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Chapter 5

Transpiration

Class 10 - Selina Concise Biology Solutions


Multiple Choice Type

(Select the most appropriate option in each case)

Question 1

Transpiration pull will be maximum under which set of the following conditions?

  1. Open stomata, dry atmosphere and moist soil ✓
  2. Open stomata, high humid atmosphere and well irrigated soil
  3. Open stomata, high humid atmosphere and dry soil
  4. Closed stomata, dry atmosphere and dry soil

Question 2

With decrease in atmospheric pressure, the rate of transpiration will

  1. increase ✓
  2. decrease rapidly
  3. decrease slowly
  4. remain the same

Question 3

One of the internal factors which affect the rate of transpiration, is

  1. big size of the leaf
  2. Colour of the leaf
  3. sunken stomata ✓
  4. sunny day

Question 4

Guttation takes place through

  1. stomata
  2. lenticels
  3. lower epidermis of leaves
  4. hydathodes ✓

Question 5

Transpiration will be fastest when the day is

  1. cool, humid and windy
  2. hot, humid and still
  3. hot, humid and windy
  4. hot, dry and windy ✓

Question 6

Most of the transpiration in tall trees occurs through

  1. Stomata
  2. Lenticels ✓
  3. Cuticle
  4. Bark

Question 7

Transpiration is best defined as

  1. loss of water by the plant
  2. evaporation of water from the aerial surfaces of a plant ✓
  3. loss of water, as water vapour, by a plant
  4. release of water by a plant into the atmosphere.

Very Short Answer Type

Question 1

Name the following:

(a) Openings on the stem through which transpiration occurs.

(b) The process by which the intact plant loses water in the form of droplets.

(c) An instrument used to find the rate of transpiration.

(d) A plant in which the stomata are sunken.

(e) The apparatus to record the rate of transpiration in a cut shoot.

(f) Any two parts of a leaf which allow transpiration.

(g) The structure in a leaf that allows guttation.

(h) Loss of water as droplets from the margins of certain leaves.

Answer

(a) The openings on the stem through which transpiration occurs are known as Lenticels.

(b) The process by which intact plant loses water in the form of droplets is called Guttation.

(c) Potometer is an instrument used to find the rate of transpiration.

(d) Nerium is the plant in which the stomata are sunken.

(e) Ganong’s photometer is the apparatus to record the rate of transpiration in a cut shoot.

(f) The two parts of a leaf which allow transpiration are stomata and cuticle.

(g) Hydathodes is the structure in a leaf that allows guttation.

(h) Loss of water as droplets from the margins of certain leaves is called Guttation.

Question 2

Fill in the blanks:

(a) Transpiration is the loss of water as water .......... from the .......... parts of the plant.

(b) Closing of .......... and shedding of leaves reduce ........... .

(c) Transpiration helps in creating .......... force and in eliminating excess .......... .

Answer

(a) Transpiration is the loss of water as water vapour from the aerial parts of the plant.

(b) Closing of stomata and shedding of leaves reduce transpiration.

(c) Transpiration helps in creating suction force and in eliminating excess water (heat).

Short Answer Type

Question 1

Given below is an example of a certain structure and its special functional activity:

chloroplasts and photosynthesis

In a similar way, write the functional activity against each of the following:

(a) Hydathodes and ..................................

(b) Leaf spines and ................................

(c) Lenticels and ...................................

(d) Xylem and ...................................

Answer

(a) Hydathodes and guttation.

(b) Leaf spines and protection and reduced transpiration.

(c) Lenticels and transpiration.

(d) Xylem and conduction of water and mineral salts.

Question 2

State whether the following statements are True (T) or False (F)? Rewrite the false statements in the correct form.

(i) Most transpiration occurs at midnight.

Answer

False

Corrected statement — Most transpiration occurs at mid-day.

(ii) Transpiration creates a pull for the upward movement of the sap.

Answer

True

(iii) Wind velocity has an effect on transpiration.

Answer

True

(iv) Atmospheric humidity promotes transpiration from a green plant.

Answer

False

Corrected statement — Atmospheric humidity reduces transpiration from a green plant.

(v) Transpiration helps to cool the body of the plant.

