Unit 1 - Cell Membranes
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Membranes are composed of a double layer of
phospholipid molecules with embedded protein molecules
Membrane structure is often described as
fluid mosaic
Membrane structures are fluid mosaic. Fluid because
the molecules are constantly moving
Membrane structures are fluid mosaic. Mosaic because
the proteins sticking out of the phospholipid bilayer are likened to the pattern seen in a tile mosaic floor
Only ______ molecules can pass through the phospholipid layer
fat soluble
Most important cell molecules are
soluble in water
Most cell molecules if they are small enough can only pass through the membrane via
pores in the embedded protein molecules
Membranes are ________ permeable
Selectively
All cells are enclosed by a plasma membrane which controls the molecules that
enter and leave a cell and so maintain a constant environment within a cell
Water enters or leaves the cell by
osmosis
Osmosis is the movement of water molecules from
a region of higher water concentration to a region of lower water concentration through a selectively permeable membrane
The body must maintain a constant blood water concentration so that the body cells
neither shrink nor burst
Blood cells would _____ if the plasma had a lower water concentration
SHRINK
Blood cells would _____ if the plasma had a higher water concentration
BURST
HYPERTONIC is when the plasma has a
lower water concentration
HYPOTONIC is when the plasma has a
higher water concentration
Diffusion is the movement of molecules from a
high concentration to a lower concentration
Fat soluble molecules diffuse through
phospholipid bilayer
Small molecules diffuse through
protein channels
Oxygen and glucose diffuse into the cell because their use in
respiration produces a lower concentration
CO2 released by respiration _____ out of the cell
diffuses
Active transport is the movement of molecules from a
low concentration to a higher concentration against a concentration gradient
The concentration of molecules in a cell can be maintained at a ______ or ______ concentration than in plasma
higher, lower
Active transport is
selective