What is stomata transpiration in biology

What is stomata transpiration in biology:- Hello friends welcome to yourstudynotes.com today Topic is stomata transpiration. I hope This topic is very use full in your study. So let’s start.

Stomata transpiration:-

transpiration usually  means stomatal transpiration. Hence its description is given below in detail-

stomata transpiration

Structure of stomata:-

Numerous small pores are found on the epidermis of green stem and leaves called stomata. Each pore is surrounded by two kidney shaped guard cells. The inner wall of gland cells is thick and non-elastic and outer wall is thin and elastic. The guard cells are surrounded from all sides by epidermal cells. These cells are called subsidiary or accessory cells.

Distribution of stomata:-

on the basis of distribution in leaves stomata are of the following five type-

  1. Apple and mulberry type:-

Stomata are present only on the lower surface. For example, apple, mulberry etc. such type of leaf is called hypostomatic.

2. Potato types:-

Stomata are present on both the surface bhut more on the lower surface than upper surface. Foe example Potato, Tomato etc. such type leaf is called amphistomatic.

3. Oat type:-

Stomata are present almost in equal number on both the surface. For example Wheat, Oat etc. such type leaf is also called amphistomatic.

4. Water lily type:-

Stomata are present only on the upper surface. For example water lily, Nymphea etc. such type of leaf is called epistomatic.

5. Potamogeton type:-

Stomata are either absent or non-funcation for example:- Potamogeton and other submerged plants.

Mechanism of stomatal opening:-

  1. First of all stored starch of guard cells is broken down into phosphoenol pyruvate in the presence of light.
  2. Phosphoenol pyruvate then combines with carbon dioxide to produce oxalo acetic acid. This reaction is catalysed by the enzyme phosphoenol pyruvate carboxylase (PEP carboxylase).
  3. oxaloacetic acid is converted into malic acid.
  4. malic acid in guard cells dissociates into malate ions and H+
  5. H+ ions form guard cells are transported to the surrounding epidermal cells and K+ ions are taken into the guard cells. This process is called ion-exchange.
  6. ion exchange is an active process in which energy is consumed which is obtained either form respiration or photophosphorylation.
  7. K+ ion react with malate ions to form potassium malate which is transferred into the vacuole of guard cells. some chloride (cl-) ion also enter the guard cells to maintain the pH.
  8. As a result of which the osmotic pressure of guard cells increase where by water enters in the guard cells form adjacent cells by end osmosis.
  9. Due to the entry of water the turgor pressure of the guard cells increase and thus stomata open.

Mechanism of stomatal closing:-

  1. During night the concentration of carbon dioxide in guard cells increase because the process of photosynthesis stops, While respiration goes on due to which pH is decreased .
  2. At low pH an inhibitor hormone abscisic acid (ABA) being to funcation which inhibits potassium ions (K+) uptake and send back the K+ ions to the epidermal or subsidiary cells form the guard cells.
  3. abscisic acid (ABA) makes the acidic medium of guard cells more acidic.
  4.  In acidic medium the organic acids are again convert into starch due to which osmotic concentration of guard cells decreases. This result in the movement of water out of the guard cells by exosmosis.
  5. The guard cells now become flaccid and stomata are closed.