CLASS 10

BIOLOGY

CHAPTER 4 (TRANSPIRATION)

A. TRANSPIRATION: The process by which loss of water takes place in the form of vapour

from the aerial parts of the plant.

B. EXPERIMENT NO.I

AIM: To demonstrate the process of transpiration.

PROCEDURE: Take a well watered potted plant and cover the pot along with soil ( to

prevent loss of soil water by evaporation) .Cover the pot with bell jar .Leave the

apparatus in the sunlight for few hours.

OBSERVATION: water droplets will be seen from the interior of the glass .

INFERENCE: water droplets are the condensed form of vapor which are released from

the leaves.

C. EXPERIMENT NO.2

AIM: To demonstrate the process of transpiration.

PROCEDURE:

SET-UP A: Take a well watered potted plant and cover the pot along with soil ( to

prevent loss of soil water by evaporation) .Cover the pot with bell jar .Leave the

apparatus in the sunlight for few hours.

SET-UP B: Keep a cobalt chloride paper in the similar set-up B.

SET-UP C: Take a bell jar and place a cobalt chloride paper in it but no potted plant(this

is also called a control experiment).

OBSERVATION:

SET-UP A: water droplets will be seen from the interior of the glass .

SET-UP B: Colour of cobalt chloride paper changes from blue to pink.

SET-UP C: Colour of cobalt chloride paper remains the same.

INFERENCE: Cobalt chloride changes the colour in the presence of water/moisture.

D. EXPERIMENT NO.3

AIM: To measure the rate of transpiration.

PROCEDURE: Take a well watered potted plant and cover the pot along with soil ( to

prevent loss of soil water by evaporation). Keep the set-up on a pan balance and note

the initial weight. Reweigh the set-up at regular interval of time.

OBSERVATION: The readings show the decrease of weight every time.

INFERENCE: weight loss due to transpiration.

G. TYPES OF TRANSPIRATION:

1. Stomatal transpiration:

2. Cuticular transpiration

3. Lenticular transpiration

H. STRUCTURE OF STOMATA :

1. They are microscopic structure surrounded by two guard cells.

2. Present in the epidermis of leaves.

3. Dicot leaves possess kidney shaped guard cells.

4. Monocot leaves possess dumb-bell shaped guard cells

5. Function: exchange of gases.

6. Guard cells surround an opening called stoma.

I. MECHANISM OF STOMATAL TRANSPIRATION: From the xylem vessels of the

veins of the leaf water diffuse out into the intercellular spaces and from these to

the guard cells. When the guard cells become turgid, the inner thick walls are

pulled apart by the inner walls of the guard cells. Due to this, the gap between

the guard cells increases, the stoma opens and transpiration occurs through it.

J. EXPERIMENT NO.6

AIM: To demonstrate that more transpiration occurs from the lower surface of a

dorsiventral leaf as compared to upper surface.

PROCEDURE: Place cobalt chloride strips on both the surface of the leaves. Fix the

strips with the help of leaf clamps.

OBSERVATION: Cobalt chloride strip on the lower surface of the leaf changes to pink

colour first.

INFERENCE: Cobalt chloride strip changes to pink colour from the lower surface first

shows that transpiration is more from the lower surface of the leaf.

K. EXPERIMENT NO.7

AIM: To demonstrate that more transpiration occurs from the lower surface of a

dorsiventral leaf as compared to upper surface by four leaf experiment.

PROCEDURE: Take four similar leaves and place at regular distance as shown in the

diagram. Label them as A, B, C and D.

(i) Apply Vaseline on both surfaces of A.

(ii) Apply Vaseline on the lower surface of B.

(iii) Apply Vaseline on the upper surface of C.

(iv) Do not apply Vaseline on D.

NOTE THE INITIAL AND FINAL WEIGHT OF THE LEAVES AFTER A FEW DAYS.

OBSERVATION:

(i) Leaf A shows negligible loss of weight.

(ii) Leaf B shows shows loss of weight but less than C.

(iii) Maximum weight loss is seen in D.

INFERENCE: Vaseline acts as an antitranspirant which does not allow transpiration to

occur. Therefore, leaf A does not transpire .C transpires more than B because leaves

transpires more from the lower surface of the leaves. D shows maximum

transpiration as it was free from Vaseline.

L. FACTORS AFFECTING THE RATE OF TRANSPIRATIO:

1. INTERNAL FACTORS:

Leaf area: more surface area of leaf , more transpiration.

Leaf structure: Structures like sunken stomata, thick cuticle, wax coating

etc reduces the transpiration.

Water content of leaves: less water absorbed by the roots will provide

insufficient water in the leaves thereby transpiration decreases.

2. EXTERNAL FACTORS:

Light: light increases the rate of transpiration that is why transpiration

occurs during the day.

Temperature: increase in temperature increases the transpiration.

Humidity: increase in humidity decreases the transpiration.

Wind: increased velocity of wind increases the transpiration.

Atmospheric pressure: increased pressure of atmosphere decreases the

transpiration.

Soil water: More soil water favours the transpiration.

Carbon dioxide: more carbon dioxide closes the stomata thus decreases

the transpiration.

