Year 8 Science · Unit 1 · Lesson 9
Challenge Worksheet
Learning Goals
Find the errors
This paragraph contains exactly three errors. Underline each one and write the correction below.
A student’s summary
The heart has four chambers: two atria and two ventricles. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the body. Blood leaves the heart in veins, which have thick walls. It then passes through capillaries, where oxygen and nutrients move into the cells. It comes back to the heart in arteries, which have valves. By the time it returns, the blood has turned blue because it has given up its oxygen.
1. Write the three corrections.
| Measurement | Typical value |
|---|---|
| Average speed of blood in the aorta (the large artery leaving the left ventricle) | 330 mm per second |
| Average speed of blood in a capillary | 0.3 mm per second |
| Length of a typical capillary | 0.6 mm |
Data: rounded averages from physiology books. Speeds change with every heartbeat and with exercise.
2. How many times faster does blood move in the aorta than in a capillary?
Answer times
3. Calculate how long blood takes to pass through one typical capillary. Then calculate how far blood in the aorta travels in that same time, in metres.
Answer s, and m
4. Someone claims: “Veins are just arteries with the blood going the other way. If you swapped their names, nothing about the body would change.” The claim is partly right: both are blood vessels in the same system, linked by capillaries. Use two differences in structure between arteries and veins to show that the claim is wrong. For each difference, explain how it suits the vessel’s job.
5. Evaluate this statement: “The fastest-moving blood does the most important work in the body.” Use Table 1 and what you know about the heart, arteries, capillaries, veins and blood. Finish with a clear judgement.
Find the errors
1. (i) Blood leaves the heart in arteries (thick walls), not veins. (ii) It comes back to the heart in veins, which have the valves, not arteries. (iii) Blood never turns blue; returning blood is dark red. Veins only look bluish through the skin. [3 marks: 1 per correction]
Your Turn
2. 330 ÷ 0.3 = 1100 times. [1 mark]
3. Time = 0.6 ÷ 0.3 = 2 s. Distance in the aorta = 330 × 2 = 660 mm = 0.66 m. [3 marks: 1 time, 1 distance in mm, 1 conversion to m]
Go Deeper
4. Any two, 2 marks each (1 difference, 1 link to job): arteries have thick walls, which suit carrying the strong surge of blood pushed out by each heartbeat; veins have thinner walls and a wider space inside, which suit holding and returning a large amount of blood; veins have valves, which stop blood flowing backwards as it returns to the heart (for example up from the legs), and arteries do not need them. [4 marks]
Show What You Know
5. Marking guide: 1 fast blood in the aorta comes from the pumping of the left ventricle and gets blood quickly to distant organs; 1 capillaries are where exchange with cells happens, through walls one cell thick; 1 data used (blood moves about 1100 times slower in capillaries, spending about 2 s in each, which gives time for exchange); 1 veins return blood to the heart, with valves, and blood carries the substances the whole way; 2 justified judgement (the statement is wrong or only partly right: the actual delivery to cells happens where blood is slowest, and speed and slowness are both needed because the parts depend on each other; 1 if the judgement has no reason). [6 marks]
Common error to watch for: in Q3, multiplying 0.6 by 0.3 instead of dividing. Time = distance ÷ speed; check that the answer is in seconds.