3a

Transpiration is the loss of water from the plant

• Caused by the evaporation and diffusion of water from the leaves
• Creates a slight shortage of water in the leaf, so more water is drawn up from the rest of the plant through the ylem vessels to replace it
• More water is drawn up from the roots, and so theres a constant transpiration stream of water through the plant
• Transpiration is a side-effect of the way leaves are adapted for photosynthesis. They have to have stomata in them so gases can exchange easily. There is more water inside the plant than in the air outside so the water escapes from the leaves through the stomata.

The Double Circulatory System

• Two circuits joined together
• First one pumos deoxygenated blood to the lungs to take in oxygen. The blood then goes to the heart
• Second one pumps oxygenated blood around all the other organs. The blood gives up its oxygen  at the body cells. Deoxygenated blood returns to the heart to be pumped to the lungs again.

• The heart is a pumping organ, made of muscle tissue
• It has valves to make sure that blood goes in the right direction.
• Has 4 chambers (right atrium, right ventricle, left atrium, left ventricle

• Blood flows into the two atria from the vena cava and pulmonary vein
• The atria contract, pushing blood into the ventricles
• The ventricles contract, forcing the blood out of the heart (via vena cava and pulmonary vein)
• The blood then flows to the organs through arteries
• Returns through veins
• The atria fill again
• This cycle then repeats

1) Arteries - these carry blood away from the heart

2) Capillaries - involved in the exchange of materials at the tissues

3) Veins - these carry blood to the heart

These carry blood under pressure

• The artery walls are strong and elastic
• The walls are thick compared to the size of the hole down the middle. 'LUMEN'
• Contain thick layers of muscle to make them strong
• Contain elastic fibres to allow them to stretch and spring back

These are really small

• Arteries branch into capillaries
• They carry the blood really close to every cell in the body to exchange substances with them
• They have permeable walls, so substances can diffuse in and out
• They supply food and oxygen
• Take away waste such as CO2
• Walls are one cell thick. This increases the rate of diffusion by decreasing the distance over which it occurs

These take blood back to the heart

• Capillaries eventually join up to form veins
• The blood is at lower pressure in the veins so the walls dont need to be as thick as artery walls
• They have bigger lumen to help blood flow
• They have valves to keep the blood flowing in the right direction

Blood is a tissue

• Carry oxygen from the lungs to all the cells in the body
• Doughnut shape to give a large surface area for absorbing oxygen
• No nucleus - more room to carry oxygen
• Contain haemoglobin

• In the lungs, haemoglobin combines with oxygen to become oxyhaemoglobin.
• In the body tissues, oxyhaemoglobin splits up into haemogolbin and oxygen to release oxygen to the cells

These defend against disease

• They can change shape to gobble up unwelcome microorganisms
• Produce antibodies to fight microorganisms
• Produce antitoxins to neutralise any toxins produced by the microorganisms
• Contain a nucleus

These help blood clot

• Small fragments of cells
• No nucleus
• They help the blood to clot at a wound - to stop all your blood pouring out and to stop microorganisms from getting in.
• Lack of platelets can cause excessive bleeding and bruising.

This is the liquid that carries everything in blood.

• This carries red and white blood cells and platelets
• Nutrients like glucose and amino acids.
• Carbon dioxide from the organs to the lungs
• Urea from the liver to the kidneys
• Hormones
• Antibodies and Antitoxins