SUBJECT- BIOLOGY CHAPTER 5: TRANSPIRATION STANDARD- X

Syllabus: Transpiration- Process & significance, Ganong’s potometer and its limitations. The

factors affecting rate of transpiration, a brief idea of guttation and bleeding.

Scope of syllabus:

Concept of transpiration and its importance to plants

Experiments related to transpiration: a. Loss in weight of a potted plant or a leafy shoot in a test tube as a result of

transpiration

b. Use of cobalt chloride paper to demonstrate unequal rate of transpiration in a dorsiventral leaf

Mechanism of stomatal transpiration on the basis of potassium ion exchange theory

Adaptation in plants to reduce transpiration

A brief idea of guttation and bleeding TOPIC 1: INTRODUCTION, DEFINITION AND DEMONSTRATION:

In a total quantity of absorbed and transported water by any plants, about 2% of water is only

used in activities of plants i.e photosynthesis & other metabolic activities.

Rest of the water is lost in the form of vapour.

Demonstration: Experiment: 1

Transpiration: The loss of water in the form of water vapour from the leaves and the

aerial parts of plants

The above experiment where polythene is applied as a covering to the plant part shows the water droplets as a condensed form of water vapour lost by plant.

So it concludes that water has lost through process Transpiration. (Click the link below to have a better understanding to the topic.) https://www.youtube.com/watch?v=YeOw-wJR9fc

Experiment: 2

Set A- Plant is kept in a jar which shows droplets of water due to loss of water by plants in a form of water vapour (Transpiration)

Set B- The same set up and results like set-A.

But the blue colour cobalt chloride paper kept in this set up turns to pink due to the presence of water droplets which is formed due to condensation of water vapour (Transpiration)

Set C- Acts as control as it is without plant. No change is observed (No transpiration) TOPIC 2: MEASUREMENT OF TRANSPIRATION

1. Weighing method :

(A) (B) (C)

In diagram (A) & (B): primary plant weight (W1) is taken and then plants are kept in

sunlight for Transpiration. After that final weight will be taken .

So W1-W2= Loss of water by transpiration

(Note: Oil is used to prevent the loss of water by direct evaporation)

In diagram (C): After keeping plant

in a Volumetric flask, the level of water is set on ‘0’ scale on graduated tube and plants are left in sunlight to have transpiration. Due to loss of water by transpiration, the roots are absorbing water from the flask and level of water in graduated

https://www.youtube.com/watch?v=YeOw-wJR9fc

2. Potometer method: (Ganong’s Potometer) Click the link below to have a better understanding to the topic. https://www.youtube.com/watch?v=gXocZZDDPaw

Procedure:

A few drops of eosin oil are added to water to make it coloured. A freshly cut twig is placed on the mouth of the glass cylinder.

A single air bubble has to be arranged at the zero reading of the horizontal bar. Lift the bent end which allows the air bubbles to enter and get trapped in the horizontal bar.

Observation:

When the experiment begins, it is observed that the air bubble at the zero reading starts to

move. Reason:

As the transpiration takes place, a transpirational pull is created by the shoot to make up for the loss. Due to this, the horizontal bubble starts moving in the direction of the twig. The transpiration rate is calculated by taking the distance covered by the air bubble in a certain time period. (Several readings were noted by repeatedly adjusting the air bubble to zero. The

average of this reading gives the transpiration rate) Limitations Of Ganong’s Potometer:

https://www.youtube.com/watch?v=gXocZZDDPawhttps://byjus.com/biology/transpiration-pull/

The potometer does not measure the transpiration rate accurately because not all the water taken up by the plant is used for transpiration. It usually measures the rate of water uptake.

The twig placed on the glass cylinder might not stay alive for a longer time. The introduction of an air bubble in the horizontal bar is very difficult and time-consuming. A slight change in the atmospheric temperature might affect the position of the air bubble

TOPIC 3: KINDS OF TRANSPIRATION:

1.Stomatal transpiration:

Leaf stomata are the primary sites of transpiration and consist of two guard cells that form a small pore on the surfaces of leaves. The guard cells control the opening and closing of the stomates in response to various environmental stimuli and can regulate the rate of transpiration to reduce water loss.

