3.3.1 Exchange between organisms and their environment

Question 1

Summarise the differences between organisms with a smaller/larger surface area : volume ratio

Answer 1

• Larger surface area:volume ratio:
• smaller organisms
• can just use diffusion
• loses more heat to the environment
• so they need a higher metabolic rate (eg respiration releases heat)
• so they use more oxygen per gram of tissue

Question 2

Why is oxygen uptake measured per gram?

Answer 2

• allows us to compare
• because organisms are different sizes

Question 3

List adaptations of an organism (eg flatworm) to increase exchange

Answer 3

Thin and flat so
* short diffusion pathway across body surface
* increased surface area: volume ratio

Question 4

Single celled organisms exchange respiratory gases by diffusion….

Answer 4

… through cell/body surface