Download 03 Movement in and out of cells

Movement in and out of cells
Cells need to take in oxygen and nutrients for respiration. They also need to remove waste
products such as CO2. The cell membrane controls movement of materials. Generally, this
is determined by the size of the molecule.
Smaller molecules move through more easily and quickly.
Diffusion
the movement of molecules from an area of high concentration to an
area of low concentration until the molecules are in equilibrium
(evenly mixed)
molecule
High concentration
Low concentration
Molecules move down a concentration gradient (high to low) until the molecules are in
equilibrium. Then, diffusion stops.
-
No energy is required
-
Only occurs with gases and liquids (not solids)
-
Examples of materials which move in and out of cells by diffusion:
.
Oxygen and carbon dioxide in the lungs
.
Antibodies diffuse in the placenta
.
Glucose
.
Amino acids
.
Small molecules like solutes and gases (e.g. glucose, amino acids and oxygen
moving into cell and carbon dioxide moving out).
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Osmosis
A form of diffusion but only involves water molecules. Only occurs across a
partially permeable membrane.
Partially permeable membrane
only allows certain molecules to pass across it, generally
it is only small molecules that can pass through.
Definition of osmosis
Osmosis is the movement of water molecules from an
area of high water potential to an area of low water
potential (concentration) across a partially permeable
membrane.
The rate of diffusion is increased across a shorter distance and if the concentration gradient
is steeper.
Partially
permeable
weak sucrose solution membrane
strong sucrose solution
high water potential
OSMOSIS
(many water molecules)
low water potential
(few water molecules)
Osmosis in plant and animal cells
Cytoplasm contains water
Animal Cell
Cell placed in solution with
much less water potential than
cytoplasm
Cell placed in a very high
water potential (e.g. water)
water moves into
cell by osmosis
cell bursts (lysed)
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cell loses water
cell shrinks (crenated)
Plant Cell
cell wall
vacuole
cell membrane
Cell placed in a very high
water potential (e.g. water)
Cell placed in solution with
much less water potential than
cytoplasm
Cytoplasm and vacuole lose water.
The cell membrane may pull away
from the cell wall as water is lost.
This is called plasmolysis. The cell
is called plasmolysed.
Cell swells but does not burst
because the cell wall resists the
increased pressure (cell wall is
strong and flexible).
The cell is turgid
Active Transport
substance
carrier
molecule
OUTSIDE
ATP
cell
membrane
ADP
INSIDE
Substance
combines with
carrier molecule
Carrier transports
substance across
membrane using
energy from ATP
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Substance is
released into cell
Active transport moves molecules against the concentration gradient.
against concentration
gradient
Low concentration
High concentration
NEEDS ENERGY – unlike diffusion, which does not.
ATP
needs a protein carrier molecule to carry the molecules across the membrane.
can be used to carry into/out of a cell
-
Adenosine triphosphate
provides ‘free’ energy for cells to do ‘work’
universal energy carrier in molecules
e.g. Active transport and muscle contraction
ATP is produced by respiration – by breaking down glucose
ADP + P
A
P
P
P
broken
down
A
P
P
+
P
+
‘free’ energy
for ‘work’
High energy
bond
ADP is Adenosine diphosphate.
Examples of active transport
Kidney
glucose leaves blood passes into the kidney but must be reabsorbed into the
blood.
Tubule
Blood
Method
High glucose concentration
No glucose
Diffusion
Equal glucose concentration Equal glucose concentration
No glucose
No diffusion
High glucose concentration Active transport
Root Hair Cells
Minerals may be taken in from the soil using active transport when the concentration in the
soil is lower than that of the root hair cell.
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Endocytosis / Exocytosis
Some cells can take in (endocytosis) or expel (exocytosis) solid particles or drops of fluid
through the cell membrane. Endocytosis occurs in single celled ‘animals’ such as
paramecium when they feed or in certain white blood cells when they engulf in bacteria
called phagocytosis.
Exocytosis takes place in the cells of some glands. A secretion forms vacuoles or granules
in the cytoplasm and these are expelled through the cell membrane to do their work outside
the cell.
nucleus bacterium
Cell membrane
Endocytis (phagocytosis) in a white blood cell
vacuole
Enzyme released
Exocytosis in a gland cell
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