7. Respiration and Breathing

Energy Content per gram of food (J) = 4.2 x temp. Rise x 20/ mass of food


There are two types of respiration;

  • Aerobic Respiration
  • Anaerobic Respiration

Aerobic Respiration takes place in living cells, inside the mitochondria, so is not present in bacteria or viruses.

Anaerobic Respiration takes place in skeletal muscles, (in arm or leg muscles), and in yeast cells.

Respiration happens so that the following functions can occur;

  • Movement,
  • Growth,
  • Sensitivity,
  • Excretion,
  • Reproduction,

We know that respiration has occurred when;

  • CO2 is produced- breathe into limewater to tell whether it is present.
  • Heat is produced.
  • Glucose/ oxygen are used up.


Aerobic Respiration

Respiration is a process that takes place in all living cells. Respiration transfers energy from food molecules in animals and in plants. The energy from respiration is used to make smaller molecules from large ones, to let muscles contract, and to keep a constant muscle temperature. Respiration releases energy from food molecules in cells.

Glucose + Oxygen                   CO2 + water + energy


Anaerobic Respiration

Anaerobic respiration occurs in the skeletal muscle cells. The main difference between them is that Aerobic respiration uses oxygen, while anaerobic respiration doesn’t

Glucose                        Lactic Acid + a little energy

You respire anaerobically when you are exercising hard, and your muscles struggle to get the oxygen to do aerobic respiration. (the heart and lungs struggle to put oxygen in the blood, and then pump it around the blood.

Without the oxygen, the glucose transfers to lactic acid, with a little energy. The problem is that the lactic cid builds up, and doesn’t let the muscles contract correctly, meaning that you get a ‘stitch’.

This lactic acid is poisonous, and must be removed. This is done by the body moving it to the liver, and then breaking it down using oxygen. This is called oxygen debt.

Gas Exchange in the Alveoli

Gas Inhaled (%) Exhaled (%)
Nitrogen 78 79
Oxygen 21 16
Carbon Dioxide 0.04 4
Other (Mainly Argon) 1 1


The lungs absorb the oxygen into the blood, and remove the carbon dioxide from it, in the alveoli.

To make this efficient, the alveoli must have a structure that brings the blood and the air very close, over a large surface area.

It has been estimated that we have over 700 000 000 alveoli, in our two lungs, with 60m2 of surface area.

The alveoli look like a bunch of grapes, covered with tiny capillaries like a net.

What Happens?

  • Blood is pumped to the lungs from the heart, which passes through the capillaries, by the alveoli.
  • The blood has carbon dioxide in it from the respiration that occurs in the cells.
  • Around the lungs, the blood is separated from the air inside each alveolus by only two layers of cells. This is so the air diffusion can be quick and easy. This is less than a thousandth of a millimetre.
  • The air in the alveolus has more oxygen in it than the blood in the capillaries do, so that the oxygen diffuses from the air and into the blood.
  • As there is more carbon dioxide in the blood than in the air, the carbon dioxide also transfers, from the blood to the air.
  • The blood has now gained oxygen, and lost carbon dioxide, so the heart pumps the blood around the body again.

What features make the lungs efficient?

  • Millions of alveoli over two lungs, meaning large surface area.
  • A thin cell wall between the alveolus and the capillaries, which makes diffusion easier
  • There are lots of capillaries surrounding the alveoli, meaning there is a good blood supply. It maintains the blood gradient.

The Alveoli

  • Air containing oxygen enters the lungs and passes into each alveolus from the outside.
  • Deoxygenated blood containing CO2 comes from the rest of the body.
  • Oxygen diffuses into the blood from the alveoli.
  • Air containing more carbon dioxide leaves the lungs.

