3.2 Transport in Animals
Humans need to exchange oxygen, carbon dioxide, glucose, urea, and 'nutrients'
between themselves and the environment in order to survive.
Surface area to volume ratio
Single-celled organisms, e.g. bacteria and amoeba, can obtain nutrients and excrete
waste simply by diffusion (large SA:V ratio).
In larger organisms, diffusion of substances would occur far too slowly to enable them
to survive (small SA:V ratio). They have specialised gas exchange surfaces and
transport systems.
SA/V
Larger organisms have larger surface area, but larger volume. As size increases,
volume rises more quickly than surface area.
Effective transport systems
Effective transport systems:
- Ensure substances move in correct direction.
- Move materials fast enough to supply needs of organism.
- Contain suitable transport medium.
- Have exchange surfaces to enable substances to enter and leave blood.
- Have system of vessels that carry substances by mass flow.
- Have two circuits: one to pick up oxygen, one to deliver oxygen to tissues.
Multi-cellular animals have specialised circulatory systems, comprising of:
- A heart
- A fluid in which substances are transported
- Vessels through which the fluid can flow
The two types of circulatory system are open and closed.
Open Circulatory Systems
Open circulatory system consists of a heart that pumps fluid called haemolymph
through short vessels and into large cavity called haemocoel.
In haemocoel, haemolymph directly bathes organs and tissues, enabling diffusion
of substances.
When heart relaxes, haemolymph blood sucked back in via pores called ostia.
Heartbeat and movement of organism moves haemolymph around haemocoel.
Circulation and O2 transport is slower.
Closed Circulatory Systems
In closed circulatory system, blood fully enclosed within blood vessels at all times.
From heart, blood pumped through series of progressively smaller vessels. In
capillaries (smallest), substances diffuse in and out of blood and into cells.
Blood then returns to heart via a series of progressively larger vessels.
Single
E.g. fish. Blood passes through two-chambered heart once in every complete circuit
of body.
Double
E.g. birds and mammals. Blood passes through four-chambered heart twice in every
complete circuit of body.
The systematic circulation consists of all vessels involved in transporting blood
between heart and body, excluding lungs.
The pulmonary circulation consists of all vessels involved in transporting blood
between heart and lungs.
Module 3 - Exchange and transport Page 1
, Double circulatory system has many advantages over single circulatory system:
- Delivers oxygen and nutrients more quickly to parts of body where needed
- Blood can be made to flow more quickly by increasing blood pressure from
heart
- Necessary for larger organisms, as a single circulatory system would not give
high enough pressure for blood to circulate around entire body
Journey of blood through systematic & pulmonary circulations
1. Pulmonary vein brings oxygenated blood to heart
2. Oxygenated blood leaves heart to rest of body via aorta (artery)
3. Blood flows into arteriole
4. Blood flows into capillaries - diffusion of substances
5. Deoxygenated blood flows into venules and into veins
6. Deoxygenated blood flows into heart via vena cava
7. Deoxygenated blood carried to lungs to become oxygenated via pulmonary
artery
Artery → arteriole → capillaries → venule → vein
Arteriole - in between artery and capillaries - lower pressure. High pressure would
damage capillaries.
Venule - increase in size.
Artery
Carries blood away from heart. Artery wall must be thick to withstand blood travelling
at high pressure.
Lumen - relatively small to maintain high pressure, and inner wall folded to allow
lumen to expand as blood flow increases.
Three layers:
- Inner layer (tunica intima) consists of thin layer of elastic tissue to allow wall to
stretch and recoil to help maintain blood pressure.
- Middle layer (tunica media) consists of thick layer of smooth muscle.
- Outer layer (tunica adventitia) is relatively thick layer of collagen and elastic
tissue. Provides strength to withstand high pressure, and recoil to maintain
pressure.
Vein
Carries blood back to heart. Walls do not need to be thick as blood at low pressure.
Lumen - relatively large, in order to ease flow of blood.
Walls have thinner layers of collagen, smooth muscle, and elastic tissue than in artery
walls, as do not need to stretch and recoil, and are not actively constricted to reduce
blood flow.
Contain valves to prevent backflow of blood. As walls are thin, vein can be flattened by
action of surrounding skeletal muscle. Contraction of skeletal muscle applies pressure
to blood, forcing it to move along in direction determined by valves.
