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Cells
Section 3-3: Cell Processes
Metabolism
The sum of all building-up
and breaking-down activities
that occur in a living cell
Respiration
 The
process in which simple food
substances such as glucose are
broken down and the energy they
contain captured in high energy
molecules that can be used as
fuel by the cell
Aerobic Respiration
Requires oxygen
 Occurs in the mitochondria
 C6H12O6 + 6O2
6CO2+ 6H2O +energy

(glucose)
(ATP)
Aerobic Respiration

Although the equation is simple the
process is complicated, involving many
different molecules and many steps
Anaerobic Respiration
Does not use oxygen
 Provides much less energy
 Fermentation (such as the process used to
make wine) is a form of anaerobic
respiration
 Used by yeast that produce alcohol and
carbon dioxide

Photosynthesis
Occurs in chloroplasts
 Also a very complex process
 6CO2+ 6H2O + energy
C6H12O6 + 6O2
(glucose)
 The energy is captured from light by
chlorophyll

Diffusion
The process by which molecules of a
substance move from an area of higher
concentration of that substance to areas of
lower concentration of that substance
 Occurs because of the constant motion of
molecules that causes them to spread out
until they are evenly distributed in the
available volume

Diffusion

Is a physical process that does not require
the input of energy from a living organism
A
B
C
Diffusion into a Cell
Diagram by Mariana Ruiz Villarreal, released to public domain
Osmosis
The diffusion of water into or out of a cell
 Many single-celled organisms that live in
fresh water use contractile vacuoles to
pump excess water out of the cell. The
water enters the cell by osmosis.

Semi-permeable Membranes
Cell membranes are semi-permeable or
selectively permeable
 This means that only certain molecules
can diffuse through them including:

 Water
 Oxygen
 Carbon
dioxide
 Small food molecules
Osmosis
Lower
Concentration
of Water
Molecules
Higher
Concentration
of Water
Molecules
Of Salt
Of Salt
Active Transport

The process by which a cell moves
molecules into and out of the cell that
cannot diffuse through the membrane

Requires energy to work
Active Transport
One method uses special transport
molecules (proteins) that pick up a specific
substance on one side of the membrane
and moves it to the other side
 This is how ions of calcium (Ca),
potassium (K) and sodium (Na) move

Active Transport
Diagram by Mariana Ruiz Villarreal, released to public domain
Active Transport
A second type of active transport is called
phagocytosis.
 A cell surrounds a food particle with a
pocket of cell membrane which pinches off
into the cell to form a food vacuole

Active Transport-Phagocytosis
Drawing of an ameba engulfing a bacterium