground. It is a natural resource, which formed by the dead plants and animals in the sea. It is a dark coloured viscous liquid and like all other oils, it is lighter than water. It is a mixture of different hydrocarbons. It undergoes fractional distillation to yield petrol, kerosene, diesel and other chemicals used in manufacture of plastics.
Question 4. How is the energy useful to us? Explain. Answer: We need energy in almost every field of our life. Without energy our life is impossible. Some of the uses of energy are:
We need energy of fuels to generate electricity and to run vehicles.
We need energy to run our electrical appliances like refrigerator, TV, radio, computer, etc.
We need energy at construction sites to construct houses, buildings, etc.
We need energy to cook our food and other domestic use.
We need energy (petrochemicals) for manufacturing fibres, plastics, paints, cosmetics, etc.
All the factories, industries, agricultural devices depend on power supply to run the machines.
Question 5. List the steps to conserve the resources. Answer: As we know, we all are dependent on the resources. But we should keep in mind that resources are limited in nature. If we misuse it, our future generation will have no resources. This is an alarming situation. We can take following steps:
We shbuld cook our food on low flame.
Devices that consume less energy like CFLs and LED lights should be preferred.
We should take care not to waste electricity.
We should cover our cooking vessels while cooking.
Instead of use of individual vehicles, use of public transport should be encouraged.
Solar or tidal energy should be developed and encouraged.
Dams should be use to generate electricity instead of burning coal or petroleum.
Materials Metals and Non Metals MCQ Questions Class 8 Science with Answers
Chapter 4
MATERIALS : METALS AND NON-METALS
Question. The property of metals by which they can be beaten into thin sheets is called ____ a) Ductility b) Sheetability c) Metallic d) Malleability
Answer : D
Question. The property of metal by which it can be drawn into wires is called ______ a) Ductility b) Sheetability c) Metallic d) Malleability
Answer : A
Question. The metal found in liquid state is a) Iron b) Aluminium c) Mercury d) Gold
Answer : C
Question. When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of a) Copper oxide and Copper Nitrate b) Copper hydroxide & Copper Carbonate c) Copper carbonate and Copper sulphate d) Copper hydroxide and Copper Nitrate
Answer : B
Question. When sulphur dioxide is dissolved in water __________ is formed. a) Sulphuric acid b) Sulphoxy acid c) Sulphurous acid d) Sulphur trioxide
Answer : C
Question. Sodium metal is stored in a) water b) Kept under open air c) alcohol d) Kerosene
Answer : D
Question. Phosphorus is stored in a) water b) Kept under open air c) alcohol d) Kerosene
Answer : A
Question. Since metals produce ringing sounds, they are said to be ____. a) Sound metal b) Sonorous c) Ring metal d) malleable
Answer : B
Question. A substance which cannot be broken down further by chemical reactions, by cooling, heating, or by electrolysis, is called ______ a) Metal b) Non Metal c) Element d) Compound
Answer : C
Question. They are not sonorous and are poor conductors of heat and electricity. These materials are a) elements b) Metals c) Compound d) Non metals
Answer : A
Question: When non-metals react with water then
a) Non-metals do not react with water
b) Hydrogen gas is formed
c) Carbon dioxide gas is formed
d) None of the options
Answer : A
Question: The metal which can be cut with a knife
a) Sodium and potassium
b) Barium and calcium
c) Sodium and mercury
d) Potassium and calcium.
Answer : A
Question: Metal oxides are of nature
a) Basic
b) Acidic
c) Netural
d) None of the options
Answer : A
Question: All metals are solids except
a) Mercury
b) Sodium
c) Calcium
d) Hydrogen
Answer : A
Question: Materials around us can be classified into
a) Metals and non-metals
b) Elements and compounds
c) Acids and bases
d) None of the options
Answer : A
Question: The non-metal which is liquid at room temperature is:
a) Bromine
b) Carbon
c) Iodine
d) Chlorine
Answer : A
Question: The metal which is stored in kerosene:
a) Sodium
b) Phosphorus
c) Magnesium
d) Magnesium
Answer : A
Question: Non-metals are:
a) Generally solids and gases
b) Generally liquids
c) Generally gases
d) Generally gases and liquids.
Answer : A
Question: The liquid metal at room temperature
a) Mercury
b) Bromine
c) Sodium
d) Gold
Answer : A
Question: The most reactive metal is:
a) Potassium
b) Iron
c) Gold
d) Zinc
Answer : A
Question: What is the product when sulphur reacts with oxygen?
a) Sulphur dioxide
b) Sulphurous acid
c) Sulphuric acid
d) Sulphur trioxide
Answer : A
Question: The solution of ash of magnesium ribbon is
a) Basic
b) Acidic
c) Neutral
d) All of the options
Answer : A
Question: Which metal is found in liquid state t room temperature?
a) Hg
b) Zn
c) Fe
d) Al
Answer : A
Question: The metals that produce ringing sounds, are said to be
a) Sonorous
b) Malleable
c) Lustrous
d) Hard
Answer : A
Question: The property of metal by which it can be drawn into wires is called
a) Ductility
b) Decorating
c) Malleability
d) Conductivity
Answer : A
Question: Which one of the following is a good conductor of electricity?
a) Iron
b) Plastic
c) Wood
d) Glass
Answer : A
Question: All materials shown property of malleability expect
a) Graphite
b) Iron
c) Aluminium
d) Silver
Answer : A
Question: The property of metals by which they can be beaten in to thin sheets is called
a) Malleability
b) Ductility
c) Conduction
d) Expansion
Answer : A
Question: Which one of the following is metal?
a) Na
b) N
c) O
d) C
Answer : A
Question: Which one of the following is non metal?
a) N
b) Fe
c) Al
d) Zn
Answer : A
Materials: Metals and Non-Metals Class 8 Extra Questions Very Short Answer Type
Question 1. Name some common metals. Answer: Copper, aluminium, iron, silver, gold, etc.
Question 2. Name some common non-metals. Answer: Hydrogen, oxygen, carbon, sulphur, phosphorus, etc.
Question 3. Give examples of metalloids. Answer: Antimony, arsenic, silicon, boron, etc.
Question 4. Name the property due to which metals shine. Answer: Lustre
Question 5. Name two metals which are soft enough to be cut. Answer: Potassium and sodium
Question 6. Name the property due to which metals can be beaten into thin sheets. Answer: Malleability
Question 7. Which non-metal does conduct heat and electricity? Answer: Carbon
Question 8. Name the property due to which metals can be drawn into wires. Answer: Ductility
Question 9. Name the metal and non-metal which occur in liquid state. Answer: Mercury (metal), bromine (non-metal).
Question 10. Due to which property a bell rings? Answer: Sonority
Question 11. Generally, non-metals are non-lustrous. Name one non-metal which is lustrous. Answer: Iodine
Question 12. State the property of non-metals due to which phosphorus is kept in water. Answer: Non-metals do not react with water.
Question 13. Why some metals displace other metals from their solution? Answer: Because of being more reactive than the metals which they displace.
Question 14. Which metal is used for wrapping food items? Answer: Aluminium
Question 15. Which metal is more reactive: Iron or zinc? Answer: Zinc
Question 16. Which metal is less reactive: Copper or zinc? Answer: Copper
Question 17. Name one metal which does not react with dilute hydrochloric acid. Answer: Copper
Question 18. Whose oxides are basic in nature: Metal or non-metal? Answer: Metal
Question 19. Whose oxides are acidic: Metal or non-metal? Answer: Non-metal4
Question 20. Name two metals which do not react with oxygen even at high temperature. Answer: Gold and silver
Question 21. Classify the following into metals and non-metals: Copper, iron, graphite, sulphur, aluminium, oxygen Answer: Metals: Copper, iron, aluminium Non-metals: Graphite, sulphur, oxygen
Question 22. Name two physical properties of metals. Answer: Malleability and sonority
Question 23. What happens when metals react with oxygen? Answer: Metal oxides are formed.
