This free quiz has 12 real AQA A-level Biology exam questions on surface area to volume ratio (24 marks, about 30 minutes). It marks itself: for each answer you check your work against the real AQA mark scheme and tick the points you made.
What the quiz covers (AQA 3.3.1)
the relationship between size and surface area to volume ratio
why oxygen uptake is a measure of metabolic rate
why larger animals need a specialised system for oxygen uptake
how the body shape of a small animal allows efficient gas exchange
why mitochondria sit close to the membrane in large cells
calculating surface area to volume ratios for agar blocks, gill filaments and people
using fish data to explain how gas exchange surfaces are adapted
surface area to volume ratio and metabolic rate in humans, and rate of osmosis per mm² in potato cubes
How to use it
Write each answer in full before you open the mark scheme, then tick only the points you really made. In the calculations, divide surface area by volume, write the ratio as x : 1 and round to the significant figures you are asked for. In explanations, link each feature to what it does, such as giving a short diffusion pathway.
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Describe a relationship. Some students gave a single example, such as “large organisms have small ratios”, instead of a relationship. Others wrote about the advantages of a large or small ratio for diffusion or gas exchange.
✔ Gains credit: as size increases, the surface area to volume ratio decreases (or smaller organisms have a larger ratio).
Feature plus explanation. Many students named body features without explaining how they allow efficient gas exchange, or mentioned a large surface area to volume ratio without linking it to a feature. “Thin membrane”, “thin wall” or “thin cells” was rejected.
✔ Gains credit: a thin or small body gives a short diffusion pathway, and a flat, long or thin body gives a large surface area to volume ratio.
Why specialised systems help. Most students described the link between size and surface area to volume ratio, but only a few gave a valid reason for the second mark.
✔ Gains credit: larger organisms have a smaller surface area to volume ratio, so a specialised system overcomes the long diffusion pathway and gives faster diffusion.
Oxygen and metabolic rate. Only 25.1% of students gained the mark. Many answers didn't mention respiration, stopped at “oxygen is used in respiration”, confused breathing with respiration, or said energy is “produced”.
✔ Gains credit: oxygen is used in respiration, which provides energy (ATP), or which is a metabolic process (chemical reaction).
Heat loss and metabolism. Many answered about small and large animals, such as an elephant and a mouse, instead of the human body, or wrote about diffusion instead of giving a relationship. Energy being “produced” was rejected.
✔ Gains credit: a larger surface area to volume ratio loses more heat, so a higher metabolic rate (respiration) releases heat to maintain body temperature.
Surface area ÷ volume. A common error in ratio calculations was dividing volume by surface area rather than the other way round.
✔ Gains credit: surface area divided by volume, written in the form x : 1.
Significant figures. Many students ignored the instruction on significant figures. Others rounded wrongly.
✔ Gains credit: the answer rounded correctly to the number of significant figures asked for, with the ratio still written as x : 1.
Keep practising
The other AQA 3.3 self-marking quizzes: Gas exchange · Digestion and absorption · Mass transport in animals · Mass transport in plants
Topic 3.2 quizzes start with cell structure
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.