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Page No: 224

1. Why does a compass needle get deflected when brought near a bar magnet?

Answer

The needle of a compass is a small magnet. That’s why when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected.

Page No: 228

Answer

Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.

2. List the properties of magnetic lines of force.

Answer

The properties of magnetic lines of force are as follows.
→ Magnetic field lines emerge from the north pole.
→ They merge at the south pole.
→ The direction of field lines inside the magnet is from the south pole to the north pole.
→ Magnetic lines do not intersect with each other.

3. Why don’t two magnetic lines of force intersect each other?

Answer

The two magnetic field lines do not intersect each other because if they do it means at the point of intersect the compass needle is showing two different directions which is not possible.

Page No: 229

1. Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.

Inside the loop = Pierce inside the table
Outside the loop = Appear to emerge out from the table
For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.

2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

The magnetic field lines inside a current-carrying long straight solenoid are uniform.

Answer

The displacement of rod AB is increased due to magnetic force exerted on it, if :

(i) If the current in the rod is increased then rod will be deflected with greater force.

Fleming’s left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.

2. What is the principle of an electric motor?

Answer

The principle of an electric motor is based on the magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is according to the Fleming’s left-hand rule.

3. What is the role of the split ring in an electric motor?

Answer

The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
→ Too many appliances should not be connected to a single socket.
→ Too many appliances should not be used at the same time.
→ Faulty appliances should not be connected in the circuit.
→ Fuse should be connected in the circuit.

Exercise

1. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is -(a) 1/25
(b) 1/5
(c) 5
(d) 25
► (d) 25

2. Which of the following terms does not represent electrical power in a circuit?
(a) I²R
(b) IR²
(c) VI
(d) V²/R
► (b) IR²

3. An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be –
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W
► (d) 25 W

4. Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be –

(a) 1:2

(b) 2:1

(c) 1:4

(d) 4:1

► (c) 1:4

 

5. How is a voltmeter connected in the circuit to measure the potential difference between two points?

Answer

To measure the potential difference between two points, a voltmeter should be connected in parallel to the points.

6. A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10⁻⁸ Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?

Answer

Area of cross-section of the wire, A =π (d/2) 2
Diameter= 0.5 mm = 0.0005 m
Resistance, R = 10 Ω
We know that

Therefore, the length of the wire is 122.7 m and the new resistance is 2.5 Ω.

7. The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below −

 

I (amperes )	0.5	1.0	2.0	3.0	4.0
V (volts)	1.6	3.4	6.7	10.2	13.2

Plot a graph between V and I and calculate the resistance of that resistor.

Answer

The plot between voltage and current is called IV characteristic. The voltage is plotted on x-axis and current is plotted on y-axis. The values of the current for different values of the voltage are shown in the given table.

V (volts)	1.6	3.4	6.7	10.2	13.2
I (amperes )	0.5	1.0	2.0	3.0	4.0

The IV characteristic of the given resistor is plotted in the following figure.

The slope of the line gives the value of resistance (R) as,

Slope = 1/R = BC/AC = 2/6.8

R= 6.8/2 = 3.4 Ω

Therefore, the resistance of the resistor is 3.4 Ω.

8. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.

Answer

Resistance (R) of a resistor is given by Ohm’s law as,V= IR
R= V/I
Where,
Potential difference, V= 12 V
Current in the circuit, I= 2.5 mA = 2.5 x 10^-3 A

Therefore, the resistance of the resistor is 4.8 kΩ

9. A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?

Answer

There is no current division occurring in a series circuit. Current flow through the component is the same, given by Ohm’s law as

V= IR

I= V/R

Where,

R is the equivalent resistance of resistances 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω. These are connected in series. Hence, the sum of the resistances will give the value of R.

R= 0.2 + 0.3 + 0.4 + 0.5 + 12 = 13.4 Ω

Potential difference, V= 9 V

I= 9/13.4 = 0.671 A
Therefore, the current that would flow through the 12 Ω resistor is 0.671 A.

