Stomata are minute pores present in the epidermis of leaves and other soft parts of the plants which are normally for the gaseous exchange during photosynthesis and evaporation of water during transpiration. In other words stomata are meant for plant to breath. Singular it is stoma is actually the pore surrounded by guard cells ( specialized epidermal cells present with the normal epidermal cells ). They are easily influenced by changing turgor pressure in the guard cells because guard cells are also connected to the adjacent epidermal cells through plasmodesmata. The cells also have chloroplast and vacuole. They can also store starch in few cases.
Gaseous Exchange Through Stomata
In most of the plants the guard cells are kidney shaped and concavo-convex curvature of the guard cells helps in the opening and closing of the pore (stoma) under the influence of changing turgor pressure in guard cells. The walls of these guard cells are thickened on inner side and walls are thinner and more elastic on the outer side. When the guard cell will have full turgor pressure then it swells up on the outer side and inner concave sides also bend out slightly as to create pore. Now the stomata is open. During closing of stomata reverse changes will takes place.
.
Opened and Closed Stomata
In cereals or most of the monocots, the guard cells are dumb-bell shaped in outline.Their extended ends are thin-walled while middle portions are highly thick-walled. In such cases opening and closing of stomatal pore is caused by expansion and contraction of thin-walled ends of the guard cells.
Dumb-bell Shaped Guard Cells
No comments:
Post a Comment