When you’re feeling stressed before exams or after a long, hectic day at school, one simple action can help calm your nerves—taking deep breaths. But have you ever wondered how this works? The answer lies in your respiratory system. When we’re anxious or stressed, our breathing becomes irregular, shallow, and quick. However, slow and deep breathing, which is a natural function of our respiratory system, signals our brain to switch to a more relaxed and positive state. By consciously slowing down our breath, we trick our brain into thinking we’re calm and in control. Give it a try and see how it works for you!
In this article, we’ll break down the key concepts of the respiratory system you need to know for the PSLE, along with useful diagrams and exam strategies to help you ace the topic.
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Overview of Respiratory System
Let’s take a look at our respiratory system! The respiratory system helps the body to take in oxygen and removes carbon dioxide.
| Parts | Function |
| Nose | · Takes in air from the surroundings and removes air from the body · Contains tiny hairs that traps dust and cleans the air entering the body |
| Windpipe | · Allows air to travel from nose to lungs |
| Lungs | · Contains many air sacs which are surrounding by many tiny blood vessels · Blood takes in oxygen from the air sacs and removes carbon dioxide (gaseous exchange) |
| Diaphragm | · Thin sheet of muscle · Controls size of lungs, allow air to enter and exit |
Why do we need oxygen?
Oxygen is needed in the process of respiration. Take note, respiration is different from breathing!
The formula for respiration is: glucose + oxygen -> carbon dioxide + energy.
After understanding the parts of respiratory system and the process of respiration, we are ready to try a question!
Let us attempt a question! (Adapted from MGS P6 SA1 2021)
The diagram below shows the human respiratory system. Exchange of gases takes place at the air sacs.
The graph below shows the amount of two gases, G and H, found in parts X and Y.
- Identify gases G and H. [1]
Gas G: _____________________
Gas H: _____________________
Let’s analyse the question!
Blood entering part X comes from all parts of the body. Hence, it is rich in carbon dioxide but poor in oxygen. As the blood flows past the air sacs, the carbon dioxide is removed from the blood and oxygen enters the blood. Therefore, gas G is carbon dioxide is oxygen while gas H is oxygen. The blood leaving at part Y will be rich in oxygen but poor in carbon dioxide.
We have to confirm our answers with the graph given. As shown from the graph, gas G decreased while gas H increased from part X to Y. This confirms that gas G is carbon dioxide and gas H is oxygen.
Ans: Gas G: Carbon dioxide
Gas H: Oxygen
Moving on to next part of the question!
Mr Ang and Mr Chen took part in a health study. One of them is a smoker. Smoking can cause substances to be trapped in the walls of the air sacs in the lungs. Both of their heart rates at rest over a period of time were measured, as shown in the graph below.
- How does smoking affect the gaseous exchange in the air sacs of the lungs? [1]
- Based on the graph above, is Mr Ang or Mr Chen more likely to be a smoker? Explain your answer. [2]
Let’s look at part B!
To answer part B, student must obtain clues from the question.
Mr Ang and Mr Chen took part in a health study. One of them is a smoker. Smoking can cause substances to be trapped in the walls of the air sacs in the lungs. Both of their heart rates at rest over a period of time were measured, as shown in the graph below.
The walls of air sacs are very thin, allowing for faster gaseous exchange. When substances are trapped in the walls of air sacs, it forms a thick layer around the walls. Gaseous exchange will be much slower as oxygen and carbon dioxide takes longer time to pass through a thicker wall.
The question term is “How”, hence, there is no need to provide reason in the answer.
Ans: Smoking causes a decrease in the rate of gaseous exchange.
Let’s apply BlueTree’s ABC answering technique for part C!
From the graph, we can observe that Mr Ang generally has a higher heart rate than Mr Chen. Hence, we can conclude that Mr Ang is the smoker.
| Answer with a choice | Mr Ang |
| Back with evidence | Mr Ang has a higher average heart rate than Mr Chen |
| Confirm concept | His air sacs walls are thicker due to smoking, hence gaseous exchange is slower. His heart needs to pump blood rich in oxygen faster to all parts of his body. |
Ans: Mr Ang as he has a higher average heart rate than Mr Chen. Mr Ang’s air sacs walls are thicker due to smoking, hence gaseous exchange is slower. His heart needs to pump blood rich in oxygen faster to all parts of his body.
Read more: Lung Model 101
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