10. How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?

Answer

For x number of resistors of resistance 176 Ω, the equivalent resistance of the resistors connected in parallel is given by Ohm’s law asV= IR
R= V/I
Where,
Supply voltage, V= 220 V
Current, I = 5 A
Equivalent resistance of the combination = R,given as

Therefore, four resistors of 176 Ω are required to draw the given amount of current.

11. Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω, (ii) 4 Ω.

Answer

If we connect the resistors in series, then the equivalent resistance will be the sum of the resistors, i.e., 6 Ω + 6 Ω + 6 Ω = 18 Ω, which is not desired. If we connect the resistors in parallel, then the equivalent resistance will be 6/2 = 3 Ω is also not desired. Hence, we should either connect the two resistors in series or parallel.
(a) Two resistor in parallel

Two 6 Ω resistors are connected in parallel. Their equivalent resistance will be

 

 

 

 

The third 6 Ω resistor is in series with 3 Ω. Hence, the equivalent resistance of the circuit is 6 Ω+ 3 Ω = 9 Ω.
(b) Two resistor in series

Two 6 Ω resistors are in series. Their equivalent resistance will be the sum 6 + 6 = 12 Ω.

The third 6 Ω resistor is in parallel with 12 Ω. Hence, equivalent resistance will be

 

 

 

 

Therefore, the total resistance is 4 Ω.

 

12. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?

Answer

Resistance R₁ of the bulb is given by the expression,
Supply voltage, V = 220 V
Maximum allowable current, I = 5 A
Rating of an electric bulb P=10watts
Because R=V²/P

∴ Number of electric bulbs connected in parallel are 110.

13. A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistances, which may be used separately, in series, or in parallel. What are the currents in the three cases?

Answer

Supply voltage, V= 220 V
Resistance of one coil, R= 24 Ω

 

(i) Coils are used separately

According to Ohm’s law,
V= I₁R₁
Where,

I₁ is the current flowing through the coil

I₁ = V/R₁ = 220/24 = 9.166 A
Therefore, 9.16 A current will flow through the coil when used separately.

 

(ii) Coils are connected in series

Total resistance, R₂ = 24 Ω + 24 Ω = 48 Ω

According to Ohm’s law,V = I₂R₂
Where,

I₂ is the current flowing through the series circuit

I₂ = V/R₂ = 220/48 = 4.58 A
Therefore, 4.58 A current will flow through the circuit when the coils are connected in series.
(iii) Coils are connected in parallel

Total resistance, R₃ is given as =

According to Ohm’s law,

V= I₃R₃
Where,
I₃ is the current flowing through the circuit I₃ = V/R₃ = 220/12 = 18.33 A
Therefore, 18.33 A current will flow through the circuit when coils are connected in parallel.

 

14. Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.

Answer

(i) Potential difference, V = 6 V
1 Ω and 2 Ω resistors are connected in series. Therefore, equivalent resistance of the circuit, R = 1 + 2 = 3 Ω
According to Ohm’s law,
V = IR
Where,
I is the current through the circuit
I= 6/3 = 2 A
This current will flow through each component of the circuit because there is no division of current in series circuits. Hence, current flowing through the 2 Ω resistor is 2 A. Power is given by the expression,
P= (I)²R = (2)² x 2 = 8 W

(ii) Potential difference, V = 4 V
12 Ω and 2 Ω resistors are connected in parallel. The voltage across each component of a parallel circuit remains the same. Hence, the voltage across 2 Ω resistor will be 4 V.
Power consumed by 2 Ω resistor is given by
P= V²/R = 4²/2 = 8 W
Therefore, the power used by 2 Ω resistor is 8 W.

