Revision - GCSE Biology - breathing


Air travels down the trachea, which then spits into two bronchi (sing. bronchus). These gradually split off into smaller tubes which end at alveoli. (See diagram for rest)

The plural membranes allow our lungs to slide over the rib cage without damaging the lung. Plural fluid acts as a lubricator and stops this action rubbing.

Air goes down the throat (which is shared by both respiratory and alimentary systems) down the glottis, past the Adams apple (voice box). The trachea is surrounded by had rings of cartilage which protect it and give it support. The trachea is also full of cilia, which waft mucus which could contain dust or bacteria up so be coughed up or swallowed.


Breathing in

Intercostals and diaphragm contract (diaphragm flattens), the sternum and rib cage move up and out, which means the volume of the thorax increases, creating a lower pressure in the thorax, meaning air rushes in.


Breathing out

As the intercostals relax the sternum and the rib cage move down and in, the diaphragm relaxes which means it moves in and up, the volume of the thorax decreases and air is forced out.

Air pressure is very important, as if there is a low air pressure then there may be problems breathing. In high altitude places you have to breathe quicker and more deeply to get enough oxygen.

Gas exchange in the lungs has already been covered earlier on page four. When the blood gets to the cells, oxygen diffuses out of the red blood cell into the cell, and carbon dioxide diffuses in the opposite direction

Respiration is converting glucose into energy, and not breathing in and out. It happens in every cell. The energy is used for loads of different things, e.g., breaking bigger molecules unto smaller ones, muscle movement and homeostasis.

Smoking is a problem because cigarettes contain carcinogens which can cause cancer. These carcinogens are found in the tar, and increase you likelihood of getting lung cancer dramatically. Chronic bronchitis also stems from smoking because extra mucus is produced to remove the smoke from the cilia, and if the bronchial tubs become infected which they easily can bronchitis sets in. Smoking also causes emphysema, where the alveoli all bunch together and the surface area is seriously decreased.

Aerobic respiration happens when there is lost of oxygen around

\displaystyle \mathsf{Glucose} + \mathsf{Oxygen} \longrightarrow \mathsf{Carbon\ dioxide} + \mathsf{Water} + \mathsf{Energy}

\displaystyle \mathsf{C_6H_{12}O_6} + \mathsf{6O_2} \longrightarrow \mathsf{6CO_2} + \mathsf{6H_20} + \mathsf{Energy}

Anaerobic respiration is like an emergency way of breaking down glucose. It releases a lot less energy than aerobic respiration, it also creates lactic acid. Lactic acid is actually poisonous and so can be painful if it builds up in muscles; it can also cause 'muscular fatigue' which basically means the muscles get tired and so cannot contract as efficiently as they would with oxygen. However, anaerobic respiration is useful in emergencies... it keeps your body going without oxygen.

\displaystyle \mathsf{Glucose} \longrightarrow \mathsf{Lactic\ acid} + \mathsf{Energy}

When you do heavy exercise your body cannot provide the muscles with enough oxygen, so the muscles begin to use anaerobic respiration. This creates a build up of lactic acid, which gets painful. When you stop you have an oxygen debt, which means you have to “repay” the oxygen that you didn’t provide the muscles before. The oxygen breaks up the lactic acid. After heavy exercise you breathe heavily for a while because when the brain detects high levels of carbon dioxide and lactic acid in the blood the pulse and breathing rate are automatically increased to try and rectify the situation. A good way to see how fit you are is to measure how long it takes you to recover from doing vigorous exercise, or your recovery time.

Definition of oxygen debt: "The additional oxygen required after anaerobic respiration to oxidise lactic acid (into carbon dioxide and water)."

Yeast creates ethanol when it respires aerobically:

\displaystyle \mathsf{Glucose} \longrightarrow \mathsf{Ethanol} + \mathsf{Carbon\ dioxide} + \mathsf{Energy}

Also See

Here are the other comprehensive GCSE Biology notes by Prometheus: