1. Introduction
Our body has different ways of getting, producing and carrying energy around to make possible the chemical reactions and processes. The body needs different substances to release energy e.g. glucose. and body cells use this energy in their reactions, which include:

  • The movement (muscle contraction)
  • Making new substances from small molecules (e.g. proteins from amino acids)
  • Growth and repair (putting together new substances to make new cells or to replace old cells
  • Active transport (moving substances through a cell membrane against a concentration gradient) (see also Active transport)
  • Nerve impulses (energy is needed for nerve cells to pass impulses along their lenght
  • Heat (keep mammals and birds at a constant body temperature)

Cells in action
Cells in action

Plants also need energy for all these processes, except for movement and nervous impulses.

2. Respiration
All organisms must have a source of energy. Animals eat food containing energy-rich substances which are broken down by the digestive system into smaller molecules, and then absorbed into cells.
Respiration takes place in the cytoplasm of cells: glucose is broken down to give carbon dioxide and water. This process also releases energy.

2.1. Aerobic respiration

Aerobic respiration means the release of energy using oxygen. Oxygen and glucose are carried by blood and into the cells.
In the cytoplasm of cells there are specialised organelles called mitochondria which contain enzymes needed for respiration. Oxygen diffuses into the mitochondria and is used to react with glucose to produce carbon dioxide and water. The chemical energy is transferred to a substance called ATP; the ATP carries the energy to the reactions where it is needed.
The word equation for aerobic respiration is:
glucose + oxygen ----> carbon dioxide + water (+ energy)
When the glucose molecules are broken down inside a cell, about a 60% of the energy cannot be transferred into ATP so it's given off as heat.

2.2. Anaerobic respiration

Anaerobic respiration is the release of energy without oxygen. When a person cannot bring enough oxygen but still needs to move, the muscle cells shortcut the respiration process. Glucose is only partly broken down, and a very little energy can be transferred to the ATP.
Word equation for anaerobic respiration:
glucose ----> lactic acid (+ some energy)
Most of the energy is left on the product lactic acid. It's a poison and makes the muscle get tired. Too much lactic acid causes cramps. The muscles need extra oxygen after doing the exercise to turn the lactic acid into carbon dioxide and water. This extra oxygen is called oxygen debt.
In plants, there is a different word equation for anaerobic respiration:

glucose ----> alcohol + carbon dioxide (+ some energy)
We can use the plants' chemical reaction for fermentation, which is used to produce some alcoholic drinks and bread.

Fermentation system
Fermentation system

3. Breathing

Ventilation is getting the air into and out off the lungs and gas exchange is getting the gases to move into or out of the blood.

Breathing system and lungs:

  1. The nose has hairs and large surface to filter dirt, warm the air, and moisted it.
  2. Intercostal muscles contract to raise the ribcage.
  3. The diaphragm contracts (becomes flattened) to breath in.
  4. Windpipe (trachea) has supportimg rings of cartilage to keep it open when pressures change.
  5. Bronchi are kept open by cartilage.
  6. Bronchioles take the air to all parts of the lungs.
  7. Airtight sacs sorround the lungs (pleural menbranes).
  8. Air sacs are sorrounded by blood capillaries.

The diffusion depends in three factors :
  1. Large surface area.
  2. Short distance.
  3. Duffusion gradient.

The breathing system is designed to make sure the gases are exchanged at the rate they are needed.

The breathing system consists of the lungs and diaphragm. They are found in the upper part of the body called the thorax. Their function is to breath in air to get oxygen and breath in air to get rid of carbon dioxide. This is called gas exchange and we do not have to think that it is the same as respiration.Respiration takes place in the cytoplasm of cells, glucose is broken down to give carbon dioxide and water.

3.1. Diseases

3.1.1. Smoking
Breathing in substances other than fresh air causes harm to the breathing system. Smoke from tobacco causes many problems and diseases like these:
  • Bronchitis: lining of the bronchiole is irritated by bacteria and smoke.
  • Emphysema: the walls of the elveolus are broken down
  • Smoker´s cough: cilia are stopped from beating so mucus is not moved out of the lungs.
  • Carbon monoxide poisoning: carbon monoxide in smoke binds with haemoglobin in red blood cell. Less oxigen can be carried in the blood.