15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Answer

Both the bulbs are connected in parallel. Therefore, potential difference across each of them will be 220 V, because no division of voltage occurs in a parallel circuit.
Current drawn by the bulb of rating 100 W is given by,Power = Voltage x Current
Current =  Power/Voltage = 60/220 A
Hence, current drawn from the line = 100/220 + 60/220 = 0.727 A

16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?

Answer

Energy consumed by an electrical appliance is given by the expression,H= Pt
Where,
Power of the appliance = P
Time = t
Energy consumed by a TV set of power 250 W in 1 h = 250 ×3600 = 9 ×10⁵ J
Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600
Energy consumed by a toaster of power 1200 W in 10 minutes = 1200 ×600
= 7.2×10⁵ J
Therefore, the energy consumed by a 250 W TV set in 1 h is more than the energy consumed by a toaster of power 1200 W in 10 minutes.

17. An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.

Answer

Rate of heat produced by a device is given by the expression for power as, P= I²R
Where,
Resistance of the electric heater, R= 8 Ω
Current drawn, I = 15 A

Therefore, heat is produced by the heater at the rate of 1800 J/s.

18. Explain the following.
(a) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?

Answer

(a) The melting point and of Tungsten is an alloy which has very high melting point and very high resistivity so does not burn easily at a high temperature.

Page No: 190

1. What is meant by power of accommodation of the eye?

Answer

The ability of the eye lens to adjust its focal length, so as to clearly focus rays coming from distant as well a near objects on the retina, is called the power of accommodation of the eye.

2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?

Answer

A person with a myopic eye should use a concave lens of focal length 1.2 m so as to restore proper vision.

3. What is the far point and near point of the human eye with normal vision?

Answer

The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm.
The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.

4. A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?

Answer

The student is suffering from myopia or short-sightedness. The defect can be corrected by the use of concave (diverging ) lens of an appropriate power.

Page No: 168

1. Define the principal focus of a concave mirror.

Answer

Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.

2. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Answer

Radius of curvature, R= 20 cm
Radius of curvature of a spherical mirror = 2 × Focal length (f)R= 2f
f= R/2 = 20 / 2 = 10
Hence, the focal length of the given spherical mirror is 10 cm.

3. Name the mirror that can give an erect and enlarged image of an object.
► Concave Mirror.

4. Why do we prefer a convex mirror as a rear-view mirror in vehicles?

Answer

We prefer a convex mirror as a rear-view mirror in vehicles because it gives a wider field of view, which allows the driver to see most of the traffic behind him. Convex mirrors always form a virtual, erect, and diminished image of the objects placed in front of it.

Page No: 171

1. Find the focal length of a convex mirror whose radius of curvature is 32 cm.

Answer

Radius of curvature, R= 32 cm
Radius of curvature = 2 × Focal length (f)
R= 2ff= R/2 = 32/2 = 16
Hence, the focal length of the given convex mirror is 16 cm.

2. A concave mirror produces three times magnified (enlarged) real image of object placed at 10 cm in front of it. Where is the image located?

Answer

Magnification produced by a spherical mirror is given by the relation,

Object distance, u= – 10 cm
v = 3 × ( – 10) = – 30 cm
Here, the negative sign indicates that an inverted image is formed at a distance of
30 cm in front of the given concave mirror.

Page No: 176

1. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?

Answer

The ray of light bends towards the normal. When a ray of light enters from an optically rarer medium (having low refractive index) to an optically denser medium (having high refractive index), its speed slows down and it bends towards the normal. Since water is optically denser than air, a ray of light entering from air into water will bend towards the normal.

2. Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 x 10⁸ ms^-1.

Answer

Refractive index of a medium, n_m = Speed of light in vacuum/Speed of light in the medium
Speed of light in vacuum, c = 3 × 10⁸ ms^-1
Refractive index of glass, n_g = 1.50
Speed of light in the glass, v = Speed of light in vacuum/ Refractive index of glass
= c/n_g
=3 × 10⁸/1.50 = 2x 10⁸ ms^-1.

3. Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.

