Gas Exchange in Fish and Plants

Question 1

Counter-current flow

Answer 1

Water flow is in the opposite direction to capillary blood flow over gill lamellae to ensure maximum gas exchange

Question 2

Why is counter-current flow efficient?

Answer 2

• Oxygen saturation is higher in the water than in the blood across the whole width of the gill lamella
• steady diffusion gradient
• more oxygen diffuses from the water into the blood

Question 3

Active fish have

Answer 3

More gill lamellae

Question 4

Unidirectional flow over gills

Answer 4

Less energy is required because the flow does not need to be reversed – important because water is dense and difficult to move

Question 5

Gill structure adaptations

Answer 5

• counter-current flow
• very thin and therefore provide a short diffusion distance (also there are many, so a large SA)
• Opercular suction and buccal pressure pumps maintain unidirectional flow of water through the fish through the mouth and out of the gills

Question 6

Describe counter-current flow

Answer 6

Blood in the capillaries and water flow in opposite directions. Hence, blood with very little oxygen flows past water partially saturated with oxygen, so diffusion of water takes place from a high concentration to a low concentration into the blood
Blood that is partially saturated with oxygen flows past water fully loaded with oxygen, so diffusion can still occur
Hence, oxygen saturation is higher in the water than in the blood across the whole width of the gill lamella, so there is a steady diffusion gradient and therefore gas exchange is maximised.

Question 7

Similarities between leaf and insect

Answer 7

• Both use pores in there outer covering (the size of which can be controlled)
• Both involve diffusion in the gas phase
• no living cell is far from air
• needed for water retention

Question 8

Differences between plant and insect

Answer 8

• Gas exchange in a plant leaf uses less of the external air due to photosynthesis which they can interchange with respiration, whereas insects do not
• Insects have tracheae, whereas plants do not
• insects create mass air flow
• insects have smaller SA:Vol

Question 9

Xerophytic features

Answer 9

• having a waxy cuticle reduces evaporation
• Hairy leaves – to trap moist air next to the leaves, reducing the water potential gradient between the inside and the outside of the leaf; reduces evaporation
• stomata distribution
• stomata in pits and grooves
• rolled leaves
• spines or needles

Question 10

Hairy leaves

Answer 10

traps moist air (reduction of air movement - increase in humidity) next to leaf surface; reduces the water potential gradient between the inside and the outside of the leaf; reduces evaporation

Question 11

Carbon dioxide into leaves

Answer 11

• The majority of the carbon dioxide comes from the external air, which diffuses from a high concentration to a low concentration through the stomata (opened by guard cells) on the underside of the leave into the air spaces and down a conc. gradient between the spongy mesophyll cells, which provides a short diffusion distance to the photosynthesising pallisade mesophyll cells in need of carbon dioxide.
• Some of the carbon dioxide produced at the mitochondria during cellular respiration can also be used by the chloroplasts in photosynthesis.