Year 8 Science · Unit 1 · Lesson 15
Challenge Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. A part can be undamaged itself and still stop working properly, because a part it depends on has been damaged.
Correct it:
2. Damage to one part always causes problems elsewhere on the same day.
Correct it:
3. Reduced gas exchange in the lungs can make leg muscles tire quickly, even though the muscles themselves are not damaged.
Correct it:
4. Leaves depend on roots for water, and roots depend on leaves for sugar.
Correct it:
5. Plants cannot show system disruption, because they do not have organs.
Correct it:
6. If the heart pumps more weakly, only the circulatory system is affected.
Correct it:
Find the errors
A student writes
“Our dog Biscuit caught a gut infection that damaged the lining of her small intestine. She will be fine, because her stomach still digests her food and her heart still pumps. Digestion is finished once food leaves the stomach, and the small intestine is just a tube that carries the leftovers out. Any damage stays in the intestine and cannot affect the rest of her body.”
1. Identify two scientific errors in the student’s writing. For each, say what is wrong.
2. Rewrite the last sentence as a cause-and-effect chain of at least three linked steps that shows how the damage could affect Biscuit’s whole body.
Scenario: a chest infection
In a bad chest infection, some of the tiny air sacs in the lungs fill with fluid. Less gas exchange can happen there, so each litre of blood leaving the lungs carries less oxygen than usual. The heart then pumps this blood to the rest of the body.
| Measurement | Healthy lungs | During the infection |
|---|---|---|
| Oxygen carried by each litre of blood leaving the lungs | 200 mL | 180 mL |
| Blood pumped to the body each minute | 5 L | 5 L (at first) |
Source: rounded figures for an adult at rest; the 180 mL figure is invented for this example.
3. Calculate the oxygen delivered to the body each minute with healthy lungs and during the infection. Then give the drop as a percentage of the healthy value.
Answer mL per minute, and %
4. How many litres of blood per minute would the heart have to pump during the infection to deliver the same oxygen as healthy lungs do? Give your answer to one decimal place.
Answer L per minute
Evaluate the claim
Someone claims
“A person with a chest infection often has a faster heartbeat than usual. So the infection must have spread from the lungs into the heart.”
5. Is the claim justified? Use your answers to Q3 and Q4 to give a different explanation for the faster heartbeat, and say what the claim gets wrong about how systems interact.
6. Evaluate this statement: “Damage only matters if it hits a vital organ like the heart or the brain. Damage to a small part, such as the fine roots of a plant or the air sacs of the lungs, stays small.” Use one plant example, one animal example and your calculation, and finish with a clear judgement.
True or false
1. True. 2. False: effects can be delayed and spread over time. 3. True. 4. True. 5. False: plants have organs (roots, stems, leaves) that depend on each other. 6. False: cells in every system then receive less oxygen and food.
Find the errors
1. Any two: digestion is not finished in the stomach; the small intestine is where digested food is absorbed into the blood, not just a tube; the damage does not stay local; the heart can only carry what has been absorbed. [2 marks: 1 per error with reason]
2. Model: the damaged lining absorbs less digested food → the blood picks up and carries less food to cells around the body → cells get less food for energy and growth → Biscuit may lose weight and have less energy. [3 marks: 1 per correct linked step]
Your Turn
3. Healthy: 200 × 5 = 1000 mL per minute. Infection: 180 × 5 = 900 mL per minute. Drop: 100 ÷ 1000 × 100 = 10%. [3 marks: 1 each value, 1 percentage]
4. 1000 ÷ 180 = 5.55… ≈ 5.6 L per minute. [2 marks: 1 method, 1 answer]
Go Deeper
5. Not justified. Each litre of blood carries less oxygen, so the heart must pump more blood per minute (about 5.6 L, not 5 L) to deliver the same oxygen. A fault in the respiratory system loads the circulatory system; an effect in one system does not mean damage in that system, because systems interact. [4 marks: 1 judgement, 1 less oxygen per litre, 1 heart must pump more (5.6 L), 1 interaction point]
Show What You Know
6. Marking guide (points expected): 1 plant chain (fine roots torn → less water taken in → leaves wilt); 1 animal chain across two systems (fluid in air sacs → less oxygen into blood → less delivered to cells, heart works harder); 1 calculation used (10% less oxygen, or 5.6 L per minute); 1 effects can be delayed or indirect; 2 judgement: wrong, because components depend on each other (1 if no reasoning). [6 marks]
Common error to watch for: in Q3, subtracting 180 from 200 and calling the answer 20% (the drop per litre is 20 mL out of 200 mL, which is 10%).