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Why are there more stomatal openings on the lower surface of a dicot leaf?

Why are there more stomatal openings on the lower surface of a dicot leaf?



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This causes more transpiration to occur from lower leaf surface. What's the exact reason for why are there more stomatal openings on the lower surface of a dicot leaf?


Firstly, it is not necessary that all dicots have stomata on their lower surface of their leaves. The lotus Nelumbo nucifera has its stomata on its upper surface, due to the lower surface of its leaves being in contact with water, and therefore unable to transpire effectively.

The reason that stomata are usually on the lower surface has been analysed in this paper, which rejects the commonly held hypothesis that stomata appear on the lower surface of leaves (hypostomatous) as a response to dryness, by citing that hypostomatous leaves are relatively less common in dry environments.

The paper then analyses the correlation observed between parameters of leaves and their stomatal locations.

By using a number of computational models (which conclude that given the set of assumptions in the paper, leaves should not generally be hypostomatous), the paper addresses the faults of the model and concludes that there is no one single reason why leaves are usually hypostomatous, and then brings up a couple other possibilities that may help in explaining the majority of plants being hypostomatous.


A. MULTIPLE CHOICE TYPE Transpiration Selina Concise for ICSE Class 10

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

(a) Open stomata, dry atmosphere and moist soil

(b) Open stomata, high humid atmosphere and well irrigated soil

(c) Open stomata, high humid atmosphere and dry soil

(d) Closed stomata, dry atmosphere and dry soil

Answer 1

(a) Open stomata, dry atmosphere and moist soil

Question 2

With decrease in atmospheric pressure, the rate of transpiration will

Answer 2

Question 3

The rate of transpiration is more when

(d) atmosphere is dry and temperature is high

Answer 3

Question 4

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

Answer 4

Question 5

Guttation takes place through

(c) lower epidermis of leaves

Answer 5

Question 6

The loss of water as water vapour from the aerial parts of a plant is known as

Answer 6

Question 7

Transpiration will be fastest when the day is

Answer 7

Question 8

Most of the transpiration in tall trees occurs through

Answer 8

Question 9

Transpiration is best defined as

(a) loss of water by the plant

(b) evaporation of water from the aerial surfaces of a plant

(c) loss of water, as water vapour, by a plant

(d) release of water by a plant into the atmosphere

Answer 9

(b) evaporation of water from the aerial surfaces of a plant

B. VERY SHORT ANSWER TYPE ICSE Class 10 Transpiration

(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 1

Question 2

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

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

Answer 2

(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.

C. SHORT ANSWER TYPE Transpiration Selina Biology Solution for ICSE Class 10

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:

Answer 1

(b) protection and reduced transpiration

(d) conduction of water and mineral salts

Question 2

(a) State whether the following statements are True (T) or False (F)?

(i) Most transpiration occurs at midnight.

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

(iii) Wind velocity has an effect on transpiration.

(iv) Voltmeter is an instrument used for measuring the rate of transpiration in green plants.

(b) Rewrite the false statements in (a) above, in the correct form by changing either the first or the last word only.

Answer 2

(i) False. Most transpiration occurs at mid-day.

(iv) False. Photometer is an instrument used for measuring the rate of transpiration in green plants.

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) Water transpired is the water absorbed.

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

(e) Cork and bark of trees help in preventing loss of water.

(f) Perspiration and transpiration help to cool the body temperature of the organism.

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

Answer 3

(a) Transpiration increases with the velocity of wind. If the wind blows faster, the water vapours released during transpiration are removed faster and the area surrounding the transpiring leaf does not get saturated with water vapour.

(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) Plants absorb water continuously through their roots, which is then conducted upwards to all the aerial parts of the plant, including the leaves. Only a small quantity of this water i.e. about 0.02% is used for the photosynthesis and other activities. The rest of the water is transpired as water vapour. Hence water transpired is the water absorbed.

(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) Cork and Bark of trees are tissues of old woody stems. Bark is thick with outermost layer made of dead cells and the cork is hydrophobic in nature. These properties make them water-proof and hence they prevent transpiration.

(f) In both perspiration and transpiration, water is lost by evapouration from the body of the organism as water vapour. This evaporation reduces the temperature of the body surface and brings about cooling in the body of the organism.

