Transpiration in plants

The nature has a lot of wonders and one of those is transpiration. Imagine, how hard it would be if humans lost the water they drank ? they would probably be dehydrated but when it comes to plants, how don't they wilt or die when this water is lost ? In this article I'm going to be giving out the answers to such small yet important questions. 

Transpiration in plants:

Transpiration is defined as loss of water from the aerial parts like stems and leaves of the plant. The plant takes up water from the soil, from that only 2% of the water is used and the rest 98% is evaporated into the atmosphere. This water uptake is due to photosynthesis and transpiration. Herbaceous plants transpire about 99% of water

Though transpiration has the same function as that of evaporation but it is different from one another. Transpiration is a physiological process that means all the parts work together in this process and evaporation is a physical process that means it takes place when there are several events made in the system. 

Transpiration is maximum seen in red light. It is a metabolic activity controlled by protoplasm. It can be reduced for increased in the suitable habitat of that plant. The device used to measure the rate of water uptake by the plant is called potometer or transpirometer

Transpiration doesn't dehydrate the plant as it would do to a human, instead it cools down the plant, changes the osmotic pressure of the cells and also there is a flow of mineral, nutrients and water from the roots to the shoots of the plant. This is because, transpiration is a physiological process. 

Types of transpiration:

By now we know what transpiration means. Now, we will look at the types of transpiration. There are three types of transpiration - cuticular transpiration, lenticular transpiration and stomatal transpiration.

1. Cuticular transpiration:

The loss of water through the cuticles which are present on the surface of the stem or leaves is called cuticular transpiration. Almost 10% of water is lost due to cuticular transpiration.

Cuticles are formed by cutin which is a wax-like substance present of the walls of epidermal cells which forms a thin and thick layer on the epidermis of the leaves and herbaceous stems

2. Lenticular transpiration:

The loss of water through the lenticles which are present on the stem and fruits is called as lenticular transpiration. About 0.1 to 1% of water is lost due to lenticular transpiration

Lenticles are tiny pores present on old parts of the plants, eg, bark of an old stem and pericarps of woody fruits. Lenticles are made up of loosely arranged cells. When the stomata is closed at night the plants transpire through lenticles and cuticles. 

3. Stomatal transpiration: 

The loss of water through stomatal openings which are present on the leaves and sometimes on the green stems is called as stomatal transpiration. This is one of the most important types. About 80 to 90% of water is lost due to stomatal transpiration

The number of stomata is always greater on the lower surface of the leaf. Stomatal transpiration only takes place in the day when the stomata is opened

Factors affecting transpiration in plants:

There are a lot of internal and external factors which affect the rate of transpiration in plants which is as follows:

External factors:

External factors affecting transpiration - Light, atmospheric moisture, wind velocity, air temperature, solar radiation and soil environment. We are going to be discussing about each one of these in brief. 

1. Light:

By know it is known that transpiration takes place from the stomata which is present on the leaf which is only open during day. Hence, rate of transpiration is much greater in light than it is in darkness. This factors affects the rate of transpiration indirectly. It receives heat from the sun which speeds up the rate of transpiration. 

Transpiration not only takes part in light but it also takes part in darkness by the help of lenticular or cuticular transpiration. 

2. Atmospheric moisture:

The atmosphere can be either dry or humid and this can affect the rate of transpiration. If the climate is too dry, evaporation of water from the leaves is high but if the climate is humid or saturated, evaporation of water from the leaves is low

3. Wind velocity:

As the wind blows fast and slow the rate of transpiration is depends on it. If the wind blows too fast then the rate of transpiration is high but if the wind is calm or slow the rate of transpiration is low as the moisture in the air is in very close contact with the transpiring plant. 

4. Air temperature:

When there is a rise in the temperature there is an increase in the rate of transpiration. For instance, if the temperature is quite high then the rate of transpiration will also be high from the normal temperature and if the temperature turns dry, the rate of transpiration increases even more. 

5. Solar radiation:

Solar radiation is the energy which is emitted out by the sun by nuclear fusion reaction. This is a physical energy. This energy rises the temperature of the leaf which indirectly gives rise to increase in the rate of transpiration. 

6. Soil environment:

Mesophyll cells are present in the leaf of the plant which absorbs the water that is being passed on from the soil. If these cells absorb more water the rate of transpiration is going to increase but if these cells absorb less water the rate of transpiration is going to be low. 

Factors such as soil water content, concentration of soil solution, soil temperature, oxygen of soil air, etc. can also affect the rate of transpiration in a plant. 

Internal factors:

Internal factors affecting transpiration - The root system, the stem and leaf structure. We are going to be discussing about each one of these in brief. 

1. The root system:

Since the roots are the once which hold onto the soil in order to keep the plant standing, they can either go til the moist layers of the soil or stay on the upper dry layer of the soil. 

If the roots on the plants reach the lower moist layer of the soil, it will absorb more water and hence more absorption of water results into higher rate of transpiration from the aerial parts of the plant, but if the plants stays on the upper dry layer of the soil there not going to be much absorption of water and hence the rate of transpiration would be low

2. The stem:

As water rises from the stem to the leaves, there are some vessels present which also decides the rate of transpiration. These are called the xylem vessels which helps in transferring the water from the soil to different parts of the plants. These vessels are either broad or narrow

If the vessels are broader, there is high flow of water and the rate of transpiration increases. If the the vessels are narrower, the flow of water is going to be less and the rate of transpiration low. 

3. Leaf structure:

Xerophytic plants are too much divided and this results in the decrease in the leaf area. In some plants there is lack of leaves and the stem of such plants become flat, leaf like, angular or round and green structure which resembles a leaf but is actually a stem. Such plants are called phylloclades. They transpire less amount of water because of this feature. 

In some plants, there are some adaptions made where there is a cavity and in these cavities the stomata is present which can transpire. In some plants, the leaf is folded inwards which protects the stomata but it decreases the rate of transpiration. 

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