Circulatory and Respiratory systems
Comparing line Graphs
This science revision note aims to help your child
– understand the techniques to interpret line graphs and
– how to write out the answer using the proper keywords.
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The graph below shows the heart rate of Olivia and James from 0 to 20 minutes when they are doing an activity. Olivia is walking while James is running.
Which graph shows the heart rate of James? Explain your answer.
STEP 1
To identify the graph:
1) Compare the two activities, walking and running – which activity has a higher intensity?
The activity with a higher intensity will result in a greater increase in heart rate. Running has a higher intensity than walking, hence, running results in a greater increase in heart rate.
2) Compare the graphs – which graph shows a greater increase in heart rate?
Graph A shows heartrate increase from 55 heartbeats to 98 heartbeats per minute (an increase of 43 heartbeats per minute) while Graph B shows a smaller increase in heartbeat rate from 70 heartbeats to 86 heartbeat (an increase of 16 hearbeats per minute). Hence, Graph A shows a greater increase in heart rate. Graph A shows the running activity.
Therefore, James’ heart rate is shown by Graph A.
STEP 2
The explanation of your answer must have four key points:
- Compare the change in heart rate (Providing evidence)
- Compare the amount of oxygen and digested food transported to the body cells
- Compare the rate of respiration
- Compare the amount of energy released
Note that each key point requires you to “compare”, meaning that you must use comparative words, such as “more”, “faster”, etc.
When applying these key points to the question, be sure to make your answer specific to the question:
- James was running, running is a more strenuous/ vigorous activity compared to walking. This results in a greater increase in heart rate compared to walking
- James’s heart pumps blood faster to transport more oxygen, water and digested food to his body cells.
- James’s cells respire faster
- to release more energy needed for his running activity.
FINALLY, put your answer together
Question: Which graph shows the heart rate of James? Explain your answer. (2m)
Answer:
Graph A.
Evidence: James was running. Running is a more strenuous/vigorous activity compared to walking. This results in a greater increase in heart rate compared to walking. (1m)
Reasoning: James’s heart pumps blood faster to transport more oxygen, water and digested food to his body cells. James’s cells respire faster to release more energy (1m) needed for his running activity.
Common mistakes
Wrong answer: Graph A. Because the final heart rate is higher.
This is wrong because you have to look at an increase in the heart rate, rather than just the final heart rate. Every person has different heart rates at rest, so their heart rate will increase to different levels after exercise. Consider this graph:
Graph A has a higher final heart rate not because the activity was more intense, but because the heart rate at rest (Zero minutes) was already much higher. Hence, you have to look at the increase in the heart rate and not just the final heart rate.
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Andy Ling
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