AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Students should be able to translate tables and bar charts of glucose,…
Full specification wording
Maintaining water and nitrogen balance in the body (biology only): Students should be able to translate tables and bar charts of glucose, ions and urea before and after filtration.
This skill requires you to interpret quantitative data on the composition of blood plasma, the initial filtrate, and urine.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 12 of 17
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This skill requires you to interpret quantitative data on the composition of blood plasma, the initial filtrate, and urine. You must compare the concentrations of glucose, ions and urea. Before filtration, blood plasma contains glucose, ions and urea. During filtration, all three pass into the kidney tubule to form the initial filtrate. However, glucose is completely reabsorbed back into the blood, so it is absent from the final urine. For example, a table might show glucose in plasma and initial filtrate as 1.0 g dm⁻³, but 0 g dm⁻³ in urine. You should describe the pattern, identify which substances are filtered and reabsorbed, and explain that filtration is selective based on molecule size.
What earns the marks
- Identify that glucose, ions and urea are present in the blood plasma and are filtered into the initial filtrate.
- State that glucose is completely reabsorbed back into the blood, so it is absent from the final urine.
- Compare numerical values from the table or bar chart, quoting specific concentrations for at least two substances.
- Explain that ions and urea are partially or not reabsorbed, so they remain in the urine.
- Recognise that the data show selective filtration based on molecule size, with large molecules such as proteins retained in the blood.
Common mistakes and how to put them right
Assuming that glucose is not filtered into the kidney tubule.
Put it right: Glucose is small enough to be filtered into the initial filtrate, but is then completely reabsorbed.
Confusing the direction of reabsorption, thinking that substances move from the blood into the filtrate.
Put it right: Reabsorption moves useful substances such as glucose from the tubule back into the blood.
Misreading bar charts by comparing bar heights without checking the axis scale.
Put it right: Read the numerical scale carefully and quote values with units.
Exam tips
- When describing data, quote specific numbers from the table or chart, including units, to support your comparison.
- Distinguish clearly between blood plasma, initial filtrate, and final urine.
- If asked to translate data, structure your answer by comparing each substance at different stages of kidney function.
Try the lesson
The start of the Maintaining water and nitrogen balance in the body (biology only): Students should be able to translate tables and bar charts of glucose, ions and urea before and after filtration. lesson, made from checked teaching notes for this specification point.
Have a go first
The table shows the concentration of glucose in the blood plasma entering the kidney and in the fluid immediately after filtration.
| Fluid | Glucose concentration in g/dm³ |
|---|---|
| Blood plasma | 1.0 |
| Fluid after filtration | 1.0 |
What does this data show about glucose?
Listen
This skill requires you to interpret quantitative data on the composition of blood plasma, the initial filtrate, and urine. You must compare the concentrations of glucose, ions and urea. Before filtration, blood plasma contains glucose, ions and urea. During filtration, all three pass into the kidney tubule to form the initial filtrate. However, glucose is completely reabsorbed back into the blood, so it is absent from the final urine. For example, a table might show glucose in plasma and initial filtrate as 1.0 g dm⁻³, but 0 g dm⁻³ in urine. You should describe the pattern, identify which substances are filtered and reabsorbed, and explain that filtration is selective based on molecule size. A strong answer earns marks for these points. Identify that glucose, ions and urea are present in the blood plasma and are filtered into the initial filtrate. State that glucose is completely reabsorbed back into the blood, so it is absent from the final urine. Compare numerical values from the table or bar chart, quoting specific concentrations for at least two substances. Explain that ions and urea are partially or not reabsorbed, so they remain in the urine. A common slip: Assuming that glucose is not filtered into the kidney tubule. Instead, glucose is small enough to be filtered into the initial filtrate, but is then completely reabsorbed. Exam tip: When describing data, quote specific numbers from the table or chart, including units, to support your comparison.
Key words
Say what each word means before you turn the card.
Selective filtration in the kidney
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Reabsorption of glucose
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Composition of blood plasma and urine
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Data interpretation from tables and bar charts
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See every definition
- Selective filtration in the kidney
- Filtration in which substances pass into the kidney tubule based on molecule size, with large molecules such as proteins retained in the blood.
- Reabsorption of glucose
- Movement of glucose from the tubule back into the blood, so that it is completely reabsorbed and absent from the final urine.
- Composition of blood plasma and urine
- Blood plasma contains glucose, ions and urea, which are filtered into the initial filtrate, while ions and urea remain in the urine.
- Data interpretation from tables and bar charts
- Reading the numerical scale carefully and quoting specific concentrations with units to compare glucose, ions and urea before and after filtration.
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