Topic 3 - SA:V Ratio

Question 1

What happens to the organisms as they increase in size?

Answer 1

Their SA:V ratio decreases
- Less surface area for absorption of nutrients and gases
- greater volume means longer diffusion distance

Question 2

Why can the exchange of substances occur via simple diffusion in single celled organisms?

Answer 2

Their small volume shortens the diffusion distance and the larger surface area allows for maximum absorption of nutrients and gases.

Question 3

Define metabolic rate

Answer 3

The amount of energy expended by that organism within a given period of time

Question 4

What is Basal Metabolic Rate (BMR) ?

Answer 4

The metabolic rate of an organism at rest

Question 5

What are the ways to calculate metabolic rate?

Answer 5

-Oxygen consumption
-Carbon dioxide production
-Heat production

Question 6

How does body mass relate to metabolic rate?

Answer 6

Greater the mass of an organism the higher the metabolic rate
(Consume more O2 and produce more CO2)

Question 7

Why is the BMR per unit of body mass higher in smaller animals?

Answer 7

Smaller organisms have a larger SA:V ratio so they lose more heat.
- They have to use up more energy to maintain body temperature

Question 8

How are the alveoli adapted for efficient gas exchange? (6marks)

Answer 8

• Alveolar epithelium is once cell thick, creating a short diffusion distance for gas exchange
• The lungs contain a large number of alveoli, providing a large surface area for gas exchange to take over
• There’s a steep concentration gradient for O2 and CO2 to keep diffusing

Question 9

Why do smaller organisms have a higher metabolic rate?

Answer 9

They have a larger S.A:V ratio so they lose heat a lot quicker, so they need to generate more energy to replace the heat lost.