Transpiration in plants

Transpiration

Transpiration is a process in which loss of water in the form of vapour from aerial parts of plants.

Loss of water vapour, exchange of carbon dioxide and oxygen occur in stomata pore.

Loss of water from stomata and lenticular cell and cuticle.

Type of transpiration

1. Stomatal transpiration
2. Cuticular transpiration
3. Lenticular transpiration

Stomatal transpiration

Transpiration occurs through stomata.

Stomata are present in leaf also present in delicate organ.

Stomatal transpiration 50 to 90 % of total.

Cuticular transpiration.

Transpiration occurs through cuticle.

It is thim wax layer.

Present on epidermis.

Mesophytes cuticle transpiration is goes to 40 to 50%.

Lenticular transpiration

transpiration occurs minute pores on body stem and epidermis of fruits.

Foliar transformation.

Total transpiration takes place through surface of leaves.

Structure of stomata.

Stomata are present on epidermal tissue of aerial part.

Stomata surrounded by guard cells.

Guard cells surrounded by subsidiary cell or accessory cell.

Guard cell are kidney or dumbell shape.

Guard cells

1. Gurd cell are bean or kidney shaped.
2. Monocot of guard cells dumbell shape.
3. Intercellular space is present.
4. Cuticle is absent.
5. Chloroplast are present.
6. Outer wall is thin and elastic.

Other epidermal cell

• Epidermal cell are barrel shaped.
• Intercellular space are absent.
• Cuticle is present
• Wall are uniformly thickened.
• Chloroplast are absent.

Points

• Guard cell of cell wall cellulose microfibrils are oriented radially.
• Gurd cell PEPcase enzyme is present.

Mechanism of opening and closing of stomata.

Potassium ion pump theory

This theory for stomatal movement.

Modern theory or abscisic acid theory.

• Integrated part of potassium ion pump theory.

according to this theory abscisic acid in gurd cell  interfere the potassium and hydrogen ion pump result in closing of stomata.

Factor affecting rate of transpiration

External factors

• Atmospheric humidit 

Humidity is inversely proportional to transpiration.

• Temperature
• Light 
• Atmospheric pressure

Internal or plant factors.

• Stomata
• Percentages of stomata
• Distribution of stomata
• Number of stomata
• Anatomy of leaf

Antitranspirants

substance which reduce the rate of transpiration all known as antitranspirants

Xerophytes stomata to minimise the loss of water.

Purpose of transpiration

• Create transpiration pool
•  supply water for photosynthesis 
• transport minerals from soil to all parts of the plant 
• leaf surface maintain the shape and structure of the plant keeping cell turgid.

Photometre

Apparatus used to measure rate of transpiration

Rate of water absorption is equal to rate of transpiration.

Porometer

Apparatus used to measure area of a stomata on leaves.