3.1.2. Asthma
Asthma develops when the bronchi get inflamed. They become narrow and mucus is trapped so that it blocks the bronchi.
Asthma is caused by an allergy to house dust containing house mite faeces.
Inhalers make the muscle walls of bronchi relax so that the tubes open and is easier to breathe, but they cannot cure the disease.

4. Circulatory system
The circulatory system transports all soluble materials around the body. It consistes of a pump, (the heart), tubes to direct the flow, (the blood vessels), and theblood as the carrying substance. It is also very efficient at taking oxygen to all of the organs and at removing carbon dioxide.

4.1. Circulation
The transport system develops very early in the embroy and is essential to make sure all the developing cells, tissues and organs get all the substances they need. Before the blood goes to any organ, it is pumped by the heart so that is always at high prssure, it travels quickly to the organs and delivers the oxygen needed for respiration.

4.2. Heart
It works as two pumps. One pump pushes the blood towards the lungs and the other pushes blood to all other organs of the body. Both pumps work at the same time and they push the same amount of blood.

Parts of the heart:
The blood flows into the heart at the top.
  • It enters the very elastic thin walled chambers, the atria.
  • Goes through open valves into the main pumping chambers, the ventricles. They contract strongly to push the blood.
  • The valves make sure that the flow of blood does not go backwards.
  • The rythm is set by patch of cells in the wall of the right atrium, the pacemaker.

4.3. Blood vessels
Blood is carried in tubes of diferent sizes called blood vessels. there are three tipes: veins, arteries
and capillaries.
  • Veins carry blood towards the heart. The blood is at a low pressure. It has thin walls with less muscle and no substances leave or enter the vessel. It has no pulse, they are flexible and squashed easily so blood is pushed farther along the vessel
  • Arteries carry blood away from th heart. Blood is a high pressure, it has thick muscular wallls and no ssubtance enter or leave the vessel.
  • Capillaries carry blood through organs and tissues. The blood is low presure and it has very thin walls fo escape of fluids.

4.4. Blood
Blood is about 50%water and 50%cells by volume. There are about 5 litres of blood in an average adult person and it makes one complete circuit of the body about once a minute, i.e. two passes through the heart, one through the lungs and once to one of the organs.
Most of the cells are red cells because they contain the substance haemoglobin. Their function is to carry oxygen from the lungs to the tissues. Each blood cell is made in the bone marrow and only lasts about four months as it travels round the body.
White blood cells have the task of fighting disease. there are about 500 times fewer white blood cells than red blood cells.
White blood cells are divided into different types, each with a special function. Phagocytes can engulf a bacterium by moving around it and enclosing it.
Other white blood cells are called lymphocytes and they produce antibodies which are released into the plasma.
A very small type of cell without a nucleus called platelet helps the blood to clot.
The liquid part of the blood is called plasma. Plasma carries small molecules such as glucose, amino acids and vitamins from the diets well as hormones and heat.

4.5. Circulatory problems
Nicotine from cigarretes smoke makes the blood more likely to form clots. Too much fat in the diet causes a type of fat called cholesterol to be left on the inside of the arteries (atheroma). This makes them narrower and so blood clot is more likely to get trapped.Some of the health problem that may occur are the following ones:
4.5.1. Heart Attack
Heartattacks are caused by a blockage in a coronary artery (the blood vessels going to the muscular wall of the heart).The heart muscle does not get enough oxygen and glucose,
A first aider will give cardiac compressions to the chest to squash the heart and so make the blood move around the body.

4.5.2. Angina
It is the first sign of heart disease with several of the arteries becoming narrower. A sharp pain develops in the left arm and the person gets tired much more quickly than they should.
4.5.3. Stroke
It happens when there is a blood clot in the blood vessels of the brain. The person becomes confused and usually becomes unconscious.