Transport Across Plasma Membranes (Diffusion and Osmosis)

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