The opening through which a leaf breathes is called stomata.

Explanation:
Stomata are tiny openings or pores found on the surface of a leaf. They are mainly located on the lower surface of the leaf, but can also be found on the upper surface. Stomata play a crucial role in the process of photosynthesis and respiration in plants.

Here is a detailed explanation of stomata:

1. Structure of Stomata:
- Stomata are composed of two specialized cells called guard cells. These cells surround a pore-like opening called the stomatal pore.
- The guard cells are bean-shaped and contain chloroplasts, which are responsible for photosynthesis.
- The inner walls of the guard cells are thicker than the outer walls, which allows them to change shape and regulate the opening and closing of the stomatal pore.

2. Function of Stomata:
- Stomata are responsible for the exchange of gases between the plant and its environment. They facilitate the entry of carbon dioxide (CO2) needed for photosynthesis and the release of oxygen (O2) produced during photosynthesis.
- Through the stomatal pore, plants also release excess water vapor in a process called transpiration. Transpiration helps in the regulation of temperature and the movement of water and nutrients through the plant.
- Stomata also allow for the uptake of water vapor from the surrounding atmosphere, which is essential for maintaining proper hydration levels in the plant.

3. Open and Closed State:
- The opening and closing of stomata are regulated by various factors, including light intensity, temperature, humidity, and the plant's water status.
- When the plant needs to carry out photosynthesis and exchange gases, the guard cells swell and create an opening, allowing carbon dioxide to enter and oxygen to exit.
- In contrast, when the plant needs to conserve water or prevent excessive water loss, the guard cells shrink and close the stomatal pore, reducing transpiration.

In conclusion, stomata are the openings through which a leaf breathes. They play a vital role in gas exchange, regulating water balance, and maintaining the overall health and functioning of plants.

Stomata