Surface Area To Volume Ratio

Question 1

Explain in terms of SA:Vol ratio why unicellular organism (eg. Amoeba) and multicellular organism (simple eg. Earthworm and complex eg. Human) affects rate of diffusion.

Answer 1

• larger SA:Vol ratio increases rate of diffusion as distance of diffusion is short

Question 2

Amoeba (bacteria)

Answer 2

• unicellular
• large SA:Vol ratio
• thin, moist membrane
• short diffusion path

Question 3

Flatworm

Answer 3

• multicellular
• flattened shape increases SA:Vol ratio
• short diffusion path
• low metabolic rate

Question 4

Earthworm

Answer 4

• multicellular
• tubular shape so large SA:Vol ratio
• moist skin secretes mucous
• low metabolic rate
• once oxygen diffuses under skin, closed circulatory system transports oxygen and increases efficiency of oxygen transport

Question 5

Springer spaniel

Answer 5

• multicellular
• specialised exchange organ
• cells as deep within body- big difference between them and the outside environment
• efficient blood system needed to carry substance to and from cells

Question 6

What does it mean if an organism has a higher metabolic rate?

Answer 6

• demands efficient transport of water out of cells and reactants into the cells

Question 7

What are the adaptations of larger organisms for increasing SA:Vol ratio?

Answer 7

• villi & microvilli for absorption of digested food
• alveoli and bronchioles for gas exchange
• spiracles and tracheoles for gas exchange
• gill filaments and lamellae for gas exchange
• thin wide leaves for gas exchange
• many capillaries for capillary network