AQA AS Biology Unit 2: Circulatory System of a Mammal

HideShow resource information
  • Created by: LucySPG
  • Created on: 22-08-13 17:10
Preview of AQA AS Biology Unit 2: Circulatory System of a Mammal

First 239 words of the document:

Circulatory System of a Mammal
Why large organisms need a transport system
All organisms need to exchange materials between themselves and the
As an organism gets bigger, the surface area to volume ratio decreases to a point where
the needs of the organism cannot be met by the body surface alone.
A specialist gas exchange surface is therefore needed to:
Absorb nutrients and respiratory gases
Remove excretory products
These exchange surfaces are located in specific regions of the organism.
A transport system is required to:
Take materials from cells to exchange surfaces
From exchange surfaces to cells.
Materials have to be transported:
between exchange surfaces and the environment
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.
This makes 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
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.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Features of Transport Systems
Any large organism encounters the same problems in transporting materials within itself.
The transport systems of many organisms have common features:
A suitable medium in which to carry E.g.…read more

Page 3

Preview of page 3

Here's a taster:

Transport Systems in Mammals
Mammals have a low surface area to volume ratio, so they need a specialised
transport system to carry materials from the specialised exchange organs to their body
The system is closed and blood is contained in the vessels.
A muscular pump called the heart circulates the blood around the body.
Mammals have a double circulatory system because the blood passes twice through
the heart for each complete circuit of the body.…read more

Page 4

Preview of page 4

Here's a taster:

Substances are then delivered to the rest of the body quickly, which is
necessary as:
Mammals have a high temperature
High rate of metabolism
Blood transports:
Respiratory gases
Products of digestion
Metabolic wastes
The vessels that make up the circulatory system of a mammal are divided
into three types:
How the circulatory system of a mammal differs to that of a fish
Fish have a simpler system.
Blood leaves the heart and goes to the gills where it picks up oxygen.…read more

Page 5

Preview of page 5

Here's a taster:

There are two circuits:
1. Takes blood from the heart to the lungs then back to the heart
2.…read more

Page 6

Preview of page 6

Here's a taster:

Blood Vessels and their
Blood circulates in a series of different kinds of blood vessels as it circulates round the body
Heart Aorta Arteries Arterioles Capillaries Venules Veins Vena Cava Heart
A blood vessel is a tube with a space in the centre called the lumen, where blood
flows.…read more

Page 7

Preview of page 7

Here's a taster:

Arteries, arterioles and veins all have the same basic layered structure.…read more

Page 8

Preview of page 8

Here's a taster:

Artery Structure related to its function
Function Transport blood rapidly
under high pressure from the
heart to the tissues.
Muscle layer Walls are thick and muscular This means smaller arteries can be
constricted and dilated in order to
control the volume of blood passing
through them.
Allows them to withstand high
Elastic layer Relatively thick It is important that blood pressure in
arteries is kept high if blood is to
reach the extremities of the body.…read more

Page 9

Preview of page 9

Here's a taster:

Arteriole Structure related to its function
Function Carry blood, under lower
pressure than arteries, from
arteries to capillaries.
Also control the flow of blood
between the two.
Muscle layer Walls are relatively thicker The contraction of this muscle layer
than in arteries allows constriction of the lumen of
the arteriole.
This restricts the flow of blood and so
controls its movement into the
capillaries that supply the tissue with
If the muscle contracts, the lumen
gets narrower, so less blood can
flow.…read more

Page 10

Preview of page 10

Here's a taster:

Vein Structure related to its function
Function Transport blood slowly,
under low pressure, from the
tissues to the heart.
Muscle layer Walls are relatively thin Veins carry blood away from tissues
compared to arteries and therefore their constriction and
dilation cannot control the flow of
blood to the tissues.
Elastic layer Relatively thin compared to This is because the low pressure of
arteries the blood within the veins will not
cause them to burst and pressure is
too low to create a recoil action.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »