M3 7.1 Specialised Exchange Surfaces

Question 1

Why do unicellular organisms need specialised exchange surfaces

Answer 1

Metabolic activity of a single celled organism is low is the O2 demands are low as well as the CO2 production

SA:V ratio of the organism is high (the bigger the organism, the smaller the ratio, so gases can’t be exchanged fast enough for it to survive)

Question 2

What is amoeba

Answer 2

A unicellular organism so get their substances for respiration through simple diffusion in the cell membrane

Question 3

Why are amoeba able to respire through simple diffusion

Answer 3

1. Because the O2 demand is low and CO2 production is also low (due to low metabolic rate)
2. Cell has a large SA:V ratio

Question 4

Why do other organisms need a specialised exchange system as they get bigger

Answer 4

1. as they get bigger, the distance for diffusion to happen is too long to transfer substances for respiration
2. the metabolic rate is much higher
3. the number of cells increases

Question 5

How do you calculate SA:V (equations)

Answer 5

cuboid:
volume=length x height x width
SA= (4 x height x length) + (2 x height x width)

cylinder:
area of a circle=pi(r)^2
circumference=2(pi)(r)
volume= (pi)(r)^2 x height 
SA= (2(pi)(r) x height) + 2(pi)(r)^2

sphere:
volume= 4/3(pi)(r)^3
SA= 4(pi)(r)^2