Topic 3---A: Exchange and Transport Systems- 1. Size and surface area Flashcards
In an organism what needs to be exchanged with the environment?
- Cells need to take in oxygen for (aerobic respiration)
- They need to excrete waste products like carbon dioxide and urea
- Organisms need to stay at roughly the same temperature so heat needs to be exchanged too
What is the relationship between size of an organism and it’s surface area?
The smaller an organism is the higher the surface area: volume ratio
- Surface area is bigger compared to their volume
How do you calculate the volume of a cyclinder?
pie x radius squared x height
How do you find the volume of a sphere?
4/3 x pie x radius cubed
How do single-celled organisms remove and supply cells with substances?
- Substances can diffuse directly into or out of the cell across the cell-surface membrane.
- Diffusion rate is quick because of the small distances the substances have to travel.
How do multi-cellular organisms remove and supply cells with substances?
- Diffusion across the outer membrane is too slow as:
1.Some cells are deep within the body so there is a big distance between them and the outside environment
2. Larger animals have a low surface area: volume ratio so it’s difficult to supply enough substances to supply a large volume of animal through a relatively small outer surface
What does the metabolic activity inside cells create?
Heat
Factors influencing body temperature?
- Body size
- Body shape
Body size
- The rate of heat loss from an organism depends on its surface area
- If an organism is large they have a small surface area: volume ratio (volume is large)
- This makes it harder for it to lose heat from the body
- If an organism is small it has a large surface area: volume ratio
- So heat is lost more easily
What do smaller organisms need to generate enough heat and stay warm?
A high metabolic rate
Body shape
- Animals of any size with a compact shape have a small surface area: volume ratio which minimises heat loss from their surface
- Animals with a less compact shape (sticky out bits) have a larger surface area to volume ratio increases heat loss from their surface
Examples of adaptations for heat exchange
- Arctic fox body temperature is 37 °c and the average outside temperature is 0°c so to reduce heat loss they have small ears and a round head
- African bat- eared fox body temperature is 37°c and their average outside temperature is 25°c so to increase heat loss they have to increase their surface area by having large ears and a more pointed nose
How do you increase heat loss?
Increase surface area: volume ratio
How do you reduce heat loss?
Smaller surface area to volume ratio
Behavioural and physiological adaptations to aid exchange
- Smaller animals may have thick layers of fur or hibernate when the weather gets cold
- Larger organisms living in hot regions like elephants and hippos find it hard to keep cool as their heat loss is relatively slow so elephants have developed large flat ears which increases their surface area allowing them to lose more heat and hippos spend much of the day in water
