surface area to volume ratio

Question 1

1. What is the relationship between the surface area and volume of different organisms?

Answer 1

As the size of the organism increases, the surface area to volume ratio decreases;

Question 2

2. What adaptations can organisms have to increase their surface area to volume ratio?

Answer 2

Be long/thin so no cell is ever far from the surface Have specialised exchange surfaces with large surface areas (e.g. lungs, gills, tracheae)

Question 3

3. How do you calculate the surface area to volume ratio?

Answer 3

To calculate a ratio, you need to divide both the numbers you are comparing by the smaller of the 2. For example if surface area = 6 and volume = 2, then 6÷2=3 and 2÷2=1, so 3:1

Question 4

4. What is Fick’s Law?

Answer 4

Diffusion ∝ surface area x difference in concentration Length of diffusion pathway

Question 5

5. What characteristics can exchange surfaces show to increase the rate of diffusion?

Answer 5

A large surface area relative to the volume of the organism, very thin layer of cells so the diffusion distance is reduced, selectively permeable (have different protein channels) to allow selected molecules to cross, movement of the medium to maintain concentration gradient (e.g. air or water), a transport system to maintain concentration gradient (e.g. blood flow)

Question 6

6. How are exchange surfaces vulnerable?

Answer 6

They may lose large volumes of water quickly or be easily damaged as they are so thin.

Question 7

7. Give the name of the process that allows substances to cross exchange surfaces.

Answer 7

Diffusion/facilitated diffusion

Question 8

8. Describe how number of protein channels/carriers will affect the rate of diffusion.

Answer 8

The higher the number of channels/carriers the faster the rate of diffusion.

Question 9

9. What is the relationship between surface area to volume ratio, heat loss to the environment and metabolic rate?

Answer 9

The larger the surface area to volume ratio, the greater the rate of heart transfer to the environment, the greater the metabolic rate to generate more heat to maintain body temperature.

Question 10

10. How do you calculate the surface area and volume of a cube?

Answer 10

SA- 6 x (length x width) Volume – length x width x height

Question 11

11. How do you calculate the surface area and volume of a cuboid?

Answer 11

SA: SA of longest sides: 4 x (length x width) SA of shorter sides: 2 x (length x width) Add the two totals together Volume – length x width x height

Question 12

12. How do you calculate the surface area and volume of a sphere?

Answer 12

SA- 4 x πr2 Volume – 4/3 x πr3

Question 13

13. Agar blocks containing sodium hydroxide and the pH indicator phenolphthalein (which is pink in alkali conditions and colourless in neutral and acidic conditions) can be used to show the effect of surface area to volume ratio on rate of diffusion. Explain how.

Answer 13

Measure each block to determine its surface area and volume. Place the different sized agar blocks in an acidic solution. Time how long it takes for the block to become completely colourless