Transpiration in Plants
Transpiration is the loss of water from plants in the form of water vapour.
Imagine, during your summer vacations, you go to play football outside. The Sun is scorching hot. One thing you need right now, more than scoring a goal, is a bottle of water! Any living being for that matter needs the same. Do you think plants also need the same?
Yes, they do.
In fact, the water does not magically disappear from a plant. Plants lose water from them through a process called transpiration.
Transpiration happens in part because plants need to breathe. Plants need to take in carbon dioxide and to do this, they need to open their stomata. When this happens, water comes out.
Transpiration is the process by which moisture is carried through plants from the roots to small pores on the underside of leaves, where it evapourates to vapour and is released to the atmosphere.
Transpiration Water Cycle
This release of water vapour into the atmosphere, through transpiration, creates a water cycle. It is called the transpiration water cycle. It occurs when:
- The water from the nearby soil is absorbed into the roots due to the hydraulic conductivity of the soil and the magnitude of the pressure gradient through the soil.
- The water flows from the roots to the leaves. This is driven by capillary action (Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules).
- The water from the leaves enters the atmosphere. The water potential in the surrounding air is lower than the water potential in the leaf airspace of the stomatal pore. Due to this, water vapour from the cells in the leaves enters the atmosphere as water
vapuor. This process is known as transpiration.
- The water vapour in the atmosphere now forms clouds through the process of condensation.
- And these clouds of water vapour turn into water droplets and fall back on earth through the process of precipitation.
- This water that falls on the land, is then absorbed by the soil and is used to nourish the plants.
This cycle keeps repeating and hence, is called the transpiration water cycle.
You will hardly need anything for this tactivity. If you have a broad leaved plant in your garden, then it is well and good, otherwise you can always head to the nearest park and look for the same.
All you need to do is wrap a plastic sheet around the leaf and close it tightly. Wait for a few hours and you will see water droplets inside the plastic sheet, as though the leaf has “sweat” – or TRANSPIRED – as shown in the video below:
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