What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Stomatal apparatus is the collective term for the stomatal aperture, guard cells, and the surrounding subsidiary cells. The subsidiary cells are specialized epidermal cells in the vicinity of guard cells that have become modified in their shape and size.
Stomata are structures present in the epidermis of leaves. They regulate the process of transpiration and gaseous exchange. Each stoma is composed of two bean-shaped guard cells which enclose the stomatal pore. In grasses, the guard cells are dumb-bell shaped.
The guard cells have a unique structure. Their outer walls (away from the stomatal pore) are thin, while their inner walls (towards the stomatal pore) are highly thickened. This differential thickening facilitates the opening and closing of stomata. Unlike other epidermal cells, guard cells possess chloroplasts.
Labelled Diagram: [Diagram showing: Guard cells (bean-shaped/dumb-bell shaped), Stomatal pore/aperture, Subsidiary cells, Epidermal cells]
Explanation
This answer is based on NCERT Class 11 Biology textbook content. The stomatal apparatus definition comes directly from the text stating 'The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus.' The structural details about guard cells (bean-shaped in most plants, dumb-bell shaped in grasses), differential wall thickening, presence of chloroplasts, and the function of transpiration and gaseous exchange are all explicitly mentioned in the provided context.
Solution Steps
Step 1: Define stomatal apparatus using the three components mentioned in text.
Step 2: Describe location and function of stomata in leaves.
Step 3: Explain guard cell structure including shape variations and wall thickening.
Step 4: Mention presence of chloroplasts in guard cells.
Step 5: Draw and label the diagram with all components.