TRANSPORT IN ANIMALS
(a) The need for transport systems in multicellular animals
● To include an appreciation of size, metabolic rate and surface area to volume
ratio (SA:V).
There a three main factors dictate the need for a specialised transport system in
multicellular organisms: their size, level of metabolic activity and the surface area to
volume ratio. As organisms get larger, the cells inside it are further from the
surface,and the diffusion pathway become too large to supply cells with all the
requirements, because it is too slow and cells use up the molecules diffusing early
on. Multicellular organisms are also very metabolically active and animals need to get
their energy from food. Animals also need to maintain their body temperature. Larger
organisms also have a larger surface area to volume ratio, so there is less area for
exchange in relation to their volume, so transport systems are needed to supply the
whole mass with sufficient nutrients.
(b) The different types of circulatory systems
● To include single, double, open and closed circulatory systems in insects, fish
and mammals.
Single
Fish have a single circulatory system. The blood flows through the heart once for
each circuit of the body, from the heart to the gills, to the body and then back to the
heart.
In the single circulatory system of a fish, the blood pressure drops as blood
passes through the tiny capillaries of the gills and as a result blood has a low
pressure as it flows through the body, and will not flow very rapidly. Consequently,
the rate at which oxygen and nutrients are delivered to respiring tissues, and carbon
dioxide and urea are removed, is limited. These are quite obvious limitations, but fish
are not as metabolically active as mammals, and they do not have to maintain their
own body temperature, so they need less energy and their single circulatory system
supplies sufficient oxygen and nutrients for their needs.
Double
Mammals have a double circulatory system. The system has two separate circuits.
One circuit carries blood to the lungs to pick up oxygen (the pulmonary circulation)
and one carried oxygen and nutrients around the body (the systemic circuit). Blood
flows through the heart twice each circuit, going heart body, heart lungs, heart.
In the double circulatory systems of mammals, the blood pressure must not be
too high in the pulmonary circulation, otherwise it may damage the delicate capillaries
in alveoli. The heart can increase the pressure of blood after it has passed through
the lungs, so the blood is under higher pressure as it flows to the body and flows
more quickly because the systemic circuit can carry blood at a higher pressure than
the pulmonary circuit. Mammals are active animals and maintain their body
(a) The need for transport systems in multicellular animals
● To include an appreciation of size, metabolic rate and surface area to volume
ratio (SA:V).
There a three main factors dictate the need for a specialised transport system in
multicellular organisms: their size, level of metabolic activity and the surface area to
volume ratio. As organisms get larger, the cells inside it are further from the
surface,and the diffusion pathway become too large to supply cells with all the
requirements, because it is too slow and cells use up the molecules diffusing early
on. Multicellular organisms are also very metabolically active and animals need to get
their energy from food. Animals also need to maintain their body temperature. Larger
organisms also have a larger surface area to volume ratio, so there is less area for
exchange in relation to their volume, so transport systems are needed to supply the
whole mass with sufficient nutrients.
(b) The different types of circulatory systems
● To include single, double, open and closed circulatory systems in insects, fish
and mammals.
Single
Fish have a single circulatory system. The blood flows through the heart once for
each circuit of the body, from the heart to the gills, to the body and then back to the
heart.
In the single circulatory system of a fish, the blood pressure drops as blood
passes through the tiny capillaries of the gills and as a result blood has a low
pressure as it flows through the body, and will not flow very rapidly. Consequently,
the rate at which oxygen and nutrients are delivered to respiring tissues, and carbon
dioxide and urea are removed, is limited. These are quite obvious limitations, but fish
are not as metabolically active as mammals, and they do not have to maintain their
own body temperature, so they need less energy and their single circulatory system
supplies sufficient oxygen and nutrients for their needs.
Double
Mammals have a double circulatory system. The system has two separate circuits.
One circuit carries blood to the lungs to pick up oxygen (the pulmonary circulation)
and one carried oxygen and nutrients around the body (the systemic circuit). Blood
flows through the heart twice each circuit, going heart body, heart lungs, heart.
In the double circulatory systems of mammals, the blood pressure must not be
too high in the pulmonary circulation, otherwise it may damage the delicate capillaries
in alveoli. The heart can increase the pressure of blood after it has passed through
the lungs, so the blood is under higher pressure as it flows to the body and flows
more quickly because the systemic circuit can carry blood at a higher pressure than
the pulmonary circuit. Mammals are active animals and maintain their body
