Exchange Surfaces
Factors affecting the amount of each material exchanged:
- Metabolic rate
- Size
Organisms with a high metabolic rate exchange more materials so they
require a large surface area to volume ratio.
These exchanges can happen:
- Passively- by diffusion or osmosis
- Actively- by active transport
Small organisms have a large SA:V and lose heat more easily because of this,
large organisms have a small SA:V lose heat less easily.
Organisms have evolved either a:
- Flattened and small shape, so that no cell is ever far from the surface
and diffusion of materials such as oxygen through the surface is enough
as it can reach every cell without a specialized exchange surface, they
have a large SA:V so diffusion is enough
- Specialized exchange surface with large areas to increase the SA:V.
Features of specialised exchange surfaces:
- A large SA relative to the V of the organism to increase the rate of
exchange
- Very thin so that the diffusion distance is short so materials can diffuse
quickly
- Selectively permeable to allow selected materials to cross
- Movement of the environmental medium, e.g. air, to maintain a
diffusion gradient
- A transport system to ensure the movement of the internal medium, e.g.
blood, to maintain a diffusion gradient.
Gas exchange in single celled organisms
- Single celled organisms are microscopic organisms made of one single
cell, they respire and move etc. they all live in water.
- They can’t be bigger otherwise their SA:V ratio would decrease, and
their cell surface membrane wouldn’t be able to supply enough
substance for the amount of volume they would be, so because they’re
single celled they have a large SA:V.
- They can be prokaryotic, eukaryotic, some fungi and algae.
, - Examples of single celled organisms are yeast, protozoa, algae, amoeba
and bacteria.
- They obtain oxygen by diffusion using their cell surface membrane
(there will always be a lower concentration of oxygen inside the cell
because they’re constantly using it up in respiration).
- They all live in water because in order for diffusion to happen into cells
and be efficient, the state of matter has to be the same both inside and
outside the cell. If they didn’t live in water their cell surface membrane
would dry out and diffusion can’t happen.
Adaptions:
- Thin- so they have a large surface area to volume ratio
- Flat body- so short distance for diffusion
Factors affecting the amount of each material exchanged:
- Metabolic rate
- Size
Organisms with a high metabolic rate exchange more materials so they
require a large surface area to volume ratio.
These exchanges can happen:
- Passively- by diffusion or osmosis
- Actively- by active transport
Small organisms have a large SA:V and lose heat more easily because of this,
large organisms have a small SA:V lose heat less easily.
Organisms have evolved either a:
- Flattened and small shape, so that no cell is ever far from the surface
and diffusion of materials such as oxygen through the surface is enough
as it can reach every cell without a specialized exchange surface, they
have a large SA:V so diffusion is enough
- Specialized exchange surface with large areas to increase the SA:V.
Features of specialised exchange surfaces:
- A large SA relative to the V of the organism to increase the rate of
exchange
- Very thin so that the diffusion distance is short so materials can diffuse
quickly
- Selectively permeable to allow selected materials to cross
- Movement of the environmental medium, e.g. air, to maintain a
diffusion gradient
- A transport system to ensure the movement of the internal medium, e.g.
blood, to maintain a diffusion gradient.
Gas exchange in single celled organisms
- Single celled organisms are microscopic organisms made of one single
cell, they respire and move etc. they all live in water.
- They can’t be bigger otherwise their SA:V ratio would decrease, and
their cell surface membrane wouldn’t be able to supply enough
substance for the amount of volume they would be, so because they’re
single celled they have a large SA:V.
- They can be prokaryotic, eukaryotic, some fungi and algae.
, - Examples of single celled organisms are yeast, protozoa, algae, amoeba
and bacteria.
- They obtain oxygen by diffusion using their cell surface membrane
(there will always be a lower concentration of oxygen inside the cell
because they’re constantly using it up in respiration).
- They all live in water because in order for diffusion to happen into cells
and be efficient, the state of matter has to be the same both inside and
outside the cell. If they didn’t live in water their cell surface membrane
would dry out and diffusion can’t happen.
Adaptions:
- Thin- so they have a large surface area to volume ratio
- Flat body- so short distance for diffusion
