Question

analysis of part 2: study of distribution of stomata on leaves

1. why is there a difference in the number of stomata on the top of the leaf and the bottom of the leaf? in other words, what would be the specific benefit to having more in one area and less in the other?
2. predict where you would find more stomata (top surface or lower surface) for a plant living in the desert. explain why.
3. predict where you would find more stomata (top surface or lower surface) for an \emergent\ plant found living on the surface of the water in a pond/marsh (like a lily pad plant). explain why.
4. assuming that environmental conditions are ideal, predict where on a tree you would expect to see more stomata. explain why.
5. how are the stomata involved in photosynthesis?

Explanation:

1. Stomata Distribution Benefit:

• The top of the leaf is more exposed to sunlight and air movement. Having fewer stomata on the top reduces water loss through transpiration. The bottom of the leaf is shaded and has less air movement, so more stomata there allow for gas exchange (intake of \(CO_2\) and release of \(O_2\)) while minimizing excessive water loss.

1. Desert Plant Stomata:

• For a desert plant, more stomata would be found on the lower surface. The desert environment is hot and dry. The lower surface is less exposed to direct sunlight and wind. Fewer stomata on the top reduce water loss, and the lower - surface stomata can still carry out gas exchange during cooler parts of the day (many desert plants have CAM photosynthesis, opening stomata at night).

1. Emergent Plant Stomata:

• An “emergent” plant like a lily pad would have more stomata on the top surface. The top surface is in contact with air, allowing for gas exchange (\(CO_2\) intake for photosynthesis and \(O_2\) release). The lower surface is in contact with water, and having stomata there would not be as effective for gas exchange as they would be submerged.

1. Tree Stomata in Ideal Conditions:

• In ideal environmental conditions (enough water, suitable temperature, etc.), more stomata would be expected on the lower surface of a tree. The basic principle of gas exchange while minimizing water loss (transpiration) still applies. The lower surface is less exposed to direct sunlight compared to the top, so having more stomata there allows for efficient gas exchange without excessive water loss.

1. Stomata and Photosynthesis:

• Stomata are involved in photosynthesis as they are the openings through which \(CO_2\) (a reactant for photosynthesis) enters the leaf. The \(CO_2\) diffuses into the leaf cells (mesophyll cells) where photosynthesis occurs. Also, \(O_2\) (a by - product of photosynthesis) exits the leaf through the stomata.

Answer:

1. Fewer stomata on top reduce water loss; more on bottom for gas exchange.
2. Lower surface. Reduces water loss in hot, dry desert (CAM - related gas exchange).
3. Top surface. Facilitates gas exchange with air (lower surface is submerged).
4. Lower surface. Efficient gas exchange with less water loss (even in ideal conditions, basic principle applies).
5. Allow \(CO_2\) entry (reactant) and \(O_2\) exit (by - product) for photosynthesis.