---
title: "Co-transport and Coupled Movement Across Membranes"
description: "A pump spends ATP to build an ion gradient, and a second protein then uses that gradient to drag another molecule in with the ion. Glucose uptake at the gut wall is the standard case."
canonical: https://lightmysky.com/learn/science/co-transport-and-coupled-movement-across-membranes-mt_pzQ8n3FWNV
source: https://lightmysky.com/learn/science/co-transport-and-coupled-movement-across-membranes-mt_pzQ8n3FWNV.md
retrieved: 2026-09-12
---

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# Co-transport and Coupled Movement Across Membranes

A pump spends ATP to build an ion gradient, and a second protein then uses that gradient to drag another molecule in with the ion. Glucose uptake at the gut wall is the standard case.

Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18
Page: https://lightmysky.com/learn/science/co-transport-and-coupled-movement-across-membranes-mt_pzQ8n3FWNV

## Ready when they can

- Separates the step that spends ATP from the step that rides the gradient.
- Traces sodium and glucose through the two proteins in the right order.
- Explains why blocking the pump stops glucose uptake although glucose transport uses no ATP directly.

## Lesson: How gut cells pull in glucose

Your gut lining must take in glucose even when glucose is already more concentrated inside its cells. The first worker is the sodium potassium pump. It burns ATP to push sodium out of the cell, which builds a steep sodium gradient across the membrane. That gradient stores energy, like water held behind a dam.

The second worker is the sodium glucose symporter. A symporter is a carrier that moves two substances together in the same direction. Sodium flows back into the cell down its gradient, and the symporter couples that downhill trip to dragging glucose uphill with it. Because the ATP step and the glucose step sit in different proteins, this is called secondary active transport.

**Example.** Walk through the order in one gut cell. First the pump burns ATP and pushes sodium out. Then the symporter lets sodium rush back in and pulls glucose in with it. Block the pump and the chain breaks: sodium piles up inside, the gradient fades, and glucose uptake halts, even though glucose transport itself never touches ATP.

**Tip.** Questions love to swap the two steps, so keep them apart. If a question asks what pays for glucose entry, answer the sodium gradient, not ATP. An antiporter is the mirror image: it swaps two substances in opposite directions while a symporter moves both the same way.

**Recap.** The pump spends ATP to build a sodium gradient, and the symporter spends that gradient to pull glucose in.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Active Transport Against the Gradient](https://lightmysky.com/learn/science/active-transport-against-the-gradient-mt_BQf1bgo9oM)

## Opens up

- [The Resting Potential and the Action Potential](https://lightmysky.com/learn/science/the-resting-potential-and-the-action-potential-mt_0sh4w30ocz)
- [Ion Channels: Selectivity, Gating and the Evidence from Single Channels](https://lightmysky.com/learn/science/ion-channels-selectivity-gating-and-the-evidence-from-single-channels-mt_2xPzPeXZZ_)
- [Equilibrium Potentials and What Sets the Resting Voltage](https://lightmysky.com/learn/science/equilibrium-potentials-and-what-sets-the-resting-voltage-mt_mRT_5vDEO1)
- [Ultrafiltration and Selective Reabsorption in the Nephron](https://lightmysky.com/learn/science/ultrafiltration-and-selective-reabsorption-in-the-nephron-mt_vSKfoJN6zh)
- [Translocation and the Mass Flow Hypothesis](https://lightmysky.com/learn/science/translocation-and-the-mass-flow-hypothesis-mt_WZ8id0kou4)