**Assertion: The process of removal of extra water through stomata is called transpiration.**

**Reason: The stomata are closed during the night, so transpiration does not take place.**

Transpiration is a vital process in plants through which they lose excess water in the form of water vapor. It occurs primarily through the stomata, which are tiny openings present on the surface of leaves and stems. The assertion states that transpiration involves the removal of extra water through stomata, while the reason suggests that transpiration does not occur at night due to the closure of stomata. Let's examine these statements in detail.

**Transpiration:**

Transpiration is an essential process in plants that aids in the movement of water from the roots to the leaves. It serves several purposes, including the transportation of nutrients, maintenance of cell turgidity, and cooling of the plant. The main driving force behind transpiration is the difference in water concentration between the plant's internal tissues and the external environment.

**Stomata:**

Stomata are microscopic openings present on the surface of leaves, stems, and other plant organs. They consist of two specialized cells called guard cells that control their opening and closing. The stomata play a crucial role in gas exchange, allowing for the intake of carbon dioxide (CO2) required for photosynthesis and the release of oxygen (O2) and water vapor (H2O) as byproducts.

**Transpiration and Stomata:**

During transpiration, water evaporates from the moist surfaces of the cells within the plant. This water vapor then diffuses through the stomata into the surrounding atmosphere. The assertion correctly states that transpiration involves the removal of extra water through stomata. As the water evaporates from the cells, it creates a water potential gradient. This gradient causes water to move from regions of high water potential (inside the plant) to regions of low water potential (outside the plant).

**Stomatal Closure at Night:**

The reason provided states that stomata are closed during the night, resulting in the absence of transpiration. This statement is accurate. Stomata are indeed closed during the night to prevent excessive water loss. Since transpiration is driven by the difference in water concentration between the plant and its surroundings, it would be unfavorable for plants to lose water when there is no sunlight available for photosynthesis. By closing their stomata, plants conserve water and reduce the risk of dehydration.

In conclusion, the assertion that transpiration involves the removal of extra water through stomata is correct. The reason stating that transpiration does not occur at night due to stomatal closure is also accurate. Stomata play a crucial role in regulating transpiration, and their closure during the night helps plants conserve water.