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Cellular Transport
Cell Membrane and Cell Wall:
• ALL cells have a cell membrane made of proteins and lipids
protein channel
Layer 1
Cell
Membrane
Layer 2
lipid bilayer
protein pump
• SOME cells have cell membranes and cell walls – ex: plants, fungi
and bacteria
Cell
Membrane
Cell Wall
• Cell membranes and cell walls are porous allowing water,
carbon dioxide, oxygen and nutrients to pass through
easily
Function of the Cell Membrane:
• Cell membrane separates the components of a cell
from its environment—surrounds the cell
• “Gatekeeper” of the cell—regulates the flow of
materials into and out of cell—selectively permeable
• Cell membrane helps cells maintain homeostasis—
stable internal balance/equilibrium
Selectively Permeable
• A property or characteristic of the
cell membrane.
• It can allow some materials to pass
through while keeping other
materials out.
• Ex: allows water and nutrients in;
wants to keep toxins out
Some things can pass through on their
own, some need help, some cannot
pass at all.
2 Types of Transport Across
the Cell Membrane
• 1. Passive Transport
– The cell uses NO energy; the molecules
don’t need any help to cross the cell
membrane
– Diffusion
– Osmosis
• Diffusion is the movement of small particles across a
selectively permeable membrane like the cell membrane
until equilibrium is reached.
These particles move from an area of high concentration
(crowded) to an area of low concentration (more space).
outside of cell
inside of cell
• Osmosis is the diffusion of water through a selectively
permeable membrane like the cell membrane
Water diffuses across a membrane from an area of high
concentration (crowded) to an area of low
concentration (more space).
Semi-permeable
membrane is
permeable to water,
but not to sugar
Osmosis
• Happens when water enters the
roots of a plant
Normal RBC
RBC in pure
distilled water
2 Types of Transport Across
the Cell Membrane
Active Transport
Active transport is the movement of molecules from LOW to
HIGH concentration.
Energy is required as molecules must be pumped against the
concentration gradient.
Proteins that work as pumps are called protein pumps.
Ex: Body cells must pump carbon dioxide out into the surrounding
blood vessels to be carried to the lungs for exhale. Blood vessels are
high in carbon dioxide compared to the cells, so energy is required
to move the carbon dioxide across the cell membrane from LOW to
HIGH concentration.
outside of cell
inside of cell
Carbon Dioxide
molecules
Equilibrium
• A state when the molecules are
spread out evenly – but remember
the molecules are still moving.
• Endocytosis and Exocytosis is the mechanism by which
very large molecules (such as food and wastes) get into
and out of the cell
Food is moved into the
cell by Endocytosis
Wastes are moved out
of the cell by
Exocytosis
Passive transportmovement of
substances with
out using energy
Diffusion- moving of
molecules where there
are many to where
there a few to even
out the number of
them
Cell membranes
control the movement
in and out of the cell
Moving
Moving
Cellular
Cellular
Material
Materials
Osmosis- the
movement of water
from an area of low
concentration to an
area of high
concentration of a
substance
Active transportthe use of energy
to move materials
into a cell
Endocytosisthe cell
membrane
surrounds
materials and takes
them into the cell
Exocytosisthe cell
membrane
surrounds material
and sends them
outside the cell