Mechanism:

1 • Stomatal transpiration

2 • Cutical transpiration

3 • Lenticular transpiration

Pallisade

eee

Spongy

Intercellular Space space

Water after absorption by roots, rises up through the stem and reaches the

tissues of the leaves

A large number of Spongy mesophyll cells have their surfaces exposed to

intercellular spaces

These surfaces of cells give out some water as a thin film (due to turgor

https://byjus.com/biology/transpiration/https://www.britannica.com/science/leaf-plant-anatomy

The lost water in this way replace by drawing more water from nearest cells where water travels through Imbibition (water absorption by surface attraction, specially by cell wall)more

and less by osmosis.

More transpiration- Dicot Leaf [as it is broad and with more number of stomata on their lower(ventral) surface as compared to their upper (Dorsal) surface]

Experiment:

The arrangement of leaf surfaces with cobalt chloride paper is shown below :

Conclusion: The lower surface contains more number of stomata as compare to upper surface in dorsiventral leaf in dicot leaves.

Stomatal regulation of transpiration:

Depends on amount of water and solutes present in a guard cells In a day time, stomata open to fulfill the need for Photosynthesis i.e diffusion of gases,

which allows transpiration .

After passing from other intercellular spaces, finally vapour reaches to sub-stomatal space

After that it escapes through Stomata by diffusion

(Higher to lower concentration) means from cells to the outside environment

If water content is falling short in a leaf, guard cells turn to flaccid (shrink) thereby closing the stomata and transpiration stops

(Click the link below to have a better understanding to the topic.) https://www.youtube.com/watch?v=JQvdXX7hGqI https://www.youtube.com/watch?v=cnk3BJDBqIo

2. Lenticular transpiration: (Click the link below to have a better understanding to the introduction of the topic.) https://www.youtube.com/watch?v=cMte2VCtZ-I

3. Cuticular transpiration: (Click the link below to have a better understanding to the topic.) https://www.youtube.com/watch?v=CdxySlXe6oc

Occurred through Lenticels (located on the bark of old woody stem)

Function :

A. Diffusion of gases for respiration and photosynthesis

B. They remain open all the time- so involves in transpiration by loosing water from

the surface of cells nearer to lenticels

Lenticular transpiration is certainly more than Cuticular transpiration

https://www.youtube.com/watch?v=JQvdXX7hGqIhttps://www.youtube.com/watch?v=cnk3BJDBqIohttps://www.youtube.com/watch?v=cMte2VCtZ-Ihttps://www.youtube.com/watch?v=CdxySlXe6oc

TOPIC 4: FACTORS AFFECTING TRANSPIRATION (Click the link below to have a better understanding to the topic.) https://www.youtube.com/watch?v=HerlEBkC8og

External factors:

Cuticle

Cuticle- a waxy layer secreted by epidermis

Use- Serves to prevent evaporation of water(Transpiration)

More the cuticle, less the transpiration

Desert plant – thick cuticle to prevent transpiration from surface

https://www.youtube.com/watch?v=HerlEBkC8og

Internal factor:

TOPIC 5: ADAPTATION IN PLANTS TO REDUCE TRANSPIRATION

•During day time for diffusion of CO2 ( for photosynthesis)- stomata open

• This favors more transpiration in more sunlight Intensity of sunlight

• More the temperature outside more the evaporation (transpiration)

• Warm air can hold more water than cold waterTemperature

•As the wind blows faster water vapour releasd during transpiration is removed faster. So transpiration increases with more wind velocityVelocity of wind

•More humidity in air reduces outward diffusion of vapour across stomata.

• So more humidity- less transpirationHumidity

•Increasing CO2 level over 0.03% causes stomata closure

• More the CO2 content- less the transpirationCO2

• Less the atmospheric pressure more the rate of transpiration

• It enhances diffusion of water vapour.(less pressure)Atmospheric pressure

•Insufficient absorption of water by roots leads to wilting of leaves

•In this condition, gyuard cells turn to flaccid which reduces transpiration Water contrent

(Click the link below to have a better understanding to of the topic.) https://www.youtube.com/watch?v=DITVGOmuHl0 https://www.youtube.com/watch?v=Ca4Hc2I6ndE

TOPIC 6: Significance of Transpiration:

Sunken stomata

e.g Nerium

Fewer stomata

e.g Rice

Narrow leaves

Nerium

Reduced exposed surface

(Wavy/rolled/folded)

Loss of leaves

e.g Cactus

Thick cuticle

e.g Banyan tree

1. Cooling effect: Evaporation reduces temperature on leaf surface and makes

it cool

2. Suction force:

Help in ascent of sap(upward conduction of sap) by suction force

Evaporation concentrates cell sap & increases osmotic pressure

https://www.youtube.com/watch?v=DITVGOmuHl0https://www.youtube.com/watch?v=Ca4Hc2I6ndE

