# Explain how the ultrastructure of a proximal convoluted tubule (PCT) cell in the kidney is adapted for the reabsorption of solutes from the glomerular filtrate.

> IB DP Biology Higher Level (2023 syllabus) — B2.3 Cell specialisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Microvilli / brush border on the apical surface greatly increase the surface area for absorption of solutes from the filtrate
2. Abundant mitochondria provide ATP for active transport of solutes (e.g. glucose, amino acids, Na⁺) against concentration gradients
3. Basal infoldings of the plasma membrane increase surface area on the basolateral side, allowing rapid transfer of reabsorbed solutes into the peritubular capillaries
4. Tight junctions between adjacent PCT cells prevent leakage of reabsorbed solutes back into the filtrate / lumen, ensuring directional (transcellular) transport

## Key terms

- [proximal convoluted tubule](https://www.gradenine.co.uk/glossary/proximal-convoluted-tubule)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-ultrastructure-of-a-3d83731b) · Published by Druglandscape Ltd.