(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.

Question 4

Which of the following statements are true and which ones are false? Give reason in support of your answer.

(a) Potometer is an instrument used for demonstration of transpiration occurring from the lower surface of a leaf.

(b) Hydathodes are similar to stomata in plant physiology.

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

(d) Some desert plants have sunken stomata on their leaves.

(e) Most transpiration occurs during mid-day.

Answer 4

Reason: Potometer is used to measure the rate of transpiration in a plant. Demonstration of transpiration occurring from the lower surface of a leaf is done by analyzing the changes in colour of pieces of dry cobalt chloride paper attached (and held in place) to the two surfaces of a leaf.

Reason: Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets are given out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water vapour. Stomatal opening is regulated by guard cells.

Reason: Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.

Reason: Desert plants need to reduce transpiration as much as possible so as to survive in the hot and dry environment. Hence some of them have sunken stomata as an adaptation to curtail transpiration.

Reason: During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. During mid-day, the outside temperature is higher, due to which there is more evaporation of water from the leaves. Therefore more transpiration occurs during mid-day.

Question 5

Differentiate between guttation and bleeding in plants.

Guttation Bleeding
It is the removal of excess of water from the plants because of excess water buildup in the plant. It is the removal of water from the plant because of injury.
Water escapes from specialised structures called hydathodes. Water escapes in the form of sap from the injured part of the plant.

D. LONG ANSWER TYPE Transpiration Concise Biology Solutions for ICSE Class 10

What is wilting? Some plants show wilting of their leaves at noon even when the soil is well watered. Why is it so?

Answer 1

Wilting refers to the loss of cellular turgidity in plants which results in the drooping of leaves or plant as a whole because of lack of water.

During noon the rate of transpiration exceeds the rate of absorption of water by roots. Due to the excessive transpiration, the cells of leaves lose their turgidity and wilt.

Question 2

Why are the stomata in most plants more numerous on the lower surface of a leaf instead of being on the upper surface?

Answer 2

The lower surface of leaf is sheltered from direct sunlight. If more stomata are on the upper surface of a leaf, then excessive transpiration would occur, resulting in quick wilting of the plant. Hence most plants have more numerous stomata on the lower surface of a leaf to control the rate of transpiration.

Question 3

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

Answer 3

Take the small 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. 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.

Question 4

Answer 4

Potometer is a device that measures the rate of water intake by a plant. This water intake is almost equal to the water lost through transpiration. Potometers do not measure the water lost due to transpiration but measure the water uptake by the shoot.

Question 5

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

Answer 5

Transpiration occurring through lenticels i.e. minute openings on the surface of old 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 6

List any three major factors that accelerate the rate of transpiration.

Answer 6

The factors that accelerate the rate of transpiration are:

(i) High intensity of sunlight

(iv) Decrease in atmospheric pressure

Question 7

There is a general belief that forests tend to bring more frequent rains. Can you explain this scientifically?

Answer 7

Forests have large number of plants especially trees. Each plant loses water in the form of water vapour everyday into the atmosphere through transpiration. A large apple tree loses as much as 30 litres of water per day. So huge amount of water is escaped into the atmosphere by forests. This increases the moisture in the atmosphere and brings more frequent rains.

Question 8

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 8

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 9

Briefly explain how the rate of transpiration is affected by:

(b) Humidity of the atmosphere

Answer 9

(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 – When the air is humid it can receive very less water vapour. 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.

E. STRUCTURED/APPLICATION/SKILL TYPE Transpiration Selina Concise Biology Solution for ICSE Class 10 Chapter 5

Question 1

In an experiment, four freshly plucked leaves (A-D) of a plant, such as those of China Rose, was treated as follows:

(A) coated with vaseline on its upper surface

(B) coated on the lower surface

(C) coated on both surfaces

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

(i) Which leaf would become most limp? Why?

(ii) Which leaf would show least limping? Why?

Answer 1

(i) The leaf D would become most limp. This is because water would be lost through transpiration from upper as well as the lower surface of leaf D since it is uncoated.

(ii) The least limping would be shown by leaf C since its upper and lower surfaces have been coated with vaseline. So no water is lost from the leaf through transpiration since the stomatal openings get blocked by vaseline.

