B3.1 Gas Exchange in Plants

Question 1

Define gas exchange.

Answer 1

The process by which organisms absorb one gas from their environment and release another.

Question 2

State the role of diffusion in gas exchange.

Answer 2

Diffusion facilitates the movement of gases across membranes, allowing organisms to absorb oxygen and release carbon dioxide.

Question 3

Explain the need for structures of larger organisms to maintain a large enough surface area for gas exchange

Answer 3

Structures of larger organisms need to maintain a large enough surface area because it increases the surface area of the cell membrane. This increases the gas exchange rate and O2 is absorbed faster.

Question 4

Pathways for gas exchange in organisms

Answer 4

Single-celled organism: the cell itself
Amphibians: blood vessel
Fishes: blood vessel
Insects: trachea
Echinoderms: papula
Mammals: alveoli

Question 5

Outline the function of the following properties of gas-exchange rate: permeability, thin tissue layer, moisture, and large surface area

Answer 5

Permeability: oxygen and carbon dioxide can diffuse freely
Thin tissue layer: keep the diffusion pathway short (gases must only diffuse across a single layer of cells in most cases)
Moisture: diffusion across a membrane is enhanced when gases are in solution
Large surface area: speed up the rate of exchange

Question 6

State the direction of movement of gases exchanged in leaves

Answer 6

CO2 in and O2 out

Question 7

Outline adaptions for gas exchange rate in leaves including: epidermis, waxy cuticle, stoma, guard cells, air spaces, spongy mesophyll, and veins

Answer 7

Leaves have a large, thin area for gas exchange.

Waxy cuticle: helps to prevent water loss, due to low permeability to gases
Stomata and guard cells: surrounded by two guard cells which open and close to regulate transpiration (most plants close their stomata at night when there is no light fir photosynthesis)
Mesophyll: specialized for photosynthesis
- the palisade later is exposed to direct sunlight
- cells in lower part of leaf are loosely arranged in the spongy layer (air sacs participate in gaseous exchange)

Question 8

Plan diagram

Answer 8

Shows areas of tissues, but not individual cells

Question 9

Xerophytes

Answer 9

Plants adapted to survive in an environment with little liquid water

Question 10

Xerophyte adaptation strategies

Answer 10

Absorb as much water as they can get from surroundings
- deep root systems
Retain water in their body for a long time
- fleshy stems and/or leaves
- thick waxy cuticle
Reduce the water loss by transpirationl
- reduced leaf size and/or number, rolled leaves, stomata in puts, leaf hairs, lower growth to earth, CAM photosynthesis

Question 12

Photosynthesis with stomata

Answer 12

Stomata open to allow for gas exchanges in and out of the leaf.

Net H2O out of the leaf
Net CO2 into the leaf
Net O2 out of the leaf

Question 13

Evaporation from the leaf leads to transpiration pull. What is transpiration pull?

Answer 13

The upward movement in water in the plant due to the “pull” caused by the continuous evaporation of water at the stomata. As a water molecule evaporates, it “pulls” on the next water in the chain

Question 14

What are the advantages of opening and closing stomata at different times of day?

Answer 14

Stoma closed: CO2 uptake low, water loss high, low pressure in cytoplasm, guard cells flaccid
Stomate opened: CO2 uptake high, water loss low, high pressure in cytoplasm, guard cells turgid

Question 15

What affects transpiration rates?

Answer 15

Temperature, wind, and light