Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Stomata are tiny pores present on the surface of leaves, primarily on the underside, which facilitate gas exchange.
Each stoma is surrounded by a pair of kidney-shaped (in dicots) or dumb-bell shaped (in monocots) cells called guard cells.
The opening and closing of the stomatal pore is regulated by the guard cells; they swell when water flows into them, causing the pore to open, and shrink when they lose water, causing the pore to close.
During photosynthesis, plants take in carbon dioxide () from the atmosphere and release oxygen () as a byproduct through these stomata.
The exchange of gases occurs through the process of diffusion, where gases move from an area of higher concentration to an area of lower concentration.
Besides gas exchange, stomata also play a major role in transpiration, which is the loss of water vapor () from the plant surface.
📐Formulae
💡Examples
Problem 1:
During a sunny day, if the concentration of is higher in the atmosphere than inside the leaf, describe the movement of the gas.
Solution:
The will diffuse from the atmosphere into the leaf through the open stomata.
Explanation:
Diffusion occurs along a concentration gradient. Since the leaf is actively using up for photosynthesis, the internal concentration stays low, allowing to enter from the outside.
Problem 2:
What happens to the guard cells when the plant needs to conserve water?
Solution:
The guard cells lose water, become flaccid, and the stomatal pore closes.
Explanation:
To prevent excessive water loss via transpiration, the plant closes its stomata. This is a survival mechanism during dry conditions or at night when photosynthesis (and the need for ) stops.