Question 24. What happens when magnesium is burnt in air? Answer: Magnesium burns with a white dazzling flame and a white powdery magnesium oxide is formed.
Question 25. What happens when metals react with water? Answer: Metals produce their hydroxides or oxides and hydrogen.
Materials: Metals and Non-Metals Class 8 Extra Questions Short Answer Type
Question 1. What is a metal? Answer: Substances having characteristic properties like malleability, ductility, sonority, conductivity, lustre, – and solidness are called metals. For example, aluminium, copper, zinc, iron, etc.
Question 2. What are non-metals? Answer: Substances which are soft and dull, i.e., non-lustrous, non-sonorous, non-ductile, non-malleable and poor conductor of heat and electricity are called non-metals. For example, oxygen, hydrogen, sulphur, etc.
Question 3. Mention the physical properties of metals. Answer: Physical properties of metals are:
Malleable
Lustre
Sonorous
Ductile
Solid
Good conductor of heat and electricity
Question 4. What are the physical properties of non-metals? Answer: The physical properties of non-metals are:
Non-malleable
Non-sonorous
Non-lustrous, i.e., dull in appearance
Non-ductile
Poor conductor of heat and electricity
Question 5. Explain the term ‘malleability’ with suitable examples. Answer: Malleability is the property of metals due to which they can be beaten into thin sheets. For example, if we beat or hammer any metal like aluminium, zinc, iron, copper, etc., it become longer and larger but does not break. Thin sheets can be obtained by this process.
Question 6. What is ductility? Explain with examples. Answer: Ductility is one of the properties of metals due to which they can be drawn into wires. For example, aluminium and copper are drawn into wires and used for electrical and different purposes.
Question 7. Why aluminium is used for wrapping of food items? Answer: Aluminium is a metal and hence possesses malleability property. It can be beaten into thin sheets and can be folded into any shape. It is cheaper than other malleable metals and does not react with food items. That is why it is used as wrapping materials for food items.
Question 8. Why metals are used in ringing bells? Answer: Metals have sonority. Due to this property, they can produce ringing sounds. That is why metals are used in ringing bells.
Question 9. What are the differences between metals and non-metals? Explain on the basis of their physical properties. Answer:
Metals are malleable and give thin sheets after hammering whereas non-metals are brittle and give no sheets.
Metals are ductile and can be drawn into wires whereas non-metals are non-ductile and can’t be drawn into wires.
Metals are sonorous and used in ringing bells whereas non-metals are non-sonorous and cannot be used in ringing bells.
Metals are good conductors of heat and electricity while non-metals are poor conductors.
Question 10. What happen when a copper vessel is exposed to moist air for long? Also write the equation. Answer: When a copper vessel is exposed to moist air for long, it acquires a dull green coating. This green material is a mixture of copper hydroxide [Cu(OH)2] and copper carbonate (CuCO3). The reaction is as follows:
Question 11. What happens when a magnesium ribbon is heated in presence of air? Answer: When a magnesium ribbon is heated in presence of air, it burns with a white dazzling flame and a white powdery magnesium oxide is formed.
Question 12. How do metals and non-metals react with water? Answer: Metals produce their hydroxides or oxides and hydrogen when they react with water. Sodium and potassium react with cold water along with the production of a large amount of heat. Magnesium react with boiling water and iron with steam. Gold, silver and platinum do not react with water. Non-metals do not react with water.
Question 13. With the help of equations, explain the reaction of non-metals with oxygen. Answer: Non-metals react with oxygen to form acidic oxides. But most of the non-metals reacts with oxygen on ignition. The equations follow as:
Question 14. How do metals and non-metals react with acids? Answer: Metals react with acids to form respective salts along with evolution of hydrogen gas that burns with a pop sound. The equation are as follows:
There are some metals like copper, silver, gold and platinum that do not liberate hydrogen with acids. Generally, non-metals do not react with acids.
Question 15. How do metals and non-metals react with bases? Answer: Most of the metals do not react with bases. However, some metals like aluminium, lead and zinc react with strong bases like sodium hydroxide (NaOH) to make complex salts and hydrogen. Generally, non-metals do not react with bases. Sometimes some complex reactions take place between non-metals and bases.
Question 16. What is a displacement reaction? Give one example. Answer: A chemical reaction in which a more reactive metal displaces a less reactive metal is called displacement , reaction. For example, when zinc (Zn) reacts with copper sulphate (CuSO2), zinc replaces copper being it more reactive than copper. The equation is
Materials: Metals and Non-Metals Class 8 Extra Questions Long Answer Type
Question 1. Distinguish between metals and non-metals on the basis of their physical properties. or Compare the physical properties of metals and non-metals. Answer: Difference between metals and non-metals on the basis of their physical properties.
Physical Properties
Non-metals
1. Malleability
Metals are malleable, i.e., they can be beaten into thin sheets. Exception: Mercury
Non-metals are non- malleable. They are broken into pieces when hammered. Hence they are also called brittle.
2. Sonority
Metals are sonorous, i.e., they produce ringing sound when struck.
Non-metals are non-sonorous.
3. Ductility
Metals are ductile, i.e., they can be drawn into wires. Exception: Mercury
Non-metals are non-ductile.
4. Lustre
Metals are lustrous, i.e., they are shiny.
Non-metals are non-lustrous, i.e., they are dull in appearance. Exception: Graphite and iodine.
5. Hardness or solidness
Metals are hard except sodium and potassium.
Non-metals are soft except diamond.
6. Conductivity
Metals are good conductor of heat and electricity.
Non-metals are poor conductor of heat and electricity. Exception: Graphite is a non-conductor of heat and electricity.
7. Density
Metals are of high density except lithium.
Non-metals are of low density.
8. Melting and boiling points.
Metals have high melting and boiling points.
Non-metals have low melting and boiling points except graphite.
Question 2. Distinguish between metals and non-metals on the basis of their chemical properties. or Compare between metals and non-metals on the basis of their chemical properties. Answer: Difference between metals and non-metals on the basis of their chemical properties.
Chemical Properties
Metals
Non-metals
1. Reaction with oxygen
Metals react with oxygen to form basic oxides which form bases when dissolve in water.
Non-metals react with oxygen to form acidic oxides which form acids when dissolve in water.
2. Reaction with water
Metals react with water to form their oxides or hydroxides.
Non-metals do not react with water.
3. Reaction with acids
Metals react with acids to produce respective salts along with evolution of hydrogen gas. Some metals like Cu, Ag, Au, etc., do not liberate hydrogen gas.
Non-metals do not react with acids except sulphur which react with hot, concentrated acid.
4. Reaction with bases
Most of the metals do not react with bases. However, some metals like Al, Pb, Zn react with strong bases like NaOH to form complex salts and hydrogen gas.
Generally, non-metals do not react with bases. Sometimes, some complex reactions take place between nonmetals and bases.
Question 3. Explain chemical properties of metals with examples. Answer: (i) Reaction with oxygen or air: Metals react with oxygen to form basic oxides. Some metals like potassium and sodium react vigorously with oxygen. For example,
Some noble metals like gold, silver and platinum do not react with oxygen. Iron (Fe) and copper (Cu) get rusted when react in presence of oxygen and water (moist air).
