AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
It also allows sugar molecules to be absorbed from lower concentrations in…
Full specification wording
Active transport: It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration.
In the gut, sugar molecules can be absorbed from the lumen into the blood even when the sugar concentration in the gut is lower than in the blood.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 4 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In the gut, sugar molecules can be absorbed from the lumen into the blood even when the sugar concentration in the gut is lower than in the blood. This is active transport because it moves sugar against a concentration gradient. Energy from respiration and carrier proteins in the cell membrane of intestinal cells are needed. The sugar then enters the blood and is carried to cells. This matters after a meal when most sugar has already been absorbed, or when blood sugar is high, because diffusion alone would not move sugar into the blood. The process helps maintain a supply of glucose for respiration.
What earns the marks
- Sugar molecules are absorbed from the gut lumen into the blood by active transport.
- The movement is against a concentration gradient because gut concentration is lower than blood concentration.
- Energy from respiration and carrier proteins in the intestinal cell membrane are required.
- The absorbed sugar enters the blood and is transported to body cells.
- Active transport allows absorption to continue even when diffusion would not occur.
Common mistakes and how to put them right
Stating that sugar moves by diffusion because it moves from gut to blood.
Put it right by noting that diffusion would require a higher concentration in the gut than in the blood.
Forgetting that carrier proteins are specific.
Put it right by stating that carrier proteins in the membrane transport sugar molecules.
Writing that the blood has a lower sugar concentration than the gut in this example.
Put it right by stating the blood has the higher concentration.
Exam tips
- Compare the concentrations in the gut and blood explicitly before naming the transport process.
- State that energy comes from respiration and is used by carrier proteins.
- Use the term concentration gradient and say whether movement is with or against it.
Try the lesson
The start of the Active transport: It also allows sugar molecules to be absorbed from lower concentrations in the gut into the blood which has a higher sugar concentration. lesson, made from checked teaching notes for this specification point.
Have a go first
Sugar molecules are absorbed from the gut, where their concentration is lower, into the blood, where their concentration is higher. Which process is responsible for this absorption?
Listen
In the gut, sugar molecules can be absorbed from the lumen into the blood even when the sugar concentration in the gut is lower than in the blood. This is active transport because it moves sugar against a concentration gradient. Energy from respiration and carrier proteins in the cell membrane of intestinal cells are needed. The sugar then enters the blood and is carried to cells. This matters after a meal when most sugar has already been absorbed, or when blood sugar is high, because diffusion alone would not move sugar into the blood. The process helps maintain a supply of glucose for respiration. A strong answer earns marks for these points. Sugar molecules are absorbed from the gut lumen into the blood by active transport. The movement is against a concentration gradient because gut concentration is lower than blood concentration. Energy from respiration and carrier proteins in the intestinal cell membrane are required. The absorbed sugar enters the blood and is transported to body cells. A common slip: Stating that sugar moves by diffusion because it moves from gut to blood. Instead, noting that diffusion would require a higher concentration in the gut than in the blood. Exam tip: Compare the concentrations in the gut and blood explicitly before naming the transport process.
See it
Key words
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Active transport
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Concentration gradient
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Carrier proteins
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Respiration
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See every definition
- Active transport
- Movement of sugar molecules from the gut lumen into the blood against a concentration gradient, needing energy from respiration and carrier proteins in the intestinal cell membrane.
- Concentration gradient
- The difference in sugar concentration between the gut and the blood; in this example the gut concentration is lower than the blood concentration.
- Carrier proteins
- Proteins in the cell membrane of intestinal cells that transport sugar molecules, using energy from respiration.
- Respiration
- The process that provides the energy needed for active transport, and which the absorbed sugar helps to supply glucose for.
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