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Cell Transport
Movement of substances in and out of
cells
Substances move in and out of cells by:
1. Passive Transport
2. Active Transport
Passive Transport
No energy (ATP) is required to move gas or liquid
molecules from one place to another!
(Is this an example of a “free lunch” or perpetual motion?… imagine if our cars
worked like this….)
Need to understand concepts of :
• Diffusion,
• Osmosis,
• Concentration gradient,
• Net movement
Diffusion
• The random movement of molecules from
an area of high concentration to an area of
low concentration.
• Down the concentration gradient.
Conc. Grad
Rate (speed) of diffusion depends on:
fast
Size of molecules
Temperature
State of matter
Concentration gradient
slow
Osmosis
• Net movement of water molecules from an
area of high water concentration to an
area of low water concentration, through a
semi-permeable membrane.
• Hypertonic – more solute and less water
• Hypotonic – less solute and more water
• Isotonic – same conc. of solute and water
Think (don’t write)
• Most marine fish die if
transferred to freshwater.
• When a drop of blood is
mixed with distilled water, the
blood cells burst.
• Living plant tissues that had
lost water become firm when
supplied with water.
Net movement
The overall movement of all molecules of a
substance back and forward along the
concentration gradient.
e.g. when oxygen or water molecules diffuse
into a cell, some molecules move out at
the same time. Overall more are moving
inwards than outwards so the net
movement is………..
Osmoregulation
• The control of water in a cell.
• Plasmolysis –
– Water leaves cell and membrane shrinks from
wall.
– Cell becomes flaccid.
– Full plasmolysis is irreversible.
• Turgor
– Water enters cell causing it to swell
– Cell becomes turgid
– Cell wall prevents rupture
Active Transport
Energy (ATP) is required for:
Endocytosis (phago- and pino-),
Exocytosis,
Ion pumps
• e.g. re-absorption of glucose by kidney,
salt uptake by the roots of plants, amino
acid uptake by fungi
• The movement of substances from an
area of low concentration to an area of
high concentration.
• Against the concentration gradient
Conc. Grad
Cytosis
1.Endocytosis
• Movement in (enter) to a cell
• Phagocytosis – cell eating – forms a food
vacuole.
• e.g. Lysosomes fuse to enable digestion.
• Pinocytosis – cell drinking – forms a
vesicle
• e.g. Amoeba and white blood cells (WBC)
– pseudopodia
2.Exocytosis
• Movement out (exit)
• Vesicles bud off from golgi apparatus or
ER, vacuole fuses with cell membrane and
expels contents
• Secretions e.g. digestive enzymes
released, glands
Ion Pumps
• Proteins in the cell membrane can actively
accumulate specific ions on one side of
the membrane to control the amount