Comparative Study - Rates Of Transpiration In The Surface Of Leaves

Aim

Compare the rates of transpiration in the upper and the lower surface of leaves.

Read more: Transpiration

Theory

What is Transpiration?

It is the process of water movement through a plant which evaporates through the aerial parts of the plant into the atmosphere. It occurs through specialized openings known as stomata that are present on leaves which are chiefly concerned with a gas exchange during the process of respiration and Photosynthesis. The stomata are girdled with specialized cells that govern the closing and the opening of the stomata known as guard cells. They assist in the regulation of the rate of transpiration.

Explore more:Photosynthesis

Material Required

• A potted plant
• Forceps
• Filter paper strips
• Wire gauze
• 3% cobalt chloride solution
• Petri Dish
• Binder clips
• Glass Slide

Procedure

• Into the Petri dish, pour the cobalt chloride solution
• Dip a few strips of filter paper into the solution
• Allow the strips to stay in the solution for a few minutes, watch them turn pink in colour
• With the help of forceps, separate the strips
• Allow the strips to dry by placing them on the wire gauze
• Upon drying, the strips turn blue in colour
• Pluck a healthy leaf from the potted plant, clean it to remove excess droplets with the help of filter paper
• After drying on the wire gauze, set the dried strips one on the upper surface of the leaf and one on the lower surface.
• Now place 2 glass slides on each surface of the leaf, i.e., the upper surface and lower surface.
• With the help of binder clips, secure the slides.
• Observe and make note of the time that is consumed by the paper to switch its colour from blue to pink.

Observation

Through the experiment carried out, it is observed that the amount of time taken for the colour change of the cobalt chloride paper from blue to pink on the lower surface of the leaf is lesser than the upper leaf surface.

Conclusion

The rapid switch of the colour of the cobalt chloride paper on the lower surfaces depicts that rate of loss of water vapour is higher on the lower surface than the upper surface.

Precautions

• The plant that is used in the experiment should always be a healthy and well-watered plant
• The paper should always be handled with forceps or well-dried hands
• The leaf should completely be wiped off excess water before placing the strips

Viva Questions

Q.1. List the importance of the process of transpiration. Any two points.

A.1. Following is the significance of the process of transpiration:

• It helps the plant to absorb water from the soil, which is transported from roots to leaves and impacts the transpiration pull.
• During the process of evaporation, it cools down the surface of plants.

Explore more: Transpiration pull.

Q.2. What are some environmental factors affecting the rate of transpiration?

A.2. Transpiration can be affected by the following:

• Transpiration is quicker in the presence of light
• Transpiration is rapid at higher temperatures as it aids the evaporation of water
• Rate of transpiration is low when the relative humidity of the surroundings is higher
• Rate of transpiration decreases when there is no breeze as the leaf surface turns humid.

Q.3. Why is water loss greater in the lower surface of the plant in comparison with the upper surface?

A.3. It is because usually the distribution and number of stomata vary in the lower and upper surface of leaves. The lower surface of leaves has a greater number of stomata to carry out the process of transpiration.

Q.4. Why is this experiment a comparative study?

A.4. It is a comparative study as the rate of transpiration of both the leaf surfaces i.e., the upper and the lower surface is compared.

Q.5. Why is cobalt chloride paper used in this experiment?

A.5. It is because this paper turns into a pink colour when it reacts with water. Hence this property of the paper can be used to demonstrate the process of transpiration.

Q.6. How is the rate of transpiration estimated in this experiment?

A.6. It can be estimated by taking into account the time the paper takes to switch its colour from blue to pink.

Learn more in detail about the transpiration, rate of transpiration, other related topics and experiments at BYJU’S Biology.

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