3. Distribution of water and minerals:

With this transpiration pull, with water, minerals are also transported to various plants parts

TOPIC 7: GUTTATION: (Click the link below to have a better understanding to the topic.) https://www.youtube.com/watch?v=IuS0DByE4gw

Site: Margins of leaf (Special pore bearing structure- Hydathodes) Observed- more in the early morning or mid-night e.g- Banana, Strawberry, Nasturtium

Reason- Excessive root pressure and less transpiration [A humid environment hampers transpiration but the roots continue to absorb water from soil which builds up root pressure]

[Bleeding: Loss of plant cell sap due to injury or cut on the stem.]

Loss of water in the form of droplets along the margins of leaves is known as

Guttation

https://www.youtube.com/watch?v=IuS0DByE4gw

WORKSHEET

1. Name the following.

a) Openings on the stem through which transpiration occurs.

b) The process by which 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 of a leaf that allows guttation.

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

i) The structure through which maximum transpiration occurs.

j) The substance used to test the presence of moisture in experiments on transpiration.

k) A process that provides cooling effects in plants.

l) The waxy layer on the surface of leaves that prevent transpiration.

m) The small pores present on the leaf,

n) The experiment to demonstrate transpiration.

o) The kidney-shaped cells present on stomata.

p) Small openings present on the bark of woody stems.

q) A chemical used to prevent excessive transpiration in plants.

r) A factor which affects transpiration.

s) Process of exudation of cell sap from injured parts of the plant.

2. State the location and give function of the following structures.

a) Stomata

b) Lenticels

c) Cuticle

d) Hydathodes

e) Guard cells

f) Leaf spines

g) xylem

3. Pick the odd one out .

a) Transpiration, Photosynthesis, Phagocytosis, Guttation.

b) Cuticular transpiration, Lenticular transpiration, Guttation, Stomatal transpiration.

c) Stomata, Cuticle, Lenticels, Hydathodes.

4. Differentiate between the following pairs.

a) Transpiration and Guttation

b) Transpiration and Evaporation

c) Stomata and Lenticels

d) Cuticular and Lenticular transpiration

e) Transpiration and Perspiration

5. Give suitable explanation for the following.

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

b) Excessive transpiration leads to wilting of the leaves.

c) Balsam plant wilts during mid-day even when the soil is well watered.

d) On a bright sunny day the leaves of certain plants roll up.

e) The stomata are found mostly on the ventral surface of leaves.

6. State true of false for the given statements. Rewrite the false statements correctly by

changing the first or the last word only.

a) Moist cobalt chloride paper is blue in color.

b) Lenticular transpiration occurs in herbs.

c) The dorsal surface of the leaf transpires more.

d) Leaves are reduced to spines in xerophytic plants.

e) Loss of water in the form of droplets is called bleeding.

f) The rate of transpiration is more if the air is humid.

g) Lower the atmospheric pressure, higher the rate of transpiration.

h) Stomata covered by hairs decreases transpiration.

7. Diagram based questions.

a) An apparatus as shown below was set up to investigate a physiological process in

plants. The set-up was kept in sunlight for two hours. Droplets of water were then

seen inside the bell jar. Answer the questions that follow.

1) Name the process being studied.

2) Explain the process above.

3) Why was the pot covered with plastic sheet?

4) Suggest a suitable control for this experiment.

5) Mention any two ways in which this process is beneficial to plants.

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

b) Given below is an apparatus to study a particular process in plants. Study the

experiment and answer the questions that follow.

1) Name the apparatus.

2) Mention one limitation of this apparatus.

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

4) What is the function of the part marked reservoir?

5) What is the role of the air bubble in the experiment?

c) The diagram given below represents a structure found in a leaf. Study the same and

answer the questions that follow.

1) Name the parts labelled 1 -3..

2) What is the biological term for the above structure?

3) What is the function of part labeled 3?

4) Redraw the apparatus opposite to what is shown in the diagram.

5) Mention where is this structure likely to be found in a leaf?

d) Given ahead is the diagram of an experimental set up to show transpiration. Study

the same and answer the questions that follow.

1) What is the color of dry cobalt chloride paper?

2) Is the experimental leaf of monocot or a dicot? Give a reason to support your

answer.

