Size and surface area Flashcards
What is metabolic rate?
The amount of energy expended by an organism in a time period.
What is metabolic demand?
How much oxygen and nutrients an organism needs to take in daily to respire enough to maintain their metabolic rate.
Describe a unicellular organisms exchange system?
They have a large SA:V so the surface area is large enough to absorb enough substances required.
They have a short diffusion distance to get from the outside to the centre of the organism so the diffusion to the whole organism is fast.
Therefore, they can exchange materials directly with the environment as all of the cell has a surface exposed to the outside. However, they can lose heat energy and water quickly and cannot survive extreme heat or cold.
Describe a multicellular organisms exchange systems?
They have a small SA:V ratio so cannot absorb enough substances to supply large volumes through small outer surface.
The diffusion distance is large to get from the outside to centre of the organism, so diffusion is too slow to supply cells efficiently.
They lose less heat energy so can survive more easily in cold environments. Some cells have no exposed surfaces so need an internal mass transport system and in hot environments they need adaptations to cool down.
Explain how an animal’s shape can help control its temperature?
Increase SA:V ratio (large ears/long nose), will increase heat loss. Decrease SA:V ratio (small ears/round head), will decrease heat loss as diffusion distance will be greater.
Give two adaptations of a small organism could have to survive in a cold environment?
They have a streamlined body shape giving it a smaller SA:V and animals with a large SA:V ratio can have thick layers of fur for insulation.
Why can a bacterium rely on diffusion of gas exchange but animals need a transport system?
Animals have a smaller SA:V ratio, so the diffusion distance is larger in animals and therefore diffusion would not supply enough oxygen.