(ii) Reaction with water: Metals react with water to form their oxides or hydroxides. Gold, silver and platinum do not react with water. Some metals like sodium, potassium react vigorously with water. For example,
(iii) Reaction with acids: Metals react with acid to form their salts followed by evolution of hydrogen gas. For example,
Some metals like gold, copper, silver, etc., do not liberate hydrogen gas with acids.
(iv) Reaction with bases: Most of the metals do not react with bases. However some metals like aluminium, zinc and lead react with strong bases like sodium hydroxide to make complex salts and produce hydrogen.
(v) Displacement reactions: More reactive metals displace less reactive metals. For example,
In the above reactions, zinc (Zn) and magnesium (Mg) are more reactive than copper (Cu), hence they replace copper from its solution.
Question 4. Explain with suitable examples the chemical properties of non-metals. Answer: Reaction with oxygen: Non-metals react with oxygen to form acidic oxides. But most of them do this on ignition. For example,
They form negative ions and are good oxidising agents. Reaction with water: Non-metals do not react with water. Reaction with acids and bases: Generally, non-metals do not react with acids and bases. How¬ever, sometimes some complex reactions take place between non-metals and bases.
Question 5. What are main uses of metals? or How are metals useful to us? Answer: Metals are very useful to us in many ways. For example, (i) Due to their thermal and electrical conductivity, metals are use to make utensils, cooking vessels, wires and appliances. For example, copper and aluminium are mainly used for these purposes.
(ii) Metals like iron and steel are used in various tools, machinery, pipes, rods, sheets, doors, windows, construction works like bridges, roads, buildings, etc.
(iii) Aluminium is used as packaging and wrapping materials. It is also used in aircrafts and automobiles, etc.
(iv) Metals like gold, silver and platinum are used to make jewellery and other decorating items.
(v) Zinc is used in galvanisation and dry cell and chromium in electroplating.
(vi) Lead is used in making electrodes and batteries.
Question 6. What are the main uses of non-metals? or How are non-metals useful to us? Answer: Like metals, non-metals also play an important role in our lives. They help us in many ways. For example, (i) We breathe oxygen which is the basis of life of all living things including human beings. Without it, no living beings can exist alive on this earth.
(ii) CO2 which is a non-metal oxide is essential for plants to carry out photosynthesis.
(iii) Non-metals like nitrogen and phosphorus are used in fertilisers for better yield of plant. Phosphorus is used in manufacturing of matchsticks and fireworks.
(iv) Non-metal like iodine is used in the purple coloured solution applied on wounds. Sulphur is also used in preparing skin medicines and making ointment due to its fungicidal properties.
(v) Non-metal like chlorine is used in water purification process. Due to its bleaching properties it is used to make bleaching powder.
(vi) Carbon, a non-metal, is used in most of the fuels.
Question 7. What is reactivity series? Suggest an activity to arrange sodium, magnesium and copper in the order of their decreasing reactivity. Answer: Reactivity series is an arrangement of metals in decreasing order of their reactivity from highest to lowest. The metals occupying the higher positions in the activity series are more reactive in displacing the other metals lying below it from the solutions of their salts.
The activity series is a useful guide for predicting the products of metal displacement reactions. For example, placing a strip of zinc metal in a copper (II) sulphate solution will produce metallic copper and zinc sulphate, since zinc is above copper on the series.
A trip of copper placed into a zinc sulphate solution will not produce an appreciable reaction, because copper is below zinc on the series and can’t displace zinc ions from solution.
Activity to arrange sodium, magnesium and copper in the order of their decreasing reactivity: (i) Take a pinch of sodium with a forceps and place in a beaker containing water. You will notice that sodium reacts vigorously. (ii) Take a small piece of magnesium ribbon and add warm water to it. Magnesium reacts with warm water to form magnesium oxide and hydrogen gas. Magnesium reacts very slowly with cold water. (iii) Take small pieces of copper turnings and add warm water to it. It doesn’t react with warm water also. Hence, increasing order of reactivity is Na > Mg> Cu.
Materials: Metals and Non-Metals Class 8 Extra Questions HOTS
Question 1. Why does calcium float in water? Answer: The hydrogen gas formed on adding calcium to water sticks to the surface of calcium solid and make it float in water.
Question 2. Zinc sulphate forms a colourless solution in water. Will you observe any colour on adding copper turning in it? Answer: No, because copper is less reactive than zinc and will not be able to displace zinc from its salt solution
Question 3. A doctor prescribed a tablet to a patient suffering from iron deficiency. The tablet does not look like iron. Explain. Answer: The tablet is not made of iron metal, instead it contains a salt of iron.
Question 4. Ram stored copper sulphate solution in a container made of iron. He observed certain changes after few hours. Can you tell what changes did he observed? Answer: Blue colour solution of copper sulphate has changed to green colour of ferrous sulphate. The iron container was found to be corroded from many places. A red powdery deposit of copper sulphate was found on the iron container.
Question 5. Imagine that gold is reactive like copper. Will it be still wanted? Why or why not? Answer: If gold becomes reactive like copper then its use in ornaments will decline. This is because due to its increase reactivity it will lose its shine frequently which in turn will reduce its demand.
Materials: Metals and Non-Metals Class 8 Extra Questions Value Based (VBQs)
Question 1. Gold is a very precious metal. Pure gold is very soft and is thus not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. But some jewellers mix a large quantity of copper and silver in gold to earn more profit.
(a) What precautions should you take while purchasing gold jewellery? (b) What standard you must see on gold ornaments? (c) What value of shopkeeper’s are shown here? Answer: (a) We must see the carat of gold jewellery, current price and BIS hallmark on it. (b) BIS hallmark. (c) Some shopkeeper’s are greedy, mean, cheater and money minder.
Question 2. Mercury is largely used in thermometers to measure the temperature. It is a very dangerous metal as its density is very high. If it get into the food chain, it leads to mercury poisoning. (a) What two precautions you must take while handling equipments containing mercury? (b) Why mercury is used in thermometers? (c) Can you suggest other alternatives to mercury thermometers? Answer: (a)
We must handle the equipments carefully and firmly.
If there is a mercury spill, we must leave the area immediately and inform our parents or teachers.
(b) Mercury is a good conductor of heat. Hence, the slightest change in temperature i° otable when it is used in a thermometer. (c) Digital thermometer and spirit thermometer.
MCQ Questions for Class 8 Science: Ch 3 Synthetic Fibres and Plastics
1. Polythene and PVC are examples of
(a) Bio degradable substance
(b) Thermosetting plastics
(c) Thermoplastics
(d) Rayon
► (c) Thermoplastics
2. _____ is blended with wool for making carpets.
(a) Rayon
(b) Nylon
(c) Polystyrene
(d) Polyester
► (a) Rayon
3. Fabric is made of
(a) steel
(b) fibre
(c) paper
(d) none of these
► (b) fibre
4. The raw materials used in making nylon
(a) Wood pulp
(b) Cellulose
(c) Coal, water, air
(d) All of these
► (c) Coal, water, air
5. Which of the following set of features belong to thermoplastics ?
(a) soft and brittle
(b) hard and strong
(c) hard and less brittle
(d) soft and less brittle
► (d) soft and less brittle
6. Which of the following is a thermosetting plastic ?
(a) Nylon
(b) PTFE
(c) Polyester
(d) Melamine
► (d) Melamine
7. First synthetic fibre formed from natural material is:
(a) Rayon
(b) Acrylon
(c) Nylon
(d) Polyester
► (a) Rayon
8. Statement incorrect for synthetic fibres is/are:
(a) non-biodegradable
(b) very expensive
(c) long lasting
(d) all the above
► (b) very expensive
9. The first man-made fibre is
(a) nylon
(b) polyester
(c) rayon
(d) cotton
► (c) rayon
10. Why is it not advisable to wear clothes made up of synthetic fibres in hot and humid weather?
(a) Synthetic fibres catch fire very easily.
