Substances move by Diffusion, Osmosis and Active Transport.

DiffusionParticles move from an area of high concentration to an area of low concentration.

Osmosis: Water molecules move through a partially permeable membrane from an area of high concentration.

Active Transport: Particles move from an area of low concentration to an area of high concentration.

Exchange surfaces are ADAPTED to maximise effectiveness.

Gases diffuse In and out of cells.

• Carbon dioxide diffuses into the air spaces within the leaf, It then diffuses into the cells where photosynthesis happens.
• The stomata ( underneath of new leaf) is an exchange surface, where CO2 diffuses in through.
• Water vapour and Oxygen diffuse out through the stomata.
• The Guard cells control the size of the stomata. If the plant is losing water faster, the guard cells close the stomata. The water is replaced by the roots.
• The flattened shape of the leaf, increases the area of this exchange surface.
• The walls of the cells inside the leaf form another exchange surface. The air spaces inside the leaf increase the area so CO2 can get into the cells.
• Water vapour escapes by diffusion. This is called transpiration, Transpiration is quickest in hot, dry and windy conditions.

The Lungs are in the Thorax:

• The thorax is in the top part of the body, separated from the lower part DIAPHRAGM.
• The lungs are like big pink sponges, protected by the rib cage.
• The air breathed in goes through the trachea. This splits into two tubes called BRONCHI, one going to each lung.
• The BRONCHI has smaller tubes called BRONCHIOLES. These end at small bags called ALVEOLI, where gas exchange takes place.

When we breathe in, Intercostal muscles and Diaphragm CONTRACT, and the Thorax volume INCREASES. Which decreases the pressure, drawing air OUT.

When we Breathe out,The Intercostal Muscles and Diaphragm RELAX, and the thorax volume DECREASES. Which forces the air OUT.

Gas exchange happens in the LUNGS.

The lungs transfer Oxygen to the blood, and remove the waste Carbon Dioxide from it. The Lungs contains millions of little air sacs, ALVEOLI where gas exchange takes place.

The ALVEOLI have:

• Large surface area.
• Moist lining for dissolving gases.
• Very thin walls.
• Copious Blood supply.

The VILLI provide a Large surface area.

The Villi, is inside the small intestine. The Villi increases the surface area so that digested food is absorbed more quickly into the blood.

They have a single layer of surface cells, and a very good blood supply to assist quick absorption.

Root hairs are specialised for absorbing water and minerals, because of the cells on the surface of plant roots, which grow into long hairs, which stick out into the cells.

The concentration of minerals is usually higher in the root hair cell then in the soil around it.

Active transport allows plants to absorb minerals against a concentration gradient. Active transport also needs ENERGY from respirtion to take place.

Active transport also happens in humans for e.g taking glucose from the gut and kidney tubules.

• The right side of the heart pumps de-oxygenated blood to the lungs, It collects oxygen and removes CO2. Where as the left side pumps the oxygenated blood around the body.
• Arteries carry blood away from the heart at high pressure.
• Arteries except the pulmonary artery carry oxygenated blood, and veins except the pulmonary vein carry de-oxygenated blood.
• The arteries then split into tiny capillaries which take blood to every cell in the body.
• The veins then collect the used blood and carry it back to the heart at low pressure to be pumped again.

Capillaries deliver food and Oxygen to each cell by diffusion, Carbon dioxide and other waste materials are taken away. The walls are only one cell thick.

Blood is made up of 4 main parts:

• White blood cells: White blood cells defend against any diseases, or bacteria entering the body.

• Red blood cells: These carry Oxygen from the lungs to the cells in the body. They have a large surface area for absorbing oxygen. They contain haemoglobin. In the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin. In body tissues the reverse happens to release oxygen to the cells.

• Plasma: This is the liquid that carries everything in the blood i.e. Carbon dioxide from the organs to the lungs. urea from the liver to the kidneys.

• Platelets: These are small fragments of cells that help blood to clot a wound.

Exercise increases the heart rate:

• Muscles are made of muscle cells , They use oxygen to release energy from glucose (respiration), which is used to contract muscles.
• Increase in muscle activity requires more Glucose & Oxygen , extra carbon dioxide needs to be removed from the muscle cells. For this to happen the blood has to flow faster.
• Physical activity increases breathing rate, and the speed at which the heart pumps. It also dilates the arteries which supply blood to the muscles.

Glycogen is used during excercise , It is mainly stored in the liver. During exercise muscles use glucose to provide more energy.

Anearobic respiration is used if their is not enough oxygen.

Glucose ---> energy + lactic acid

Anaerobic respiration leads to an oxygen debt. You have to repay oxygen that didn't get to your muscles before.

Nephrons are filtration units in the kidneys.

• Ultra filtration: High pressure squeezes water, urea,ions and sugar out of the blood and into the Bowman's Capsule.The membranes between the blood vessels and the bowman's capsule act as filters. So big molecules like protein and blood cells re not squeezed out.
• Re absorption: Useful substances are reabsorbed back into the blood. All the sugar is reabsorbed.This involves active transport against the concentration gradient. Sufficient ions and water are reabsorbed, Active transport is again needed.
• Release of wastes: The remaining substances ( including urea) continue out of the Nephron, into the ureter and down to the bladder as urine.

The kidneys remove waste substances from the blood. People with kidney failure are kept alive by having a dialysis treatment or a kidney transplant.

Dialysis machines filter the blood.It keeps concentrations of dissolved substances in the blood at normal levels. It alos removes waste substances. The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood. This is so dissolved ions and glucose won't be lost from the blood during dialysis.

Transplanted organs can be rejecected by the body. A donor with a tissue type that closely matches the patient is chosen.