Module 2 - Mass Transport Systems

Question 1

Small Unicellular Organisms…

e.g. amoeba.

Answer 1

• They obtain all nutrients and oxygen they require to survive by simple diffusion across their cell surface membrane.
• They have a large surface area to volume ratio and they are not very active so have a low metabolic rate.

Question 2

Large Multicellular Organisms…

e.g. elephant.

Answer 2

• They are very active organisms with a large number of cells which respire quickly (high metabolic rate).
• So they have a higher demand for nutrients and a great production of waste products.
• They have a small surface area to volume ratio.
• Diffusion is too slow to deliver nutrients/oxygen and remove waste products at an appropriate rate.
• Thus a mass transport system is needed to meet the demand of all cells.

Question 3

Large Multicellular Organisms…

e.g. human.

Answer 3

• Large multicellular organisms have specialised exchange systems.
• Substances move from these specialised exchange surfaces to other parts of the body where they are needed by a mass flow system.
• In mammals a pumping mechanism is used to speed up the movement of substances.

Question 4

Large Multicellular Organisms…

e.g. plant.

Answer 4

• Plants are not very active but they are large and multicellular.
• They have a small surface area to volume ratio.
• Diffusion distance is too large and diffusion is too slow to meet its needs thus a mass transport system is needed.