(b) Synthetic fibres do not absorb sweat.
(c) Synthetic fibres stick to the body.
(d) Both (b) and (c).
► (d) Both (b) and (c).
11. A man- made fibre obtained from natural source is :
(a) Acrylic
(b) Nylon
(c) Rayon
(d) Polyester
► (c) Rayon
12. Fibre obtained by chemical treatment of wood pulp is called ___________.
(a) Natural silk
(b) Rayon
(c) Nylon
(d) Polyester
► (b) Rayon
13. When plastics are burnt they release:
(a) oxygen gas
(b) biogas
(c) toxic gases
(d) nitrogen gas
► (c) toxic gases
14. The strongest fibre is called:
(a) rayon
(b) nylon
(c) acrylic
(d) none of these
► (b) nylon
15. Remoulding can be done of :
(a) Polyvinyl chloride
(b) Bakelite
(c) Melamine
(d) Formaldehyde
► (a) Polyvinyl chloride
16. Raw materials for the synthetic fibres are derived from :
(a) petroleum products
(b) plant products
(c) animal products
(d) only coal
► (a) petroleum products
17. The lightweight plastic material is :
(a) Polypropylene
(b) Polythene
(c) Bakelite
(d) Polyester
► (a) Polypropylene
18. The small units used in making synthetic fibres are:
(a) molecules
(b) polymers
(c) cells
(d) none of these
► (b) polymers
19. Which of the following is not a characteristic of plastics?
(a) Plastics are poor conductors of heat.
(b) Plastics are insoluble in water.
(c) Plastics are non-inflammable.
(d) Plastics do not react with water and air.
► (c) Plastics are non-inflammable.
20. The oldest synthetic plastic is :
(a) Polyester
(b) Bakelite
(c) Melamine
(d) Polythene
► (b) Bakelite
21. Plastics are generally made from
(a) coal
(b) plant products
(c) kerosene
(d) petroleum
► (d) petroleum
22. Which of the following is used for making stockings and parachutes?
(a) Bakelite
(b) Wool
(c) Nylon
(d) Cotton
► (c) Nylon
23. Which of the following materials is the best for making garments and jackets that can be used in wet or damp environment?
(a) Polyester
(b) Wool
(c) Cotton
(d) None of these
► (a) Polyester
24. The fibre made up by the chemical treatment of wood pulp is
(a) Rayon
(b) Nylon
(c) Polyester
(d) None of these
► (a) Rayon
Synthetic Fibres and Plastics Class 8 Extra Questions Short Answer Questions
Question 1. What are polymers? Answer: Polymers are compounds that are made up of same, small repeating units, joined together through bonds in a linear pattern.
Question 2. What is cellulose? Answer: Cellulose is a polymer made up of large number of glucose units.
Question 3. List the two ways in which synthetic fibres can be synthesised. Answer: Synthetic fibres may be synthesised by two ways:
By regenerating them from natural fibres, like in rayon.
By using entirely chemicals and chemical reactions, like in nylon.
Question 4. What is rayon? Answer: Rayon is a man-made fibre which is produced by the chemical processing of wood pulp, i.e., a natural substance.
Question 5. List two uses of rayon. Answer: The two uses of rayon are:
It is used to make apparels like shirts, blouses, etc.
It is used to make furnishings and upholstery.
Question 6. List any two properties of rayon. Answer: The two properties of rayon are:
Rayon is a versatile fibre.
It can be dyed in different colours.
Question 7. Draw a diagram to show the: (a) linear arrangement of units in plastic. (b) cross-linked arrangement of units in plastic. Answer:
Question 8. Write some advantages of synthetic fibres. Answer: Advantages of synthetic fibres are:
Synthetic fibres are strong and durable.
They do not shrink.
They are moth and insect resistant.
Question 9. What are plastics? Answer: Plastics are those substances which are mostly synthetic in nature, obtained mainly from petrochemi¬cal sources and can be moulded into different shapes.
Question 10. What is plasticity? Answer: Plasticity is the property of materials by which they can be moulded into any shape.
h
Question 11. What are thermosetting plastics? Answer: Thermosetting plastics are those which when moulded once, cannot be softened again and lose their plasticity.
Question 12. List any three properties of plastics. Answer: The three properties of plastics are:
They are non-corrosive in nature.
They are light in weight and durable.
They do not conduct heat.
Question 13. What are the uses of polyester? Answer: The uses of polyester are:
It is used in making home furnishings and apparels.
Polyester is used for finishing on guitars and pianos.
Question 14. Why is it advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen? Answer: The synthetic fibres melt on heating. This is actually a disadvantage with synthetic fibres. If the cloth catches fire it can be very disastrous. The fabric melts and sticks to the body of the person wearing it. It is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire in the kitchen.
Question 15. Write some properties and uses of melamine. Answer: Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.
Synthetic Fibres and Plastics Class 8 Extra Questions Long Answer Questions
Question 1. Describe about nylon. Write its uses and properties. Answer: Nylon is the strongest amongst all the synthetic fibres. It is fully synthetic polymer which is prepared from coal, water and air. It is a polymer of amides. It was made in 1931 for the first time. It was used as a supplement of silk when silk got deficient during World War II for many military applications. Uses of Nylon
Nylon is used in toothbrushes, combs, etc.
It is used to make parachutes, tents, ropes, etc.
It is used to make socks and stockings as it is elastic.
It is widely used for making clothes, carpets, etc.
Properties of Nylon
It melts on heating.
It absorbs less water.
It is resistant to moths and fungi.
It has high tensile strength.
It is durable.
Question 2. Write the advantages of synthetic fibres. Answer: Synthetic fibres has many advantages as compared to natural fibres. Some of them are as follows:
They are very strong and durable.
They are cheaper in cost as compared to natural fibres.
They absorb less water and are quick to dry.
They do not shrink.
They are very useful for saving our trees and animals as they are made up of chemicals.
They are moth and insect resistant.
Question 3. List the common varieties of polyester. Also mention the natural fibres which are used for blending to enhance their properties. Answer: Polyester could be blended with natural fibres to enhance its properties. The common varieties of polyester are:
PET (Polyethylene terephthalate)
Terrycot: It is made by blending polyester and cotton.
Terrysilk: It is made by blending polyester iaiid silk.
Terrywool: It is made by blending polyester and wool.
Question 4. Explain the properties of plastics. Answer: Plastics are those substances which are mostly synthetic in nature. Following are the properties of plastics:
Plastics are non-corrosive in nature, i.e., they do not react easily with air and water. They are unaffected by most of the chemicals in normal conditions.
Plastics are the bad conductor of heat. They do not get heated up like metals.
Plastics are non-biodegradable, i.e., they do not get decomposed by microorganisms.
Plastics are very durable.
