2.2 gas exchange in animals and plants

Question 1

state what is meant by diffusion

Answer 1

Movement of molecules from an area of higher concentration to a lower concentration through a permeable membrane

Question 1

respiratory system must be:

Answer 1

• thin ( short diffusion pathway )
• moist ( allow gas to diffuse easily and more )
• large surface area ( increase area for gas exchange to take place )
• permeable to gas ( good supply to maximise diffusion )

Question 2

how have flatworms adapted to the challenge of gas exchange?

Answer 2

• Multicellular and aquatic
• Smaller surface area to volume ratio
• Flattened body to reduce diffusion distance so rate of oxygen diffusion through body surface meets demand

Question 3

how have amoeba organisms adapted to the challenge of gas exchange?

Answer 3

• single celled
• large SA:V ratio
• cell membrane is thin, short diffusion pathway to middle of cell
• Rate of oxygen diffusion through external surface meets demand.
• A low metabolic rate means oxygen demand is low.

Question 4

how have earthworms adapted to the challenge of gas exchange?

Answer 4

• Multicellular
• Even smaller surface area to volume ratio
• Body surface still used for gas exchange but circulatory system needed to distribute oxygen. Blood vessels are close to skin surface and blood has haemoglobin with a high affinity for oxygen.
• Mucus secreted to moisten surface and slow moving to reduce oxygen demand