Exchange surfaces

Question 1

What does exchange between an organism and its environment depend on?

Answer 1

Surface area to volume ratio

Question 2

The larger the organism, the … the surface area to volume ratio

Answer 2

smaller

Question 3

How are substances exchanged in a single celled organism?

Answer 3

Diffuse directly in

Large surface area to volume ratio

Question 4

Why doesn’t simple diffusion work in multi-cellular organisms to exchange substances with the environment

Answer 4

Smaller surface area to volume ratio - not enough substances can diffuse from their outside surface to supply their entire volume

Question 5

How do multi cellular organisms exchange substances with their environment?

Answer 5

Exchange surface

Question 6

How are exchange surfaces adapted to maximise effectiveness?

Answer 6

Thin membrane - short diffusion distance
Large surface area - lots of substances can diffuse at once
Good blood supply - maintains concentration gradient
Ventilated (in lungs) - maintains concentration gradient

Question 7

How are the alveoli adapted for gaseous exchange?

Answer 7

Large surface area (75m2)
Moist lining - dissolve gases
Thin walls - short diffusion distance
Good blood supply
Ventilation

Question 8

How are the villi in the small intestine adapted for absorption?

Answer 8

Increase surface area
Single layer of cells
good blood supply

Question 9

Describe how substances are exchanged in leaves

Answer 9

CO2 diffuses into air spaces within leaf and into cells where photosynthesis occurs
Stomata - allows CO2 to diffuse in
Oxygen and water vapour diffuse out through the stomata
Size of stomata controlled by guard cells
Flattened shape of the leaf increases area of exchange surface
Walls of cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the aread of the surface
Water vapour evaporates from inside cell to outside leaf

Question 10

When do the guard cells cause stomata to close?

Answer 10

When cell is losing too much water vapour - faster than roots can replace it

Question 11

Describe how the gills are adapted for gas exchange

Answer 11

Gill filaments form each gill - thin large surface area
Gill filaments covered in lamellae which increase surface area even more
Lamellae have lots of blood capillaries to increase diffusion
Thin cells - minimise diffusion distance
Opposite direction of blood and water flow - counter current maximises concentration gradient

Question 12

Describe the concentration gradient of oxygen in the gills

Answer 12

Oxygen concentration is always higher in water than blood

Question 13

Describe the movement of water through fish

Answer 13

Enters through mouth and passes out of the gills