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2.3 Adaptations for transport
Structures of transport systems
1. Multicellular animals have a transport system.
Movement of oxygen by diffusion alone would be a very slow process. An internal
transport system provides a rapid means of transport to multicellular organisms.
Transport systems carry oxygen, nutrients, carbon dioxide and waste products to and
from the exchange surfaces.
Most transport systems consist of:
a pumping or contractile device to propel the fluid around the body, e.g. heart
circulatory fluid, typically containing a respiratory pigment
vessels which transport the fluid.
2. Insects have an open circulatory system, with a dorsal tubeshaped heart, and a fluidfilled body
In an open blood system blood is pumped at low pressure
from the dorsal heart, which runs the length of the body, into
The blood bathes the tissues directly and exchange of
materials takes place there is little control over the direction.
Blood returns very slowly to the heart.
The blood is moved to the head region by valves and waves of contractions from
muscles. There is no respiratory pigment oxygen is delivered directly to tissues via the
3. The earthworm has a closed circulatory system, with blood under pressure. Organs are not in direct
contact with the blood. Respiratory gases are transported
Blood is under high pressure as it
pumped by a muscular heart
exchange occurs via tissue fluid
the earthworm has dorsal and ventral
vessels and five pseudo hearts.
4. Mammals have a circulatory system comprising
closed, double circulation and a heart with two atria
and two ventricles.
closed systems can either have single or or double circulation
fish have single circulation: blood goes through the heart once during one circulation
mammals have double circulation :
The pulmonary circuit: the right side of the heart pumps deoxygenated blood to the
lungs which the returns to the left side of the heart
the systemic circuit: the left side of the heart pumps oxygenated blood to the tissues
deoxygenated blood then returns to the right side of the heart
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The major blood vessels of the heart include: aorta, vena cava, pulmonary veins, pulmonary arteries,
blood vessels form a network of tubes which carry blood throughout the body.
6. The heart is a specialised organ having: cardiac muscle, own blood supply, variation in thickness of
valves control the flow and vessels distribute the blood.
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Their pressure depends on whether
they are dilated or contracted. As the blood enters the capillaries, they have a large
crosssectional area and this prevents a resistance to
flow and pressure also drops due to leakage from the capillaries into tissues.
11. Capillaries have a small diameter and friction with the walls slows the blood flow. Although the
diameter is small, there are many capillaries in the capillary bed, providing a large total crosssectional
area which further reduces blood flow.…read more