Plants: Gas Exchange (Part 2)

Question 1

Give a comparison of O2 and CO2 levels in cellular respiration and photosynthesis.

Answer 1

In cellular resp., exhaled air contains lower levels of O2 and higher levels of CO2 than inhaled.

In photosynthesis, plants consume CO2 and H20 and produce O2.

Question 2

Define turgor pressure.

Answer 2

In biology, turgor pressure pertains to the pressure that is exerted by the fluid (e.g. water) against the cell wall.

Question 3

What is the function of leaves for gas exchange?

Answer 3

Gasses diffuse into the stomata of plant leaves and move through air spaces between the spongy and palisade tissue cells.

CO2 dissolves into the watery film around the cells and diffuses into the leaf cells where chloroplasts use the CO2 for photosynthesis.

O2 produced diffuses out of the leaf cells and leaves through the stomata.

Question 4

What is the function of lenticles for gas exchange?

Answer 4

Some gas exchange occurs in surface cells.

In woody plants, layers of dead bark cells and waxy substances prevent gas exchange.

Lenticles, which appear as slashes on the stems of trees and herbaceous plants, are natural pores through which gas exchange can occur.

Question 5

What is transpiration?

Answer 5

Gas exchange is tied to water loss
It is the evaporation of water through stomata (out of leaves)
Transpiration and gas exchange are controlled by the shape of the guard cells.

Question 6

What happens if there is an open stomata?

Answer 6

• This occurs when high water pressure (turgor pressure) causes water to move into the guard cells by osmosis. The guard cells swell and the stomata open, allowing transpiration.
• Occurs most during the day, to get photosynthesis.

1. Resting guard cells (normal shape)
2. (Salts) Minerals are actively transported in to create a hypertonic guard cell
3. Water moves into the hypertonic cells, causing swelling = GAP

Question 7

What happens if there is a closed stomata?

Answer 7

• Occurs when the amount of water in the guard cells drops and they shrink, and the stomata close
• Occurs most at night, except in desert plants, where stomata only open at night due to dry conditions—they get some sunlight and save it until night to get the CO2 part.
• This is to save water.

1. Swollen with water/salts
2. Salts passively diffuse out
3. Water goes to hypertonic surroundings

Question 8

Photosynthesis and cellular respiration can occur in two parts. Explain.

Answer 8

At day, they get photosynthesis, but wait to make the sugars
At night, they make the sugars, and perform respiration.

Especially for desert plants.

Question 9

Why do plants wilt?

Answer 9

Result from reduced turgor pressure as a result of water loss. Maybe, the surroundings are hypertonic.