Transcript MATERIALS MOVE ACROSS THE CELL`S MEMBRANE

MATERIALS MOVE ACROSS
THE CELL’S MEMBRANE
• SOME MATERIALS MOVE BY
DIFFUSION
– Diffusion= the process by which molecules
spread out, or move from areas of high
concentration to areas of less concentration
– Occurs because molecules are always in
constant motion; cells use diffusion to carry
out life functions
• SOME TRANSPORT REQUIRES
ENERGY
• CELL SIZE AFFECTS TRANSPORT
DIFFUSION
• Occurs naturally as
particles move from area
of high concentration to
area of lower concentration
• The greater the difference
in concentrations, the
quicker diffusion occurs.
• Diffusion is how materials
move in photosynthesis &
cellular respiration.
• Diffusion is a type of
passive transport (materials
move without using cell’s
energy.)
• Polar substances
(sugar/salts/amino acids)
diffuse via protein channel
(still passive- no energy)
OSMOSIS
• Diffusion of water
through a
membrane is
OSMOSIS.
• If you forget to
water a plant, the
soil dries, the roots
dry, and water
leaves the plant
cells by osmosis, so
the cell shrinks and
the plant “wilts”.
Some Transport Needs Energy
• ACTIVE TRANSPORT
– Uses energy to move material through membrane
– Marine iguanas that swim & feed in salty ocean which
causes lots of salt in blood.
– They have special glands using active transport to
remove salt from blood & blow it out of their nostrils.
– Similar to our kidneys filtering blood for us.
TRANSPORT REQUIRING
ENERGY, CONTINUED
• ENDOCYTOSIS:
large bits of material
get captured in pocket
of membrane
• Pocket breaks off and
forms package that
moves into cell.
• Cells use this to fight
bacteria & viruses by
absorbing them.
• EXOCYTOSIS: a
membrane within the cell
encloses material needed
to be removed
• Package moves to cell
membrane, joins with it,
and expels material
• Cells use this to flush out
waste or expel proteins &
hormones made by the
cell.
CELL SIZE AFFECTS
TRANSPORT
• Most cells are very small; most human cells are
about 50 micrometers (.05mm), while bacteria
are only 3-5 micrometers.
• The amount of cell membrane limits the ability of
a cell to transport materials into and out of a cell.
• As a cell gets larger, there is a time when its
volume grows more than its surface area, so not
enough resources can get into the cell to feed it.
• Thin, flat cells or long skinny cells (muscle &
nerve) give lots of surface area for plenty of food
and resources to get into the cell.