Answer

True

Question 3

Give suitable explanation for the following:

(a) A higher rate of transpiration is recorded on a windy day rather than on a calm day.

(b) Excessive transpiration results in the wilting of the leaves.

(c) Some plants show wilting of their leaves at noon even when the soil is well-watered.

(d) More transpiration occurs from the lower surface of a dorsiventral leaf.

(e) The stomata in most plants are more numerous on the lower surface of a leaf as compared to the upper surface.

(f) Forests tend to bring more rains.

(g) On a bright sunny day, the leaves of certain plants roll up.

Answer

(a) Transpiration increases with the velocity of wind. If the wind blows faster, the water vapour released during transpiration is removed faster and the area outside the leaf does not get saturated with water vapour. So, higher rate of transpiration is recorded on a windy day rather than a calm day.

(b) When the rate of transpiration far exceeds the rate of absorption of water by roots, the cells lose their turgidity. Hence, excessive transpiration results in wilting of the leaves.

(C) In some plants, e.g. balsam, the leaves of the plants wilt during the midday inspite of the fact that there is plenty of water in the soil because during the midday the rate of transpiration exceeds the rate of absorption of water by the roots. The cells, therefore, lose turgidity. In evening or at night, the stomata are narrowed or constricted and the temperature is not high, therefore, there is no loss of water through transpiration and turgidity of leaves is re-acquired and they stand erect.

(d) There are more stomatal openings on the lower surface of a dorsiventral leaf. More the number of stomata, higher is the rate of transpiration. Hence more transpiration occurs from the lower surface.

(e) Stomata are minute openings in the epidermal layer of leaves. The stomata in most plants are more numerous on the lower surface of a leaf as compared to the upper surface because lower surface does not face direct sunlight. This arrangement helps to reduce the rate of transpiration.

(f) Due to transpiration, huge quantities of water are released into the atmosphere by vast stretches of forests. Thus, transpiration increases the moisture in the atmosphere and brings more rain.

(g) On a bright sunny day, the rate of transpiration is much higher than any other days. The leaves of certain plants roll up on a bright sunny day to reduce the exposed surface and thus reduce the rate of transpiration.

Descriptive Type

Question 1

Define the following terms:

(a) Transpiration

(b) Exudation

(c) Potometer

(d) Wilting

(e) Hydathodes

(f) Cuticle

Answer

(a) Transpiration — Transpiration is the loss of water in the form of water vapour from the aerial parts (leaves and stem) of the plant.

(b) Exudation — The process by which plants lose water or other fluids along with dissolved substances directly in liquid form and not as water vapour is called exudation.

(c) Potometer — Potometer is a device that measures the rate of water intake by a plant and this water intake is almost equal to the water lost through transpiration.

(d) Wilting — The drying out, drooping and withering of the leaves of a plant due to inadequate water supply, excessive transpiration, or vascular disease.

(e) Hydathodes — Special pore-bearing structures present on the margins of the leaf to allow exudation are called hydathodes.

(f) Cuticle — Cuticle is a waxy layer secreted by the epidermis on the two surfaces of the leaf which prevents evaporation of water from the leaf surfaces.

Question 2

Distinguish between the following pairs:

(a) Stomata and Lenticels

(b) Guttation and Bleeding

(c) Transpiration and Evaporation

Answer

(a) Difference between stomata and lenticels

StomataLenticels
They are minute openings in the epidermal layer of leaves.They are minute openings on the surface of old woody stems.
Maximum transpiration occurs through stomata.Lesser transpiration occurs through lenticels.

(b) Difference between Guttation and Bleeding

GuttationBleeding
It occurs from the edges of leaves by hydathodes in uninjured plants.It occurs from any cut or injured part of a plant.
The exudate is mainly water with some dissolved mineral salts.The exudate is mainly plant sap and sugars.
It occurs during early mornings or late nights.It occurs at the time of injury.
It happens in certain plants like Banana, Nasturtium, Strawberry.It occurs in all plants that have been cut or injured.

(c) Difference between Transpiration and Evaporation

TranspirationEvaporation
It is the loss of water in the form of vapour from the aerial parts of the plant.It is the loss of water from the surface of water bodies in the form of vapour.
It is a slow process.It is comparatively a faster process.

Question 3

Suppose you have a small rose plant growing in a pot. How would you demonstrate transpiration in it?

