Question

The diagram given represents a structure found in a leaf.

Study the same and answer the questions that follow.

1. Name the parts labeled A and B.
2. What is the biological term for the above structure?
3. What is the function of the part labeled A?
4. Mention two structural features of A, which help in the function mentioned in (3) above.
5. Where is this structure likely to be found in a leaf?
6. The above structure helps in the process of transpiration. Explain the term transpiration.
7. How many other cells are found surrounding this structure as seen in the diagram?

Answer 1

1. Parts labeled A and B:

1. In the given diagram, A is the Guard cell and B is a Stoma.

1. Guard cells: A stoma is surrounded by two bean-shaped cells called guard cells. They regulate gaseous exchange in and out of plant leaves as epidermal cells by modulating the opening and closing of apertures known as stomas.
2. Stoma: Stoma (plural: Stomata) is a pore on the surface of leaves and other aerial portions of most angiosperms that allows CO₂ to be taken in for photosynthesis while also allowing water vapor to be lost through transpiration.

2. Biological term for the given structure:

• The biological term used for the given structure is ‘Stoma’.
• Stoma (plural: Stomata) is a pore on the surface of leaves and other aerial portions of most angiosperms that allows CO₂ to be taken in for photosynthesis while also allowing water vapor to be lost through transpiration.

3. Function of the part labeled A:

• In the given diagram, parts labeled A are Guard cells.
• There is a pair of guard cells that encircle the stoma found in the leaf epidermis.
• Guard cells regulate CO₂ and O₂ input and outflow from leaves, respectively.
• By opening and closing the stomata, they also help in controlling the rate of transpiration.

4. Structural features of A, which help in its functioning:

• The design of guard cells and their bean shape make it easy to close and open the stoma to control gaseous exchange and water release.
• The walls of guard cells vary in thickness. It has a thick inner wall towards the stomatal pore and a thin outer wall.
• Guard cells regulate the opening and closure of stomata by regulating their turgidity and flaccidity.

5. Location of the structure given in diagram:

• Stomata are mostly present on the lower epidermis of leaves.
• But their exact location varies from plant to plant.

6. Transpiration:

• Plants take a huge volume of water from the soil, but only a small portion of it is utilized by the plant, and the majority of this absorbed water is released as water vapor from the plant's aerial parts. The process of losing water is known as transpiration.

7. Other cells surrounding the given structure:

1. There are five other cells surrounding the stoma of the leaf in the given diagram.
2. These cells are epidermal cells and are known as accessory or subsidiary cells.
3. The primary purpose of subsidiary cells is to offer strength and aid the guard cells in their functions.