KS3 · Biology

The effects of exercise on the body

Sprint for a bus and you puff, your heart pounds and you get hot. Three separate things? No — they all start in one place, inside your muscle cells.

Start inside a working muscle

Build the web: from one muscle cell to everything you feel

Your challenge: show how puffing, a pounding heart and getting hot are connected. Pick a factor, pick what it leads to, and add the arrow. Start with the muscles doing the work and keep asking 'so what does that cause?' When your web feels complete, compare it with the lesson's.

Muscles contract more
Muscle cells respire faster
More oxygen and glucose needed, more carbon dioxide made
More heat released
Breathing rate rises
Heart rate rises
The body sweats

Add a link

This factor……made this happen or worse

No links yet.

Two words people mix up

Breathing or respiration?

You've just sprinted for the bus and you're gasping for air. Your friend says: "That's your respiration going crazy."

Be honest — which of these is closest to what you think respiration is?

Respiration is just the science word for breathing.Respiration happens in the lungs, when the oxygen goes in.Breathing gives your muscles their energy directly.Breathing moves gases in and out; respiration is a chemical process in cells that provides energy.

How sure are you?

I'm sureI think soI'm guessing

Respiration is just the science word for breathing.

This is a common misconception

This is the most common mix-up in this topic, so you're in good company — but they are two different processes. Breathing is mechanical: it moves air so oxygen gets into the body and carbon dioxide gets out. Respiration is chemical: it happens inside cells, and its job is to provide energy. Your friend is only half right. You're gasping BECAUSE respiration in your muscle cells has sped up.

Respiration happens in the lungs, when the oxygen goes in.

This is a common misconception

The lungs are where breathing brings oxygen in and where gases swap between the air sacs and the blood. But respiration itself happens inside cells — and during exercise, the cells that matter are your muscle cells, in their mitochondria. The lungs are the delivery entrance, not the place the energy is provided.

Breathing gives your muscles their energy directly.

This is a common misconception

Breathing never hands energy to a muscle. What breathing does is bring in the oxygen. The blood carries that oxygen, along with glucose, to the muscle cells, and then respiration in those cells uses them to provide the energy. Breathing is the supply chain; respiration is where the energy is actually provided.

Breathing moves gases in and out; respiration is a chemical process in cells that provides energy.

This matches the evidence

Exactly right. Breathing is the mechanical job of getting oxygen in and carbon dioxide out. Respiration is the chemical process in your cells that provides energy. And the two are linked: when your muscle cells respire faster, you have to breathe faster to keep up.

Breathing moves the gases. Respiration provides the energy. You breathe faster during exercise because your cells are respiring faster.

Measure it yourself

Taking a pulse rate — and making it reliable

Ravi wants to know his pulse rate in beats per minute (bpm). He counts 38 pulses in 30 seconds. Then, to get a more reliable result, he takes three repeat readings. Work through his method — you supply the missing steps.

Find the pulse: place the first two fingers of one hand gently on the thumb side of the wrist of the other hand.
Count the pulses for 30 seconds: Ravi counts 38.
missing step

Which line is step 3?

38 ÷ 2 = 19 bpmA minute is two lots of 30 seconds, so multiply by 2: 38 × 2 = 76 bpm.38 × 60 = 2280 bpm38 + 30 = 68 bpm

Check the plan

Spot the slip in Leah's investigation

Leah is investigating the question: "How does the amount of exercise affect pulse rate?" Here is her plan. Every line is right except one. Which line goes wrong?

Leah's plan — which line goes wrong?

Independent variable (what I change): the amount of exercise — resting, moderate (20 jumping jacks in a minute) and vigorous (30 jumping jacks in a minute).
Dependent variable (what I measure): my pulse rate, in beats per minute.
Control variables (what I keep the same): the same person each time, and the same length of time spent exercising.
Results table: amount of exercise in the left-hand column, units in the column headings, three repeat readings for each amount of exercise, then a mean.
Graph: my exercise levels go up in order, from resting to vigorous, so I will draw a line graph.
Plotting: I will join my three points up, from resting to vigorous.
Axes: amount of exercise on the x-axis, and mean pulse rate (bpm) on the y-axis.

Predict, then check

Look at where each curve meets its dashed line.

Asha and Ben do the same exercise for the same length of time. Afterwards, each draws a line graph of their pulse rate against time, with their resting pulse rate drawn as a dashed horizontal line. Asha's curve reaches her dashed line at an earlier time than Ben's reaches his. Who is fitter?

The bigger picture

What regular exercise does for your health

Sort each benefit of regular exercise: is it physical, mental or social wellbeing?

Still to sort

Physical (0)

Your body: muscles, bones, heart.

Where the line is: Physical benefits change your body itself — how strong or flexible it is.

Mental (0)

How you think and feel.

Where the line is: Mental is about what's going on inside your own head; social is about you and other people.