Answer

Take a medium-sized small well-watered potted rose plant and cover it with a transparent polythene bag. Tie its mouth around the base of the stem. Leave the plant in sunlight for an hour or two.
Drops of water will soon appear on the inner side of the bag due to the saturation of water vapour given out by the leaves (the water vapours condense only if the outside temperature is cool enough.)
A similar empty polythene bag with its mouth tied and kept in sunlight will show no drops of water. This is the control to show that plants transpire water in the form of water. If tested with dry cobalt chloride paper, the drops will be confirmed as water only.

Suppose you have a small rose plant growing in a pot. How would you demonstrate transpiration in it? Transpiration, Concise Biology Solutions ICSE Class 10.

Question 4

What is lenticular transpiration? Mention one major difference between lenticular transpiration and stomatal transpiration.

Answer

Transpiration occurring through lenticels which are minute openings on the surface of old woody stems is called lenticular transpiration.

Stomatal transpiration is controlled by the plant by altering the size of the stoma, where as this does not happen in case of lenticular transpiration. This is because the lenticels never close, but remain open all the time.

The amount of stomatal transpiration is much more than the amount of lenticular transpiration.

Question 5

Droplets of water may sometimes be seen along the margins of the leaves of a banana plant, growing in wet soil in the mornings. Are these dew drops? Comment upon your answer.

Answer

No, they are not dew drops.

This is water given out by the plant body through guttation. Since the banana plant is growing in humid environment, transpiration is hampered. But the roots continue to absorb water from the soil. This builds up a huge hydrostatic pressure within the plant and forces out the excess water from the hydathodes, which are pores present at the tips of veins in the leaf. This is observed especially during the mornings.

Question 6

Briefly explain how the rate of transpiration is affected by:

(a) Intensity of light

(b) Humidity of the atmosphere

(c) Temperature

Answer

(a) Intensity of light — During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. At night they are closed. Hence more transpiration occurs during the day. During cloudy days, the stomata are partially closed and the transpiration is reduced.

(b) Humidity of the atmosphere — Transpiration is reduced if the air outside is humid. Thus, high humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.

(c) Temperature — If the outside temperature is higher, there is more evaporation from the leaves, therefore, more transpiration. Increase in temperature allows more water to evaporate and the decrease in temperature reduces evaporation. Warm air can hold more water than cold air.

Structured / Application / Skill Type

Question 1

The given figure represents an experiment:

The given figure represents an experiment. Leaf A was coated with grease on both the surfaces. Leaf B was coated with grease on the lower surface. Leaf C was coated with grease on the upper surface. Leaf D was left without any application of grease. All the four leaves A, B, C and D were left in a room for about 24 hours. Which leaf dries first? Give reason. Which leaf dries last? Give reason. Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Leaf A was coated with grease on both the surfaces.
(b) Leaf B was coated with grease on the lower surface.
(c) Leaf C was coated with grease on the upper surface.
(d) Leaf D was left without any application of grease.

All the four leaves A, B, C and D were left in a room for about 24 hours.

(i) Which leaf dries first? Give reason.
(ii) Which leaf dries last? Give reason.

Answer

(i) Leaf D — The leaf with no greasing on either surfaces would dry first because it would lose water from both surfaces i.e. it would lose maximum quantity of water.

(ii) Leaf A — It was coated with grease on both the surfaces. Hence, it would dry last because greasing prevents evaporation of water and transpiration occurs through stomata which are present more on the lower surface of the leaf.

Question 2

Given below is the diagram of an apparatus used to study a particular phenomenon in plants:

Given below is the diagram of an apparatus used to study a particular phenomenon in plants. Name the apparatus. What is it used for? What is the role played by the air-bubble in this experiment? What is the use of the reservoir? Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Name the apparatus.

(b) What is it used for?

(c) What is the role played by the air-bubble in this experiment?

(d) What is the use of the reservoir?

(e) What happens to the movement of the air-bubble if the apparatus is kept:

  1. In the dark
  2. In sunlight
  3. In front of a fan

Give a reason in each case.

Answer

(a) Name of the apparatus is Ganong's potometer.

(b) Ganong’s potometer is used to measure the rate of water intake by a plant.

