Exchange between organisms and their environment Flashcards
Why does organisms exchange between 2 environments?
There’s the external and internal environment, transfer of materials usually involves crossing cell plasma membranes.
Cells need to take in oxygen for aerobic respiration and nutrients. Also, need to excrete waste products like carbon dioxide and urea.
Most organisms need to stay at roughly at the same temperature so heat needs to be transferred too.
What is the environment around the cells of the multicellular organism?
Tissue fluid.
How do size and metabolic rate affect the amount of material that is exchanged?
Organisms with high metabolic rate exchange more materials so require a larger SA:V ratio.
Who has a larger SA:V? Smaller or larger organisms?
Smaller organisms have higher SA:V ratio than larger organisms.
What are the features of exchange surfaces which allow effective transfer?
- Large SA in comparison to its volume to increase the rate of exchange.
- Very thin so diffusion distance is shortened and materials can exchange across rapidly.
- Selectively permeable to allow selected materials to cross.
- A concentration gradient must be obtained.
Use an equation to express the relationship between the factors that affect diffusion.
Diffusion = SA x Conc. difference/ Diffusion pathway.
What is the diffusion rate like for a single-celled organism?
- Substances can diffuse directly into or out of the cell across the cell surface membrane. The diffusion rate is quick because of the small distances the substance needs to travel.
What is the diffusion rate like for a multicellular organism?
The diffusion across the outer membrane is too slow:
- Some cells are deep within the body, there’s a big distance between them and the outside environment.
- Larger organisms have a low SA:V, so it’s difficult to exchange enough substances to supply a large volume animal through a relatively small outer surface.
What would happen to heat loss in a large and small organism?
A large organism would have a large volume and small SA, therefore, a smaller SA:V, heat loss will be harder.
A small organism has a smaller volume, and a higher surface area. Since there is a high surface area where heat exchange can happen, these organisms need to have higher metabolic rate to generate more heat for it to stay warm.
How does shape affect heat loss?
Different shapes mean different SA. Animals with a more compact shape would have a smaller SA so it does not need a high metabolic rate to minimise heat loss. Then an animal with less compact shape would have a larger SA so it needs a higher metabolic rate to maintain body temperature.