Social (0)

You and other people.

Where the line is: Social benefits need other people — they come from doing things together.

10 of 10 still to sort.

Health isn't just 'not being ill'. It's a range from good health to ill health, and it covers three kinds of wellbeing: physical, mental and social. Regular exercise helps all three.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Why your breathing, your heart and your temperature all change when you exercise — and how to measure it.

What you need to know

During exercise, muscles contract more, and the energy for contraction is provided by respiration in the mitochondria of muscle cells.
Breathing rate rises to get more oxygen in and more carbon dioxide out; the gases move between the air sacs and the blood by diffusion.
Heart rate rises so the blood delivers more oxygen and glucose to the muscles and takes more carbon dioxide back to the lungs.
Faster respiration releases more heat, so the body sweats to cool down.
Breathing is not respiration: breathing moves gases in and out; respiration is a chemical process in cells that provides energy.
Pulse rate (bpm) = pulses counted in 30 seconds × 2; a mean = total of the repeats ÷ number of repeats.
Recovery time is how long the heart rate takes to return to its resting rate; fitter people have a shorter recovery time.

The big picture

When you exercise, your muscles contract more, and contraction needs energy from respiration in the mitochondria of the muscle cells. Faster respiration needs more oxygen and glucose, makes more carbon dioxide and releases more heat — so your breathing rate rises, your heart rate rises and you sweat. You can measure the effect by taking your pulse, and fitter people have a shorter recovery time. Regular exercise also benefits your physical, mental and social wellbeing.

Key points

1One cause, three effects: faster respiration in muscle cells explains faster breathing, a faster heart rate and sweating.

2Breathing moves gases; respiration provides energy — two different processes.

3Diffusion is the movement of particles from a high concentration to a low concentration: oxygen moves from the air sacs into the blood, carbon dioxide from the blood into the air sacs.

4In an exercise investigation: independent variable = amount of exercise, dependent variable = pulse or breathing rate, control variables = the person and the time spent exercising.

5The amount of exercise is categoric, so results go on a bar chart; a pulse-rate-against-time graph is a line graph, and the recovery time is where the curve meets the dashed resting line.

6Health is a range from good to ill health and covers physical, mental and social wellbeing — regular exercise benefits all three.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

A class investigated how the amount of exercise affects pulse rate. Their mean pulse rate was lowest at rest, higher after moderate exercise and highest after vigorous exercise. Describe and explain these results.

⚠ Watch out

Saying you breathe faster during exercise 'to make more energy', as if breathing and respiration were the same thing. Breathing only moves oxygen in and carbon dioxide out; the energy is provided by respiration inside the muscle cells.

🧠

Memory hook

Puff, pound, sweat — all from one cell. Breathing swaps the gases, the heart delivers them, respiration uses them — and the heat respiration releases is why you sweat.

✓

Check yourself

A friend says their heart races on a run 'because it's tired'. Using the word respiration, explain the real reason — and name one other change with the same cause.

Flashcards

(15)

What counts as exercise?

An activity that needs physical effort, done to keep up or improve health and fitness.

Is walking moderate or high intensity? And running?

Walking is moderate intensity — it raises your heart rate, but not very high. Running is high intensity.

How much activity should children and young people aim for?

An average of 60 minutes of moderate or high intensity activity every day — plus moving more in everyday life, like walking to school and using the stairs.

How much activity do adults need each week?

150 minutes of moderate intensity activity, or 75 minutes of high intensity activity.

Define breathing rate.

The number of breaths taken per minute.

Define heart rate, and give its unit.

The number of times the heart beats in a minute, recorded in beats per minute (bpm).

What is diffusion?

The movement of particles from where they are in a high concentration to where they are in a low concentration.

In the lungs, which way does each gas diffuse?

Oxygen: from the air sacs into the blood. Carbon dioxide: from the blood into the air sacs, to be breathed out.

Where in a muscle cell does respiration happen?

In the mitochondria.

Why does exercise make you hot?

Respiration releases heat. Faster respiration releases more heat, so the body gets hot — and sweats to cool down.

Why take three repeat readings and work out a mean?

It makes the results more reliable.

What is recovery time?

The time it takes for the heart rate to return to its resting rate (the pulse rate before exercise) after exercise.

What does being physically fit mean?

Your body's systems work together efficiently, so you can do normal daily activities and other physical activity easily.

Name four things that can indicate fitness.

Heart health, flexibility, endurance and body mass index (BMI).

What is osteoporosis, and how can exercise help?

A bone disease in which bones become more prone to breaking. Regular exercise strengthens bones, lowering the risk.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

Build the web: from one muscle cell to everything you feel

Breathing or respiration?

Taking a pulse rate — and making it reliable

Spot the slip in Leah's investigation

What regular exercise does for your health

More KS3 Biology topics