Answer

Highest optical density = Diamond
Lowest optical density = Air
Optical density of a medium is directly related with the refractive index of that medium. A medium which has the highest refractive index will have the highest optical density and vice-versa.

It can be observed from table 10.3 that diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical
density.

4. You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.

Answer

In water light travel faster as compare to kerosene and turpentine because the refractive index of water is lower than that of kerosene and turpentine. The speed of light is inversely proportional to the refractive index.

5. The refractive index of diamond is 2.42. What is the meaning of this statement?

Answer

The refractive index of diamond is 2.42. This means that the speed of light in diamond will reduce by a factor of 2.42 as compared to its speed in air.
In other words, the speed of light in diamond is 1/2.42 times the speed of light in vacuum.

Page No: 184

1. Define 1 dioptre of power of a lens.

Answer

The SI unit of power of lens is dioptre which is denoted by the letter D. 1 dioptre is defined as the power of a lens of focal length 1 metre.

2. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

Answer

Since the image is real and same size. The position of image should be at 2F.

It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of 50 cm.

Object distance, u= – 50 cm
Image distance, v= 50 cm
Focal length = f
According to the lens formula,

3. Find the power of a concave lens of focal length 2 m.

Answer

Focal length of concave lens, f = 2 mPower of lens, P= 1/f = 1/(-2)= -0.5D

Page No: 143

1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Answer

Trait B because in asexual reproduction traits which are present in the previous generation are carried over to next generation with minimal variations. Trait B have higher percentage so it is likeliy to have arisen earlier.

2. How does the creation of variations in a species promote survival?

Answer

Variations occur due to sexual reproduction and also due to inaccurate copying of DNA. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacteria variants which can withstand heat have better chances to survive in a heat wave non-variant bacteria having no capacity to tolerate heat wave. Thus, variations in a population of a species help in survival of a species.

Page No: 147

1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer

The trait which appears in all the members of F₁ generation and also in 75% numbers of F₂ generation obtained by self fertilization of F₁ generation is dominant character.
The trait which does not appear in F generation but after self-fertilization of F₁ generation, reappears in 25% of F₂ generation is known as recessive.
2. How do Mendel’s experiments show that traits are inherited independently?

Answer

Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F₁ generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F₁ yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded , 3 short round seeded and one short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.

3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

No. This information is not sufficient to determine which of the traits – blood group A or O – is dominant. This is because we do not know about the blood group of all the progeny.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.

4. How is the sex of the child determined in human beings?

Answer

In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.

Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

Answer

Individuals with a particular trait may increase in a population as a result of the following:
→ Natural selection: When that trait offers some survival advantage.
→ Genetic drift: When some genes governing that trait become common in a population.
→ When that trait gets acquired during the individual’s lifetime.

2. Why are traits acquired during the life-time of an individual not inherited?

Answer

This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.

3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer

The small number of members in a population of tigers do not allow large number of variation to occur which are essential to survival of the species. A deadly disease or calamity may cause death of all the tigers. The small number of tiger also indicates that existing tiger variants are not well adopted to the existing environment and may extinct soon.

Page No: 151

1. What factors could lead to the rise of a new species?

Answer

Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.

Answer

Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in this case.

3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer

No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offsprings that leaves no chance of speciation. However, geographical isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated population.

Page No: 156

1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer

Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptile.

2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer

The wing of a butterfly and the wing of a bat are similar in function. They help the butterfly and the bat in flying. Since they perform similar function, they are analogous organs and not homologous.

3. What are fossils? What do they tell us about the process of evolution?

Answer

Fossils are the remains of organisms that once existed on earth.
They tell us about the development of the structures from simple structured to complex structured organisms.They tell us about the phases of evolutions through which they must have undergone in order to sustain themselves in the competetive environment.

Page No: 158

1. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer

A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are genetic but also environmentally controlled. Various human races are formed based on these features. All human races have more than enough similarities to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.