Question 2

Given alongside is the diagram of an experimental set-up to demonstrate a certain phenomenon in plants.

(a) Name the phenomenon being demonstrated.

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

(c) What is the purpose of the spring balance in the set-up?

(d) Would it make a difference if the experimental set-up is kept in bright sunshine?

Answer 2

(b) Oil is put on the surface of water to prevent loss of water by evaporation.

(c) Yes, the transpiration rate will increase. Transpiration would occur faster. The observable changes will occur in less time.

(d) The spring balance progressively measures the change in weight of the set-up. This because as the plant transpires, it creates the suction force in plant which allows roots to absorb more water from the test tube. Hence, the water in the test will get reduced. Thus, the weight of the entire set will decrease.

Question 3

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

(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:

Give a reason in each case.

Answer 3

(b) Ganong’s potometer is used to measure the water intake of a plant which is almost equal to the water lost through transpiration.

(c) The movement of the air bubble and its position in the capillary tube indicates the volume of water lost through transpiration in a given time.

(d) The water in the reservoir can be released into the capillary tube by opening the stop cock. This allows the air bubble to restore back to its original position.

(i) 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.

(ii) If the apparatus is kept in bright sunlight, 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.

(iii) 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 4

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:

(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 4

(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 5

The apparatus shown in the following diagram is Garreau’s potometer designed to demonstrate unequal transpiration from the two surfaces of a dorsiventral leaf. Before keeping the leaf in between the cups, anhydrous calcium chloride (CaCl2) contained in two small vials were weighed and placed in both 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.

(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 5

(a) CaCl2 is a hygroscopic compound that absorbs moisture/water without changing its state. CaCl2 vials 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. In order to measure the pressure exerted by the fluid, the fluid is allowed to exert pressure on one of the closed ends of the tube. Under the effect of the pressure, the liquid inside the manometer tube gets displaced and the amount of displaced liquid is measured.

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

Question 6

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

(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

Answer 6

(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.

Question 7

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:

(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 7

(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.


Stomata distribution in a dicot leaf

Aim: To investigate and compare the distribution density of stomata in the upper and lower epidermis of a dicotyledonous leaf.

Stomata are the principle means of gas exchange in plants. Stomata are small pores they are controlled by guard cells which control the opening and closing of stomata. Stomata allow carbon dioxide to enter the plant, and allow water and excess oxygen to escape. About 90% of water is lost from the leaf during transpiration.

The number of stomata on leaf surface varies among different species. The lower epidermis tends to have the most number of stomata than the upper surface.

In order to carry out the experiment 3 methods were used:

(1) Calibration of the eyepiece graticule- done in order to work out field of view area.

(2) Counting of the stomata using the microscope.

(3) Calculating stomata density.

Place the graticule scale into the eyepiece of the microscope.

This is done by unscrewing the top lens and dropping the scale into the lens body. Then screw the top lens back on. Put the stage micrometer on the stage and hold in place by the clips. Look through the microscope and focus at x40 so you can see both scales clearly. Move the stage micrometer carefully so that the starting units of the two scales coincide. Count along the two scales until there is again a coincidence between the two scales. Note the number of divisions along each scale. Repeat for x100 and x400 magnification.

On the upper surface of the leaf paint a thick layer of clear nail varnish. Allow the leaf to completely dry. Once it has dried stick a piece of clear tape over the.

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ICSE Solutions for Chapter 4 Transpiration Class 10 Selina Biology


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) Thick cuticle and .

Solution 1: (a) guttation
(b) protection and reduced transpiration
(c) transpiration (d) reduced transpiration

Question 2: (a) State whether the following statements are True (T) Or False (F)?
(i) Most transpiration occurs at midnight.
(ii) Transpiration creates a pull for upward movement of the sap.
(iii) Wind velocity has an effect on transpiration.
(iv) Voltmeter is an instrument used for measuring the rate of transpiration in green plants.
(b) Rewrite the false statements, in (a) above, in the correct form by changing either the first or the last word only.

Solution 2: (a)
(i) False
(ii) True
(iii) True
(iv) False

(b) (i) Most transpiration occurs at mid-day.
(iv) Potometer is an instrument used for measuring the rate of transpiration in green plants.