Question 5. ‘Plastics are hazard to environment’. Explain this statement. Answer: Yes, plastics are hazard to environment. They make versatile materials but are very dangerous to the environment. Plastics are non-biodegradable in nature. It takes more than 100 years to decompose. If use of plastics are not reduced, our earth would turn into a big garbage bin. The major problems due to plastics are:
If plastics are burnt, they evolve poisonous gases. These gases destroys the ozone layer of the earth and also pollute the environment.
If the plastics are disposed in drains, they choke the drains causing waterlogging.
If these plastics are swallowed by the innocent animals along with their food, they harm their di-gestive system which leads to their death.
They are manufactured by the consumption of a large amount of petroleum.
Question 8. List the strategies for plastic waste management. Answer: Some of the strategies for plastic waste management are:
We should use paper bags and jute bags instead of using plastic bags.
The government should ban the use of plastic bags.
Plastics should be recycled to make other useful products which do not harm the environment.
We should use a special garbage bins to dispose plastic wastes.
We should not throw plastic wastes in water bodies.
Practicing 4R’s principle, i.e., Reuse, Recycle, Reduce and Recover should be encouraged.
MCQ Questions for Class 8 Science: Ch 2 Microorganisms: Friend and Foe
1. Identify bacteriophage.
(a) Algae
(b) Virus
(c) Protozoa
(d) Fungi
► (b) Virus
2. Microbiology is the study of :
(a) Useful products prepared from microbes
(b) Parts of living organisms
(c) Microbes
(d) Diseases caused by microorganisms
► (c) Microbes
3. _______ are the agents that act as carriers of a pathogen and spread diseases.
(a) Microbes
(b) Parasites
(c) Vectors
(d) DNA
► (c) Vectors
4. Rhizobium bacteria
(a) Help in digestion
(b) Cause diseases
(c) Help in nitrogen fixation
(d) All of these
► (c) Help in nitrogen fixation
5. Malaria is caused by
(a) Protozoa
(b) Virus
(c) Algae
(d) Bacteria
► (a) Protozoa
6. Scientists who study microorganisms are called
(a) microbiologists
(b) microscopists
(c) microorganists
(d) microtypist
► (a) microbiologists
7. The moist bread becomes mouldy after a few days when it is left in a container with a cover. Which of the following conditions favour the growth of the fungus?
(a) Absence of water
(b) Absence of light
(c) Presence of sunlight
(d) Presence of carbon dioxide
► (b) Absence of light
8. What process takes place when yeast is added to grape juice and left for a week?
(a) Decomposition
(b) Fermentation
(c) Distillation
(d) Oxidation
► (b) Fermentation
9. Which is a fungal disease in human?
(a) amoebiasis
(b) tuberculosis
(c) anthrax
(d) Athlete’s foot
► (d) Athlete’s foot
10. Which of the following disease causing pathogens is / are carried by mosquitoes?
(a) Dengue fever
(b) Malaria
(c) Cholera
(d) Both (A) and (B)
► (d) Both (A) and (B)
11. Which of the following terms is given to the microorganisms that cause diseases?
(a) Antigens
(b) Antibodies
(c) Pathogens
(d) Vectors
► (c) Pathogens
12. Amoeba belongs to
(a) Algae
(b) Fungi
(c) Protozoa
(d) Virus
► (c) Protozoa
13. Yeast is not used in the preparation of :
(a) bread
(b) alcohol
(c) dhokla
(d) antibiotic
► (d) antibiotic
14. Microorganisms are :
(a) saprophytes
(b) autotrophs
(c) autotrophs & heterotrophs
(d) hetrotrophs
► (c) autotrophs & heterotrophs
15. Which of the following can affectively prevent the ringworm disease?
(a) Vaccination
(b) Vector control
(c) Improving personal hygiene
(d) Using antibiotics
► (c) Improving personal hygiene
16. What are pond scum?
(a) algae
(b) protozoa
(c) fungi
(d) bacteria
► (a) algae
17. A plant disease called citrus canker is caused by a _________ .
(a) Virus
(b) Protozoa
(c) Bacteria
(d) Fungi
► (c) Bacteria
18. Bacteriophage is a :
(a) fungi
(b) protozoa
(c) virus
(d) bacteria
► (c) virus
19. Which of the following statements describes bacteriophage correctly?
(a) It is a bacterium which causes diseases in plants.
(b) It is a type of virus which attacks bacteria.
(c) It is a bacterium which kills viruses.
(d) It can multiply inside both living and non-living cells.
► (b) It is a type of virus which attacks bacteria.
20. Which of the following is the smallest microorganism?
(a) Algae
(b) Bacterium
(c) Protozoan
(d) Virus
► (d) Virus
21. Which of the following enzymes is secreted by bacteria that can digest cellulose?
(a) Amylase
(b) Cellulase
(c) Lipase
(d) Protease
► (b) Cellulase
22. Which of the following microorganism lives alone:
(a) Amoeba
(b) All Bacteria
(c) Fungi
(d) All Cyanobacteria
► (a) Amoeba
23. Which two words are synonyms?
(a) Microorganism and pathogen
(b) Microorganism and microbe
(c) Microbe and aerobe
(d) Microbe and anaerobe
► (b) Microorganism and microbe
24. Curd formations needs :
(a) citric acid bacterium
(b) acetic acid bacterium
(c) lactic acid bacterium
(d) all the above
► (c) lactic acid bacterium
25. TMV causes disease in :
(a) tobacco plant
(b) human infants
(c) timber plants
(d) none of the above
► (a) tobacco plant
26. Scientist who discovered the fermentation
(a) Alexander Fleming
(b) Louis Pasteur
(c) John Mendal
(d) Charles Darwin
► (b) Louis Pasteur
Important Questions Class 8 Science Chapter 2 – With Solutions
Question 1. Pathogenic microorganisms present in host cells are killed by ____.
antibiotics
antibodies
vaccines
pain killers
Answer 1: The correct option is A- Antibiotics.
Explanation:
Antibiotics are those substances that may inhibit or kill the growth of different microbes. Antibiotics are antimicrobial drugs from other organisms (such as moulds, fungus and some soil bacteria) to combat harmful microorganisms. The consumption of these antibiotics kills the microorganisms causing infection in host bodies. The definition of a pathogenic organism is the organism capable of causing disease in its host. A human pathogen has the capability of causing illness in humans. Common examples of various pathogenic organisms include specific strains of bacteria like Salmonella, Listeria and E. coli, and other viruses such as Cryptosporidium. An antibiotic is a chemical substance that inhibits the growth of these harmful bacteria. They hinder the bacteria’s reproductive cycle inside the host’s body.
Question 2. How do vaccines work?
Answer 2:
Vaccines are treatments that improve your immunity to a certain disease. Vaccines contain dead or weakened but alive microorganisms of a particular disease. When a vaccine containing dead or alive microorganisms is introduced into a healthy body, orally (by mouth) or by injection, that person’s body triggers an immune response. The immune system of the person, in turn, responds by producing some substances called antibodies in its blood to protect against the pathogens introduced. These antibodies kill the ‘live’ disease-causing microorganisms present in the vaccine. Some of the antibodies remain in the person’s blood for a very long time and fight against the same microorganism and kill them if they enter the body naturally later. So, due to antibodies in the blood, a person remains protected from that disease. With a vaccine, the immune system can safely learn to recognize them as hostile invaders, produce antibodies, and remember them for the future.
Thus, a vaccine develops immunity from a disease.
Question 3. Write a paragraph on the harms caused by microorganisms.
