Starter quiz
- The role of the circulatory system is to deliver ______ and nutrients to cells and take away waste products.
- 'oxygen' ✓
Where in the lungs does gas exchange take place?- 'alveoli' ✓
- Which of the following statements about diffusion are correct?
- molecules move in one direction
- it requires energy from respiration
- it is a passive process ✓
- molecules move randomly ✓
-
- Where are nutrients absorbed into the bloodstream?
- oesophagus
- small intestine ✓
- stomach
-
- Which blood vessel is only one cell thick?
- 'capillaries' ✓
What is the surface area to volume ratio of this shape?- 2 : 4 : 4
- 8 : 2
- 8 : 4
- 2 : 1 ✓
- 32 : 32
-
Exit quiz
- Which factors does the surface area and volume affect?
- rate of diffusion ✓
- diffusion distance ✓
- which substances can diffuse in and out of a cell
-
- True or false? Large living organisms have a large surface area to volume ratio.
- True
- False ✓
- Why is a small surface area a disadvantage to organisms?
- Decreasing SA : V decreases diffusion rate. ✓
- Decreasing SA : V increases diffusion rate.
-
Having many villi ______ the surface area over which diffusion can take place.- increases ✓
- decreases
- does not impact
-
What are the advantages of a circulatory system?- It means substances don't have to diffuse.
- It moves nutrients and waste products around the body. ✓
- It reduces the time taken for substances to diffuse from the blood to the cells. ✓
- It brings blood near to the surface of cells which reduces diffusion distance. ✓
- It means active transport will occur instead of diffusion.
-
- How are the alveoli adapted for efficient diffusion?
- good blood supply ✓
- large surface area ✓
- thin cells ✓
- thick cells
- small surface area
-
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Consequences for living organisms of relationship between surface area:volume ratio and diffusion time.
- Reasons why a small surface area (relative to volume) could be a disadvantage to living organisms.
- The circulatory system minimises diffusion distance for oxygen and food molecules so cells can be supplied quickly.
- Examples of exchange surfaces in humans (e.g. alveoli in lungs, villi in digestive system).
- The exchange surfaces are adapted to maximise surface area for diffusion of particles of essential substances and waste.
Common misconception
Pupils may think that villi and alveoli increase surface area without changing volume.
These ideas are explored in detail with examples and demonstrations using cube animals. The issue of surface area to volume ratio and diffusion rate is covered thoroughly, along with solutions to the issues in humans.
Keywords
Surface area - The total area of the surface of an object.
Surface area to volume ratio - The relationship between the surface area and the volume of a shape.
Diffusion - The net movement of particles from an area of higher concentration to an area of lower concentration.
Exchange surfaces - A specialised surface which enables the efficient exchange of substances.
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