3.1.2 Transport in animals
(a) the need for transport systems in multicellular animals
Transport systems
The need for an exchange system is affected by:
▪ size
▪ surface area to volume ratio
▪ activity levels
In small organisms, 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.
Small organisms have a large S.A: vol ratio so have a larger surface over which exchange can
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎
take place. Surface area: vol ratios are 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 nutrients and oxygen to supply cells for energy from
respiration for movement. Mammals that regulate their body temperature also need more
energy.
(b) the different types of circulatory systems
Features of an efficient exchange surface
- a fluid or medium to carry nutrients, oxygen and waste (blood)
- a pump to create pressure that will push the fluid around the body (heart)
- exchange surfaces that enable substances to enter and leave the blood (capillaries)
- tubes/ vessels to carry the blood by mass flow
- two circuits – one to pick up oxygen and another to deliver oxygen to tissues
Types of circulatory systems
Single circulatory system: Double circulatory system:
The blood flows through the heart once for The blood flows through the heart twice for each
each circuit of the body circuit of the body
Systemic Pulmonary
circulation circulation
Blood pressure drops as blood passes Blood pressure in pulmonary circulation cannot
through tiny capillaries of the gills be too high as it may damage delicate lung
capillaries
Blood has a low pressure as it flows towards Systemic circulation can carry blood at a higher
the body and will not flow quickly pressure than pulmonary circulation
Slow rate at which oxygen and nutrients are The heart can increase the blood pressure, so it is
delivered to respiring tissues, and CO2 and under higher pressure when it flows to the body
urea is removed and will flow to tissues more quickly
Fish are less metabolically active than Mammals are active and need to maintain body
mammals so single circulation supplies temperature so need a lot of energy i.e. fast supply
sufficient energy of oxygen and nutrients.
(a) the need for transport systems in multicellular animals
Transport systems
The need for an exchange system is affected by:
▪ size
▪ surface area to volume ratio
▪ activity levels
In small organisms, 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.
Small organisms have a large S.A: vol ratio so have a larger surface over which exchange can
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎
take place. Surface area: vol ratios are 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 nutrients and oxygen to supply cells for energy from
respiration for movement. Mammals that regulate their body temperature also need more
energy.
(b) the different types of circulatory systems
Features of an efficient exchange surface
- a fluid or medium to carry nutrients, oxygen and waste (blood)
- a pump to create pressure that will push the fluid around the body (heart)
- exchange surfaces that enable substances to enter and leave the blood (capillaries)
- tubes/ vessels to carry the blood by mass flow
- two circuits – one to pick up oxygen and another to deliver oxygen to tissues
Types of circulatory systems
Single circulatory system: Double circulatory system:
The blood flows through the heart once for The blood flows through the heart twice for each
each circuit of the body circuit of the body
Systemic Pulmonary
circulation circulation
Blood pressure drops as blood passes Blood pressure in pulmonary circulation cannot
through tiny capillaries of the gills be too high as it may damage delicate lung
capillaries
Blood has a low pressure as it flows towards Systemic circulation can carry blood at a higher
the body and will not flow quickly pressure than pulmonary circulation
Slow rate at which oxygen and nutrients are The heart can increase the blood pressure, so it is
delivered to respiring tissues, and CO2 and under higher pressure when it flows to the body
urea is removed and will flow to tissues more quickly
Fish are less metabolically active than Mammals are active and need to maintain body
mammals so single circulation supplies temperature so need a lot of energy i.e. fast supply
sufficient energy of oxygen and nutrients.
