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A level Biology Circulatory System FULL A/A* SUMMARY notes

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Unit 3

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OCR

A level Biology Circulatory System FULL A/A* SUMMARY notes. Cheap and affordable notes. Easy to understand. Heart, circulation in animals and humans. Suitable for IB, GCSE, A-levels, Cambridge. Exam boards AQA, OCR A, OCR B, Eduqas, Cambridge, Edexcel. Notes typed by an A/A* student. Suitable for e...

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circulatory
system
heart
transport
transport in animals
animals
exchange
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circulatory system
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Unit
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3.2.1: Transport in animals
Difference between exchange surface and transport system
- Exchange surface: a surface through which exchange of substances can occur,
e.g. capillaries
- Transport system: a means by which substances can be transported around the
body, e.g. through blood.
What influences the need for transport system = what influences the need for
exchange surface (see topic 3.1)

- size of organism: increased diffusion distance, simple diffusion can’t happen
- SA:V ratio: smaller ratio will need a transport system as simple diffusion isn’t
sufficient
- level of metabolic activity = more active organisms need more oxygen and
nutrients

Features of a good transport system

- a medium to carry nutrients, oxygen and wastes around the body  blood
- a pump to create pressure for pushing the medium around the body  heart
- exchange surfaces that enable substances to enter and leave the blood when
needed  capillaries
- tubes/vessels to carry blood by mass flow (veins and arteries)
- two circuits – one to pick up oxygen and one to deliver it to tissues

Single and double circulatory systems:

Fish: single circulatory system:

Blood flows through heart 1x for each circuit around the body.

 gills  body 

Mammals: double circulatory system:

Blood flows through heart 2x for each circuit around the body.

 body   lungs 

Advantages of double circulation

In single circulation in fish:

blood pressure blood has low slow rate of
drops as it passes pressure so flows transport to
through tiny slowly towards the body
capillaries in gills body

Fish are less metabolically active than mammals because they don’t maintain body
temp. Thus, single circulation provides sufficient energy.

In double circulation in mammals:

blood pressure in after pulmonary
pulmonary circulation faster rate of
circulation, blood
can’t be too high as it transport to
pressure in systemic
may damage delicate body
circulation can
capillaries in lungs increase and move

, Mammals are more active and need to maintain body temp. The energy needed for this
is released by food during respiration. Cells therefore need a good supply of nutrients
and oxygen, as well as the removal of waste products. This is supplied by the double
circulation which transports faster.

3.2.2: Blood vessels
Open circulatory systems
 In most animals, including insects.
 Blood isn’t held within blood vessels.
 It circulates through the body cavity so that tissues and cells bathed directly in blood.

 In some animals, movement makes blood circulate. No movement = no oxygen and
nutrients transported.
 In other animals, e.g. insects, there is a muscular pumping organ, much like a heart.
This is a long, muscular tube that lies just under the dorsal surface of the body.
 Blood from the body enters the heart through pores called ostia.
 The heart then pumps blood towards the head by peristalsis.
 At the forward end of the heart (nearest the head), the blood simply pours out
into the body cavity.
 Circulation can continue when the insect is at rest, but body movements can still
affect it.
 Larger and more active insects, like locusts, have open-ended tubes attached to the
heart. These direct the blood towards active parts of the body like leg and wing
muscles.

 Have disadvantages:
 low blood pressure therefore flow is slow
 circulation affected by body movements/lack of body movements

Closed circulatory systems
 In larger animals
 When blood stays entirely inside vessels
 Separate fluid (tissue fluid) is what bathes the tissues and cells

 Have advantages over open circulatory systems:
 high blood pressure therefore quicker flow
 rapid delivery of O2 and nutrients, rapid removal of CO2
and wastes
 transport is independent of body movements

Blood vessels
All blood vessels have an inner lining made of a single layer of
cells, called the endothelium. It is smooth to reduce friction.

Arteries
 carry blood away from heart
 thick walls to withstand high pressure
 small lumen to maintain pressure
 folded inner wall to allow lumen to expand as flow increases

The wall has 3 layers:

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