Answer 3:
Microorganisms are causative agents in many infectious diseases. Therefore, microbes are termed pathogens. Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so tiny that they can be seen only under a microscope. These include many organisms such as bacteria, viruses, fungi, algae, protozoa, etc. Some microbes prove beneficial; however, most microorganisms can be very harmful to us. They cause many diseases in humans, plants and animals that prove to be fatal.
Harmful effects of microorganisms are:
Some microorganisms are pathogens which cause diseases to humans, animals and plants.
Bacteria and fungi cause food spoilage and make them unfit for eating. Consumption of such food causes food poisoning.
Human diseases like the common cold, tuberculosis, measles, chicken pox, polio, cholera, typhoid, hepatitis B, malaria, etc., are caused by microorganisms.
Some serious diseases like anthrax are also caused in animals by microbes.
Microbes also cause diseases in plants like blights in potatoes, sugarcanes, oranges etc. Some viruses can affect cattle by causing foot and mouth disease.
They are also responsible for reducing crop yield, causing loss to farmers.
Microbes also spoil clothing and leather products. They reduce the lifespan and the quality of the product.
Question 4. What are the major groups of microorganisms?
Answer 4:
Microorganisms are very minute organisms that are invisible to the human eye. Microorganisms are so minute that they can only be seen under the microscope. Microorganisms include bacteria, fungi, archaea or protists. Microorganisms differ in size and structure, habitat, metabolism, and many other characteristics. Most bacteria are harmless or helpful, but some are pathogens, causing disease in humans and other animals.
There are five major groups of microorganisms. They are enlisted as
Bacteria:
It is a single-celled organism.
They can be spiral, rod-shaped, spherical-shaped, or comma-shaped.
It causes diseases like cholera, tetanus and tuberculosis.
Fungi:
Fungi are usually multicellular organisms that cause several diseases.
Symptoms depend on the area affected
The moulds formed on bread are a specific type of fungi.
Protozoa:
Protozoa can either be multicellular or unicellular.
Amoeba and Plasmodium are a few examples of protozoa.
They can be harmful to humans as well as different other organisms.
Virus:
Viruses are disease-causing microorganisms that can only divide inside a host organism/cell.
They remain inactive outside the cell.
It can affect plants, animals as well as humans.
HIV in humans and TMV virus occurring in plants are some examples of viruses.
Algae:
These are the only microorganisms that are multicellular.
Algae have photosynthetic pigments.
They are also known as precursors of plants.
Spirogyra and Chlamydomonas are some examples of algae.
Question 5. The bread or idli dough rises because of ______.
heat
grinding
growth of yeast cells
kneading
Answer 5: The correct option is C- growth of yeast cells
Explanation:
Yeast can be utilised as a leavening agent in bread and idli making. The yeast consumes the sugar in the dough and burps carbon dioxide gas and ethanol. This gas is trapped inside the bread dough due to gluten present in it, thus making the dough rise. The alcohol also gets evaporated in the baking process. While bread-making, the dough is left in a warm place. During fermentation, carbon dioxide gas is produced and gets trapped in tiny pockets of air within the dough. This makes the dough rise. If you let the dough rise for too long, the finished bread’s taste and texture suffer. Due to different yeast cell development, the dough of bread or idli rises. If there is lots of food present around to take advantage of the food, the yeast cells reproduce in great numbers. They normally develop a tiny bud from one edge of themselves when they reproduce. Then a small nucleus is placed and pinched off to make a smaller new yeast cell. The leavening agent or yeast converts sugars in the dough to carbon dioxide and derives energy from this reaction. Due to this, yeast cells grow, and the dough also expands. Hence, the bread and idli develop a soft and spongy texture.
Question 6. Explain the nitrogen cycle.
Answer 6:
The nitrogen cycle is the continuous process of exchanging nitrogen between organisms and the environment. Nitrogen is an essential nutrient needed to make amino acids and other important organic compounds. Still, most organisms cannot use free nitrogen, which is abundant as a gas in the atmosphere. This is a biogeochemical process through which nitrogen is converted into many forms, consecutively passing from the atmosphere to the soil to the organism and back into the atmosphere. Nitrogen is an important plant nutrient. However, plants and animals cannot directly use the plentiful nitrogen in the atmosphere. Nitrogen nitrification, nitrogen fixation, decay, and putrefying are among the mechanisms that pass from the ambience to the soil to the organism and then return to the atmosphere. Nitrogen gas exists in both organic as well as inorganic forms.
Organic nitrogen primarily exists in living organisms, and it gets passed through the food chain by consuming other living organisms.
While the inorganic forms of nitrogen are present in abundance in our atmosphere. This inorganic form of nitrogen is available for plants through symbiotic bacteria, which converts the inert nitrogen into a more usable form – such as nitrates and nitrites. Nitrogen will undergo a wide range of transformations to maintain a good ecosystem balance. This process extends to diverse biomes. The marine nitrogen cycle is known to be one of the most intricate biogeochemical cycles.
The nitrogen cycle is about the movement of nitrogen occurring between various elements on Earth (like air, soil, living organisms etc.). The amount of the element nitrogen in the atmosphere remains constant.
The atmosphere contains approximately 78% nitrogen.
Atmospheric nitrogen gets fixed into the soil.
N2 fixing microbes facilitate the conversion of atmospheric N2 into nitrogen compounds like NH3.
The plants utilise nitrogen from soil through their roots.
Animals utilise nitrogen, feeding on plants.
When plants & animals die, nitrogenous wastes are returned to the soil.
Decomposers convert some parts to nitrogen compounds to be used by plants.
Denitrifying bacteria convert into atmospheric N2.
Question 7. What are antibiotics? What precautions must be taken while taking antibiotics?
Answer 7:
Antibiotics are medicines produced by certain microorganisms which kill or stop the growth of microorganisms in our body. These are very effective in preventing the effects of microorganisms. Antibiotics are made from bacteria and fungi. Antibiotics treat various human and animal diseases as they target bacteria and viruses. They have significantly enhanced our ability to treat severe diseases like plague, whooping cough, and leprosy. Examples of general antibiotics are streptomycin, tetracycline, erythromycin etc.
Precautions to be taken while taking antibiotics:
Antibiotics should only be taken under the guidance of a skilled physician.
Antibiotics must only be taken when needed and in an adequate amount. Otherwise, they may be harmful and will become less effective in future.
The antibiotic course should be finished according to the doctor’s instructions.
Antibiotics must be administered in the correct dosage and at the appropriate time.
Antibiotics that are given in the wrong dose become useless.
Excessive medication usage might also harm the beneficial bacteria in our bodies.
Read more about Science Class 8 Chapter 2 important questions on Extramarks.
Question 8. Write ten lines on the usefulness of microorganisms in our lives.
Answer 8:
Microorganisms are very minute organisms that are invisible to the naked eye. However, these microbes are vital to plants and the environment. Here are some uses of microorganisms in our daily life.
Some microorganisms are used as a probiotic (live bacteria and yeasts that are good for the digestive system and maintain the good health of the host). They are called ‘good’ or ‘useful’ bacteria.
In pulse plants’ roots, rhizobium fixes nitrogen from the air and supplies nitrogen compounds to the pulse plants. It also helps to make the soil more fertile.
Microorganisms are used in winemaking, baking, pickling, and other food-making processes.
Alcoholic fermentation by yeast is widely used for the commercial preparation of wine and bread. Yeast makes idli, bhaturas, bread, pastries, and cakes.
Microbes are used to reduce pollution. For example, decomposers like bacteria and fungi break down dead bodies and excreta for forming inorganic compounds, which plants can easily absorb.
