The Need for Transport Flashcards

All 7 cards in this deck

Name the six substances that must be transported into or out of organisms.

Oxygen, carbon dioxide, water, dissolved food molecules, mineral ions and urea.

Why must urea be transported out of the body?

It is a toxic waste product (made in the liver from excess amino acids) and must be removed by the kidneys in urine.

Why must oxygen be transported into cells and carbon dioxide transported out?

Oxygen is needed for aerobic respiration; carbon dioxide is the waste product of respiration and is toxic if it builds up.

What are the steps to calculate the surface area : volume ratio of a cube?

e.g. a cube of side $2$ cm

1. Surface area $= 6 \times$ side $\times$ side $= 6 \times 2 \times 2 = 24$ cm$^2$
2. Volume $=$ side$^3 = 2^3 = 8$ cm$^3$
3. Divide both by the volume: $24 : 8 = 3 : 1$

What happens to an organism's surface area : volume ratio as it gets larger?

It decreases — volume increases faster than surface area.

True or false? A single-celled organism needs a transport system to move substances around it.

False. It has a large surface area : volume ratio and short diffusion distances, so diffusion across its surface alone is fast enough.

Why do multicellular organisms need exchange surfaces and a transport system?

They have a small surface area : volume ratio and large diffusion distances, so diffusion alone is too slow to supply all their cells.