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B8- Transport in animals
3.1.2 Transport in animals
(a) The need for transport systems in multicellular animals.
• Can’t rely on diffusion alone to move substances around the body.
• So transport systems are needed for: metabolic rate; SA:V ; size and transporting molecules.
• Metabolic demands are high so diffusion over long distances is not enough.
• SA:V gets smaller as organism gets bigger so the size of the SA available to absorb or remove
substances becomes relatively smaller.
• Molecules will be digested by one organ system and need to transported to every cell for
metabolic reactions so need a transport system to travel easily.
(b) The different types of circulatory systems.
Key words:
Mass transport systems- when substances are transported in a mass of fluid within a
mechanism for moving the fluid around the body.
Open circulatory system- a circulatory system with a heart but few vessels to contain the
transport medium.
Haemolymph- a fluid equivalent to blood in most invertebrates, occupying the hamocoel, which
doesn’t carry oxygen or carbon dioxide.
Hamocoel- open body cavity in most invertebrates containing haemolymph.
Ostia- pores which suck haemolymph blood back in, when heart relaxes.
Closed circulatory system- a circulatory system where the blood is enclosed in blood vessels
and doesn’t not come into direct contact with the cells of the body beyond the blood vessels.
Single circulatory system- a circulatory system where the blood flows through the heart and is
pumped out to travel around the body before returning to the heart.
Double circulatory system- a circulatory system where the blood travels twice through the heart
for each circulation of the body.
Common features of circulatory systems:
• Liquid transport medium.
• Vessels to carry the transport medium.
• Pumping mechanism to move fluid around the system.
Single closed circulatory system Double closed circulatory system
Description - Blood flows through the heart and is pumped out - Most efficient transport system.
to travel all around the body before returning to - Involves two separate circulations:
the heart, the blood travels only once through the - Blood pumped from the heart and is pumped out
heart for each complete circulation of the body. to travel all around the body before returning to
- Blood passes through two sets of capillaries the heart again.
before it returns to the heart. It exchanges oxygen - Blood travels twice through the heart for each
and carbon dioxide. In the second act of circuit of the body. Each circuit only passes
capillaries substances are exchanged between through one capillary network, which means a
the blood and cells. relatively high pressure and fast flow of blood can
- As a result of passing through these two sets of be maintained.
very narrow vessels, the blood pressure in the - More efficient because more oxygen is taken up
system drops considerably so blood returns to in a double system than a single as single
the heart quite slowly. contains both carbon dioxide and oxygen.
- Limits efficiency of the exchange processes so - Blood passes through a four-chambered heart
activity levels of animals tend to be low. twice in every circuit.
- Fish are an exception.
Advantages • Less complex, doesn’t require complex organs • Heart can pump blood further around the body
• Sufficient for less metabolically active animals, • Blood pressure can be increased after it has
who don’t maintain their body temperature so passed through the delicate capillaries of the
need less energy pulmonary circulation system
• High pressure
• Fast flow of blood
Disadvantages • Blood travels slowly • Complex, requires complex organs
• Less efficient so deliver nutrients more slowly
• Slower supply of oxygen
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Open circulatory system Closed circulatory system
Description - Few vessels - Blood is fully enclosed within vessels
- Comes in direct contact with tissues and cells - Doesn’t come in direct contact with tissues and
- Transport medium returns to the heart through an cells
open-ended vessel - Heart pumps blood around the body under
- Consists of a heart that pumps haemolymph pressure and relatively quickly, and blood returns
through short vessels into an open body cavity directly to the heart
(haemocoel) transports medium under low pressure - Substances leave and enter the blood by
- When heart relaxes, haemolymph blood is sucked diffusion through the walls of blood vessels
back in via pores called Ostia - Blood flowing to a particular tissue can be
adjusted by widening or narrowing blood vessels
- Contains a blood pigment that carries the
respiratory gases
Examples - Mainly found in invertebrates - Found invertebrate groups
- Arthropods/insects and molluscs - E.g. cephalopods and annelid worms
- Haemolymph transports food, nitrogenous waste
and cells involved in defence against disease, not
CO2 and O2
- Low pressure
- Body cavity is split by membrane
- Heart extends along the length of the thorax and
abdomen of the insect
- Haemolymph circulates but steep conc. gradient
can’t be maintained by diffusion
- Haemolymph flowing to tissue can’t vary to meet
demand
Advantages • Exchange of materials is direct between the • Fine-scale control over the distribution of blood to
haemolymph and tissues different body regions is possible
• There is no diffusion barrier • Muscular walls of vessels can constrict and dilate
to vary the amount of flow through specific
vessels
• Blood pressure are fairly high and the circulation
can be vigorous
Disadvantages • Little fine control over distribution of the • It is a more complex system
haemolymph to body regions • It requires more energy for blood distribution
• No mechanisms for reducing flow to a specific part
of an organ
(c) The structure and functions of arteries, arterioles, capillaries, venules and veins.
• Blood vessels are part of closed circulatory systems.
• Elastic fibres- are made of elastin. They stretch and recoil providing the vessels with flexibility.
• Smooth muscle- contracts and relaxes changing the size of the lumen.
• Collagen- provides structural support to maintain shape and volume of the vessel.