Microbes also play a crucial role in the preparation of medicines. Antibiotics are chemicals produced by microorganisms to kill bacteria. Penicillin is an antibiotic made from penicillium.
Bacteria in our intestine help in proper digestion and release vitamin B, absorbed by the intestine. They induce immunity in our bodies.
Many vaccines are prepared from microorganisms. These vaccines are usually given to children to protect them from the disease.
Certain microbes are used in the biological treatment of sewage and industrial effluents.
Lactobacillus is used in dairy industries for the setting of curd and cheese making. Microorganisms carry out the processing and ageing of cheese.
Question 9. What measures can be taken to prevent the spread of communicable diseases?
Answer 9:
Infectious diseases are communicable diseases that can spread from one person to another. Chickenpox, mumps, influenza etc., are a few examples of communicable diseases.
Precautions to prevent the spreading of communicable diseases:
Wash your hands often: This is mainly important before and after preparing food, eating, and after the toilet is used.
Get vaccinated: Immunisation can have a drastic reduction in your chances of contracting many diseases. Keep the recommended vaccinations up-to-date.
Use of antibiotics sensibly: Take antibiotics only when you are prescribed. Unless directed, or unless you are allergic to these antibiotics, take all prescribed doses of your antibiotic, even though you begin to feel better before you have finished the medication.
Stay at home if you observe signs and symptoms of an infection: Don’t go to work or class if you’re vomiting, have diarrhoea or are running a fever.
Be smart in food preparation: Keep counters, and kitchen surfaces clean when preparing meals. In addition, promptly refrigerate your food leftovers. Never let the cooked foods remain at room temperature for a long period.
Practice safer sex: Use condoms. Get tested for various sexually transmitted diseases (STDs), and have your partner get tested— or abstain altogether.
Don’t share personal items: Use your toothbrush, comb or razor blade. Avoid sharing drinking glasses or dining utensils.
Travel wisely: Avoid going to public places or events when ill.
Benefits of Solving Important Questions Class 8 Science Chapter 2
Science is a broad subject with multiple theories and concepts. All of this makes it difficult for students to understand and remember. Students are encouraged to go through Extramarks question bank of Important Questions Class 8 Science Chapter 2. Students can gather confidence by answering the important questions and going over their provided solutions. The Important Questions Class 8 Science Chapter 2 provides a strong foundation of basic concepts among students. These step-wise solutions will help you to attain perfection on the concepts involved in the chapter ‘Microorganisms: Friend and Foe’.
Mentioned below are some benefits of solving Important Questions Class 8 Science Chapter 2:
These solutions will help students to save time while preparing for their upcoming examination and cover the entire chapter as well as revise crucial concepts covered in the chapter.
Important Questions Class 8 Science Chapter 2 covers the majority of concepts of the entire chapter-Introduction to microorganisms, their habitats, classes of microorganisms like bacteria, fungi, protozoans and viruses, mode of their reproduction, use of microorganisms, harmful microorganisms, pathogens, soil microorganisms, nitrogen fixation by bacteria.
Students can entirely rely upon these important questions as these solutions are prepared following all the guidelines laid by CBSE.
Class 8 Science Chapter 2 important questions are compiled by the experts at Extramarks who have experience in teaching Biology and Science related subjects for several years.
Extramarks provides students from Class 1 to Class 12 with comprehensive learning solutions. Our website has abundant study materials and resources, along with important questions and solutions. Students can easily click on the links given below to get access to important questions Class 8 Science Chapter 2 along with some of these other resources:
MCQ Questions for Class 8 Science: Ch 1 Crop Production and Management
1. Weedicides are used to destroy:
(a) insects
(b) weeds
(c) pests
(d) none of these
► (b) weeds
2. Cutting mature crop manually or by a machine is called:
(a) Irrigating
(b) Harvesting
(c) Breeding
(d) Weeding
► (b) Harvesting
3. Grains are separated from stalks by a process called________
(a) Harvesting
(b) Threshing
(c) Weeding
(d) Winnowing
► (b) Threshing
4. The medium of growth for plants is :
(a) Cell
(b) Soil
(c) Water
(d) Air
► (b) Soil
5. Breeding, rearing and management animals for human use is :
(a) Aniculture
(b) Animal husbandry
(c) Animal culture
(d) None of these
► (b) Animal husbandry
6. The rearing of honey bees on large scale is called:
(a) sericulture
(b) tissue culture
(c) pisciculture
(d) apiculture
► (d) apiculture
7. Any plant cultivated at a large stretch of land is called :
(a) Crop
(b) Weed
(c) Cereal
(d) Fibre
► (a) Crop
8. Watering the crops is called:
(a) sowing
(b) manuring
(c) tilling
(d) irrigation
► (d) irrigation
9. Crop plants may be attacked by pests which affect the crop production. Fungi are such type of pests which cause diseases like
(a) Smut of wheat
(b) Citrus canker
(c) Blight of potato
(d) Both (a) and (c)
► (d) Both (a) and (c)
10. The manure prepared from green plants is :
(a) FYM
(b) Compost
(c) Green manure
(d) all the above
► (c) Green manure
11. Which of the following tools would a farmer use to remove weeds from the field?
(a) Hoe
(b) Axe
(c) Plough
(d) Cultivator
► (a) Hoe
12. Take a beaker and fill half of it with water. Put some wheat seeds in it, stir it and wait for some time. Which of the following holds true regarding the observation and inference of this experiment?
(a) Healthy seeds being lighter float on the surface of water.
(b) Damaged seeds being lighter float on the surface of water.
(c) Some healthy seeds and some damaged seeds float on the surface of water.
(d) Damaged seeds being heavier settle down at the bottom.
► (b) Damaged seeds being lighter float on the surface of water.
13. Combines are used for:
(a) sowing of seeds
(b) harvesting the crops
(c) threshing
(d) harvesting and threshing both
► (d) harvesting and threshing both
14. Peas are rich in:
(a) vitamins
(b) carbohydrates
(c) proteins
(d) fats
► (c) proteins
15. Improper use of fertilizers can cause:
(a) soil alkalinity & soil acidity
(b) soil acidity only
(c) soil acidity and soil erosion
(d) soil erosion
► (a) soil alkalinity & soil acidity
16. The system of irrigation wherein water is supplied drop by drop near the roots of plants, is called
(a) Sprinkler system
(b) Pulley system
(c) Lever system
(d) Drip system
► (d) Drip system
17. Wheat and gram belong to
(a) Rabi crops
(b) Kharif crops
(c) Both of these
(d) None of these
► (a) Rabi crops
18. The agricultural implement used for removing weeds and for loosening soil is :
(a) Combine
(b) Drill
(c) Hoe
(d) Cultivator
► (c) Hoe
19. The cutting and gathering of crop after it is matured is called X. After this, grains are separated from the crop by a process called Y. Z is the process of separating the hay and chaff from the grains. Which of the following statements is/are correct regarding X, Y and Z?
(a) Z is done with the help of wind in which grains along with husk is allowed to fall from a height.
(b) X is done mechanically by combine and manually by plough and harrow.
(c) X is the process known as threshing whereas Y is the process known as winnowing.
(d) Both (a) and (b)
► (a) Z is done with the help of wind in which grains along with husk is allowed to fall from a height.
