Download Cellular Processes

Cellular Processes
*Transportation of Substances In/Out
of Cell (Active vs. Passive
Transport)  Unit Three
*Respiration  Unit Three
*Photosynthesis  Unit Three
Transporting Substances
Across Cell Membrane
*All cells are constantly moving substances
in / out of cell to maintain homeostasis.
*It is the job of the cell membrane to
regulate this function.
*Substances such as oxygen, carbon
dioxide, water, electrolytes (charged
ions such as Mg+, Na+, etc.), glucose
molecules, and waste are necessary to
travel in / out of cell.
*There are two types of transport,
depending on size of molecule:
1)
2)
Passive Transport
Active Transport
Passive Transport:
*requires NO input of energy
from the cell (no ATP)to get
substances in/out of cell;
process occurs naturally.
WHY?
substances getting in/out are
either very small (carbon
dioxide, oxygen, water) or the
flow is going with the natural
force of gravity.
-
the “natural flow” of
substances across the cell
membrane is based upon the
concentration.
Oxygen, Carbon Dioxide,
and Water travel from
where there is more to
where there is less.
(from high to low
concentration).
Types of Passive Transport
Diffusion – movement of molecules from
an area of high concentration to an
area of low concentration; substances
that easily diffuse through cell
membrane include water, carbon
dioxide, and oxygen.
- the substances will continue to spread
out to a lower concentration until it is
evenly distributed throughout the
space; this even distribution is called
equilibrium.
- not ALL substances has
the ability to easily diffuse
across the cell membrane; it
depends on the type and size
of substance.
Example of Diffusion?
Osmosis: A Special
Type of Diffusion
*Osmosis - a special type of diffusion in
which WATER is moved from a region
of high concentration to a region of low
concentration.
- water moves in or out of the
cell depending on where the water level
is the greatest/least  water is always
competing for space with larger
molecules, such as Na+, Mg+, Cl-!!
- naturally, cells’ liquid environment has
these dissolved solutes (electrolytes)
in their liquid (ex: Na+, K+, Mg+).
Areas of the cell that have high
solute concentration have low water
levels.
- To determine which way water will
move, you need to establish the
environment on BOTH sides of cell
membrane (extracellular and
intracellular):
-
-
water tends to naturally move to
levels where water is low (via
osmosis); therefore....
water tends to diffuse in/out of
cell where solute
concentration is the highest!!!
Example: Which Way Will
Water Move?
*The aqueous environment that cells are
“bathed” in can be described as....
1) Hypotonic
2) Hypertonic
3) Isotonic
Hypertonic – outside solution contains more
solutes than water compared to inside
cell.....water rushes out of the cell.
(draw scenario)
Hypotonic – outside solutions contain less
solutes than water compared to inside
cell......water rushes into the cell.
(draw scenario)
Isotonic – both the outside and inside solution is
equal in solute and water concentration; no
net movement.
(draw scenario)
Other Examples
RED = solute BLUE = water
Real-Life Examples
Will Diffusion or
Osmosis Ever Stop?
*Theoretically, diffusion / osmosis
will stop when both sides are
equal in concentration. This is
known as equilibrium.
*Equilibrium is easy to achieve
outside living organisms.
Internally, equilibrium is only
short-lived....all living organisms
are constantly fighting for
equilibrium.
Facilitated Diffusion – a type of diffusion
in which substances traveling across the
cell membrane need help; a special
protein called a carrier protein (a type of
peripheral protein in the cell membrane)
helps the substance travel across;
- no energy in needed by the cell;
therefore facilitated diffusion is still
passive transport.
Example:
Glucose molecules are too big to diffuse
across, but are too small for the cell to
waste its energy on.
2)
Active Transport:
- unlike passive transport, active
transport carries substances across
the cell membrane AGAINST the
natural flow of substances (against a
concentration gradient from LOW to
HIGH concentration).
- requires input of energy from cell
(in the form of ATP).
- substances are usually too large to
passively cross cell membrane.
- two types of active transport:
Cellular Pumps
Endo/Exocytosis
Sodium-Potassium Pumps
-
type of active transport in which special carrier
proteins of the cell membrane “carry” charged
ions (Na+, K+, etc.) across the membrane,
AGAINST a concentration gradient.
-
these charged ions are very important to the
cell because they are responsible for
conducting electrical impulses from one body
part to another.
- Dehydration can lead to an imbalance of these
ions causing fatigue, delirium, loss of muscle
control, coma, and eventually death.
Endocytosis / Exocytosis
-
VERY large substances that are not charged
ions and cannot move across the cell
membrane use this process (large lipids,
proteins, etc.)
-
Since large molecules are moving against the
concentration gradient, cell has to use ATP.
-
endo -/exocytosis is a process in which the
membrane “engulfs” (by use of vesicles) the
substance to get it across the cell membrane.
-
Endocytosis – a type of active transport in
which substances are transported into the cell.
-
Exocytosis – a type of active transport in
which substances are transported out of the
cell.
-
endo - / exocytosis can be further
categorized by the TYPE of substance
being transported in/out of cell:
-
Pinocytosis – transport of fluids (NOT
WATER!!!) in/out of cell by
endo/exocytosis.
-
Phagocytosis – transport of large,
solid substances in/out of cell by
endo/exocytosis.