🫁 Human Respiratory System
Primary 5 Science — Summary Notes
Created by Miss Clarissa Ng · www.clartutors.com
1. Earth's Atmosphere — What's in the Air
- Nitrogen (78%) — the most abundant gas in Earth's atmosphere.
- Oxygen (21%) — oxygen and nitrogen together make up nearly 99% of the air.
- Trace gases (1%) — this small slice includes argon, carbon dioxide and other minor gases.
Shifting water vapour
The amount of water vapour varies based on local humidity and geography. Humid regions contain more water vapour; dry regions contain significantly less.
2. Breathing vs Respiration
Breathing is Physical
A physical process of inhaling and exhaling that takes place in the lungs.
Respiration is Chemical
A chemical process in every cell that breaks down glucose to release energy.
⭐️ KEY POINT
Breathing takes place in the lungs; respiration takes place in every cell of the body. Breathing brings in oxygen for respiration to happen.
3. Parts of the Respiratory System
Function: to enable gaseous exchange between the surroundings and the body.
It consists of the nose, windpipe and lungs.
| Part | What it does |
|---|---|
| Nose | When we inhale, air enters our bodies through the nose. The inside of our nose is wet and warm, and tiny hairs in the nose trap dirt and dust in the air that we breathe in. The air becomes warmer, cleaner and more moist after it passes through the nose. |
| Windpipe | Connects the nose to the lungs. Carries air to and from the lungs. |
| Lungs | Enables gaseous exchange to take place. |
The diaphragm is not part of the respiratory system, but it helps in breathing. It is an elastic sheet of muscle located below the lungs.
4. Parts of the Lungs
- The lungs are made up of tiny air sacs, which are surrounded by many tiny blood vessels.
- The air sacs in the lungs increase the exposed surface area of the lungs, allowing gaseous exchange between the air in the lungs and the bloodstream to take place faster.
- Oxygen in the air enters the bloodstream. The blood then transports oxygen to all parts of the body.
- Carbon dioxide is removed from the lungs when a person exhales.
🧪 EXAM TIP
Whenever a question asks why gaseous exchange is faster, the answer is surface area — air sacs in the lungs, gill filaments in fish, stomata in leaves.
5. Gaseous Exchange — Inhaled and Exhaled Air
| Component | Inhaled air | Exhaled air |
|---|---|---|
| Nitrogen | Same | Same |
| Oxygen | About 21% | Less ⬇️ |
| Carbon dioxide | About 0.04% | More ⬆️ |
| Other gases including water vapour | 0.96% (less water vapour) | More water vapour ⬆️ |
| Temperature | Room temperature | About body temperature ⬆️ |
| Dust particles | More dust particles | Cleaner ⬇️ |
6. Breathing Rate
- The breathing rate is the number of breaths taken in one minute.
- The rate and depth of our breaths increase when we engage in vigorous activities.
- These changes enable more oxygen to be taken into the lungs, and more carbon dioxide to be removed from the body.
MEMORISE! (BE BORED)
When we exercise, our Body needs more Energy. Thus, we Breathe faster to take in more Oxygen to undergo a greater rate of Respiration to release more Energy. This also allows our body to remove carbon Dioxide (given out during respiration) faster.
| Letter | Stands for | The answer, in full |
|---|---|---|
| B | Body | Our body needs more energy. |
| E | Energy | Our body needs more energy. |
| B | Breathe | We breathe faster. |
| O | Oxygen | To take in more oxygen. |
| R | Respiration | To undergo a greater rate of respiration. |
| E | Energy | To release more energy. |
| D | Dioxide | Carbon dioxide given out during respiration is removed faster. |
7. Fish Respiratory System
- Fish breathe underwater using gills, which allow gaseous exchange to take place.
- Fish take in dissolved oxygen from the water through their mouth, which is absorbed into the bloodstream at the gills.
- When water enters the mouth of the fish and passes through the gills, dissolved oxygen enters the bloodstream and is transported to all parts of the fish.
- Carbon dioxide in the bloodstream passes through the walls of the blood vessels and is removed when water flows out from under the gill covers.
- The gill filaments increase the exposed surface area of the gills, allowing gaseous exchange between the gills and the surrounding water to take place faster.
8. Fish vs Human Respiratory System
| Similarities | Differences |
|---|---|
| Both the air sacs in the human lungs and the gill filaments of the fish increase the exposed surface area of the lungs and gills respectively, enabling gaseous exchange to take place faster. | Gills take in dissolved oxygen in the water, but lungs take in oxygen from the surrounding air. |
| Both gills and lungs allow oxygen to enter the blood and carbon dioxide to leave the blood. | |
| Both gills and lungs have a rich supply of blood vessels. |
9. Plant Respiratory System
- Plants respire all the time.
- Gaseous exchange between the plant and the surrounding air takes place mainly through the tiny openings (stomata) found mostly on the underside of leaves.
| In the presence of light | In the absence of light | |
|---|---|---|
| Process | Photosynthesis | Respiration |
| Take in… | Carbon dioxide | Oxygen |
| Give out… | Oxygen | Carbon dioxide |
The stomata also allow water vapour to escape.
- The size of each tiny opening on the leaves can change.
- In the day, when the plant photosynthesises, the tiny openings become bigger for the plant to take in more carbon dioxide to make more food.
- At night, when sunlight is absent and photosynthesis cannot take place, the tiny openings become smaller to reduce the amount of water vapour lost through the openings, leaving only a small gap for gaseous exchange.
10. Humans, Fish and Plants — Respiration
- Humans and plants take in oxygen from the air, while fish take in dissolved oxygen in water.
- Humans, fish and plants carry out respiration by taking in oxygen and giving out carbon dioxide.
- Plants carry out respiration and photosynthesis in the day: carbon dioxide is taken in and oxygen is given out.
👀 TO BE DETECTED
In the day a plant gives out oxygen (more than it uses) because photosynthesis is faster than respiration — but the plant is still respiring at the same time.
11. Common Question — Lung Model
Match each part of the model to the part of the respiratory system it represents:
| Part of the model | Represents |
|---|---|
| Straw | Windpipe |
| Bottle | Ribcage |
| Balloons | Lungs |
| Cut balloon | Diaphragm |
| Air space inside the bottle | The space inside the chest |