IB Biology Topic B2.1.3: Simple Diffusion Across Membranes Notes

Simple Diffusion Moves Particles Down a Concentration Gradient Without Energy

Diffusion is the passive movement of particles caused by their constant random motion.

Particles spread from high to low concentration, giving a net movement down the concentration gradient.

Diffusion needs no energy, it is entirely passive.

Definition

Simple diffusion

Simple diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration, down their concentration gradient, without requiring energy (ATP).

Only Small, Nonpolar Molecules Cross the Bilayer Directly

Simple diffusion happens when particles pass straight through the phospholipid bilayer.

Only molecules that can permeate the bilayer cross this way.

Nonpolar molecules such as oxygen and carbon dioxide diffuse easily.
Small polar molecules such as urea and ethanol diffuse more slowly.

The centre of the membrane is hydrophobic, so charged ions struggle to pass through.

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Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

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IB Biology Topic B2.1.3: Simple Diffusion Across Membranes Notes

Simple Diffusion Moves Particles Down a Concentration Gradient Without Energy

Only Small, Nonpolar Molecules Cross the Bilayer Directly

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Excepteur sint occaecat cupidatat non proident

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Simple Diffusion Moves Particles Down a Concentration Gradient Without Energy

Only Small, Nonpolar Molecules Cross the Bilayer Directly

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic B2.1.3: Simple Diffusion Across Membranes Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Simple Diffusion Moves Particles Down a Concentration Gradient Without Energy

Only Small, Nonpolar Molecules Cross the Bilayer Directly

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Simple Diffusion Moves Particles Down a Concentration Gradient Without Energy

Only Small, Nonpolar Molecules Cross the Bilayer Directly

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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