3 Organisms exchange substances with their environment

Question 1

Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer. ( 2 marks )

Answer 1

Mark in pairs :1and 2 OR 3 and 4
1. Flattened cells
OR
Single layer of cells;
Reject thin cell wall/membrane Accept thin cells
Accept ‘one cell thick’
2. Reduces diffusion distance/pathway;
3. Permeable;
4. Allows diffusion of oxygen/carbon dioxide;

Question 2

Explain what is meant by counter-current system in fish.

Answer 2

• blood and water flow in opposite directions
• diffusion/concentration gradient ( maintained) along (length of) lamellae/filament

Question 4

Describe and explain the relationship between surface area to volume ratio of the human body and metabolic rate. (3 marks )

Answer 4

1. As surface area to volume ratio increases, metabolic rate increases
   OR
   (Humans with) a large surface area to volume ratio have a high/fast
   metabolic rate;
2. (A large(r) surface area to volume ratio will) lose more heat;
3. (A high(er) rate of metabolism/respiration) releases / provides /
   replaces heat
   OR
   (A high(er) rate of metabolism/respiration) maintains body
   temperature;