Science notes, unit 2

Humans

Textbook Science Year 4 (DLP), pages 23–52

What this chapter covers

You can name the organs used in breathing and say where they are (2.1.1)
You can describe the path of air during inhalation and exhalation (2.1.2)
You can say how inhaled air and exhaled air are different (2.1.3)
You can describe how the chest moves when we breathe in and out (2.1.4)
You can explain how the rate of breathing changes with activity (2.1.5)
You can suggest ways to keep the lungs healthy (2.1.6)
You can explain what excretion and defecation are, and name the organs and products of excretion (2.2.1, 2.2.2)
You can explain why excretion and defecation are important and how to keep them healthy (2.2.3, 2.2.4)
You can explain stimulus and response and name the sensory organ for each (2.3.1, 2.3.2)
You can explain why we need to respond to stimuli and which habits disrupt response (2.3.3, 2.3.4, 2.3.5)

Your body is busy all day long, even when you sit still! In this unit you will learn how humans breathe, how the body gets rid of waste, and how we respond to changes around us.

2.1Human breathing

Organs used in breathing

Inhalation means taking air into the lungs. Exhalation means pushing air out of the lungs. Together they make up breathing.

Three organs are involved in human breathing: the nose, the trachea (windpipe) and the lungs. Air can also enter through the mouth.

The human body showing the nose, the trachea and the two lungs, each with a label — The nose, trachea and lungs are the organs of breathing.

Did you know? The left lung is a little smaller than the right lung because the heart sits on the left side.

The air passage

Process	Path of air
Inhalation	Nose → trachea → lungs
Exhalation	Lungs → trachea → nose

The path is the same, but the direction is opposite.

Exchange of gases in the lungs

Exchange of gases takes place in the lungs: oxygen goes into the lungs and carbon dioxide leaves the lungs.

Lungs with a close-up in which blue oxygen is carried into the lungs and red carbon dioxide is carried out — Oxygen (blue) is carried in. Carbon dioxide (red) is carried out.

Gas	Inhaled air	Exhaled air
Oxygen	More	Less
Carbon dioxide	Less	More

The air around us is a mixture of oxygen, carbon dioxide, nitrogen, other gases and water vapour.

Careful! Exhaled air still has some oxygen in it. It has less oxygen than inhaled air, not none.

Write the air passage during exhalation.

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Lungs, then trachea, then nose.

Chest movement

Put your hand on your chest and breathe slowly. Your chest moves!

A boy with a hand on his chest. Top: air is inhaled and the chest moves upwards. Bottom: air is exhaled and the chest moves downwards — Inhaling: the chest moves **upwards**. Exhaling: the chest moves **downwards**.

In the activity with a book on the chest, the book goes up when we inhale and down when we exhale. The book moves because the chest moves.

Rate of breathing

The rate of breathing is the number of upward and downward chest movements in one minute.

The more intense the activity, the higher the rate of breathing. The body needs more oxygen when it works harder.

Bar chart: reading 16, walking 24, running 38 chest movements in one minute — Example results. Running has the tallest bar, so it gives the highest rate (38 in one minute).

Reading a result

Observation: Running gives 38 chest movements in one minute; reading gives 16.
Inference: Maybe the body needs more oxygen when running.
Conclusion: The more active we are, the higher the rate of breathing.

Did you know? The type of activity is not the only thing that matters. Other things, such as being ill or very anxious, can also change how fast we breathe.

Keeping the lungs healthy

Haze is dry air with gases, dust and tiny floating particles. It makes it hard to see far and it is unhealthy for people. Smoke, open burning and cigarette smoke also harm the lungs.

Wear a mask when the air is hazy.
Stay away from smoke, open burning and smoking areas.
Do not smoke.
Do exercise in a clean place, such as a park with fresh air.
Stay indoors when the haze is bad.

A person is always in polluted air. What may happen to the lungs?

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The lungs may be damaged, so the person has trouble breathing and can fall ill (for example, coughing or breathing difficulty).

2.2Excretion and defecation

What they mean

Excretion is the removal of waste products from the body, such as urine, sweat, carbon dioxide and water vapour.

Defecation is the removal of faeces through the anus.

Faeces are food that the body could not digest. Defecation is kept separate from excretion.

A boy holding his stomach while he needs the toilet, with a close-up of faeces leaving the body through the anus — Defecation: faeces leave the body through the anus.

Excretory organs and their products

A boy with the lungs, kidneys and skin shown. Lungs release carbon dioxide and water vapour, skin excretes sweat, kidneys excrete urine — Three excretory organs and what they excrete.

Organ	Product
Kidneys	Urine
Skin	Sweat
Lungs	Carbon dioxide and water vapour

Careful! Faeces are not a product of excretion. Removing faeces is called defecation.

Why they are important

Waste products must leave the body so we do not fall ill.
If urine cannot leave, kidney stones may form.
If faeces are hard and cannot leave, we get constipation.

A healthy lifestyle

Eat a balanced diet with plenty of fibre (fruit and vegetables).
Drink enough water.
Exercise regularly and sleep enough.
Use the toilet when the body needs to.

Name the organ that excretes (a) urine (b) sweat.

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(a) Kidneys (b) Skin.

2.3Response to stimuli

Stimulus and response

A stimulus is a change in the surroundings. A response is the action we take towards the stimulus.

Our sensory organs receive stimuli such as light, smell, sound, taste and touch.

Two examples. A girl touches a thorn and moves her hand away. A girl hears thunder and is startled — Stimulus: a thorn. Response: moving the hand away. Stimulus: the sound of thunder. Response: startled.

Stimulus	Sensory organ	Example of response
Light (too bright)	Eyes	Close the eyes or shade them
Sound (alarm clock)	Ears	Wake up
Smell (fried chicken)	Nose	Sniff, feel hungry
Taste (tea with no sugar)	Tongue	Say it is tasteless
Touch (cold)	Skin	Shiver, put on a jacket

Why we need to respond

To avoid injury (move away from a hot or sharp object).
To save ourselves (smell smoke, escape and call for help).
To get information and communicate (hear the horn or siren and give way).

Habits that disrupt response

Habit	What it can cause
Drinking alcohol	Intoxication; the person cannot respond quickly
Glue sniffing	Hallucination and addiction; disturbs the sensory organs and the brain, so response is slow
Drug abuse	Hallucination, blackouts and addiction; the sensory organs do not work well

Medicine is useful when taken as the doctor says. It is abuse that harms the body.

You hear thunder and you are startled. What is the stimulus, the response and the sensory organ?

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Stimulus: the sound of thunder. Response: being startled. Sensory organ: the ears.

Pictures: Science Year 4 (DLP) textbook, pp. 23–52 (breathing organs p. 24, gas exchange p. 27, chest p. 31, rate of breathing p. 33, defecation p. 37, excretory organs p. 38, stimuli p. 43).

Summary

Breathing organs: nose, trachea, lungs. Inhalation: nose, trachea, lungs. Exhalation: lungs, trachea, nose.
Oxygen enters the lungs and carbon dioxide leaves them. Inhaled air has more oxygen; exhaled air has more carbon dioxide.
The chest moves up when we inhale and down when we exhale. The more active we are, the higher the rate of breathing.
Excretion removes waste products (kidneys: urine, skin: sweat, lungs: carbon dioxide and water vapour). Defecation removes faeces through the anus.
A stimulus is a change in the surroundings; a response is the action taken. Alcohol, glue sniffing and drug abuse disrupt response.