Video Transcript
Complete the following. Oxygen enters the leaves of vascular plants via blank. (A) Osmosis, (B) active transport, (C) the open stomata, or (D) the breakdown of
carbon dioxide.
During photosynthesis, plants synthesize sugars from carbon dioxide and water in the
presence of light energy. They then perform aerobic respiration, a process in which the sugars are converted to
energy in the presence of oxygen. The energy produced during respiration is stored as ATP. You may have noticed that both photosynthesis and cellular respiration have gaseous
products and reactants. Because of this, plants have evolved adaptations that allow them to take up needed
gases from their environment and release any excess gas, a process called gas
exchange.
The question asks us how oxygen enters the leaves of a plant. As we can see, oxygen is a product of photosynthesis and a reactant in aerobic
respiration. The result is that plants typically don’t need to take in large amounts of oxygen for
respiration, because it is already supplied by photosynthesis.
If a vascular plant does require extra oxygen, it can enter the leaves through small
pores called stomata, or stoma in the singular. Other gases, including carbon dioxide and water vapor, are also exchanged through
stomata. Special cells called guard cells surround each stoma and are responsible for opening
and closing them based on the plant’s needs for various gases. For example, if the plant is losing too much water, the guard cells will lose their
turgor pressure. This causes the stomata to close, thereby preventing additional water vapor loss.
Now, let’s take a look at our answer choices to see which one correctly explains how
oxygen enters leaves.
Osmosis refers to the movement of water from areas of low-solute concentration to
areas of high-solute concentration, not the movement of oxygen. So we can eliminate choice (A).
Active transport processes require ATP. But gas exchange through leaves is a passive process. So we can rule out answer (B).
We can also eliminate choice (D) because although plants do use carbon dioxide and
produce oxygen during photosynthesis, the breakdown of carbon dioxide doesn’t directly cause oxygen to enter leaves.
Therefore, the correct answer is (C). Oxygen enters the leaves of vascular plants via the open stomata.
