# Explain why the cells lining the small intestine need active transport to absorb amino acids from the intestine into the blood, even when the concentration of amino acids inside the blood is already lower than inside the intestinal fluid.

> Edexcel GCSE Biology (1BI0) — 1.5 Transport in cells · Explain · 4 marks

> After a protein-rich meal has been digested, amino acids are present in the small intestine. The cells lining the small intestine must move these amino acids into the blood. In some situations, the concentration of amino acids in the blood is actually higher than in the intestinal fluid.

## Mark scheme (4 marks)

1. Active transport moves substances against a concentration gradient (from a lower to a higher concentration)
2. Diffusion alone cannot move amino acids into the blood when the concentration in the blood is higher than in the intestinal fluid
3. Active transport requires energy (from respiration / ATP) to move amino acids
4. Active transport uses carrier proteins (in the cell membrane) to move amino acids into the blood

## Key terms

- [active transport](https://www.gradenine.co.uk/glossary/active-transport)

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-cells-lining-the-193e00d0) · Published by Druglandscape Ltd.