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) Water transpired is the water absorbed.
d) More transpiration occurs from the lower surface of a dorsiventral leaf.
e) Cork and bark of trees help in preventing loss of water.
f) Perspiration and transpiration help to cool the body temperature of the organism.
g) On a bright sunny day, the leaves of certain plants roll up.

Solution 3: (a) Transpiration increases with the velocity of wind. If the wind blows faster, the water
vapours released during transpiration are removed faster and the area surrounding the transpiring leaf does not get saturated with water vapour.

(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) Plants absorb water continuously through their roots, which is then conducted upwards to
all the aerial parts of the plant, including the leaves. Only a small quantity of this water i.e. about 0.02% is used for the photosynthesis and other activities. The rest of the water is
transpired as water vapour. Hence water transpired is the water absorbed.

(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) Cork and Bark of trees are tissues of old woody stems. Bark is thick with outermost layer
made of dead cells and the cork is hydrophobic in nature. These properties make them water-proof and hence they prevent transpiration.

(f) In both perspiration and transpiration, water is lost by evaporation from the body of the
organism as water vapour. This evaporation reduces the temperature of the body surface and brings about cooling in the body of the organism.

Question 4: Which of the following statements are true and which ones are false? Give reason in support of your answer.
(a) Potometer is an instrument used for Demonstration of transpiration occurring from the lower surface of a leaf.
(b) Forest contribute in bringing rains.
(c) Hydathodes are similar to stomata in plant physiology.
(d) Atmospheric humidity promotes transpiration from a green plant.
(e) Some desert plants have sunked stomata on their leaves.
(f) Most transpiration occurs during midday.

Solution 4: (a) False
Reason: Potometer is used to measure the rate of transpiration in a plant. Demonstration of transpiration occurring from the lower surface of a leaf is done by analyzing the changes in colour of pieces of dry cobalt chloride paper attached (and held in place) to the two surfaces of a leaf.

(b) True
Reason: Transpiration carried out by the large number of trees in a forest. This increases
the moisture in the atmosphere and brings rain.

(c) False
Reason: Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets are given out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water
vapour. Stomatal opening is regulated by guard cells.

(d) False
Reason: Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata,
thereby reducing the rate of transpiration.

It is the removal of excess of water from the plants because of excess water buildup in the plant.

It is the removal of water from the plant because of injury.

Water escapes from specialized structures called hydathodes.

Water escapes in the form of sap from the injured part of the plant.

D. Long Answer Type

E. Structure/Application/Skill Type


Question 1: In an experiment, four freshly plucked leaves (A-D) of a plant, such as those of china – rose, were treated as follows:
(a) Coated with Vaseline on its upper surface.
(b) coated on the lower surface.
(c) coated on both surface
(d) left uncoated.

All the four leaves A, B, C & D were left in a room for about 24 hours.
(i) which leaf would become most limp? Why?
(ii) which leaf would show least limping? Why?

Solution 1: (i) The leaf D would become most limp. This is because water would be lost through transpiration from upper as well as the lower surface of leaf D since it is uncoated.


(a) Label the parts numbers 1-3
(b) Is this state, open or closed?
(c) Is this stoma, of a dicot leaf or a monocot leaf?
(d) Redraw a sketch of the stomatal apparatus in the state opposite to the one shown here.

Solution 2: (a) 1- Guard Cell 2- Inner wall of the Guard Cell 3- Stoma/Stomatal Aperture

(c) The structure of stoma remains same in monocots as well as in dicots. Hence, the stoma from the diagram can be of a monocot leaf or of a dicot leaf.


Stomata of Monocot vs Dicot Plants

Stomata are important for gaseous exchange in leaves of both monocot and dicot plants. Two guard cells always surround the stomata. The guard cells of dicot stomata have shapes like beans while guard cells of monocot stomata have shapes like dumbells. The stomata of most dicot plants are present in the lower epidermis of the leaf whilst in monocot plants, they are present in both upper and lower epidermis. These are some of the differences between stomata of monocot and dicot plants.


