Topic 1 - Cell biology: Transport in cells

Question 1

(a) What is meant by the term diffusion? 2

Answer 1

(a) movement / spreading out of molecules / particles
from (an area of) high(er) concentration to (an area of) low(er)
concentration

Question 2

Which two changes will increase the rate at which carbon dioxide diffuses
into the mesophyll cells?

Answer 2

increased carbon dioxide concentration in the air
1
increased number of stomata that are open

Question 3

Explain how the human lungs are adapted for efficient exchange of gases
by diffusion

Answer 3

(many) alveoli
* provide a large(r) surface area (: volume)

capillaries are thin
* which provides short diffusion path

lungs are ventilated
* to bring in (fresh) oxygen + to maintain a concentration / diffusion gradient

good blood supply
* to maintain a concentration / diffusion gradient

Question 4

Explain how the nitrate ions in Figure 3 are transported into the root hair
cell.

Answer 4

active transport

(because) energy is needed

(to move nitrate ions) from a low(er) concentration (in the soil) to a
high(er) concentration (in the root / cell)

Question 5

Describe how one feature of the axolotl’s gills increases the rate of
diffusion of oxygen.

Answer 5

many gills
increase sa

Question 6

Give two reasons why a kidney transplant is a better method for treating
kidney disease than dialysis

Answer 6

-cheaper in the long run
- fewer hospital visits

Question 7

Suggest why a large surface area to volume ratio is an advantage

Answer 7

increases / more gas exchange

Question 8

(b) Describe how water moves from roots to the leaves.

Answer 8

by transpiration stream / pull

in xylem

Question 9

Explain how the human circulatory system is adapted to:
* supply oxygen to the tissues
* remove waste products from tissues. 6

Answer 9

dual / double circulatory system which means that it has higher blood pressure and a greater flow of blood to the tissues

• heart pumps blood to lungs in pulmonary artery so that oxygen can diffuse
  into blood from air in alveoli
• blood returns to heart via pulmonary vein where muscles pump blood to
  the body via aorta
• oxygen carried by specialised cells which contain haemoglobin to bind oxygen and have no nucleus so there is more space available to carry oxygen
• arteries carry oxygenated blood to tissues where capillaries deliver oxygen
  to cells for respiration and energy release
• thin walls allow for easy diffusion to cells

Question 10

Describe how ions, water and sugar are obtained and transported through
plants. 6

Answer 10

Water:
(P) taken up by osmosis
* from an area of low to high concentration
travels in the xylem
(M) to the leaves or from the roots / soil
(P) transpiration stream
* movement replaces water as it evaporates from leaves
Sugar:
(P) made during photosynthesis
travels in the phloem
(M) to other parts of the plant/ travels up and down/ storage organs as starch