Question

Leaves of the plant have tiny pores for the exchange of oxygen and carbon dioxide. These small pores are known as
A. Nodule
B. Stomata
C. Radicle
D. None of the above

Answer 1

Hint: Plants make their own food by the process of photosynthesis. Photosynthesis happens due to the presence of specialised pigments present in small organs that have pores needed for the exchange of gases and release of water during transpiration.

Complete answer:
Leaves are the principal lateral appendages that arise from the stems of vascular plants. They are specialised to perform photosynthesis and make food for the plant. They have a flattened, broad surface which is effective in gathering sunlight. The cells of a leaf make a sandwich between two epidermal layers that cover the leaf with a wax-like coating making it impermeable thus protecting it from excess water loss. Exchange of carbon dioxide from the external environment and oxygen to the external environment happens with the help of small openings present underside of the leaf that are known as stomata. Stomata are the principal elements of photosynthesis. They keep on opening and closing in order to exchange the gases. Mesophyll tissues are present along with the stomata and can be differentiated into spongy and palisade layers which are evenly packed with the chloroplasts.
-Each stomata is surrounded by guard cells that help in opening and closing of stomata by generating osmotic pressure. When a lot of moisture is available then the guard cells swell up with water thereby opening the stomata and allowing the exchange of gases. When the moisture is not abundant then the guard cells turn flaccid or deflate and close the stomata thereby preventing any loss of water by transpiration or any exchange of gases.

-Nodules are mostly found in the roots of leguminous plants and are formed by the symbiotic association of nitrogen fixing bacteria and the plant. They are very sensitive to oxygen.
-Radicle is the first organ to appear when the seed starts to germinate and it is responsible for the formation of the root system in plants. It grows downward into the soil.

Hence, the correct answer is option (B).

Note: When the stomata are open then they take in carbon dioxide which is needed for photosynthesis and release oxygen and water to the environment which is the end product of photosynthesis. In desert plants the stomata remain closed during day time and open up during the night time to avoid any water loss.