topic 8

Question 1

Describe the need to transport substances into and out of a range of organisms, including urea

Answer 1

all organisms must take in substances that they need from the environment and get rid of any waste products.

Question 2

Describe the need to transport substances into and out of a range of organisms, including oxygen and carbon dioxide

Answer 2

Cells need oxygen for aerobic respiration, which produces carbon dioxide as a waste product. These two gases move between cells and the environment by diffusion.

Question 3

Describe the need to transport substances into and out of a range of organisms, including water and dissolved food molecules

Answer 3

Water is taken up by cells by osmosis.

In animals, dissolved food molecules (the products of digestion) and mineral ions diffuse along with it.

Question 4

Describe the need to transport substances into and out of a range of organisms, including urea

Answer 4

Urea (a waste product produced by excess amino acid breakdown) diffuses from cells to the blood plasma for removal from the body by the kidneys.

Question 5

Explain the need for exchange surfaces and a transport system in multicellular organisms including the calculation of surface area:volume ratio

Answer 5

• multicellular organisms have a smaller surface area compared to their volume
• this makes it difficult to exchange enough substances to supply their entire volume across their body

-so there are exchange surfaces to allow for efficient diffusion and a mass transport system to move substances between the exchange surface and the rest of the body.

Question 6

Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

Answer 6

-the alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide.

• moist lining: dissolving gases.
• good blood supply: maintain the concentration gradients of oxygen and carbon dioxide.
• very thin walls: minimising the distance that gases have to move.
• an enormous surface area

Question 7

Describe the factors affecting the rate of diffusion, including surface area

Answer 7

-The more surface area there is available for molecules to move across, the faster they can get from one side to the other.

Question 8

Describe the factors affecting the rate of diffusion, including concentration gradient

Answer 8

-substances diffuse faster if there’s a big difference in concentration between the area they are diffusing from and the area they are diffusing to.

If there are lots more particles on one side, there are more there to move across

Question 9

Describe the factors affecting the rate of diffusion, including diffusion distance

Answer 9

-substances diffuse more quickly when they haven’t as far to move.

Question 10

Calculate the rate of diffusion using Fick’s law

Answer 10