Transpiration in Plants

Transpiration in Plants. Transpiration is the process by which plant lose water in form of water to atmosphere

  • Transportation is also a process in plants that take place in the leaves and some stems.
  • Transpiration takes place in plants through the stomata of leaves, lenticels and in the cuticle of stems

Experiments to show that plants lose water

  1. Get a transparent polythene paper/ plastic bag without a hole on it
  2. Look for a plant which is well placed in the sunlight
  3. Tie the polythene paper one of the branches or around the shoot.
  4. Leave it there for about 2-5 hours

Illustration showing transpiration in plant leaves

transpiration in plants

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Results or observations

Droplets of water are found on the side of the polythene bag /paper


Plants give off water inform of water vapor

Importance of transpiration to plants.

  • Plants are able to absorb water and mineral salts from the soil through their roots up to the rest of the plant parts.
  • Transpiration helps in cooling the plant during a hot day.


The transpired vapour from the plants helps in the formation of rain.

Dangers of transpiration

  • Plants lose even the useful water they need during a dry season. This may make plants dry up to death
  • It lowers the crop yields due to less water left in the plant.

Ways plants reduce the rate of transpiration.

  • Some plant leaves are modified into thorns
  • Some plant leaves have few stomata and distributed at the lower part of the leaf.
  • Some plants have leaves with a small surface area to reduce the rate of water loss
  • Some plants reduce the rate of transpiration by shedding their leaves especially during dry season e.g. deciduous plants (Mvule,Oak & fig trees)
  • Leaves have a wax-like layer to cover their stomata to limit the water loss.
  • Stems have tough cuticles and lenticels to guard against water loss.

Factors that affect the rate of transpiration in plants;

The following are the conditions that either increase or decrease the rate of transpiration;


Wind blows off the water molecules on the plant leaf giving chance or space for more vapour to come out. This increases the rate of transpiration.

  • Humidity is the amount of water vapour in the atmosphere.
  • High rate of humidity lowers the rate of transpiration and vice versa.

High temperature during hot days causes plant leaves to lose a lot of water than on cool days.


Heat from the sun causes the opening of the stomata, lenticels and cuticle hence creating more chances of losing water.

Surface area of the leaf:

Plants with small surface area of their leaves lose water at a lower rate than those with larger leaf surface area.

Number of stomata:

Plant leaves with fewer stomata have a low rate of transpiration

The higher the number of stomata, the higher the rate of transpiration

Some leaves have stomata at the lower side of the leaf

NB: Most transpiration takes place in leaves

Note: when a plant loses more water that it gains through the roots, the plants wilts.

Wilting plant has droopy leaves and the stem is very weak. If water is provided the plant soon recovers from the wilt.