(c) The air bubble which was introduced into the horizontal graduated capillary tube moves along as transpiration proceeds. As the water is lost from the twig, a suction force is set up which pulls the water from the beaker and the bubble in the capillary tube moves along.

(d) Reservoir is used to release the water into the capillary tube by opening the stop cock.

(e) The movement of air bubble is affected as follows:

  1. If the apparatus is kept in the dark, there will be no transpiration as the stomata would be closed. As a result, there would be no movement of the air bubble and it would remain stable.
  2. During the day, the stomata are open to facilitate the inward diffusion of CO2 for photosynthesis. At night they are closed. Therefore, more transpiration occurs during the day. As a result, the movement of the air bubble would be larger since there would be more loss of water due to transpiration.
  3. If the apparatus is kept in front of a fan, the rate of transpiration will be more. As a result, the movement of the air bubble would be larger since there would be more loss of water due to transpiration as the velocity of wind/air increases.

Question 3

Given ahead is the diagram of an experimental set up to study the process of transpiration in plants. Study the same and then answer the questions that follow:

Given ahead is the diagram of an experimental set up to study the process of transpiration in plants. Study the same and then answer the questions that follow. Name the colour of dry cobalt chloride paper. Is the experimental leaf a monocot or a dicot? Give a reason to support your answer. Why are glass slides placed over the dry cobalt chloride papers? After about half an hour what change, if any, would you expect to find in the cobalt chloride paper placed on the dorsal and ventral sides of the leaf? Give a reason to support your answer. Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Name the colour of dry cobalt chloride paper.

(b) Is the experimental leaf a monocot or a dicot? Give a reason to support your answer.

(c) Why are glass slides placed over the dry cobalt chloride papers?

(d) After about half an hour what change, if any, would you expect to find in the cobalt chloride paper placed on the dorsal and ventral sides of the leaf? Give a reason to support your answer.

Answer

(a) Blue.

(b) The experimental leaf is a dicot leaf as it shows reticulate venation and there are more number of stomatal openings on the undersurface of a dicot leaf. Hence, transpiration is more and can be easily observed.

(c) Glass slides are placed over the dry cobalt chloride papers so as to retain the strips in their position.

(d) The cobalt chloride paper on the dorsal side will turn less pink or turns pink in a much longer time while the one on the ventral side will turn more pink. This occurs because the ventral surface has more number of stomata as compared to the dorsal surface. As a result, the rate of transpiration is more on the ventral side than on the dorsal side of a dicot leaf.

Question 4

An outline sketch of a tree is shown in a diagram below. Study the same and answer the questions that follow:

An outline sketch of a tree is shown in a diagram below. Study the same and answer the questions that follow. Name and define the phenomenon labelled A in the diagram. Write the significance of the process mentioned in A for the plants. What do the direction of arrows in B and C indicate? Name the phenomenon. Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Name and define the phenomenon labelled A in the diagram.

(b) Write the significance of the process mentioned in A for the plants.

(c) What do the direction of arrows in B and C indicate? Name the phenomenon.

(d) Draw a neat and labelled diagram of an opened stomata.

Answer

(a) A is transpiration. Transpiration is the evaporative loss of water from the aerial parts (leaves and stem) of the plants.

(b) Significance of transpiration for the plants:

  1. Cooling effect.
  2. Creating suction force.
  3. Distribution of water and minerals.

(c) Arrow B indicates water passing up the trunk and the phenomenon is ascent of sap. Arrow C indicates water absorbed by roots from the soil and the phenomenon is called Endosmosis.

(d) Below diagram shows an opened stomata:

Draw a neat and labelled diagram of an opened stomata. Transpiration, Concise Biology Solutions ICSE Class 10.

Question 5

The figure given below represents an experimental set up with a weighing machine to demonstrate a particular process in plants. The experimental set up was placed in bright sunlight. Study the diagram and answer the following questions.

The figure represents an experimental set up with weighing machine to demonstrate a particular process in plants. The experimental set up was placed in bright sunlight. Name the process intended for study. Define the above mentioned process. When the weight of the test tubes A and B is taken before and after the experiment, what change is observed? Justify. What is the purpose of keeping the test tube B in the experimental setup? What is the purpose of putting oil in the test tube? Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Name the process intended for study.

(b) Define the above mentioned process.

(c) When the weight of the test tubes A and B is taken before and after the experiment, what change is observed? Justify.

(d) What is the purpose of keeping the test tube B in the experimental setup?

(e) What is the purpose of putting oil in the test tube?

Answer

(a) Transpiration

(b) Transpiration is a process by which water is lost in the form of water vapour from aerial parts of the plant.

(c) Weight of test tube A before the experiment was more than its weight after the experiment. This is because water from test tube A has evaporated due to transpiration.

Weight of test tube B remains the same before and after the experiment, because no loss of water occurs in test tube B.

(d) Test tube B is used here as a control. This makes the observation of the change in test tube A easy.

(e) The purpose of putting oil in the test tube is to prevent loss of water from the test tube by evaporation.

Question 6

An apparatus as shown below was set up to investigate a physiological process in plants. The setup was kept in sunlight for two hours. Droplets of water were then seen inside the bell jar. Answer the questions that follow:

An apparatus as shown was set up to investigate a physiological process in plants. The setup was kept in sunlight for two hours. Droplets of water were then seen inside the bell jar. Name the process being studied. Explain the process. Why was the pot covered with a plastic sheet? Suggest a suitable control for this experiment. Mention two ways in which this process is beneficial to plants. List three adaptations in plants to reduce the above mentioned process. Transpiration, Concise Biology Solutions ICSE Class 10.

(a) Name the process being studied.

(b) Explain the process named above in (a).

(c) Why was the pot covered with a plastic sheet?

(d) Suggest a suitable control for this experiment.

(e) Mention two ways in which this process is beneficial to plants.

(f) List three adaptations in plants to reduce the above mentioned process.

Answer

(a) Transpiration

(b) Transpiration is a process during which water is lost in the form of water vapour through aerial parts of the plant.

(c) The pot is covered with a plastic sheet to prevent evaporation of water from the soil.

(d) A control for this experiment will be an empty polythene bag with its mouth tied.

(e) Transpiration is beneficial to plants in the following ways:

  1. It creates a suction force in the stem which enables the roots to absorb water and minerals.
  2. It helps in cooling the plant in hot weather.

(f) Some plants have developed adaptations to reduce transpiration to cut down loss of water such as:

  1. Sunken stomata
  2. Narrow leaves
  3. Reduced exposed surface by rolling or folding of leaves.

Question 7

The apparatus shown in the following diagram is Garreau's potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Equal amounts of calcium chloride (CaCl2) was taken in two vials, which were placed in two cups. The leaf was placed between the cups. The ends of the cups were closed with corks through which two mercury manometers were connected. After few hours, CaCl2 vials were taken out and weighed again.

The apparatus shown in the diagram is Garreau's potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Equal amounts of calcium chloride (CaCl2) was taken in two vials, which were placed in two cups. The leaf was placed between the cups. The ends of the cups were closed with corks through which two mercury manometers were connected. After few hours, CaCl2 vials were taken out and weighed again. What is the purpose of keeping CaCl2 vials inside the cup? After few hours CaCl2 vials were taken out and weighed again. Will you expect any difference in weight? If so, give reason. What is the purpose of using a manometer? What do you mean by transpiration? Transpiration, Concise Biology Solutions ICSE Class 10.

(a) What is the purpose of keeping CaCl2 vials inside the cup?

(b) After few hours CaCl2 vials were taken out and weighed again. Will you expect any difference in weight? If so, give reason.

(c) What is the purpose of using a manometer?

(d) What do you mean by transpiration?

Answer

(a) CaCl2 is a hygroscopic compound that absorbs moisture/water without changing its state. CaCl2 vials are placed inside the cup to absorb water.

(b) Yes, after few hours the weight of the CaCl2 vials will increase because they will absorb water lost by the leaf of the plant due to transpiration.

(c) Manometer is used to measure the pressure exerted by the water vapour that is released by the leaf through Transpiration. A change in vapour pressure within the cups shown by the manometers is indicative of the fact that either the connections are not air-tight or that all the vapour given out by the leaf surface is not being absorbed by the CaCl2 within the vials.

(d) Transpiration is the loss of water in the form of water vapour from the aerial parts (leaves and stem) of the plant.

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