Final answer:
Carbon dioxide enters and oxygen leaves the plant through the stomata, which are regulated by guard cells. These stomata are essential for the process of photosynthesis and the plant's water balance. The correct answer is C) Stomata.
Step-by-step explanation:
Gas Exchange in Plants
Plants perform a crucial exchange of gases with their environment that is necessary for their survival. This process primarily takes place in a specialized structure known as the stomata (singular: stoma). The stomata are small openings typically found on the underside of plant leaves. Surrounding these stomata are guard cells, which function to regulate the opening and closing of these openings. This regulation is important for controlling water loss as well as for the exchange of gases; specifically, carbon dioxide (CO2) entering for photosynthesis and oxygen (O2) being released as a byproduct.
During photosynthesis, plants absorb carbon dioxide which enters through the stomata and, in turn, release oxygen. Moreover, stomata play a critical role in transpiration, which is the movement of water from the roots through the plant and eventually evaporating into the atmosphere through these openings. If the guard cells do not function properly, it would affect not only the photosynthesis process due to the lack of CO2 but also hamper the plant's water balance and the transport of water. The correct answer to the question of through which part carbon dioxide enters and oxygen leaves the plant is therefore C) Stomata.