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Class Notes for Chapter 8 Transport in Animals AS Level Biology A OCR
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Transport in Animals Transport systems in multicellular animals
Blood vessels
Blood, tissue fluid and lymph
Transport of oxygen and carbon dioxide in the
blood
The heart
,Transport systems in multicellular animals
All organisms exchange materials between themselves and their environment. Small
animals can carry out this exchange over their body surface e.g. amoeba. However, as the
organism’s size increases, the surface area to volume ratio decreases to a point where is not
possible. Larger organisms require specialised exchange surfaces for the exchange of
materials and a mass transport system to transport materials around the organism.
Specialised transport systems are needed because:
- The metabolic demands of most multicellular animals are high. Diffusion couldn’t supply
the quantity of oxygen needed as the distance it would have to travel is too great.
- The surface area to volume ratio gets smaller as multicellular organisms get bigger. This
means as well as diffusion distances increasing, the surface area over which to absorb or
remove substances becomes relatively smaller.
- Molecules such as hormones and enzymes may be made in one place but needed in
another.
- Food will be digested in one organ system but the products will need to be transported to
all cells for use in respiration and other metabolic processes.
- Waste products of metabolism need to be transported from the cells to excretory organs.
Transport systems have some common features:
Feature Example in Humans
A medium to carry materials. It is usually a Blood, air in lungs
water-based liquid as water is a good
solvent for gases.
A form of mass transport in which the Circulatory systems
transport is moved around in bulk over
large distances – faster than diffusion.
A closed system of tubular vessels contains Arteries, veins, capillaries
the transport medium and forms a
branching network to distribute it to all
parts of the organism.
A mechanism for moving the transport Pumping action of the heart
medium within vessels, relies on pressure
differences.
A mechanism to maintain the mass flow Valves
movement in one direction.
A means of controlling the flow of the Mass transport of substances
transport medium to suit the changing
needs of different parts of the organism.
, Open circulatory systems
Some invertebrates have an open circulatory system – blood isn’t enclosed in blood vessels
all of the time. Instead, it flows freely through the body cavity.
1) The heart is segmented. It contracts in a wave, starting from the back, pumping the
blood into a single main artery.
2) The artery opens up into the body cavity.
3) The blood flows around the insect’s organs, gradually making its way back to the
heart segments through a series of valves.
Closed circulatory systems
All vertebrates have a closed circulatory system – the blood is enclosed inside blood
vessels.
1) The heart pumps blood into arteries. These branch out into millions of capillaries.
2) Substances like oxygen and glucose diffuse from the blood in the capillaries into the
body cells, but the blood stays inside the vessels as it circulates.
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