Difference Between Transpiration and Evaporation

Introduction

Transpiration and evaporation are the processes that naturally occur in the atmosphere and they both differ from each other. Transpiration involves the loss of water in the form of vapour from the aerial parts of plants like leaves, etc. Evaporation involves the transformation of water from its liquid state to its gaseous state. It differs from transpiration as it is a physical process that not only occurs in living organisms but also occurs in non-living entities.

Transpiration

It is a slow biological process that results in the loss of water from the aerial parts of the plants like leaves, stems and flowers. It helps in regulating the temperature of plants by cooling them and pumping water as well as minerals from the roots to the leaves to carry out photosynthesis (it is a process that involves the preparation of food with the help of sunlight, water and oxygen).

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Factors affecting transpiration

Radiation from the sun

Solar radiation is the major factor that leads to transpiration as the stomata open during daytime and radiation can lead to immense loss of water from plant parts.

Temperature

Increase in temperature can lead to an increase in the rate of diffusion of water molecules from the leaves and thus will result in transpiration.

Light

The increase in the intensity of the light results in the opening of the stomata and diffusion of the water which will, in turn, lead to transpiration.

Humidity

The fall or decrease in humidity results in the reduction of the concentration of water molecules outside the leaves which increases the diffusion rate resulting in transpiration.

Evaporation

It is a natural process that involves the conversion of water from its liquid phase to its gaseous phase i.e. in the form of vapours. It takes place only when there is the availability of water. The evaporation of water can be done through water bodies like oceans, ponds, rivers or also from the soil. A large amount of energy is required to carry out evaporation.

Factors affecting evaporation

Temperature

The increase in temperature leads to an increase in evaporation of water into water vapours as there is an increase in heat energy which readily evaporates water faster.

Relative humidity

Relative humidity is the amount of moisture present in the air as compared to the ability of the air to capture the moisture. The lower the relative humidity higher is the evaporation.

Wind speed

The increase in the speed of wind results in the blowing of water vapours in the atmosphere which results in the decrease of relative humidity. A decrease in humidity ultimately leads to an increase in evaporation.

Atmospheric pressure

The increase in the air pressure on the surface of the water bodies leads to a decrease in evaporation rate. This is because the air pressure pushes down the water, making it difficult to evaporate.

Difference between transpiration and evaporation

Transpiration	Evaporation
Transpiration is a biological process and is comparatively slower than evaporation.	Evaporation is a physical process and is comparatively faster than transpiration.
In this, water is lost from the plant cells i.e it occurs in living tissues.	In this, water is lost from the plant surface and also from water body i.e. it can also occur in non-living entities.
It occurs during day time.	It can occur during the day as well as at the night.
It is controlled by the osmotic and water potential.	It is an independent process.
It makes the leaf surface wet and protects it from sunburn.	It makes the leaf surface dry.

Evapotranspiration

It is a combination of two processes in which there is loss of water from the soil through evaporation and also there is loss from the plant parts due to transpiration. Wind, solar radiation, relative humidity, temperature, etc are the factors that cause evapotranspiration.

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Transpiration and groundwater

The groundwater sometimes plays a role in transpiration as it affects the hydraulic redistribution process in the plants i.e in various regions the top layer of the soil is present above the water table and thus the soil is often wet but is not saturated totally as the soil is below the water table. So the soil will get wet only when there is rainfall but without rain, it will get dry. On the other hand, where the water table is near the plant roots, the roots can penetrate themselves into the saturated zone absorbing the water which will help plants to transpire water. Hence, transpiration depends on the groundwater level.

Conclusion

Transpiration and evaporation are two different processes that naturally occur in an atmosphere. About 97 to 99% of water is lost from the plants during transpiration. There are three main types of transpiration i.e. stomatal, cuticular and lenticular. Factors like solar radiation, temperature, light, etc affect the rate of transpiration. Evaporation takes place in plants as well as in non-living entities like rivers, oceans, etc and about 600 calories is the amount of heat energy required to evaporate one gram of water. Factors like temperature, relative humidity, soil type, etc affect evaporation. The process that involves evaporation, as well as transpiration, is called evapotranspiration. The transpiration depends on the levels of groundwater.

FAQs

Q1. Explain the types of transpiration that occurs in plants.

Ans. There are three types of transpiration that occurs in plants −

• Stomal transpiration −
  Stomata are the epidermal structure of leaf cells that open to eliminate water and also is involved in respiration.

• Cuticular transpiration −
  The cuticle is a waxy impermeable layer that surrounds the outer surface of the leaves and stem.

• Lenticular transpiration −
  Lenticels are the smaller openings in the bark or the older cells of the tree and transpiration is seen in such cells.

Q2. What is the transpiration ratio?

Ans. The ratio of the total mass of water transpired to the mass of dry matter produced is called the transpiration ratio. The transpiration ratio of the crops falls between 200 to 1000 i.e. plants transpire about 200 to 1000 kg of water for every kg of dry matter produced.

Q3. Write down the benefits of transpiration.

Ans. They are given as follows

• It increases crop productivity without increasing irrigation.
• It cools down the plant and pumps water and minerals from the soil.

Q4. Write down the effects of evaporation.

Ans.

• It dries the upper levels of the soil and makes it hard.
• It results in sunburn in plants.

Q5. Which organ is involved in transpiration?

Ans. Stomata is involved in the process of transpiration. They are located on the aerial parts of the leaves.

Q6. Enlist some fundamental plant processes.

Ans. Photosynthesis, tropisms, respiration, nastic movements, photoperiodism, circadian rhythms, photomorphogenesis, seed dormancy and germination are a few fundamental plant processes.