3.1 Surface area to volume ratio

Question 1

Describe the relationship between the size and structure of an organism and its surface area

Answer 1

• As size increases, SA:V tends to decrease
• More thin/flat strutures increase SA:V ratio

Lungs and Gills also increase SA:V

Question 2

How is SA:V calculated

Answer 2

Divide surface area (Size length x wide width x number of sides) by volume (Length x width x depth)

Question 3

Suggest an advantage of calculating SA:Mass for organisms instead of SA:V

Answer 3

It is easier and quicker to find and more accruate due to irregular shapes
More accurate / less error

Question 4

What is metabolic rate? Suggest how it can be measured

Answer 4

• Metabolic rate=amount of energy used up by an organism within a given period of time
• Often measured by oxygen uptake–> as used in aerobic respiration to make ATP for energy release

Question 5

Explain the relationship between SA:V and metabolic rate

Answer 5

As SA:V increases metabolic rate uncreases because:
* Rate of heat loss per unit body mass increases
* So organisms need a higher rate of respiration
* To release enough heat to maintain a constant body temperature e.g. replace lost heat

Question 6

Explain the adaptations that facilitate exchange as SA:V reduces in larger organisms

Answer 6

1.Changes to body shape e.g. long/thin
* Increases SA:V ratio and reduces long diffusion distance/pathway
2.Development of systems, Such as specialised surface/ organ for gaseous exhange e.g. lungs
* Increases internal SA:V and reduces long diffusion distance and pathway
* maintain a conc gradient for diffusion e.g. by ventiliation/good blood supply

Question 7

What are features of specialised exchange surfaces

Answer 7

Selectively permeable to allow selected materials to cross
Very thin so that the diffusion pathway shortens
Large SA:V ratio–>Incrfeases the rate of exchange
Movement of the enviornmental medianm e.g. air, to maintian a diffusion gradient
A transport system to ensure the movement of the internal medium e.g. blood in order to maintain a diffusion gradient

Question 8

Ficks law

Answer 8

Diffusion is directly proportional to
Surface area x difference in conc/ Length of diffusion pathway

Question 9

Explain one way in which a large size is advanatge for large animals

Answer 9

They have a very small surface area to volume ratio and so loses less heat to the water than it would if it were small