Gas exchange in plants

Question 1

Why is the leaf thin?

Answer 1

To provide a shorter diffusion distance for rapid gas exchange.

Question 2

How does the spongy layer help with gas exchange?

Answer 2

It has air gaps that increase surface area for rapid gas exchange (higher SA to volume ratio).

Question 3

What is the function of stomata in the lower epidermis?

Answer 3

Stomata allow gases to diffuse in and out of the leaf. (CO2 in, O2 out)

Question 4

What is the role of guard cells?

Answer 4

They control the opening and closing of stomata.

Question 5

Why is moisture present between spongy mesophyll cells?

Answer 5

To dissolve gases, allowing easier diffusion.

Question 6

What happens at high light intensity in terms of the movement of CO₂?

Answer 6

The rate of photosynthesis is higher than the rate of respiration, so:

• CO₂ diffuses in.
• O₂ diffuses out.

Question 7

What happens at low light intensity (dark conditions) in terms of the movement of CO₂?

Answer 7

The rate of respiration is higher than the rate of photosynthesis, so:

• CO₂ diffuses out.
• O₂ diffuses in.

Question 8

What are the color changes of hydrogen carbonate indicator based on CO₂ concentration?

Answer 8

• Acidic (high CO₂): Yellow.
• Neutral CO₂ level: Red.
• Alkaline (low CO₂): Purple.

Question 9

How is hydrogen carbonate indicator used in an experiment?

Answer 9

A plant is placed underwater with hydrogen carbonate indicator to observe CO₂ changes.

Question 10

What happens if the rate of respiration is greater than the rate of photosynthesis? (Effects on hydrogen carbonate indicator)

Answer 10

1. CO₂ concentration increases (CO₂ is an acidic gas).
2. Hydrogen carbonate indicator turns yellow.

Question 11

What happens if the rate of respiration is lower than the rate of photosynthesis? (Effects on hydrogen carbonate indicator)

Answer 11

1. CO₂ concentration decreases (CO₂ is used up in photosynthesis).
2. Hydrogen carbonate indicator turns purple.

Question 12

What happens to guard cells when there is high light intensity? (mechanism of guard cells, 3 points)

Answer 12

1. Guard cells actively uptake mineral ions, increasing cytoplasm concentration (low water potential).
2. Water enters guard cells by osmosis.
3. Guard cells become turgid, stretching the cell and opening stomata.

Question 13

What happens to guard cells in the dark? (mechanism of guard cells, 3 points)

Answer 13

1. Mineral ions leave the guard cell.
2. Water moves out of the cell by osmosis.
3. Guard cells become flaccid, causing stomata to close.