2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer

Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment.

Page No: 128

1. What is the importance of DNA copying in reproduction?

Answer

DNA is the genetic material present in the cells of all organisms. The genetic information from generation to generation is carried by DNA. It is therefore possible for the organism to produce organism of its own type due to DNA copying only. For the inheritance of traits of the parent, DNA copying is a must. DNA copying also brings about variation ,which forms the basis for the origin of new species.

2. Why is variation beneficial to the species but not necessarily for the individual?

Answer

Variations are beneficial to the species than individual because sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, then most of the bacteria living in that water would die. Only few variants that are resistant to heat would be able to survive. However, if these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, all variations are not necessarily beneficial for the individual organisms.

Page No: 133

1. How does binary fission differ from multiple fission?

Answer

In binary fission a single cell divides into two equal halves.Amoeba and Bacteria divide by binary fission.
In multiple fission, a single cell divides into many daughter cells simultaneously. Plasmodium divide by multiple fission.

2. How will an organism be benefited if it reproduces through spores?

Answer

Advantages of spore formation:
→ Large numbers of spores are produced in one sporangium.
→ Spores are distributed easily by air to far-off places to avoid competition at one place.

3. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?

Answer

Higher complex organisms cannot give rise to new individuals through regeneration because complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new individuals through regeneration.

4. Why is vegetative propagation practised for growing some types of plants?

Answer

Vegetative propagation is practiced for growing some types of plants because of following advantages:

→ It helps to introduce plants in new areas where the seed germination fails to produce mature plant due to change in environmental factors and the soil.→ It is more rapid, easier and cheaper method.
→ By this method a good quality of a race or variety can be preserved.

5. Why is DNA copying an essential part of the process of reproduction?

Answer

DNA copying is an essential part of reproduction as it passes genetic information from parents to offspring. It determines the body design of an individual. The reproducing cells produce a copy of their DNA through some chemical reactions and result in two copies of DNA. The copying of DNA always takes place along with the creation of additional cellular structure. This process is then followed by division of a cell to form two cells.

Page No: 140

1. How is the process of pollination different from fertilization?

Answer

Pollination is the process of transfer of pollens from anther to stigma. It occurs with the help of certain pollinators such as air, water, birds, or some insects.
Fertilization, is the fusion of the male and female gametes. It occurs inside the ovule and leads to the formation of zygote.

2. What is the role of the seminal vesicles and the prostate gland?

Answer

The secretions from seminal vesicles and prostate glands lubricate the sperms and provide a fluid medium for easy transport of sperms. Their secretion also provides nutrient in the form of fructose, calcium, and some enzymes.

3. What are the changes seen in girls at the time of puberty?

Answer

The changes seen in girls at the time of puberty are:
→ Increase in breast size and darkening of skin of the nipples present at the tips of the breasts.
→ Appearance of hair in the genital area.
→ Appearance of hair in other areas of skin like underarms, face, hands, and legs.
→ Increase in the size of uterus and ovary.
→ Beginning of menstrual cycle.
→ More secretion of oil from the skin, which results in the appearance of pimples.

4. How does the embryo get nourishment inside the mother’s body?

Answer

After fertilization the lining of uterus thickens and is richly supplied with blood to nourish the growing embryo. The embryo gets nutrition from the mother’s blood with he help of a special tissue called placenta. It is embedded in the uterine wall. Placenta contains Villi on the embryo’s side of the tissue and blood spaces on mother’s side surrounding the villi. This provides a large surface from mother to the embryo and waste products from embryo to mother.

5. If a woman is using a copper-T, will it help in protecting her from sexually transmitted diseases?

Answer

No, because copper-T will not prevent contact body fluids. Thus it will not protect her from sexually transmitted diseases.

Exercise

1. The kidneys in human beings are a part of the system for
(a) nutrition.

► (c) excretion.

