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Question 1

Respiratory surface

Answer 1

Site of gas exchange

Question 2

Gas Exchange

Answer 2

Diffusion of gases down a concentration gradient

Question 3

Criteria for a respiratory surface (4 points)

Answer 3

• Large SA/V ratio
• Thin, short diffusion pathways
• Permeable
• Have a method of creating a steep concentration gradient

Question 4

Unicellular

Answer 4

Single-celled organisms

Question 5

Unicellular properties (3) and therefore they can (2)…

Answer 5

• Large SA/V ratio
• Thin cell membrane so rapid diffusion
• Short diffusion distance
• Absorb O2 across cell membrane to meet respiration needs
• Remove CO2 fast enough to prevent making the cytoplasm too acidic

Question 6

Multicellular

Answer 6

made up of many cells

Question 7

Multicellular flaws (2)

Answer 7

• lower SA/V ratio

- diffusion is not efficient enough for gas exchange

Question 8

Flatworms property + explanation

Answer 8

• Flat so larger SA/V than spherical organism

Question 9

Earthworm properties + explanation (5)

Answer 9

• Cylinder shape so lower SA/V
• Skin kept moist by secreting mucus so has to stay in damp soil
• low O2 requirement bc slow-moving with a low metabolic rate
• Capillaries carry O2 away from surface maintaining gradient
• CO2 diffuses out skin down a gradient

Question 10

Multicellular properties + explanation (4)

Answer 10

• Higher metabolic rate so need more O2/remove more CO2
• cells are bigger w/ more specialisation so more independent
• have a ventilation mechanism to maintain steep gradient
• respiratory surface is thin so they are fragile and have to be protected inside organism