Human body systems, Year 8: respiration and heart rate

In every living cell

提示Not just in the chest: think much smaller, and all over the body.

为什么Each cell needs its own supply of energy, so each one carries out respiration for itself.

Respiration

提示It is the reason you need food as well as air.

为什么It is a chemical reaction. In its usual form, glucose reacts with oxygen and energy is released for the cell to use.

Breathing

提示The other one is a chemical reaction.

为什么Breathing is a physical movement of the ribs and diaphragm. Respiration is the reaction in cells that uses the oxygen which breathing brings in.

Cells use it in respiration to release energy

提示Think about what has to happen to the glucose from your food.

为什么Without oxygen, cells cannot get enough energy from glucose. Brain cells begin to be damaged within minutes.

No — it carries on

提示The blood still holds a store of oxygen.

为什么Cells respire all the time, awake or asleep. Holding your breath stops fresh air arriving, but the reaction continues with the oxygen already in the blood.

The number of heartbeats per minute

提示You can feel it at your wrist or neck.

为什么Each beat of the heart pushes a surge of blood along the arteries, and you can feel that surge wherever an artery runs near the skin.

72

提示There are four lots of 15 seconds in a minute.

为什么18 × 4 = 72. Counting for a quarter of a minute and multiplying up is quicker than counting for the full minute.

Muscles need more oxygen and glucose

提示Think about what the cells doing the work are running short of.

为什么Harder-working muscles respire faster. The heart beats more often so that blood delivers supplies and removes carbon dioxide more quickly.

It falls back to its resting rate

提示The demand for oxygen has dropped again.

为什么Once the muscles need less, the heart slows. The time this takes is called the recovery time, and it is shorter in fitter people.

To give a resting value to compare with

提示Without it you cannot tell how much changed.

为什么The effect of the exercise is the difference between the two readings. One reading alone says nothing about the change.