M. ADAPTATIONS IN PLANTS TO REDUCE TRANSPIRATION:

1. Thick cuticle

2. Loss of leaves

3. Narrow leaves

4. Fewer stomata

5. Sunken stomata

N. SIGNIFICANCE OF TRANSPIRATION:

1. Advantages:

Ascent of sap

Absorption of water

Transport of minerals

Cooling effect

Improvement in quality of fruits

2. Disadvantages:

Wilting injury

Stunted growth

O. ANTITRANSPIRANTS: Agents or chemicals that reduces the rate of transpiration.

Example : PMA (phenyl –mercuric acetate), a fungicide and abscisic acid(growth

regulator).

P. GUTTATION: Loss of water in the form of liquid from the specialized structures

present on the tips and margins of the leaf called hydathodes.

Q. BLEEDING: Exudation of cell sap from the cut or injured part of the plant.

QUESTIONS-ANSWERS:

Q1. Name the following:

(i) The structure through which most of the transpiration takes place.

(ii) The structure through which guttation takes place.

(iii) Exudation of sap from injured parts of a plant.

(iv) Small openings present on the bark of woody stems.

(v) The plant having sunken stomata.

A1.

(i) Stomata

(ii) Hydathodes

(iii) Bleeding

(iv) Lenticels

(v) Nerium

Q2. Give the function of the following :

(i) Hydathodes

(ii) Xylem

(iii) Lenticels

(iv) Stoma

A2.

(i) Guttation

(ii) Conduction of water and dissolved minerals from roots to leaves .

(iii) Exchange of respiratory gases.

(iv) transpiration

Q3. Give reasons for the following:

(i) Herbaceous plants growing in well watered soils are found to wilt on a hot day.

(ii) Leaves of certain plants roll up on a bright sunny day.

(iii) Xerophytes have their leaves modified to spines or reduced in size.

A3.

(i) On a hot day rate of transpiration is more than the rate of absorption so herbaceous

plants wilt.

(ii) On a bright sunny day, the transpiration rate is higher than the rate of absorption so

rolling of leaves of certain plants on a bright sunny day is an adaptation to reduce

the rate of transpiration by reducing the exposed leaf surface area.

(iii) Xerophytes are growing in scarcity of water. In order to decrease the rate of

transpiration their leaves are modified into spines or reduced in size.

Q4. List three adaptations in plants to reduce excessive transpiration.

A4.

(i) sunken stomata

(ii) leaf modified to form spines.

(iii) Presence of thick cuticle.

Q5. Name three factors which affects transpiration.

A5.

(i) Sunlight

(ii) Humidity

(iii) Wind.

Q6. Given is an apparatus used to study a particular process in plants. Study the same and

answer the questions that follow:

(i) Name the apparatus.

(ii) Mention one limitation of this apparatus.

(iii) Which phenomenon is studied with the help of this apparatus?

(iv) What is the function of the part marked ‘reservoir’?

(v) What is the role of air bubble in the experiment?

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

(a) In the dark.

(b) In sunlight.

(c) In front of a fan.

A6.

(i) Potometer

(ii) Introduction of air bubble in the graduated capillary tube is not easy.

(iii) Transpiration.

(iv) When the air bubble in the horizontal tube of the photometer reaches the end of

the narrow tube, the stopcock of the reservoir is opened and water from it runs

down. This drives back the air bubble and the experiment is restarted without

disturbing the experiment.

(v) The rate of movement of the air bubble indicates the rate of transpiration.

(vi) To provide water to the potometer.

(a) Movement of the air bubble will be decreases or slowed.

(b) Movement of the air bubble will be faster.

(c) Movement of the air bubble will be faster.

Q7. Given below is the diagram of an experimental set-up to study the process of transpiration

in plants. Study the same and the answer the questions that follow:

(i) What is the colour of dry cobalt chloride paper?

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

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

(iv) 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 reason to

support your answer.

(v) Define transpiration.

A7.

(i) Blue

(ii) Dicot. It has reticulate venation.

(iii) In order to prevent atmospheric moisture from coming in contact with cobalt

chloride paper.

(iv) Cobalt chloride paper on dorsal side remains blue as less no. of stomata are present

on the dorsal surface.

Cobalt chloride paper on the ventral side changes to pink as more stomata are

present on the ventral surface of the leaf.

(v) The process by which loss of water takes place in the form of vapour from the aerial

parts of the plant.

Q8. The apparatus shown 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

manometers were connected. After a few hours CaCl2 vials were taken out and weighed again.

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

(ii) After a few hours, CaCl2 vials were taken out and weighedagain. Will you expect any

difference in weight? If so, give reasons.

(iii) What was the purpose of using a manometer?

(iv) What do you mean by transpiration?

A8.

(i) To absorb the moisture formed by transpiration.

(ii) Yes, the weight of CaCl2 vials kept on the lower side will be more because

transpiration will be more on the lower surface and the moisture absorbed.

(iii) To check the outside and inside pressures.

(iv) The loss of water in the form of water vapour from the aerial parts of a plant.

ACTIVITIES:

1. LEARN ALL THE TOPICS –DEFINITIONS, STRUCTURE, FUNCTIONS AND LOCATION.

2. Differentiate :

(i) Stomata and lenticels

(ii) Transpiration and guttation

(iii) Lenticular transpiration and stomatal transpiration.