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Exchange surfaces

OCR Yr12 Biology A 3.1.1 Exchange surfaces

What is surface area to volume ratio? The surface area of an organism divided by its volume, expressed as a ratio.
Which 3 main factors affect the need for an exchange system? 1. Size 2. SA:Vol ratio 3. Level of activity
Why do many multicellular organisms require specialised exchange surfaces. They have several layers of cells creating a longer diffusion pathway and therefore diffusion is too slow and inefficient to supply the innermost cells.
Describe the SA:Vol ratio of small organisms Large SA:Vol ratio
Describe the SA:Vol ratio of large organisms Small SA:Vol ratio
Some organisms increase their surface area without increasing their volume excessively, eg. flatworms have thin, flat bodies. What are the limitations of this? It limits the overall size of the organism. Most large organisms need a range of tissues for support and strength this increases the thickness and therefore the volume of their bodies.
How is the surface area of a sphere calculated? 4 pie r squared
How is the volume of a sphere calculated? 4/3 pie r cubed
Why do mammals and organisms with high metabolic rates need specialised exchange systems? More oxygen and nutrients are required for energy release in aerobic respiration.
Root hairs in a plant are an example of which feature of a good exchange system? Increased surface area with many additional folds in the membranes.
Describe the features of barriers found in good exchange systems. Give an example. They are thin and permeable providing a short diffusion pathway for efficient exchange. Alveoli walls are 1 cell thick providing a barrier of only 0.3 micrometers between blood and air.
How does a good blood supply aid an efficient exchange surface? Give an example. It maintains a steep concentration gradient so that diffusion occurs rapidly. Eg. gills in fish.
Created by: MsPJB
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