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Study Guide:
Movement of Materials Through the Cell Membrane
I. The Cell Membrane
a. Selectively Permeable or _semi-permeable_
The cell membrane only certain molecules to pass through the membrane freely
b. Molecular Movement
Constantly colliding, moving down a concentration gradient from H to L,(trying to
get to area of lower concentration so they can move and not collide, pioneers E to W)
1. H2O, O2, CO2, Amino Acids: move freely across the cell membrane because they
are small molecules
2. Carbohydrates, Proteins, larger molecules: they are bigger molecules so they need
help moving across the membrane
3. Ions: charged molecules so they need help across the membrane
c. Concentration Gradient
difference between the number of molecules inside vs. outside the cell
d. Dynamic Equilibrium
NO difference in the number of molecules on either side of the membrane
II. Movement of Materials In and Out of the Cell
a. Diffusion
net movement of the same molecules down a concentration gradient (H to L), no energy
b. Osmosis
diffusion of water across a semi-permeable membrane from H to L
1. Isotonic: has an equal concentration of dissolved particles as the inside of a cell,
water flows in and out at the same rate. (paramecium in fresh water, has
contractile vacuole to expel excess water)
Students will use the
diagrams for isotonic,
hypertonic, and hypotonic
to conceptualize these
terms.
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2. Hypertonic: has a higher concentration of dissolved particles than the inside of a
cell, water mostly OUT (ocean water to human cells or fresh water fish in salt
water, salt on a slug)
3. Hypotonic: has a lower concentration of dissolved particles than the inside of a
cell, water mostly IN (distilled water to human cells or salt water fish in fresh
water)
c. Facilitated Diffusion: molecules transported across the membrane by channel/transport
proteins
d. Active Transport: movement of molecules against the concentration gradient using
energy, L to H
1. Endocytosis: taking items into a cell by membrane folding (bulk transport); red
blood cells engulf invaders
i. Pinocytosis: taking in small amounts of liquid (paramecium/contractile
vacuole)
ii. Phagocytosis: taking in food or solid particles
2. Exocytosis: removal of particles from the cell by membrane folding;
(paramecium/contractile vacuole)
Name: _______________
Class: _______________
Date: _______________