Selina Concise Biology Class 10 ICSE Solutions Transpiration

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 10 Biology Chapter 5 Transpiration. You can download the Selina Concise Biology ICSE Solutions for Class 10 with Free PDF download option. Selina Publishers Concise Biology for Class 10 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina ICSE Solutions for Class 10 Biology Chapter 5 Transpiration

Solution A.1.
(a) Open stomata, dry atmosphere and moist soil

Solution A.2.
(a) increase

Solution A.3.
(b) temperature is high

Solution A.4.
(c) sunken stomata

Solution A.5.
(d) hydathodes

Solution A.6.
(d) transpiration

Solution A.7.
(d) hot, dry and windy

Solution A.8.
(b) Lenticels

Solution A.9.
(b) evaporation of water from the aerial surfaces of a plant

Solution B.1.
(a) Lenticels
(b) Guttation
(c) Potometer
(d) Nerium
(e) Ganong’s photometer
(f) Stomata and cuticle
(g) Hydathodes
(h) Guttation

Solution B.2.
(a) vapour, aerial
(b) stomata, transpiration
(c) suction, water (heat)

Solution C.1.
(a) guttation
(b) protection and reduced transpiration
(c) transpiration
(d) reduced transpiration

Solution C.2.
(i) False
(ii) True
(iii) True
(iv) False
(v) Most transpiration occurs at mid-day.
(vi) Potometer is an instrument used for measuring the rate of transpiration in green plants.

Solution C.3.
(a) Transpiration increases with the velocity of wind. If the wind blows faster, the water vapours released during transpiration are removed faster and the area surrounding the transpiring leaf does not get saturated with water vapour.

(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) Plants absorb water continuously through their roots, which is then conducted upwards to all the aerial parts of the plant, including the leaves. Only a small quantity of this water i.e. about 0.02% is used for the photosynthesis and other activities. The rest of the water is transpired as water vapour. Hence water transpired is the water absorbed.

(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) Cork and Bark of trees are tissues of old woody stems. Bark is thick with outermost layer made of dead cells and the cork is hydrophobic in nature. These properties make them water-proof and hence they prevent transpiration.

(f) In both perspiration and transpiration, water is lost by evapouration from the body of the organism as water vapour. This evaporation reduces the temperature of the body surface and brings about cooling in the body of the organism.

(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.

Solution C.4.
(a) False
Reason: Potometer is used to measure the rate of transpiration in a plant. Demonstration of transpiration occurring from the lower surface of a leaf is done by analyzing the changes in colour of pieces of dry cobalt chloride paper attached (and held in place) to the two surfaces of a leaf.

(b) True
Reason: Transpiration carried out by the large number of trees in a forest. This increases the moisture in the atmosphere and brings rain.

(c) False
Reason: Hydathodes are special pores present on the ends of leaf veins through which guttation occurs and water droplets are given out. Their openings cannot be regulated. Stomata on the other hand are minute openings in the epidermal layer of leaves through which exchange of gases as well as transpiration occurs. Water is given out as water vapour. Stomatal opening is regulated by guard cells.

(d) False
Reason: Transpiration is reduced during high atmospheric humidity. High humidity in the air reduces the rate of outward diffusion of the internal water vapour across stomata, thereby reducing the rate of transpiration.

(e) True
Reason: Desert plants need to reduce transpiration as much as possible so as to survive in the hot and dry environment. Hence some of them have sunken stomata as an adaptation to curtail transpiration.

(f) True
Reason: During the day, the stomata are open to facilitate the inward diffusion of carbon dioxide for photosynthesis. During mid-day, the outside temperature is higher, due to which there is more evaporation of water from the leaves. Therefore more transpiration occurs during mid-day.

Solution C.5.

Guttation Bleeding
It is the removal of excess of water from the plants because of excess water buildup in the plant. It is the removal of water from the plant because of injury.
Water escapes from specialisedstructures called hydathodes. Water escapes in the form of sap from the injured part of the plant.

Solution D.1.
Wilting refers to the loss of cellular turgidity in plants which results in the drooping of leaves or plant as a whole because of lack of water.
During noon the rate of transpiration exceeds the rate of absorption of water by roots. Due to the excessive transpiration, the cells of leaves lose their turgidity and wilt.

