Module 3 – Exchange and transport
3.1.1 Exchange surfaces
(a) the need for specialised exchange surfaces
Exchange systems
The need for an exchange system is affected by:
size
surface area to volume ratio
activity levels
In very small organisms, exchange of oxygen, nutrients and waste products can happen over the
surface of their body as they have a large SA:Vol ratio. This means the cytoplasm of their cells is
very close to the environment, so diffusion will supply enough oxygen and nutrients to keep
them alive. Large organisms have multiple layers of cells, so the diffusion pathway is too long –
diffusion is too slow to enable a sufficient supply to inner cells. Surface area: volume ratios are
Surface Area
always expressed as a ratio of x:1. Ratio=
Volume
Metabolic activity uses energy from food and requires oxygen to release the energy in aerobic
respiration. Active organisms need more oxygen to supply cells for energy from respiration for
movement. Mammals that regulate their body temperature also need more energy.
(b) the features of an efficient exchange surface
Features of an efficient exchange surface
Surface area
Large surface area allows more molecules to pass through per second
Achieved by folding membranes
E.g. root hair cells
Thin walls
A thin barrier reduces the diffusion distance for molecules
Cell walls just one cell thick
E.g. alveoli walls
Blood supply
Supplies the surface with new molecules or removes waste molecules
Maintains steep concentration gradient to increase diffusion rate
E.g. fish gills
(c) the structures and functions of the components of the mammalian
gaseous exchange system
Trachea: the main airway leading from the back of
the mouth to the lungs
Bronchi and bronchioles: smaller airways leading
into the lungs
Intercostal muscles: muscles between the rubs.
Contraction of the external intercostal muscles
raises the ribcage.
Diaphragm: a layer of muscle beneath the lungs
Alveoli: tiny folds of the lung epithelium to increase
surface area
3.1.1 Exchange surfaces
(a) the need for specialised exchange surfaces
Exchange systems
The need for an exchange system is affected by:
size
surface area to volume ratio
activity levels
In very small organisms, exchange of oxygen, nutrients and waste products can happen over the
surface of their body as they have a large SA:Vol ratio. This means the cytoplasm of their cells is
very close to the environment, so diffusion will supply enough oxygen and nutrients to keep
them alive. Large organisms have multiple layers of cells, so the diffusion pathway is too long –
diffusion is too slow to enable a sufficient supply to inner cells. Surface area: volume ratios are
Surface Area
always expressed as a ratio of x:1. Ratio=
Volume
Metabolic activity uses energy from food and requires oxygen to release the energy in aerobic
respiration. Active organisms need more oxygen to supply cells for energy from respiration for
movement. Mammals that regulate their body temperature also need more energy.
(b) the features of an efficient exchange surface
Features of an efficient exchange surface
Surface area
Large surface area allows more molecules to pass through per second
Achieved by folding membranes
E.g. root hair cells
Thin walls
A thin barrier reduces the diffusion distance for molecules
Cell walls just one cell thick
E.g. alveoli walls
Blood supply
Supplies the surface with new molecules or removes waste molecules
Maintains steep concentration gradient to increase diffusion rate
E.g. fish gills
(c) the structures and functions of the components of the mammalian
gaseous exchange system
Trachea: the main airway leading from the back of
the mouth to the lungs
Bronchi and bronchioles: smaller airways leading
into the lungs
Intercostal muscles: muscles between the rubs.
Contraction of the external intercostal muscles
raises the ribcage.
Diaphragm: a layer of muscle beneath the lungs
Alveoli: tiny folds of the lung epithelium to increase
surface area
