biology / Cells & Energy / free

Membrane Transport

Move particles across a membrane and see gradients do the work.

Follow the mechanism1 / 3

A concentration gradient exists. Unequal concentration creates a potential direction for net movement, but it does not guarantee that a molecule can cross.

selective membranepassive diffusion

Transport mode

Focus the idea

gradient68%

permeability58%

directionhigh → low

net flow39

Concentration difference 68%Membrane permeability 58%Available ATP energy 24%

Particles move high → low without ATP. The gradient creates the push; permeability controls how much gets through.

A membrane can be selective and directional: passive transport follows a gradient, while active transport uses ATP to push against it. In this model the ATP supply must first cover an uphill cost that grows with the gradient (0.4 × gradient), so the pump stalls below that level and slows as the gradient steepens; above it, flow rises smoothly and levels off. The particle motion is symbolic, not a molecular-scale simulation.

Guided journey

Walk through the process.

Step 1 of 3: 01 / Start with a gradient

Particles are more concentrated on one side of the membrane.

What changes next: That difference creates a possible direction for net movement.

04 / PRACTICE

Make the biology yours.

0 / 3 checked

Answer from the model, then use the explanation to connect the visual mechanism to the biological rule.

CHECK 1 / 3

Membrane Transport

Walk through the process.

Particles are more concentrated on one side of the membrane.

Make the biology yours.

What can move without ATP in this model?