Human body systems, Year 8: respiration and heart rate

In every living cell

HintNot just in the chest: think much smaller, and all over the body.

The whyEach cell needs its own supply of energy, so each one carries out respiration for itself.

Respiration

HintIt is the reason you need food as well as air.

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

Breathing

HintThe other one is a chemical reaction.

The whyBreathing 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

HintThink about what has to happen to the glucose from your food.

The whyWithout oxygen, cells cannot get enough energy from glucose. Brain cells begin to be damaged within minutes.

No — it carries on

HintThe blood still holds a store of oxygen.

The whyCells 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

HintYou can feel it at your wrist or neck.

The whyEach 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

HintThere are four lots of 15 seconds in a minute.

The why18 × 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

HintThink about what the cells doing the work are running short of.

The whyHarder-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

HintThe demand for oxygen has dropped again.

The whyOnce 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

HintWithout it you cannot tell how much changed.

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