Module 3 - Exchange and transport Page 2
Humans need to exchange oxygen, carbon dioxide, glucose, urea, and 'nutrients'
between themselves and the environment in order to survive.
Surface area to volume ratio
Single-celled organisms, e.g. bacteria and amoeba, can obtain nutrients and excrete
waste simply by diffusion (large SA:V ratio).
In larger organisms, diffusion of substances would occur far too slowly to enable them
to survive (small SA:V ratio). They have specialised gas exchange surfaces and
transport systems.
SA/V
Larger organisms have larger surface area, but larger volume. As size increases,
volume rises more quickly than surface area.
Effective transport systems
Effective transport systems:
- Ensure substances move in correct direction.
- Move materials fast enough to supply needs of organism.
- Contain suitable transport medium.
- Have exchange surfaces to enable substances to enter and leave blood.
- Have system of vessels that carry substances by mass flow.
- Have two circuits: one to pick up oxygen, one to deliver oxygen to tissues.
Multi-cellular animals have specialised circulatory systems, comprising of:
- A heart
- A fluid in which substances are transported
- Vessels through which the fluid can flow
The two types of circulatory system are open and closed.
Open Circulatory Systems
Open circulatory system consists of a heart that pumps fluid called haemolymph
through short vessels and into large cavity called haemocoel.
In haemocoel, haemolymph directly bathes organs and tissues, enabling diffusion
of substances.
When heart relaxes, haemolymph blood sucked back in via pores called ostia.
Heartbeat and movement of organism moves haemolymph around haemocoel.
Circulation and O2 transport is slower.
Closed Circulatory Systems
In closed circulatory system, blood fully enclosed within blood vessels at all times.
From heart, blood pumped through series of progressively smaller vessels. In
capillaries (smallest), substances diffuse in and out of blood and into cells.
Blood then returns to heart via a series of progressively larger vessels.
Single
E.g. fish. Blood passes through two-chambered heart once in every complete circuit
of body.
Double
E.g. birds and mammals. Blood passes through four-chambered heart twice in every
complete circuit of body.
The systematic circulation consists of all vessels involved in transporting blood
between heart and body, excluding lungs.
The pulmonary circulation consists of all vessels involved in transporting blood
between heart and lungs.
Module 3 - Exchange and transport Page 1
, Double circulatory system has many advantages over single circulatory system:
- Delivers oxygen and nutrients more quickly to parts of body where needed
- Blood can be made to flow more quickly by increasing blood pressure from
heart
- Necessary for larger organisms, as a single circulatory system would not give
high enough pressure for blood to circulate around entire body
Journey of blood through systematic & pulmonary circulations
1. Pulmonary vein brings oxygenated blood to heart
2. Oxygenated blood leaves heart to rest of body via aorta (artery)
3. Blood flows into arteriole
4. Blood flows into capillaries - diffusion of substances
5. Deoxygenated blood flows into venules and into veins
6. Deoxygenated blood flows into heart via vena cava
7. Deoxygenated blood carried to lungs to become oxygenated via pulmonary
artery
Artery → arteriole → capillaries → venule → vein
Arteriole - in between artery and capillaries - lower pressure. High pressure would
damage capillaries.
Venule - increase in size.
Artery
Carries blood away from heart. Artery wall must be thick to withstand blood travelling
at high pressure.
Lumen - relatively small to maintain high pressure, and inner wall folded to allow
lumen to expand as blood flow increases.
Three layers:
- Inner layer (tunica intima) consists of thin layer of elastic tissue to allow wall to
stretch and recoil to help maintain blood pressure.
- Middle layer (tunica media) consists of thick layer of smooth muscle.
- Outer layer (tunica adventitia) is relatively thick layer of collagen and elastic
tissue. Provides strength to withstand high pressure, and recoil to maintain
pressure.
Vein
Carries blood back to heart. Walls do not need to be thick as blood at low pressure.
Lumen - relatively large, in order to ease flow of blood.
Walls have thinner layers of collagen, smooth muscle, and elastic tissue than in artery
walls, as do not need to stretch and recoil, and are not actively constricted to reduce
blood flow.
Contain valves to prevent backflow of blood. As walls are thin, vein can be flattened by
action of surrounding skeletal muscle. Contraction of skeletal muscle applies pressure
to blood, forcing it to move along in direction determined by valves.
Module 3 - Exchange and transport Page 2
