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TRANSPORT
Cell Membrane
** The cell membrane controls the passage of
materials into and out of the cell.
• Cell membranes are semi-permeable
• Cell membranes are made of phospholipids
(fats) and proteins
– The fat molecules have hydrophilic (water-loving)
heads and hydrophobic (water-hating) tails.
– The fat molecules form a double layer with heads
out and tails in
– Proteins are embedded in the phospholipid bilayer
• See pg. 145 (biozone)
Phospholipid Bilayer
http://www.bio.davidson.edu/people/macampbell/111/membswf/membranes.swf
Passive Transport
• Movement of materials without using
energy
• Particles move along a concentration
gradient from high concentration to low
concentration
• There are 2 types of passive transport:
– Diffusion
– Osmosis
Diffusion
• All particles of matter are constantly
moving at random.
• Diffusion is the movement of particles
down a concentration gradient until
evenly distributed.
– Example: if someone sets off a stink bomb
in one corner of the room, the smell will
gradually move to fill the room evenly or
food colouring
– Raise your hand when……..
• The rate of diffusion varies depending
on:
–
–
–
–
Size of molecules (small-fast, big-slow)
Temperature (warm-fast, cool-slow)
State of matter (gas-fast, liquid-slow)
Concentration gradient (steep-fast, gentleslow)
– Distance involved (short-fast, long-slow)
– Surface Area involved (large-fast, smallslow)
• Facilitated diffusion occurs when a
substance is helped across a membrane
by a protein-carrier
Osmosis
• Osmosis is the movement of water molecules
from an area of high water concentration to
an area of low water concentration through a
semi-permeable membrane.
• Example: If you have a 5% salt solution on one
side (95% water) and a 15% salt solution (85%
water) on the other side, the water will move
from the 5% solution side to the 15% solution
side.
• Osmoregulation is the control of water
in a cell.
– If a plant cell loses water, it becomes
flaccid (floppy) and the cytoplasm pulls
away from the cell wall. This is
plasmolysed.
– If a plant cell gains water, it swells and
becomes turgid (stiff).
– Since animal cells have no cell wall, if they
have too much water they burst. This is
called lysed.