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

4) 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.

e) The figure given here represented an experimental set up in with a weighing machine

to demonstrate a particular process in plants. The experimental set up was kept in

bright sunlight. Study the diagram and answer the following questions.

1) Name the process intended to study.

2) Define the above mentioned process.

3) When the weight of the test tube A and B is taken before and after the

experiment, what change is observed? Give reason to justify your answer in A and

B.

4) What is the purpose of keeping the test tube B in the experimental set up?

______________________________________________________

ANSWERS

1. a) Lenticels

b) Guttation

c) Ganong’s potometer

d) Nerium

e) Ganong’s potometer

f) Cuticle and Stomata

g) Hydathodes

h) Guttation

i) Stomata

j) Cobalt chloride paper

k) Transpiration

l) Cuticle

m) Stomata

n) Bell jar experiment

o) Guard cells

p) Lenticels

q) Anti-transpirant

r) Temperature/atmospheric pressure/humidity

s) Bleeding

2. LOCATION

a) On the epidermal layer of leaves

b) Bark of the woody stem

c) Mostly on the dorsal surface of leaves

d) Margins of the leaves

e) Ventral surface of leaves/ around the stomata

f) In xerophytes

g) Inside the stem/root/veins of leaves

FUNCTION

a) Diffusion of gases

b) Lenticular transpiration

c) Cuticular tramspiration

d) Guttation

e) Regulate the opening and closing of stomata

f) Reduce transpiration

g) Transportation of water

3. a) Phagocytosis

b) Guttation

c) Hydathodes

4. a)

Transpiration Water is lost in the form of water vapour

Guttation Water is lost in the form of droplets

b)

Transpiration The loss of water from the aerial parts of plant

Evaporation The loss of water from the surface of water body

c)

Stomata Present in the leaves

Lenticels Present on the bark of woody stems

d)

Cuticular transpiration Occurs through the cuticle

Lenticular transpiration Occurs through the lenticels

e)

Transpiration It takes place in plants through stomata

Perspiration It takes place in animals through skin

5.

a) On a windy day the water transpired out is easily carried away thus creating more

space for transpiration to occur.

b) Excessive transpiration causes the leaf cells lose turgidity thus it results in wilting of

leaves.

c) During the mid-day the rate of transpiration exceeds the rate of absorption therefore

balsam plant wilts even when the soil is well watered.

d) On a bright sunny day the leaves of certain plants roll up to reduce transpiration.

e) The stomata are found mostly on the lower surface to minimize water loss by

transpiration as the lower surface is not exposed directly to the sun.

6. a) False, moist cobalt chloride paper is pink in colour.

b) False, lenticular transpiration occurs in woody stems.

c) False, the ventral surface of leaf transpires more.

d) True

e) False, loss of water in the form of droplets is called guttation.

f) False, the rate of transpiration is more if the air is dry.

g) True

h) True

7 a)

1) Transpiration

2) Transpiration is the loss of water as water vapor from the aerial parts of the plants.

3) To prevent evaporation of water from the pot.

4) A bell jar covering an empty pot.

5) It brings cooling effect in plants.

6) Sunken stomata, Narrow leaves, Reduced surface area.

b)

1) Ganong’s photometer

2) Introduction of the air bubble is not easy.

3) Transpiration.

4) To relocate the air bubble/ to restart the experiment.

5) The air bubble moves only when there is a suction force created that pulls the

water from the beaker. The redings on the capillary tube gives the volume of water

lost.

c)

1) 1- guard cell,2-inner wall , 3- stomata.

2) Stomatal apparatus.

3) Diffusion of gases.

4)

5) Mostly on the ventral surface of leaf.

d) 1) Blue

2) Dicot leaf. It has a reticulate venation.

3) In order to prevent the atmospheric moisture from coming in contact with the cobalt

paper, glass slides are placed over the papers.

4) The cobalt chloride paper on the dorsal side remains blue in colour as there are less

number of stomata present on the dorsal surface of a dicot leaf.

The cobalt chloride paper on the ventral side turns pink in color because there are more

stomata present on the ventral surface of a dicot leaf.

e)

1) Transpiration

2) Transpiration is the loss of water as water vapor from the aerial parts of the plants.

3) It is observed in test tube A after the experiment, the weight has decreased, and in test

tube B, the weight remains the same.

In test tube A, has taken place and the weight decreased. In test tube B is used as a

control, no plant is kept, oil is added and so no transpiration has taken place.