Double Award - Science for GCSE

Chapter 3

Breathing and respiration

1.	Breathing involves: inhalation (breathing in) exhalation (breathing out) When we breathe in (inhale), our ribs move up and out. The diaphragm becomes flat and air flows into our lungs. When we breathe out (exhale), our ribs move down and in. The diaphragm goes up into a dome shape and air is pushed out of the lungs.
2.	Gas exchange Breathing involves an exchange of gases in our lungs and allows oxygen to reach our cells for respiration. Oxygen diffuses from the inside of tiny alveoli (air sacs), through their thin walls (only one cell thick), into the blood capillaries covering the alveoli. The oxygen is picked up by red blood cells in the capillaries and carried to all our body cells. Carbon dioxide diffuses in the opposite direction, from the blood capillaries covering the alveoli and into the lungs. It is then breathed out.

3.	Respiration occurs when chemical reactions take place in the cells of our bodies. These reactions use up digested food molecules, such as glucose, and produce energy. We need the energy from respiration to move, to keep warm, to grow and to repair damaged tissues.
4.	Aerobic and anaerobic respiration Respiration normally occurs in the presence of air (oxygen) and this is called aerobic respiration. During aerobic respiration, food molecules like glucose react with oxygen, producing carbon dioxide, water and energy.

	Respiration can also occur in the absence of air (oxygen) and this is called anaerobic respiration. During anaerobic respiration, food molecules like glucose decompose, producing smaller molecules and energy. But the energy produced is much, much less than that produced by aerobic respiration.
	Anaerobic respiration occurs in: fermentation (production of beers and wines) bread making muscle cells devoid of oxygen
5.	Smoking The main toxic (poisonous) substances in tobacco smoke are: Carbon monoxide which forms a strong bond with haemoglobin, reducing the capacity of the blood to carry oxygen. Nicotine which is a carcinogen, causing cancer in the respiratory system. Tar which paralyses the cilia in the nasal cavity and clogs up the alveoli. Smoking can cause: Cancers of the throat, bronchus and lungs. Bronchitis and emphysema (breathlessness due to tar-damaged alveoli) Arteriosclerosis (poor circulation due to fatty deposits in the arteries) and heart diseases.