Biology · Anatomy of Flowering Plants · NEET
Two. Each stoma is made of two bean-shaped (kidney-shaped) guard cells. These two cells surround and enclose one central opening called the stomatal pore. So the count is: 2 guard cells + 1 pore = 1 stoma. NEET often asks this, so remember the pair.
'Stoma' is the singular; 'stomata' is the plural of stoma. The 'stomatal pore' (also called the aperture) is only the small hole in the middle. One stoma = two guard cells + the pore between them. Do not use 'stomata' when you mean just the pore.
The inner wall (the one facing the stomatal pore) is thick and highly thickened. The outer wall (away from the pore) is thin. This uneven thickening is the key point NEET tests. When the guard cell becomes turgid, the thin outer wall stretches more and bends the cell, which opens the pore.
Yes. Guard cells are living epidermal cells and, unlike other epidermal cells, they contain chloroplasts. Because they have chloroplasts and stay living, they can change their turgor (water pressure) and control the opening and closing of the pore. This is why guard cells are special epidermal cells.
The stomatal apparatus is the whole working unit: the stomatal aperture (pore) + the two guard cells + the surrounding subsidiary cells taken together. NEET uses the term 'stomatal apparatus' for the complete structure, not just the pore. Subsidiary cells are nearby epidermal cells that changed their shape and size.
In most plants (dicots) guard cells are bean-shaped or kidney-shaped. But in grasses (monocots) the guard cells are dumb-bell shaped, meaning narrow in the middle and swollen at the two ends. This is a very common NEET one-liner, so keep 'grass = dumb-bell' in mind.
Specialized epidermal cells surrounding the guard cells are called:
In the given figure of the stomatal apparatus, which component has thin outer walls and highly thickened inner walls?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Stomata are found in the epidermis of leaves, mainly on the lower (abaxial) surface. They also occur on young green stems. They regulate transpiration and gaseous exchange.
Stomata control two things: the exchange of gases (CO2 in, O2 out) and transpiration (loss of water vapour). The guard cells open and close the pore to manage these processes.
The thick inner wall is stiff and the thin outer wall is flexible. So when water enters and the guard cell swells, only the outer wall stretches, bending the cell away from the pore. This bending pulls the pore open.
No. Ordinary epidermal cells lack chloroplasts. Only the guard cells among epidermal cells contain chloroplasts, which is one reason they can control the stomata.
The outer wall is away from the pore and it is thin. The inner wall is towards the pore and it is thick. Remembering this direction is important for NEET diagram questions.