Solution D.2.
The lower surface of leaf is sheltered from direct sunlight. If more stomata are on the upper surface of a leaf, then excessive transpiration would occur, resulting in quick wilting of the plant. Hence most plants have more numerous stomata on the lower surface of a leaf to control the rate of transpiration.

Solution D.3.
Take the small 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. 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.

Solution D.4.

Potometer is a device that measures the rate of water intake by a plant. This water intake is almost equal to the water lost through transpiration. Potometers do not measure the water lost due to transpiration but measure the water uptake by the shoot.

Solution D.5.

  • Transpiration occurring through lenticels i.e. minute openings on the surface of old 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.

Solution D.6.
The factors that accelerate the rate of transpiration are:

  • High intensity of sunlight
  • High temperature
  • Higher wind velocity
  • Decrease in atmospheric pressure
    (Any three)

Solution D.7.
Forests have large number of plants especially trees. Each plant loses water in the form of water vapour everyday into the atmosphere through transpiration. A large apple tree loses as much as 30 litres of water per day. So huge amount of water is escaped into the atmosphere by forests. This increases the moisture in the atmosphere and brings more frequent rains.

Solution D.8.
The advantages of transpiration to the plants are:

  • Transpiration brings about a cooling effect to the plant body since evaporation of water reduces the temperature of leaf surface.
  • Transpiration helps in the ascent of sap by producing a suction force acting from the top of the plant.
  • Transpiration helps in distributing water and mineral salts throughout the plant body.
  • Transpiration helps in eliminating excess water.

Solution D.9.

  1. If the water content of the leaves decreases due any reason, the guard cells turn flaccid, thereby closing the stomatal opening and transpiration stops.
  2. Some plants have sunken stomata whereas others have reduced number of stomata to reduce transpiration.
  3. In some plants, leaves may be dropped or may be absent or changed into spines as an adaptation to reduce transpiration.
  4. The leaves may be covered by thick cuticle such as in Banyan tree, so as to reduce transpiration.

Solution D.10.
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.

Solution D.11.
(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 – When the air is humid it can receive very less water vapour. 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.

Solution E.1.

(i) The leaf D would become most limp. This is because water would be lost through transpiration from upper as well as the lower surface of leaf D since it is uncoated.

(ii) The least limping would be shown by leaf C since its upper and lower surfaces have been coated with vaseline. So no water is lost from the leaf through transpiration since the stomatal openings get blocked by vaseline.

Solution E.2.
(a)
Guard Cell
Inner wall of the Guard Cell
Stoma/Stomatal Aperture
(b) Open state
(c) The structure of stoma remains same in monocots as well as in dicots. Hence, the stoma from the diagram can be of a monocot leaf or of a dicot leaf.

Solution E.3.
(a) Transpiration
(b) Oil is put on the surface of water to prevent loss of water by evaporation.
(c) Yes, the transpiration rate will increase. Transpiration would occur faster. The observable changes will occur in less time.
(d) The spring balance progressively measures the change in weight of the set-up. This because as the plant transpires, it creates the suction force in plant which allows roots to absorb more water from the test tube. Hence, the water in the test will get reduced. Thus, the weight of the entire set will decrease.

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Difference between Dicot and Monocot Leaf

Sl. No.Dicot Leaf
Dorsiventral Leaf
Monocot Leaf
Isobilateral Leaf
1Dicot leaves are dorsiventralMonocot leaves are isobilateral
2Upper surface of the leaf is dark green and the lower surface is light greenBoth the surfaces of the leaf are equally green
3Epidermal cells are not silicified (silica deposition absent)Epidermal cells are silicified (heavy deposition of silica)
4Bulliform (motor) cells absent in the epidermisBulliform cells are present
5Leaves usually hypostomatic (stomata present on the lower surface of the leaf)Leaves usually amphistomatic (stomata present on both the surface of leaf)
6Stomata are arranged randomly on the epidermisStomata are arranged in parallel rows in the epidermis
Stomata
7Stomatal guard cells are kidney-shapedStomatal guard cells are dumb-bell shaped
Guard Cell
8Mesophyll is differentiated into palisade and spongy tissuesMesophyll undifferentiated (composed of loosely packed isodiametric cells with intercellular spaces)
Mesophyll
9Leaf veins are reticulateLeaf veins are parallel
10Protoxylem elements are indistinguishableProtoxylem elements are distinguishable as protoxylem lacuna
11Bundle sheath with single layer of cellsBundle sheath with single or multiple layers
12Bundle sheath cells usually lack chloroplastBundle sheath cells usually possess chloroplasts
13Bundle sheath extension is parenchymatousBundle sheath extension is sclerenchymatous
14Lower portion of the mid-rib is collenchymatousLower portion of mid-rib is sclerenchymatous

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What you'll learn:

In the leaves of monocot plants, the stomata are observed to be the tiny pores that are present in the lower epidermis and the upper epidermis of the monocot leaves, and surrounding them are the pairs of the dumbbell-shaped guard cells. The distribution of stomata in monocots is called an amphistomatic distribution because the monocot's stomata are distributed equally in both the lower and the upper epidermis. In monocots, because of the amphistomatic stomata distribution, the transpiration frequency can be higher than the frequency of transpiration in a dicot leaf. Hence, when there is excess sunlight present, the monocot leaves get rolled so that the leaf's surface area is reduced and there is the prevention of water loss. Gymnosperms ideally contain sunken stomata that are embedded deeply in the plant's leaves, and this is an adaptation that prevents excess transpiration.


11. TRANSPORT IN PLANTS

It is the evaporative loss of water by plants through the stomata in the leaves.

Less than 1% of the water reaching the leaves is used in photosynthesis and plant growth. The remaining is lost by transpiration.

Transpiration can be studied using cobalt chloride paper. It turns colour (blue to pink) on absorbing water.

During transpiration, exchange of O2 & CO2 in the leaf also occurs.

Stomata are open in day time and close during night.

Opening or closing of stomata is due to change in the turgidity of the guard cells.

The inner wall of guard cell lining stomatal aperture is thick and elastic and the outer wall is thin.

When turgidity of guard cells increases, the outer walls bulge out and pull the inner walls into a crescent shape.

Cellulose microfibrils in the guard cells are oriented radially rather than longitudinally making it easier for the stoma to open.

The guard cells lose turgidity due to water loss (or water stress) and the inner walls regain their original shape. As a result, the stoma closes.

Usually lower surface of a dicot leaf has more stomata. In monocot leaf, they are about equal on both surfaces.

  • External factors: Temperature, light, humidity, wind etc.
  • Plant factors: Number & distribution of stomata, number of stomata open, water status of plant, canopy structure etc.
  • Cohesion: Mutual attraction between water molecules.
  • Adhesion: Attraction of water molecules to polar surfaces (e.g. surface of tracheary elements).
  • Surface Tension: In liquid phase, water molecules are more attracted to each other than in gas phase.

Xylem vessels supply the water from the root to leaf vein. There is a continuous thin film of water over the cells. So, as water evaporates through the stomata, water pulls into the leaf from the xylem. In atmosphere, concentration of water vapour is lower than that in substomatal cavity and intercellular spaces. This also helps water to diffuse into the surrounding air. This creates a ‘pull’.

The forces generated by transpiration can create pressures to lift a xylem sized column of water over 130 m high.

Photosynthesis is limited by available water which is swiftly depleted by transpiration.

The humidity of rainforests is mainly due to the cycling of water from root to leaf to atmosphere and back to the soil.

C4 photosynthetic system helps to maximise the availability of CO2 and minimise water loss.

C4 plants are twice as efficient as C3 plants in fixing carbon (making sugar). However, C4 plants lose only half as much water as a C3 plant for the same amount of CO2 fixed.


Leaf Adaptations

Coniferous plant species that thrive in cold environments, such as spruce, fir, and pine, have leaves that are reduced in size and needle-like in appearance. These needle-like leaves have sunken stomata and a smaller surface area, two attributes that aid in reducing water loss. In hot climates, plants such as cacti have succulent leaves that help to conserve water. Many aquatic plants have leaves with wide lamina that can float on the surface of the water a thick waxy cuticle on the leaf surface that repels water.


Watch the video: Practical Comparing the abundance of stomata on the upper and lower surfaces of a dicot (August 2022).