Respiration and Gaas Exchange Notes

Respiration: respiration is NOT breathing in and out, respiration is what happens in each cell of the body, it is the process of releasing energy from glucose and the energy is released as chemical and heat energy.

Aerobic Respiration needs plenty of oxygen: It only happens when there is a plentiful supply of oxygen and is the most efficient way to release energy from glucose.

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Glucose + Oxygen → Carbon dioxide + water (+ energy)

C6H12O6 + 6O2 → 6CO2 +6H2O (+ energy)

Anaerobic Respiration doesn’t use Oxygen at all: when you are doing vigorous exercise your body can’t get enough oxygen in at the rate it’s being used so you start to respire anaerobically. If the lactic acid builds up in muscles it’s painful.

Glucose → Lactic Acid (+ energy)

Anaerobic respiration in plants is slightly different, plants can respire without oxygen too and they produce ethanol (alcohol).

Glucose → Ethanol + Carbon Dioxide (+ energy)

Investigation of Respiration

We can see the bi product of CO2 due to respiration when the organisms respire to this we can test with hydrogen carbonate solution.

The hydrogen carbonate turns from an orange colour to a yellow colour in the presence of carbon dioxide.

We can also measure the heat created by respiration by putting a thermometer in with the organism in a vacuum and then we find the temperature increase due to respiration.

Gas Exchange – Flowering plants

When plants photosynthesis they use up carbon dioxide and produce oxygen, its vice versa when they respire.

When the plant is photosynthesising it uses a lot of carbon dioxide so there isn’t any left in the plant, this makes the carbon dioxide enter the plant through diffusion due to the concentration gradient.

It makes a lot of oxygen as a bi product and uses some to respire and the rest diffuses through out of the stomata.

The net exchange of gas depends of light intensity. In the day photosynthesis is happening so carbon dioxide is diffusing in while oxygen is diffusing out from respiration. In the night the plant only respires so it takes in oxygen through diffusion and releases carbon dioxide like humans.

Leaves are adapted for efficient gas exchange.

1. Leaves are broad so a large surface area for diffusion.

2. They are thin so gases only have to travel short distances to the cells where needed.

3. There are air spaces I.e. the spongy mesophyll so it increases the surface area for gas exchange.

4. Stomata closes when it dark as photosynthesis doesn’t happen in the night so doesn’t need carbon dioxide. This stops water from leaking out stopping the plant from becoming dry.

5. The opening and closing of stomata is controlled by the guard cells around the stomata.

Once again we can use hydrogen carbonate to test from CO2.

Because plants need carbon dioxide for photosynthesis they use it up, so the hydrogen carbonate will display the fact carbon dioxide levels have run out by turning purple.

We can use hydrogen carbonate to test how carbon dioxide levels are effected when the plant is covered, in a vacuum etc.

The respiratory System (Humans)

The thorax is the top part of your body breathing anatomy.

It is separated from the lower body by the diaphragm.

The lungs are like big pink sponges and are protected by the ribcage

The air goes through the trachea and it splits into the bronchi

The bronchi then splits into bronchioles

These then go to alveoli.

Breathing In: Intercostal muscles and diaphragm contracts and the thorax increases, this increases pressure drawing the air in.

Breathing Out: Intercostal muscles and diaphragm relax, thorax volume decreases and then air is forced out.


The lungs contain millions of them, the blood that passes next to them is just from rest of the body so doesn’t have much oxygen but lots of carbon dioxide.

Oxygen diffuses out of the alveolus and the carbon dioxide diffuses into the alveolus to be breathed out.

When the blood reaches the body cells oxygen is release from the red blood cells and diffuses into the body cells. At the same time carbon dioxide is diffusing out into the blood and its carried back to the blood.

Specialised Alveoli

There are millions giving an enormous surface area alveolus

There is a moist lining for gas to dissolve

The alveoli have one cell thick wall so the gases don’t have to diffuse far

They have a constant blood supply to keep a high concentration gradient

The walls are permeable so gases can easily diffuse

Smoking Tobacco can cause problems for you!!!!

It damages the alveolus decreasing surface area so less gas is diffused in and out making you breathless easier

The tar in the cigarettes damage the cilia in your throat by making them create a lot of mucus so more chest infections

Tar irritates the bronchi and it encourages mucus which can’t be cleared by the damaged cilia

Carbon monoxide reduces amount of oxygen that blood can carry so heart rate increases and you can get heart disease


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