OCRA Biology OCRA A Level and OCRA Biology AS Module 3(3.2) Transport in animals Summary notes and revision notes.
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Course
OCRA Biology AS Module 3 Transport in animals
Institution
OCR
Biology A level and Biology AS level Biology. Module 3 (3.2) Transport in animals.
H020 and H420. OCR Specification. Breadth and depth of biology. Paper 1,2,3
8.1 The need for specialised transport systems in animals:
1. Metabolic demands
The metabolic demands of most multicellular animals are high as they need lots of
oxygen and food.
Diffusion over long distances isn’t enough to supply the quantities needed
2. SA:V ratio
The surface area to volume ratio gets smaller as multicellular organisms get bigger so
not only do the diffusion distances get bigger but the amount of surface area
available to absorb or remove substances gets relatively smaller
3. Transport of hormones and enzymes
They will be needed in other places to where their made
4. Waste products
The waste products of metabolism need to be removed from cells and transported
to excretory organs.
Types of circulatory systems
Features of a good transport system:
• liquid medium that circulates around the system
• exchange surfaces to enable substances to enter the blood
• pumping mechanism to move the fluid around
When substances are transported in a mass of fluid with a mechanism its known as a mass
transport system
Open circulatory system
• no vessels to contain the transport medium
• Example: invertebrates, insects
• Their blood is called haemolymph, it doesn’t carry oxygen or carbon dioxide but
transports waste and cells involved in their immune system.
Closed circulatory system
• vessels to contain the transport medium
• Example = the human circulatory system
Single closed circulatory system:
• blood flows through the heart once
• fish have a single circulatory system heart>gills>body>heart
Disadvantages of a single circulatory system:
• Blood pressure drops as blood passes the capillaries of the gills
• blood has a low pressure as it flows towards the body
• rate at which oxygen is delivered to the respiring tissues is limited
, Double closed circulatory system:
• Blood flows through the heart twice
• High pressure
Advantages of double circulatory system:
• Heart can increase the pressure of the blood after it has passed through the lungs so
it flows more quickly.
8.2 Blood Vessels:
Arteries:
• They carry blood away from the heart.
• The blood is at a high pressure so the artery wall must be thick to withstand that
pressure.
• The lumen is relatively small in order to maintain high pressure and the inner wall is
folded to allow the lumen to expand as blood flow increases.
• Tough collagen layer-Strength to withstand high pressures
• Many elastic fibres- allow the walls to stretch and recoil to maintain blood
pressure. Arteries near to the heart have more elastic tissue to even out
fluctuation in blood pressure.
• Thick layer of smooth muscle-contracts and relaxes to change the size of
the lumen
Arterioles: • Endothelium can reduce/minimise friction
• Arterioles are small blood vessels that distribute the blood from an artery to the
capillaries
• They have more smooth muscle and less elastic fibres as they have little pulse surge
Capillaries:
• Very thin wells as they allow the exchange of materials between the blood and
tissue fluid.
• The lumen is very narrow-the diameter is the same of a red blood cell to reduce the
diffusion distance
• Layer of flattened endothelial cells to reduce the rate of flow and increase resistance
• leaky walls to allow blood plasma and dissolved substances to leave the blood
Capillaries are adapted to their role by:
• Providing a large surface area for the exchange of substances
• slow movement of blood to give time for exchange
• walls are one cell thick
Veins:
• carry blood back to the heart at low pressures.
• Veins carry blood at a low pressure so they contain pocket valves to help the blood
flow to the heart and prevent back flow
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