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CELL IN ITS ENVIRONMENT
Diffusion
 The cell membrane is selectively permeable,
which means that some substances can pass
through the membrane while others cannot.
 Diffusion- is the process by which molecules
move from an area of higher concentration to
an area of lower concentration.
 Concentration- is the amount of a substance
in a given volume.
What causes diffusion?
 Molecules are always moving. As they move
they bump into each other.
 The more molecules in an area the more they
will collide.
 Collisions cause molecules to move away
from each other.
 The molecules will continue to spread out
until they are eventually evenly spread out
throughout the area.
Diffusion of oxygen
 There is higher concentration of oxygen
molecules in water than inside the cell.
 The cell membrane is permeable to oxygen
molecules.
 Oxygen molecules diffuse from the higher
concentration to lower concentration
Osmosis!!
 Osmosis- is the diffusion of water molecules
through a selectively permeable membrane
 Because cells cannot function properly
without adequate water, many cellular
processes depend on osmosis.
Osmosis and diffusion
 In osmosis water molecules move by diffusion
from an area where they are highly
concentrated through the cell membrane to
an area where they are less concentrated.
Effects of osmosis
 9A, concentration of water
is the same as it is inside
the cell (normal shape)
 9B, the concentration of
water molecules outside
the cell is lower than the
concentration of water
molecules inside the cell.
(water moves out)
 9C, the concentration of
water outside the cell is
greater than it is inside the
cell. (water moves in)
Active transport
 Passive transport- the movement of dissolved
materials through a cell membrane without
using cellular energy. (down hill)
 Active transport- the movement of materials
through a cell membrane using cellular
energy. (up hill)
 Active transport requires the cell to use its
own energy, while passive transport does
not.
Active Transport proteins
 Transport proteins in the cell “pick up” molecules
outside the cell and carry
them in, using energy.
 Can also carry molecules out
of the cell
 Substances that are carried
include calcium, potassium,
and sodium
Active transport by engulfing
 The cell membrane
surrounds and engulfs, or
encloses, a particle
 One the particle is
engulfed, the cell
membrane wraps around
the particle and forms a
vacuole within the cells.