Transport in Animals Flashcards

All 14 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.

Name the three factors that affect the rate of diffusion.

Surface area, concentration gradient (concentration difference) and diffusion distance (membrane thickness).

State Fick's law as a formula.

rate of diffusion $\propto \dfrac{\text{surface area} \times \text{concentration difference}}{\text{thickness of membrane}}$

What are the steps to calculate a relative rate of diffusion using Fick's law?

e.g. surface area $= 4$, concentration difference $= 6$, membrane thickness $= 2$

1. Multiply surface area by concentration difference: $4 \times 6 = 24$
2. Divide by the membrane thickness: $24 \div 2 = 12$
3. Relative rate of diffusion $= 12$ (no units)

True or false? Doubling the thickness of an exchange surface doubles the rate of diffusion.

False. Rate is inversely proportional to thickness, so doubling the thickness halves the rate.

Using Fick's law, what happens to the rate of diffusion if the surface area is doubled and everything else stays the same?

The rate of diffusion doubles — rate is directly proportional to surface area.

True or false? The steeper the concentration gradient, the faster the rate of diffusion.

True. Rate of diffusion is proportional to the concentration difference across the surface.

True or false? In an agar cube experiment, dye reaches the centre of the largest cube in the shortest time.

False. The smallest cube is coloured throughout first — it has the largest surface area : volume ratio and the shortest diffusion distance to its centre.