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1. Active transport: Energy-requiring movement of molecules across a mem-
brane from a region of lower concentration to a region of higher concentration.
2. Cell membrane: Forms a boundary between a cell and the surrounding envi-
ronment and controls the passage of materials into and out of the cell.
3. Concentration gradient: Difference in the concentration of a substance from
one location to another.
4. Diffusion: Movement of dissolved molecules in a fluid or gas from a region of
higher concentration to a region of lower concentration.
5. Endocytosis: Uptake of liquids or large molecules into a cell by inward folding
of the cell membrane.
6. Exocytosis: Release of substances out of a cell by the fusion of a vesicle with
the membrane.
7. Facilitated diffusion: Diffusion of molecules assisted by protein channels that
pierce a cell membrane.
8. Fluid mosaic model: Model that describes the arrangement and movement of
the molecules that make up a cell membrane
9. Hypertonic: Solution that has a higher concentration of dissolved particles
(solutes) compared with another solution.
10. Hypotonic: Solution that has lower concentration of dissolved particles
(solutes) compared with another solution.
11. Isotonic: Solution that has an equal concentration of dissolved particles com-
pared with another solution.
12. Osmosis: Diffusion of water molecules across a semipermeable membrane
from an area of higher water concentration to an area of lower water concentration.
13. Passive transport: Movement of molecules across the cell membrane without
energy input from the cell.
14. Phagocytosis: Uptake of a solid particle into a cell by engulfing the particle.
15. Phospholipid: Molecule that forms a double-layered cell membrane consist-
ing of a phosphate group, glycerol, and two fatty acids
16. Receptor: Protein that detects a signal molecule and performs an action in
response
17. Selective permeability: Condition allowing some but not all materials to cross
a barrier or membrane.
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