Year 8 Science · Unit 1 · Lesson 3
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Learning Goals
Match each system to its components and job
Write the matching letter in the middle column. Each letter is used once.
| Organ system | Letter | Components and major function |
|---|---|---|
| Circulatory | A. Stomach and intestines: break down food and absorb useful substances. | |
| Respiratory | B. Brain, spinal cord and nerves: carry messages and control the body. | |
| Digestive | C. Lungs and air passages: gas exchange. | |
| Nervous | D. Heart, blood vessels and blood: transport substances around the body. |
Put the oxygen’s journey in order
Number the steps from 1 (first) to 6 (last) to show how oxygen gets from the air to a leg muscle cell.
| Step number | What happens |
|---|---|
| Blood flows through tiny vessels (capillaries) in the leg muscle. | |
| Air is breathed in through the nose and trachea to the lungs. | |
| The muscle cells use the oxygen to release energy. | |
| The heart pumps the oxygen-rich blood out through arteries. | |
| Oxygen moves from the lungs into the blood. | |
| Oxygen moves out of the blood into the muscle cells. |
1. Which system does the first step belong to? Which system does the step you numbered 3 belong to?
2. The respiratory and circulatory systems meet in the lungs. Explain why the leg muscle cells would run short of oxygen if either system stopped working, even if the other one was healthy.
Scenario: an asthma flare-up
Priya has asthma. During a flare-up, the muscle around her air passages tightens and their lining swells, so the passages get narrower. Her lungs themselves are not damaged. Each morning she blows as hard as she can into a peak-flow meter, which measures how fast she can push air out of her lungs. Her best-ever reading is 400 L/min. Her sample action plan uses three zones: green 320 or more, yellow 200 to 319, and red below 200 (get medical help urgently).
| Day | Peak flow (L/min) | Zone (green, yellow or red) |
|---|---|---|
| Monday | 390 | |
| Tuesday | 370 | |
| Wednesday | 300 | |
| Thursday | 240 | |
| Friday | 190 | |
| Saturday | 330 |
Source: sample results and a sample action plan. A real action plan is written by a doctor for each person.
3. Complete the Zone column in Table 1. Then calculate Friday’s reading as a percentage of Priya’s best reading.
Answer %
Cause and effect
Complete the chain for Priya’s flare-up on Friday. Each box is caused by the box before it.
4. Priya’s lungs were not damaged. Use the idea of components and roles to explain why her respiratory system still could not do its job properly on Friday.
5. A Year 7 student says: “Blood, air and food all just get moved around, so those three systems are really doing one job.” Correct this student. For the circulatory, respiratory and digestive systems in turn, name two parts and what each part does, then state that system’s major job. Finish by showing how two of these systems rely on each other.
Match each system to its components and job
Circulatory → D; Respiratory → C; Digestive → A; Nervous → B.
Put the oxygen’s journey in order
Reading down the table as printed: 4, 1, 6, 3, 2, 5.
1. Step 1 (breathing in): the respiratory system. Step 3 (the heart pumps blood out through arteries): the circulatory system. [2 marks]
2. The respiratory system brings oxygen into the lungs, and the circulatory system carries it from the lungs to the muscle. If the respiratory system stopped, no oxygen would enter the blood; if the circulatory system stopped, oxygen would reach the lungs but never get to the leg. Each system needs the other to finish the job. [2 marks: 1 each system’s role, 1 dependence]
Go Deeper
3. Zones: Monday green, Tuesday green, Wednesday yellow, Thursday yellow, Friday red, Saturday green. Friday: 190 ÷ 400 × 100 = 47.5%. [3 marks: 2 for all six zones (1 if four or five are right), 1 for the percentage]
Cause and effect: box 2: less air can flow in and out of the lungs. Box 3: less oxygen moves from the lungs into the blood, so the blood carries less oxygen to the body.
4. The respiratory system has several components with different roles. The air passages carry air to and from the lungs, and the lungs exchange gases with the blood. With the passages narrowed, too little air reaches the lungs, so gas exchange falls even though the lungs are healthy. The system only works when all its components do their jobs. [2 marks: 1 role of the air passages, 1 link to the whole system’s function]
Show What You Know
5. Marking guide: 1 per system (up to 3) for two components with correct roles (circulatory: heart pumps, blood vessels carry blood, blood transports substances; respiratory: air passages such as the trachea carry air, lungs exchange gases; digestive: stomach breaks down food, intestines absorb useful substances); 2 for three different major functions (transport, gas exchange, break down food and absorb it; 1 if two are right); 1 for a clear link (for example, food absorbed by the digestive system is carried to cells by the circulatory system; oxygen taken in by the respiratory system is carried by the blood). [6 marks]
Common error to watch for: in the ordering task, putting “the heart pumps” before “oxygen moves into the blood”. The blood must pick up oxygen in the lungs before it can be pumped out to the muscle.