The Respiratory System

  • Tongue- Tastes food
  • Diaphragm- Moves up and down to help you breathe.
  • Nasal Cavity- Cleans, warms, and moistens the air you breathe.
  • Bronchus- Carries the air to the bronchioles.
  • Pleural Membranes- Stops the lungs from collapsing.
  • Heart- Pumps blood around the body.
  • Alveoli- Gets the oxygen into and carbon dioxide out of, the blood.
  • Ribs- Protects the lungs.
  • Lungs- Contains millions of alveoli
  • Intercostal Muscles- Muscles between the ribs that helps you breathe.
  • Epiglottis- Stops food entering the windpipe.
  • Voice Box- Responsible for speech.
  • Gullet- Takes food to your stomach
  • Bronchioles- Tiny tubes that take air from the bronchi to the alveoli.
  • Windpipe- Contains cilia that trap dust before the air enters your lungs.



  1. The brain sends signals via your nerves to your diaphragm and external intercostal muscles.
  2. The external intercostal muscles contract.
  3. The external intercostal muscles move the ribcage up and out.
  4. The diaphragm contracts and flattens.
  5. The thorax (chest cavity) increases in size.
  6. The pressure inside the thorax decreases.
  7. The pressure is now lower than the pressure in the atmosphere.
  8. Air moves into your lungs down a pressure gradient.

Smoking and its effects


  • Tar is the name to describe the chemical substances in cigarettes, and is the most harmful substance in a tobacco cigarette.
  • It is tar that makes your fingernails, teeth and skin go yellow.
  • The cilia that line your trachea and bronchus try to trap the tar from the cigarette, as their job is to trap dirt. When they try to trap the tar, instead the tar covers them and stops them working effectively, and will eventually kill them. Now they can’t work, you can catch really nasty illnesses.
  • Emphysema is one of those really horrible diseases. When you inhale, the lungs expand and then pulled back to their original state by their elastic tissues. When you have emphasyma, these elastic tissues get damaged because of the tar deposits, and so the lungs aren’t as elastic. The result of this is that you can’t get as much diffusion from a breath.
  • Other illnesses include cancer of the lungs and throat.


  • Cigarette smoke contains drugs and poisons which can cause serious health problems for the mother and child.
  • Problems for the baby include;
  • Can be up to 200g lighter
  • Cot death is 3 x more likely
  • Poorer lung function and poorer respiratory problems
  • 3 x more likely to die within a week
  • Malnutrition from poor milk production
  • Lower oxygen levels in the blood
  • Higher infant mortality rate
  • Less immunity to flu and diarrhoea
  • More likely to become smokers when older.
  • Problems for the mother include;
  • Higher risk of miscarriage
  • Reduces fertility
  • During labour, complications like premature detachment of the placenta and the membranes rupturing can occur as well as bleeding. Ectopic pregnancy is more common too. During the pregnancy, a baby depends on the placenta, and umbilical cord for transferring vital nutrients and oxygen; if these organs are damaged, the baby can be at risk.

Illnesses that you can contract

Illnesses that you can get are;

  • Oral cancer (risks increase by 3 times)
  • Bladder Cancer (risks increase by 3 times)
  • Cervical Cancer (risks increase by 2 times)
  • Leukaemia (risks increase)
  • Diabetes (smoking raises your blood levels, so increases the risks of developing it)
  • Strokes (causes plaque to build up in your arteries, and blocks the blood flow to the brain)

Nicotine on the Circulatory System

  • Nicotine is the addictive substance in the tobacco smoke. It creates a dependency so those smokers become addicted.
  • Nicotine affects the circulatory system, and is the leading cause of heart disease. It is one of the components of cigarette smoke.
  • Nicotine causes the blood vessels to constrict. As the blood vessels narrow, the blood pressure rises. Undetected high blood pressure leads to heart disease.
  • While the half-life of nicotine is two hours, a smoker takes several drags of nicotine at any one time, meaning it stays there a lot longer.
  • Nicotine causes the adrenal glands to release adrenaline. Once the nicotine is absorbed into the alveoli, the adrenaline is released. The rapid release of the adrenaline causes the heart rate to rise.
  • The narrowing of the arteries also affect the cardiovascular system. Constriction of the blood vessels means that major limbs and organs become blood deprived.