OCR AS level transport in animals notes

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Unit 1 Section 5: Transport in Animals
The Ciculatory System
Be able to explain the need for transport systems in multicellular animals in terms of
size, level of activity and surface area : volume ratio.
Be able to explain the meaning of the terms 'single circulatory system' and 'double
circulatory system', with reference to the circulatory systems of fish and mammals.
Be able to explain the meaning of the terms 'closed circulatory system' and 'open
circulatory system', with reference to the circulatory systems of fish and insects.
The need for transport systems in organisms - Why do large organisms need a transport
system?
In small organisms, exchange takes place satisfactorily over the surface of the body. With
increasing size, however, the surface area to volume ratio decreases to a point where the needs
of the organism cannot be met. A specialist exchange surface is therefore needed to absorb
nutrients and respiratory gases and to remove excretory products. These exchange surfaces are
located in specific regions of the organism. A transport system is required to take materials
from the cells that need them or produce them to or from the exchange surfaces that absorb
or remove them. However, not only do materials have to be transported between those organs
and the environment, they also need to be transported between different parts of the
organism. As organisms have evolved into larger and more complex structures, the tissues and
organs of which they are made have become more specialised and dependent upon one
another, making a transport system all the more essential. Whether or not there is a specialised
transport medium, and whether or not it is circulated by a pump, depends on two factors - the
surface area to volume ratio and how active the organism is. The lower the surface area to
volume ratio, and the more active the organism, the greater is the need for a specialised
transport system with a pump.
A lot of multicellular organisms are also very active. This means that a large number of cells are
all respiring very quickly, so they need a constant, rapid supply of glucose and oxygen.
In mammals the transport system it is the circulatory system, which uses blood to carry
glucose and oxygen around the body. It also carries hormones, antibodies and waste.
Single and double circulatory systems

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The human circulation system is a double circulatory system. One part serves the lungs, and this
is called pulmonary circulation. The other part serves the rest of the body, and is called the
systemic circulation.
Fish, however, have a single circulatory system. Here the blood is pumped out of the heart to
the gills where it picks up oxygen. But, instead of going back to the heart, the blood continues
on around the body.…read more

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Structure of the cardiac muscle
The outer and inner layers of the heart are made up of epithelial cells and connective tissue.
Myocardium comprises of cardiac muscle which can contract and relax for a long time without
fatigue. It is made up of actin and myosin. Cardiac muscle is made up of short fibres. Where
these meet end to end, there are distinct dark bands called intercalated discs.…read more

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The pulmonary vein is connected to the left atrium and brings oxygenated blood back
from the lungs. Unusually for a vein it carries oxygenated blood.
Supplying the cardiac muscle with oxygen
The heart muscle is supplied by its own blood vessels called coronary arteries, which branch off
the aorta shortly after it leaves the heart. Blockage of these arteries, e.g.…read more

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The cardiac cycle
ESSENTIAL AS BIOLOGY PAGE 130-133
Blood vessels
Arteries carry blood away from the heart. Blood has a high pressure as it is pushed out
of the heart, so arteries carry blood at high pressure. Their walls are thick and muscular
and have elastic tissue to cope with the high pressure produced by the heartbeat. The
inner lining (endothelium) is folded, allowing the artery to expand ­ this also helps to
cope with high pressure.…read more

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Smooth muscle in Relatively large amount in Small amount. All blood None
wall small arteries and in veins is travelling back
arterioles. Contraction of to the heart, so there is
this muscle reduces the no advantage in being
size of the lumen, which able to divert it into
can divert blood from tissues.
one area to another.
Thickness of wall Relatively thick. Artery Relatively thin. The blood One cell thick.…read more

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Red blood cells
Erythrocytes are biconcave discs. Around 78µm in diameter, there are 5 million in each mm3 of
blood and each lives for around 120 days.
Made in the bone marrow.
Red blood cells have no nucleus, mitochondria, rough endoplasmic reticulum or Golgi apparatus
when mature ­ although it gives them a shorter life-span, it makes them more efficient at their
job.…read more

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Blood pumped by the heart passes along arteries, arterioles and the capillaries. This creates
hydrostatic pressure of around 4.8 kPa at the arterial end of the capillaries, which tends to force
liquid out of the blood. The outward pressure is opposed by two forces:
Hydrostatic pressure of the tissue fluid outside the capillaries which prevents outward
movement of liquid
Osmotic forces due to the plasma proteins, which tend to pull water back into the
capillaries.…read more

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Enlargement of the thorax during breathing in reduces pressure in the thorax, drawing
lymph into this region and away from the tissues.…read more

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The walls of the alveoli are made of two types of cell:
Type I pneumocytes ­ squamous epithelial cells
Type II pneumocytes ­ special type of epithelial cell which produces a chemical called
surfactant
Surfactants reduce the surface tension of substances, most commonly water. They are best
known for their role in detergents. As you are probably aware, detergents such as washing up
liquid make things less sticky and more slippery.…read more

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