Osmosis and Water Movement

Overview

This lecture introduces osmosis, explains water concentration and solutes, and demonstrates how osmosis works in relation to cells.

Diffusion is the net movement of particles from an area of higher concentration to one of lower concentration.
Molecules like oxygen and glucose enter cells by diffusing down their concentration gradients.

Osmosis is a special case of diffusion, involving only water molecules.
Osmosis is the net movement of water across a partially permeable membrane from a region of higher water concentration to lower water concentration.

Water concentration refers to the amount of water relative to the amount of dissolved substances (solutes) like sugars or salts.
Higher solute concentration means lower water concentration, and vice versa.
It’s the proportion of water compared to solutes, not the absolute volume of water, that determines concentration.

Cells have a partially permeable membrane that allows only certain molecules, like water, to pass through.
If the outside of a cell has fewer solutes (higher water concentration) than the inside, water moves into the cell by osmosis.
Osmosis is water moving down its concentration gradient, from high to low water concentration.

Diffusion — Net movement of particles from high to low concentration.
Osmosis — Net movement of water molecules across a partially permeable membrane from high to low water concentration.
Partially Permeable Membrane — A barrier that allows some molecules (like water) to pass through but not others.
Solute — Substance dissolved in a liquid (e.g., sugar or salt in water).
Concentration Gradient — Difference in concentration between two regions.

Review the previous lesson on diffusion if unsure about the concept.
Complete the lesson and practice questions for this topic on the learning platform (link provided in the video description).