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B8 Respiration and gas exchange - Coggle Diagram
B8 Respiration and gas exchange
Features of gas exchange surfaces
The surfaces where gas exchange occurs in an organism are very different and different organisms have evolved different mechanisms for getting the gases to the gas exchange surface depending on size, where they live etc.
All gas exchange surfaces have features in common
These features allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time
They include
:
Large surface area t
o allow faster diffusion of gases across the surface
Thin walls
to ensure diffusion distances remain short
Good ventilation with air
so that diffusion gradients can be maintained
Good blood supply
to maintain a high concentration gradient so diffusion occurs faster
Structure of the breathing system
Ribs
: bone structure that protects internal organs such as the lungs
Intercostal muscle
: muscles between the ribs which control their movement causing inhalation and exhalation
Diaphragam
: sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation
Trachea
: windpipe that connects the mouth and nose to the lungs
Larynx
: also knows as voice box, when air passes across here we are able to make sounds
Bronchi
: large tubes branching off the trachea with one bronchus for each lung
Bronchioles
: bronchi slipt to form smaller tubes called bronchioles in the lungs connected to alveoli
Alveoli
: tiny air spaces where gas exchange takes place
Differences between inhaled and exhaled air
Air that is breathed in and air that is breathed out has different amounts of gases in it due to exchanges that take place in the alveoli
Atmospheric air contains around 20 – 21% oxygen, of which we only absorb around 4 – 5%, breathing out air containing around 16% oxygen
oxygen is removed from the blood by respiring cells so blood returning to lungs has a lower oxygen concentration than the air in the alveoli which means oxygen diffuses into the blood in the lungs
Normal carbon dioxide content of air is around 0.04% and, as carbon dioxide diffuses into the alveoli from the blood, we breathe out air containing around 4% carbon dioxide
carbon dioxide is produced by respiration and diffuses into blood from respiring cells; the blood transports the carbon dioxide to the lungs where it diffuses into the alveoli as it is a higher concentration in the blood than in the air in the alveoli
The air we breathe out contains more water vapour than when we breathe it in, and the temperature of exhaled air is higher than inhaled air
water evaporates from the moist lining of the alveoli into the expired air as a result of the warmth of the body
The function of cilia and mucus
The passages down to the lungs are lined with ciliated epithelial cells
Cilia comes from the Latin for eyelash, so unsurprisingly these cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed
The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup
The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them getting into the lungs and damaging the cells there
Explaining the effect of exercise on breathing
Frequency and depth of breathing increase when exercising
This is because muscles are working harder and aerobically respiring more and they need more oxygen to be delivered to them (and carbon dioxide removed) to keep up with the energy demand
If they cannot meet the energy demand they will also respire anaerobically, producing lactic acid
After exercise has finished, the lactic acid that has built up in muscles needs to be removed as it lowers the pH of cells and can denature enzymes catalysing cell reactions
It can only be removed by combining it with oxygen – this is known as ‘repaying the oxygen debt’
This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal – the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid