AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Students should be able to use simple compound measures such as rate and…
Full specification wording
The heart and blood vessels: Students should be able to use simple compound measures such as rate and carry out rate calculations for blood flow.
Rate is a compound measure that compares a quantity with time.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 11 of 11
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Rate is a compound measure that compares a quantity with time. For blood flow, rate can be calculated as volume of blood divided by time taken, or as distance travelled by blood divided by time. For example, if 70 cm³ of blood flows through a vessel in 10 seconds, the rate is 70 cm³ ÷ 10 s = 7 cm³/s. They should also interpret rates from graphs or tables, and compare rates to describe changes in blood flow. This skill is assessed through calculations and data interpretation in both foundation and higher tier.
What earns the marks
- Rate of blood flow = volume of blood ÷ time taken.
- Rate can also be calculated as distance travelled by blood ÷ time taken.
- Units for rate of blood flow include cm³/s, cm³/min, dm³/min and m/s, depending on the quantities used.
- Rearranging the equation allows calculation of volume (rate × time) or time (volume ÷ rate).
- When comparing rates, ensure the time units are the same before calculating or comparing.
- Interpret rate from a graph by calculating the gradient of a straight-line section.
Common mistakes and how to put them right
Dividing time by volume instead of volume by time.
Put it right: Divide the volume by the time to obtain the rate.
Mixing units, such as using seconds for one measurement and minutes for another.
Put it right: Convert all times to the same unit before calculating.
Forgetting to include units in the final answer.
Put it right: State the correct compound unit, for example cm³/s.
Exam tips
- Write down the equation, substitute the values with units, then calculate and give the unit.
- Check whether the question asks for rate, volume or time, and rearrange the equation before substituting numbers.
- Use the gradient of a distance–time graph to find speed of blood flow when the graph is a straight line.
Try the lesson
The start of the The heart and blood vessels: Students should be able to use simple compound measures such as rate and carry out rate calculations for blood flow. lesson, made from checked teaching notes for this specification point.
Have a go first
A volume of 300 cm³ of blood flows through a vessel in 60 seconds. What is the rate of blood flow?
Listen
Rate is a compound measure that compares a quantity with time. For blood flow, rate can be calculated as volume of blood divided by time taken, or as distance travelled by blood divided by time. For example, if 70 cm³ of blood flows through a vessel in 10 seconds, the rate is 70 cm³ ÷ 10 s = 7 cm³/s. They should also interpret rates from graphs or tables, and compare rates to describe changes in blood flow. This skill is assessed through calculations and data interpretation in both foundation and higher tier. A strong answer earns marks for these points. Rate of blood flow = volume of blood ÷ time taken. Rate can also be calculated as distance travelled by blood ÷ time taken. Units for rate of blood flow include cm³/s, cm³/min, dm³/min and m/s, depending on the quantities used. Rearranging the equation allows calculation of volume (rate × time) or time (volume ÷ rate). A common slip: Dividing time by volume instead of volume by time. Instead, divide the volume by the time to obtain the rate. Exam tip: Write down the equation, substitute the values with units, then calculate and give the unit.
See it
Key words
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Rate
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Rate of blood flow
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Rearranging the equation
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Interpret rate from a graph
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See every definition
- Rate
- A compound measure that compares a quantity with time.
- Rate of blood flow
- Volume of blood divided by time taken, or distance travelled by blood divided by time taken.
- Rearranging the equation
- Allows calculation of volume (rate × time) or time (volume ÷ rate).
- Interpret rate from a graph
- Calculating the gradient of a straight-line section.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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