Structure and Functions in Living Organisms - Gas Exchange (Paper 2)

Question 1

what is the role of diffusion in gas exchange?

Answer 1

• diffusion is the process by which gas exchange occurs
• single-celled organisms, such as amoeba, can exchange gases sufficiently by simple diffusion through the cell membrane
• multicellular organisms (such as plants and animals), however, have exchange surfaces and organ systems that maximise the exchange of materials

Question 2

how does respiration use gas exchange?

Answer 2

• respiration requires the uptake of oxygen and the release of carbon dioxide
• the oxygen diffuses down the concentration gradient from a high concentration (outside the leaf) to a low concentration (inside the leaf) to be respired

Question 3

how does photosynthesis use gas exchange?

Answer 3

• photosynthesis requires the uptake of carbon dioxide and the release of oxygen
• carbon dioxide diffuses down the concentration gradient from a region of high concentration (outside the leaf) to a region of low concentration (inside the leaf)

Question 4

what are adaptions of a leaf cell for gas exchange?

Answer 4

stomata, guard cells, thin, flattened shape and air spaces

Question 5

how do stomata make gas exchange more efficinent?

Answer 5

open to allow the diffusion of carbon dioxide into the leaf for photosynthesis, and the diffusion of waste products of oxygen and water vapour out of the leaf

Question 6

how do guard cells make gas exchange more efficinent?

Answer 6

• ontrols the opening and closing of Stomata depending on the time of day to enable gas exchange
• guard cells become turgid during daytime to open stomata and allow diffusion of carbon dioxide into the leaf for photosynthesis (for example)

Question 7

how does the leafs thinness make gas exchange more efficinent?

Answer 7

minimises the diffusion length, therefore increasing the rate of gas exchange

Question 8

how does the leafs flattened shape make gas exchange more efficinent?

Answer 8

larger surface area to volume ratio increases rate of gas exchange

Question 9

how do air spaces make gas exchange more efficinent?

Answer 9

larger internal surface area to volume ratio for absorption of carbon dioxide into the leaf, therefore increasing the rate of gas exchange

Question 10

what are the stomata?

Answer 10

mouth-shaped opening flanked and controlled by guard cells to regulate gas exchange and prevent water loss (via transpiration)

Question 11

what is the role of the stomata in gas exchange?

Answer 11

during the day:
- high light intensity stimulates guard cells to absorb water via osmosis
- guard cells become turgid and stomata opens
- carbon doxide diffuses in, oxygen and water diffuse out
during the night:
- low light intenisty stimulates guard cells to loose water via osmosis
- guard cells become flaccid and stomata closes
- net exchange of gases doesnt occur

Question 12

when do respiration and photosynthesis happen?

Answer 12

respiration happens during the day and night
photosynthesis happpens during the day but not at night

Question 13

what colour does hydrogencarbonate indicator change to in different carbon dioxide concentrations?

Answer 13

yellow in high carbon dioxide concentrations
red at atmospheric level
purple at low carbon dioxide concentrations

Question 14

how would you investigate the effect of light on gas exchange?

Answer 14

• lace pondweed in a beaker of hydrogen carbonate indicator
• place light source at a set distance to adjust light intensity
• allow plant to adapt to adjusted environment for a few minutes
• observe and record the colour of indicator
• change light intensity and repeat process