AQA GCSE Biology (8461), Higher tier · Cell biology › Transport in cells
Practise Diffusion. 14 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Substances move into and out of cells by diffusion.
(a) What is meant by diffusion?[2]
(b) Which substance diffuses out of body cells into the blood plasma so that it can be excreted by the kidneys? Tick (✓) one box.[1]
Glucose
Oxygen
Starch
Urea
(c) Give two factors that affect the rate of diffusion.[2]
Show the answer and mark scheme
(a)
the (net) movement / spreading out of particles (of a gas or a substance in solution)
from an area of higher concentration to an area of lower concentration
(b)Answer: Urea
(c)
difference in concentration / concentration gradient
temperature
surface area (of the membrane)
Question 2Medium7 marks
Fish take in oxygen and remove carbon dioxide at their gills. Each gill is made of many thin filaments. The filaments have a good blood supply. Water flows over the filaments all the time.
(a) Explain how the gills are adapted for efficient gas exchange.[3]
(b) Explain why oxygen moves from the water into the blood in the gills.[2]
(c) Out of water, the gill filaments stick together. Suggest why a fish soon dies when it is taken out of water, even though air contains more oxygen than water.[2]
Show the answer and mark scheme
(a)
many filaments give a large surface area
thin filaments / membranes give a short diffusion path
good blood supply carries oxygen away
water flow brings more oxygen, so a steep concentration gradient is maintained
(b)
the concentration of oxygen is higher in the water than in the blood
(so oxygen) diffuses from a higher to a lower concentration
(c)
the surface area for gas exchange is greatly reduced
so not enough oxygen diffuses into the blood (for respiration)
Question 3Hard7 marks
Flatworms are small animals that have no gas exchange organs and no blood system. A scientist modelled the body of a flatworm as a cuboid 8 mm long, 4 mm wide and 0.5 mm thick.
(a) Calculate the surface area : volume ratio of the flatworm model. Give your answer in the form x : 1[3]
(b) A cube with the same volume as the flatworm model has a surface area : volume ratio of 2.4 : 1. Explain how the shape of the flatworm allows it to survive without gas exchange organs or a blood system.[3]
(c) Flatworms can only live in water or in very damp places. Suggest one reason why.[1]