Biology Chapter 4

• Passive transport is the movement of substance across a membrane without energy(ATP) input from the cell.
• Diffusion is the general term for the movement of material in a fluid or gas from a region of higher concentration to a region of lower concentration sometimes through a membrane. Natural motion causes collisions and the scatter of ions and molecules.
• Concentration is the number of ions and molecules in a given volume.
• Concentration gradient is the difference in concentration of a substance from one place to another.
• Equilibrium is when the particle concentration is the same throughout volume.
• Ions/particles/molecules diffuse down concentration gradients from areas of high concentration to areas of lower concentration attempting to reach equilibrium.
• Some materials that diffuse are ions, food coloring, perfume, and water.
• Diffusion in cells plays an important role in moving substances across the cell membrane.
• Osmosis is the diffusion of water across a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration.
• Water concentration is the opposite of the dissolved particle(solute) concentration in a solution.
• There are 3 types of solutions cells are bathed in: hypertonic solution, hypotonic solution, and isotonic solution.
• Hypertonic solution the cell over time shrinks due to a lower solute concentration to a higher water concentration inside the cell and a higher solute concentration to a lower water concentration outside the cell.
• Hypotonic solution the cell over time swells and could rupture due to there being a higher solute concentration to a lower water concentration inside the cell and a lower solute concentration to a higher water concentration outside the cell.
• Isotonic solutions stay the same over time because the solute and water concentration levels are the same inside and outside the cell.
• Some animals and unicellular organisms have special adaptations to live in hypotonic solutions which allow them to remove excess water that is diffusing in.
• Facilitated diffusion is the diffusion of ions or molecules across a membrane through a transport protein. It moves from an area of higher concentration to an area of lower concentration. This enables materials that cannot cross the phospholipid bi-layer(cell membrane) to diffuse through transport proteins.
• Water moves through aquaporins(transport proteins for water).
• Most transport proteins are specific and designed to allow certain molecules or ions pass through.