Exchanging Substances

Question 1

Why do cells use diffusion?

Answer 1

To take in substances they need and get rid of waste products.

Question 2

Name 2 examples of cells using diffusion to take in or get rid of substances.

Answer 2

1. Oxygen and carbon dioxide are transferred between cells and the environment during gas exchange.
2. In humans, the urea defuses out of cells into the blood plasma to be removed from the body by the kidneys

Question 3

What is key about larger organisms in the surface area to volume ratio?

Answer 3

Larger organisms have a smaller surface area compared to their volume.

Question 4

How can substances diffuse through the membrane of a single-celled organism and still have enough nutrients for the organism?

Answer 4

In the SA:V ratio, their surface area is much larger than their volume so enough substances can diffuse through to supply the volume of the cell.

Question 5

If single-celled organisms don’t need intricate systems for diffusion in the body, then why do multicellular organisms?

Answer 5

Multicellular organisms have a much smaller surface area compared to their volume. This means that they need some sort of exchange surface to make diffusion efficient.

Question 6

Name 4 ways that exchange substances have adapted.

Answer 6

1. Thin membrane
2. Large surface area
3. Lots of blood vessels
4. Gas exchange surfaces are ventilated

Question 7

Why do exchange substances need a thin membrane?

Answer 7

So substances only have a short distance to diffuse.

Question 8

Why do exchange surfaces need a large surface area?

Answer 8

So lots of substances can diffuse at once.

Question 9

Why do exchange surfaces and animals have a lot of blood vessels?

Answer 9

To get substances in and out of the blood quickly.

Question 10

Gas exchange surfaces and animals are often ventilated. What does ventilated mean?

Answer 10

Air moves in and out.

Question 11

In simple terms, what is the job of the lungs referring to 2 different gases?

Answer 11

To transfer oxygen into the blood and remove waste carbon dioxide from it.

Question 12

How do the lungs diffuse so much gas?

Answer 12

They contain millions of little air sacs called alveoli.

Question 13

Name four ways that alveoli are specialised to make gas exchange efficient.

Answer 13

1. They have an enormous surface area.
2. They have a moist lining to dissolve gases.
3. They have very thin walls.
4. They have a very good blood supply.