20. Examples of kharif crops are
(a) Wheat and maize
(b) Gram and maize
(c) Paddy and maize
(d) All of these
► (c) Paddy and maize
21. Seed drill is used to
(a) sow the seeds
(b) remove the weeds
(c) remove the pest
(d) mix manure in the soil
► (a) sow the seeds
22. Cereals provide us mainly :
(a) carbohydrates
(b) proteins
(c) fats
(d) fibre
► (a) carbohydrates
23. Food provides _________ and materials required for the growth and maintenance of our body
(a) energy
(b) nutrition
(c) power
(d) none of the above
► (a) energy
24. Coconut provides us mainly :
(a) fat
(b) milk
(c) protein
(d) carbohydrate
► (c) protein
Crop Production and Management Class 8 Extra Questions Short Answer Type
Question 1. What is a crop? Answer: Crop is the term used to describe a plant that is grown in a field on a large scale. For example, cereal crops, wheat crops.
Question 2. What do you mean by produce? Answer: The products obtained from the crops are called produce.
Question 3. What do you mean by the term agricultural practice? Answer: Agricultural practices are those practices which involve the necessary steps to be taken during production of crops.
Question 4. Explain the term levelling. Answer: Levelling is the process of breaking down the larger lumps of soil, and then levelling them by using a leveller.
Question 5. What are the advantages of levelling? Answer: Following are the advantages of levelling:
Levelling helps to prevent soil erosion caused by wind or air.
It helps in sowing the seeds uniformly, and thus helps the plants to grow uniformly too.
It helps in proper irrigation by allowing the water to get distributed uniformly throughout the soil.
Question 6. What is a plough? Answer: A plough is an equipment for ploughing. It is mainly made of a wooden shaft called a plough-shaft, attached to a triangular iron blade called ploughshare.
Question 7. What is a cultivator? Answer: Cultivator is a farm implement used for stirring and pulverizing the soil for planting crops.
Question 8. Explain the term transplantation. Answer: Some of the crops are first grown in the nurseries and then transferred to the main field. This process is known as transplantation.
Question 9. What are the advantages of manure? Answer: Following are some advantages of manure:
It enhances water-holding capacity of soil.
It improves soil quality.
It promotes the growth of soil friendly microbes.
It is renewable, biodegradable and eco-friendly.
Question 10. What are weedicides? Give some examples. Answer: Weedicides are the chemicals that are used to remove weeds. Some commonly used weedicides are 2, 4-D and metachlor.
Crop Production and Management Class 8 Extra Questions Long Answer Type
Question 1. What do you mean by the term crop? Explain briefly the types of crops. Answer: Crop is the term used to describe a plant that is grown in a field on a large scale. For example, cereal crops, pulses and fruit crops. The crops grown in India can be classified as kharif and rabi.
Kharif crops are sown in the rainy season by June/July and are harvested by September/October. Thus they are also known as summer season crops. For example, rice, maize, etc.
Rabi crops are sown in the winter season in October or November and are harvested by March/April. Thus, they are also called winter season crops. For example, mustard, wheat, potato, etc.
Question 2. What is ploughing or tilling? State its advantages. Answer: The process of loosening and turning of the soil is called tilling or ploughing. This is done by using a plough. Ploughs are made of wood or iron. Following are the advantages of ploughing or tilling:
Ploughing loosens the soil and makes it aerated.
It helps in mixing organic matter with the soil uniformly.
It initiates the growth of natural agents and microorganisms and thus, keeps the soil fertile.
It increases the water holding capacity of soil.
It helps in easy penetration of root into the soil.
Question 3. Define the term agricultural practices and also state the important steps taken during crop production. Answer: Agricultural practices are those practices which involves the necessary steps to be taken during production of crops. There are number of steps of crop production which are to be done very carefully to ensure that crops get produced timely. Some of the most important steps taken during crop production are as under:
Soil preparation
Sowing
Adding manure and fertilisers
Irrigation
Weeding
Harvesting
Threshing and winnowing
Storage of grains
Question 4. What is irrigation? Name the two main methods of irrigation and define them briefly. Answer: The artificial method of watering the plants for assisting in the growth of the plants is called irrigation. The two main methods of irrigation are: (i) Traditional method: The traditional method of irrigation is very less expensive and they often lead to wastage of water. Traditional method of irrigation involves chain pump, dhekli, moat (the pulley system) and rahat (lever system).
(ii) Modern method: Modern methods of irrigation are more inclined towards the use of diesel, bio¬gas, solar energy and electricity for lifting water. The two most important modern system of irrigation are:
Sprinkler irrigation system
Drip irrigation system
Question 5. What do you mean by weeding? Why the process of weeding necessary? Name the methods applied for weeding. Answer: The undesirable plants that grow among the crops are called weeds. The process of removing these weeds is known as weeding. Weeds compete with the crop plants for nutrients and space. They grow much rapidly than the crop plant. So weeding is necessary.
Methods applied for weeding are as follows: (i) Manual method: Manual method of removing weeds is the most time consuming method. In this system weeds are controlled by hand pulling, digging, shallow tillage, etc., by using certain implements like khurpi, hoe, etc.
(ii) Chemical method: In this method chemicals called, weedicides are used to remove weeds. For example, metachlor and 2, 4-D.
(iii) Biological control method: This method is the most commonly used method of weed control. It involves the use of some specific insects that destroy the growth of some specific weeds. For example, leafy spurge, a weed, is controlled by using flea beetles.
Question 6. Write short note on the terms: (i) Storage (ii) Harvesting Answer: (i) Storage: Storage of produce is an important task. If the crop grains are to be kept for longer time, they should be safe from moisture, insects, rats and microorganisms. Before storing, the grains are properly dried in the sun to reduce the moisture in them. This prevents the attack by insect pests, bacteria and fungi. Grains are stored by farmers in jute bags or metallic bins. However, large scale storage of grains is done in silos and granaries to protect them from pests like rats and insects.
(ii) Harvesting: After maturation of crop, harvesting is an important task. In harvesting, crops are pulled out or cut close to the ground. It usually takes 3 to 4 months for a cereal crop to mature. Harvesting in our country is either done manually by sickle or by machine called harvester.
Crop Production and Management Class 8 Extra Questions HOTS
Question 1. Why the depth at which seeds are planted is important? Answer: If the seed is planted too deep then it will not get enough sunlight to germinate. If the seed is planted too shallow then it will not get enough soil to support germination. The depth for sowing seed also depends upon the seed size.
Question 2. Why sowing seeds with seed drill is better than broadcasting? Answer: Seed drill sows the seeds uniformly at proper distances and depths, whereas broadcasting of seeds scatter them non-uniformly on the ground surface which are susceptible to be picked up by birds.
Question 3. How can nitrogen be replenished in soil naturally? Answer: Through crop rotation with a leguminous crop the nitrogen can be replenished in soil naturally. The leguminous plants, like peas, beans, soybeans, peanuts, etc., have nitrogen-fixing bacteria in their root nodules. The nitrogen-fixing bacteria, viz., Rhizobium, fixes atmospheric nitrogen (N2) into ammonium (NH4+) which is used by the plants.
Question 4. Why is it advisable to wash fruits and vegetables before using them? Answer: Fruits and vegetables may contain many pesticides, used during the crop production practices, on them along with other germs and dust.
Question 5. What is biological control of pest? How is it beneficial? Answer: Method of controlling pests including insects, mites, weeds, etc., with the help of other living organisms are known as biological control of pest. The controlling agents are very much particular of their host pest. For example, lady bugs controls aphids, mites, scale insects, etc., which harm the crops. A wasp eats up bollworms or other caterpillars on cotton plant. Benefits of biocontrol agents are:
Less costly
Give protection to the crop throughout the crop period
Eco-friendly
Harmless to human beings and beneficial to flora and fauna
