Transport Across Plasma Membranes (Diffusion and Osmosis)

The cell’s inner pool is called: Intracellular fluid. In a multicellular organism, the fluid outside the cell is extracellular fluid. Movement between fluid compartments are governed in part by gradients, differences in the concentration of materials in one part compared to those in another.

Two Kinds of Transport: 1. Passive (Diffusion): materials move from regions of higher concentration to regions of lower concentration, without energy expenditure by the cell. 2. Active: movement of substances against concentration gradients (from low to high), requiring the expenditure of energy by the cell.

Passive Transport and the Movement of Water (Osmosis) Water moves from a region of higher water concentration to a region of lower water concentration.

Solution (Solute and Solvent) Solute: a substance that has been dissolved in a solvent. Solvent: a substance capable of dissolving other molecules.

Solutions can be: Isotonic: two solutions having the same concentration of solutes. Cells placed in isotonic solutions maintain their shapes.

Hypotonic: having a lower concentration of solutes than another solution. Cells swell in hypotonic solutions.

Hypertonic: having a higher concentration of solutes than another solution. Cells shrink in hypertonic solutions.

True-false questions 1. A cell placed in an isotonic solution will swell. 2. A cell placed in hypertonic solution will swell. 3. A cell placed in hypotonic solution will swell.

Answers 1. F 2. F 3. T