2. The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
► (a) transport of water.

3. The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.
► (d) all of the above.

4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.
► (b) mitochondria.

5. How are fats digested in our bodies? Where does this process take place?

Answer

Fats are present in the form of large globules in the small intestine. The small intestine receives the secretions from the liver and the pancreas. The bile salts (from the liver) break down the large fat globules into smaller globules so that the pancreatic enzyme lipase can easily act on them. This is referred to as emulsification of fats. This process takes place in the small intestine.

6. What is the role of saliva in the digestion of food?

Answer

The role of saliva in the digestion of food:
→ It moistens the food for easy swallowing.
→ It contains a digestive enzyme called salivary amylase, which breaks down starch into sugar.

7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer

Autotrophic nutrition takes place through the process of photosynthesis. Carbon dioxide, water, chlorophyll pigment, and sunlight are the necessary conditions required for autotrophic nutrition. Carbohydrates (food) and O₂ are the by-products of photosynthesis.

8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Answer

9. How are the alveoli designed to maximise the exchange of gases?

Answer

Alveoli provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO₂ from the blood brought from the body, diffuses out into the air.

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer

Haemoglobin is the respiratory pigment that transports oxygen to the body cells for cellular respiration. Therefore, deficiency of haemoglobin in blood can affect the oxygen supplying capacity of blood. This can lead to deficiency of oxygen in the body cells. It can also lead to a disease called anaemia.

11. Describe double circulation in human beings. Why is it necessary?

Answer

During a single cycle blood goes twice in the heart which is known as double circulation. It is necessary in human being to separate oxygenated and de-oxygenated blood because this makes their circulatory system is more efficient and helps in maintaining constant body temperature.

12. What are the differences between the transport of materials in xylem and phloem?

Answer

13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Answer

Page No: 81

1. Did Dobereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.

Answer

Yes, Dobereiner’s triads also exist in the columns of Newlands’ Octaves. One such column is Li, K, Na.

2. What were the limitations of Dobereiner’s classification?

Answer

Limitation of Dobereiner’s classification:
All known elements could not be classified into groups of triads on the basis of their properties.

3. What were the limitations of Newlands’ Law of Octaves?

Answer

Limitations of Newlands’ law of octaves:
→ It was not applicable throughout the arrangements. It was applicable up to calcium only. The properties of the elements listed after calcium showed no resemblance to the properties of the elements above them.
→ Those elements that were discovered after Newlands’ octaves did not follow the law of octaves.
→ The position of cobalt and nickel in the group of the elements (F, Cl) of different properties could not be explained.
→ Placing of iron far away from cobalt and nickel, which have similar properties as iron, could also not be explained.

Page No: 85

1. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, Al, Si, Ba.

Answer

K is in group 1. Therefore, the oxide will be K₂O.
C is in group 4. Therefore, the oxide will be CO₂.
Al is in group 3. Therefore, the oxide will be Al₂O₃.
Si is in group 4. Therefore, the oxide will be SiO₂.
Ba is in group 2. Therefore, the oxide will be BaO.

2. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)

Answer

Scandium and germanium.

3. What were the criteria used by Mendeleev in creating his Periodic Table?

Answer

Mendeleev used atomic mass of the elements as the unique criteria of the elements. He proposed that the chemical properties of elements are the periodic function of their atomic masses. And thus, he arranged the elements in the increasing order of their atomic masses.

4. Why do you think the noble gases are placed in a separate group?

Answer

Noble gases are inert elements. Their properties are different from the all other elements. Therefore, the noble gases are placed in a separate group.

Page No: 90

1. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?

Answer

Various anomalies of Mendeleev’s Periodic Table removed as follows in the Modern Periodic Table:

→ In Modern Periodic Table there was no problem of the place of isotopes, as isotopes have same atomic mass with different atomic numbers.

→ Elements having same number of shells were put under the same period.
→ Position of hydrogen became clarified in as it is kept in the group with the elements of same valence electrons.

2. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?

Answer

Calcium (Ca) and strontium (Sr) are expected to show chemical reactions similar to magnesium (Mg). This is because the number of valence electrons (2) is same in all these three elements and since chemical properties are due to valence electrons, they show same chemical reactions.

3. Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.

Answer

(a) Lithium (Li), sodium (Na), and potassium (K) have a single electron in their outermost shells.
(b) Magnesium (Mg) and calcium (Ca) have two electrons in their outermost shells.
(c) Neon (Ne), argon (Ar), and xenon (Xe) have filled outermost shells.

4. (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?

Answer

(a) Yes. The atoms of all the three elements lithium, sodium, and potassium have one electron in their outermost shells.

(b) Both helium (He) and neon (Ne) have filled outermost shells. Helium has a duplet in its K shell, while neon has an octet in its L shell.

5. In the Modern Periodic Table, which are the metals among the first ten elements?

Answer

Among the first ten elements, lithium (Li) and beryllium (Be) are metals.

6. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristic?

Answer

Since Be lies to the extreme left hand side of the periodic table, Be is the most metallic among the given elements.

Page No: 61

1. What would be the electron dot structure of carbon dioxide which has the formula CO₂?

Answer

2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (Hint – the eight atoms of sulphur are joined together in the form of a ring.)

Answer

1. How many structural isomers can you draw for pentane?

Answer

Three structural isomers are possible for pentane.

2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?

Answer

The two features of carbon that give rise to a large number of compounds are as follows:
→ Catenation – It is the ability to form bonds with other atoms of carbon.
→ Tetravalency – With the valency of four, carbon is capable of bonding with four other atoms.

3. What will be the formula and electron dot structure of cyclopentane?

Answer

The formula for cyclopentane is C5H10. Its electron dot structure is given below.

Page No: 69

4. Draw the structures for the following compounds.
(i) Ethanoic acid (ii) Bromopentane*
(iii) Butanone (iv) Hexanal
*Are structural isomers possible for bromopentane?

Answer

(ii) There are many structural isomers possible for bromopentane. Among them, the structures of three isomers are given.

5. How would you name the following compounds?

Answer

(i) Bromoethane
(ii) Methanal (formaldehyde)
(iii) Hexyne

Page No: 71

1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?

Answer

CH₃CH₂OH + (Alkaline KMnO₄) → CH₃COOH
Since, in this reaction one oxygen is added to ethanol, hence it is an oxidation reaction.

2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Answer

2HC ≡ CH + 5O₂ → 4CO₂ + 2H₂O + Heat
When ethyne is burnt in air, it gives a sooty flame. This is due to incomplete combustion caused by limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 3000°C because of complete combustion. This oxy-acetylene flame is used for welding. It is not possible to attain such a high temperature without mixing oxygen. This is the reason why a mixture of ethyne and air is not used.

Page No: 74

1. How would you distinguish experimentally between an alcohol and a carboxylic acid?

Answer

We can distinguish between an alcohol and a carboxylic acid on the basis of their reaction with carbonates and hydrogen carbonates. Acid reacts with carbonate and hydrogen carbonate to evolve CO₂ gas that turns lime water milky.

Alcohols, on the other hand, do not react with carbonates and hydrogen carbonates.

2. What are oxidising agents?

Answer

Oxidising agents are the substances that gain electrons in redox reaction and whose oxidation number is reduced.

Page No: 76

1. Would you be able to check if water is hard by using a detergent?

Answer

Detergent gives lather with hard and soft water both, while a soap gives lather with soft water only. Thus, it is not possible to check if water is hard; by using a detergent.

2. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Answer

A soap molecule has two parts namely hydrophobic and hydrophilic. With the help of these, it attaches to the grease or dirt particle and forms a cluster called micelle. These micelles remain suspended as a colloid. To remove these micelles, it is necessary to agitate clothes.