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Cell Transport
Cell Membranes help maintain
homeostasis by controlling what
substances enter and leave cell. The
movement of substances may or may
not require energy.
Diffusion
the process by which molecules spread
from areas of high concentratiion, to
areas of low concentration
 Animation

Osmosis
The diffusion of water through a
selectively permeable membrane.
(Think of the diffusion of the smell
of perfume through the air)
Types of Solutions
Isotonic – equal concentration inside and
outside a cell
 Hypotonic – concentration of a dissolved
substance is higher inside the cell than
outside; water moves into the cell
 Hypertonic – concentration of a dissolved
substance is higher outside the cell than
inside; water moves out of the cell

Concentration Gradient
 Difference
between the concentration
inside a cell and outside cell. Particles
naturally move with the concentration
gradient which is from high to low
concentration trying to achieve a
balance. (floating downstream)
 Against concentration gradient means
from low to high (rowing up stream)
Passive Transport
Moves a substance with the
concentration gradient;
Requires no energy input from
the cell (passive = no energy)
Passive Transport
Diffusion - net movement of substances
from an area of high to low concentration.
 Osmosis – diffusion of water
 Facilitated diffusion – assisted by transport
proteins; from high to low concentration; no
energy required

Active Transport
Moves a substance against the
concentration gradient
Reqires energy input from the cell
(active = energy)
Active Transport
 Movement
of large particles that
requires energy occurs through
endocytosis and exocytosis.
 Exocytosis - particles “spit out” by cell
(vacuole becomes part of cell
membrane)
 Endocytosis – particles surrounded and
taken into a cell (forms vacuole)
Types of Endocytosis

Phagocytosis “cell eating” taking in of
larger particles or even whole cells

Pinocytosis “cell drinking” taking in of
fluids or solutes
Cell Membrane Pumps

Carrier Proteins that move substances
against their concentration gradient.