Agriculture notes prepared by IAS Topper for all agriculture based competitive exams-Physiology-Transpiration

Transpiration

Difference between Transpiration and Evaporation……………

Difference between Transpiration and Gutation………………..

Transpiration is Unavoidable: Transpiration is incidental because of presence of stomata, which are important for gaseous exchange. So for photosynthesis and respiration to happen in plants, transpiration has been an added phenomenon.

Transpiration is Dangerous: Loss of water does not serve any good purpose in plant life. Many plants die due to over transpiration. Unnecessary energy consumption by the plant due to transpiration and water absorption by roots is also a undesirable effect.

Transpiration is Necessary: Chief function of transpiration is dissipation of canopy heat, which is absorbed by plant from sun. Therefore, transpiration avoids sunburn injury to plants.

Transpiration is advantageous to plan:

• For Ascent of sap in taller plants
• Absorption of water and minerals by root
• Evaporation of excess water
• Translocation of food materials in plants
• Maintenance of suitable temperature of leaves
• Bring out opening and closing of stomata and therefore indirectly controlling photosynthesis and respiration.

How stomata open and close?

The most accepted theory is proton transport and hormonal regulation

Opening of stomata:

Influx of proton ions inside the guard cells increases the osmotic concentration of guard cells. The osmotic entry of water from outside results in turgidity thereby the stomata open. The entry of potassium ions is balanced by outflow of hydrogen as well as equal negative charges inside. It is provided by the organic acids resulted out of physiological mechanism in guard cells. Therefore possible pathway is

Light-Malic acid production from starch---Dissociation into malate ion and H---influx of potassium ions and outflow of H---transport of potassium malate into vacuoles---osmotic entrance of water into guard cells---increase in turgor pressure-opening of stomata

Closing of stomata

Abscisic acid is responsible for the closing of stomata. This growth retardant inhibits potassium uptake by changing the diffusion and permeability of guard cell. Potassium moves out of the guard cells followed by lowering down of PH of the cell by ABA mediated acidification. Therefore osmotic concentration in guard cell reduces, and water moves out of the subsidiary cells. Therefore stomata become flaccid and remain closed.

Factors affecting rate of transpiration

a) External factors

• Water vapour saturation deficit
• Temperature
• Wind velocity (mild wind increases transpiration)
• Light increases the leaf temperature and also controls the opening and closing of stomata
• Atmospheric pressure increases transpiration as it decreases
• Water supply to the plant

b). Internal factors

• Stomatal frequency – No. of stomata per unit area of leaf surface. Stomatal Index is used as a reference for calculating stomatal frequency

  S

I =

            E+S

 I - Stomatal Index

S - No. of stomata/unit area,

E - No. of epidermal cells/unit area

• Structural peculiarities as the No. of stomata and their distribution differs from plants of xerophytes to hydrophytes. Ex. Sunken stomata

 Gutation…………………..

Fatty Acid Metabolism

Lipid=Fatty acid=Glycerol

So three important events are important for synthesis of lipids

a). Synthesis of Fatty acid

Basic Material: Acetyl COA

Other Factors: Biotin, Mn++, ATP and CO2

Addition of two carbons at a time to a carbon skeleton, because Acetyl COA is added at every step during Fatty acid synthesis. That is why fatty acids have carbon atoms even in number.

Steps