B8- Transport in animals
3.1.2 Transport in animals
(a) The need for transport systems in multicellular animals.
• Can’t rely on diffusion alone to move substances around the body.
• So transport systems are needed for: metabolic rate; SA:V ; size and transporting molecules.
• Metabolic demands are high so diffusion over long distances is not enough.
• SA:V gets smaller as organism gets bigger so the size of the SA available to absorb or remove
substances becomes relatively smaller.
• Molecules will be digested by one organ system and need to transported to every cell for
metabolic reactions so need a transport system to travel easily.
(b) The different types of circulatory systems.
Key words:
Mass transport systems- when substances are transported in a mass of fluid within a
mechanism for moving the fluid around the body.
Open circulatory system- a circulatory system with a heart but few vessels to contain the
transport medium.
Haemolymph- a fluid equivalent to blood in most invertebrates, occupying the hamocoel, which
doesn’t carry oxygen or carbon dioxide.
Hamocoel- open body cavity in most invertebrates containing haemolymph.
Ostia- pores which suck haemolymph blood back in, when heart relaxes.
Closed circulatory system- a circulatory system where the blood is enclosed in blood vessels
and doesn’t not come into direct contact with the cells of the body beyond the blood vessels.
Single circulatory system- a circulatory system where the blood flows through the heart and is
pumped out to travel around the body before returning to the heart.
Double circulatory system- a circulatory system where the blood travels twice through the heart
for each circulation of the body.
Common features of circulatory systems:
• Liquid transport medium.
• Vessels to carry the transport medium.
• Pumping mechanism to move fluid around the system.
Single closed circulatory system Double closed circulatory system
Description - Blood flows through the heart and is pumped out - Most efficient transport system.
to travel all around the body before returning to - Involves two separate circulations:
the heart, the blood travels only once through the - Blood pumped from the heart and is pumped out
heart for each complete circulation of the body. to travel all around the body before returning to
- Blood passes through two sets of capillaries the heart again.
before it returns to the heart. It exchanges oxygen - Blood travels twice through the heart for each
and carbon dioxide. In the second act of circuit of the body. Each circuit only passes
capillaries substances are exchanged between through one capillary network, which means a
the blood and cells. relatively high pressure and fast flow of blood can
- As a result of passing through these two sets of be maintained.
very narrow vessels, the blood pressure in the - More efficient because more oxygen is taken up
system drops considerably so blood returns to in a double system than a single as single
the heart quite slowly. contains both carbon dioxide and oxygen.
- Limits efficiency of the exchange processes so - Blood passes through a four-chambered heart
activity levels of animals tend to be low. twice in every circuit.
- Fish are an exception.
Advantages • Less complex, doesn’t require complex organs • Heart can pump blood further around the body
• Sufficient for less metabolically active animals, • Blood pressure can be increased after it has
who don’t maintain their body temperature so passed through the delicate capillaries of the
need less energy pulmonary circulation system
• High pressure
• Fast flow of blood
Disadvantages • Blood travels slowly • Complex, requires complex organs
• Less efficient so deliver nutrients more slowly
• Slower supply of oxygen
, 2 of 14
Open circulatory system Closed circulatory system
Description - Few vessels - Blood is fully enclosed within vessels
- Comes in direct contact with tissues and cells - Doesn’t come in direct contact with tissues and
- Transport medium returns to the heart through an cells
open-ended vessel - Heart pumps blood around the body under
- Consists of a heart that pumps haemolymph pressure and relatively quickly, and blood returns
through short vessels into an open body cavity directly to the heart
(haemocoel) transports medium under low pressure - Substances leave and enter the blood by
- When heart relaxes, haemolymph blood is sucked diffusion through the walls of blood vessels
back in via pores called Ostia - Blood flowing to a particular tissue can be
adjusted by widening or narrowing blood vessels
- Contains a blood pigment that carries the
respiratory gases
Examples - Mainly found in invertebrates - Found invertebrate groups
- Arthropods/insects and molluscs - E.g. cephalopods and annelid worms
- Haemolymph transports food, nitrogenous waste
and cells involved in defence against disease, not
CO2 and O2
- Low pressure
- Body cavity is split by membrane
- Heart extends along the length of the thorax and
abdomen of the insect
- Haemolymph circulates but steep conc. gradient
can’t be maintained by diffusion
- Haemolymph flowing to tissue can’t vary to meet
demand
Advantages • Exchange of materials is direct between the • Fine-scale control over the distribution of blood to
haemolymph and tissues different body regions is possible
• There is no diffusion barrier • Muscular walls of vessels can constrict and dilate
to vary the amount of flow through specific
vessels
• Blood pressure are fairly high and the circulation
can be vigorous
Disadvantages • Little fine control over distribution of the • It is a more complex system
haemolymph to body regions • It requires more energy for blood distribution
• No mechanisms for reducing flow to a specific part
of an organ
(c) The structure and functions of arteries, arterioles, capillaries, venules and veins.
• Blood vessels are part of closed circulatory systems.
• Elastic fibres- are made of elastin. They stretch and recoil providing the vessels with flexibility.
• Smooth muscle- contracts and relaxes changing the size of the lumen.
• Collagen- provides structural support to maintain shape and volume of the vessel.
