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CELL TRANSPORT
The ABSORPTION and CIRCULATION of materials into a cell.
Regents Biology
OBJECTIVES
Upon completion of this unit students will be able to:
1. Define the key terms associated with the processes of the
cell membrane.
2. State the difference between diffusion and osmosis.
3. Explain the differences between passive transport and active transport.
4. List and briefly describe the various types of active and passive transport.
5. State the difference between EXOcytosis and ENDOcytosis.
6. State the difference between pinocytosis and phagocytosis.
7. Identify and differentiate isotonic, hypotonic, and hypertonic solutions.
KEY TERMS
Active Transport
Cell Membrane
Diffusion
Endocytosis
*Equilibrium
Exocytosis
*Fluid-Mosaic Model
Hypertonic Solution
Hypotonic Solution
Isotonic Solution
*Kinetic Energy
Osmosis
* NOT IN GLOSSARY, SO USE INDEX OF TEXTBOOK OR DICTIONARY.COM
Passive Transport
Phagocytosis
Pinocytosis
Solute
Solution
Solvent
INTRODUCTION: CELL TRANSPORT
• Vital materials, such as OXYGEN AND DIGESTED FOODS
that allow a living organism to survive must REACH ALL
CELLS OF THE ORGANISM. Also, the waste materials must
be carried away and released into the environment.
• The life function of TRANSPORT is responsible for this
movement and is defined as THE LIFE FUNCTION BY
WHICH ORGANISMS ABSORB AND DISTRIBUTE
MATERIALS NECESSARY TO MAINTAIN LIFE
• We will talk about both absorption and circulation as
separate processes.
A. ABSORPTION
• Absorption is THE 1ST STAGE OF TRANSPORT; CELLS
TAKE DISSOLVED MATERIALS THROUGH THE CELL
MEMBRANE TO THE INTERIOR
I. THE CELL MEMBRANE
• The key organelle involved with cell transport is the CELL
MEMBRANE
• The function of the cell membrane is to CONTROL what
enters and leaves the cell. Because not all substances can
easily go into and out of the cell, the cell membrane is said
to be SELECTIVELY PERMEABLE.
REMEMBER: The cell membrane is a LIPID
bilayer with floating PROTEINS (“floating
icebergs of protein in a fatty sea”)
•The model on the previous page is used to describe
the structure of the cell membrane and is called the
FLUID-MOSAIC MODEL. Fluid because the lipid
bilayer continually moves around and is never
motionless. Mosaic because that is how it appears;
a mosaic is A PIECE OF ART THAT IS MADE UP
OF LOTS OF LITTLE PIECES PUT TOGETHER
•Factors that affect the movement of materials into
and out of a cell include:
1. SIZE OF THE MOLECULES
2. ELECTRICAL PROPERTIES OF MOLECULES
3. TYPE OF CELL
I. PASSIVE TRANSPORT
1. Diffusion
• No cellular energy is expended in this absorption
process.
• Diffusion is a natural process by which molecules
move from and area of HIGH CONCENTRATION to
an area of LOW CONCENTRATION
• Diffusion occurs because THE MOLECULES ARE
IN CONSTANT RANDOM MOTION and only if
THERE IS A CONCENTRATION GRADIENT
(DIFFERENCE IN CONCENTRATION)
• As a result of diffusion, THE MOLECULES
EVENTUALLY BECOME EVENLY DISTRIBUTED
THROUGHOUT THE AVAILABLE SPACE
 EQUILIBRIUM IS WHERE THE MOLECULES ARE STILL IN
MOTION, BUT THERE ARE EQUAL AMOUNTS OF MOLECULES
MOVING OUT OF A GIVEN AREA AS ARE MOVING INTO THE
AREA
BEFORE
AFTER
Look at all the students in one corner.
This is a HIGH CONCENTRATION.
Where there are no students, it is a
LOW CONCENTRATION.
A few minutes later, after the students
were milling around, look what
happened. They all spread out. There
really isn’t a high or low concentration at
all, but rather an equal amount, or
EQUILIBRIUM of students
in every part of the room.
2. Osmosis
• Osmosis is the THE DIFFUSION OF WATER MOLECULES INTO
OR OUT OF A CELL THROUGH THE CELL MEMBRANE
• It is also a form of PASSIVE transport because it DOES NOT
REQUIRE ENERGY
• Whether there is a net movement if water into or out of a cell
depends on THE CONCENTRATION GRADIENT; WHETHER
THERE IS A HIGHER CONC’N OF WATER ON ONE SIDE OF THE
CELL MEMBRANE THAN THE OTHER
REMEMBER:
All osmosis is diffusion BUT
not all diffusion is osmosis
1.ISOTONIC SOLUTION: CONC’N GRADIENT IS ZERO; NO
NET GAIN OR LOSS OF WATER BY THE CELL
2.HYPOTONIC SOLUTION: CONC’N OF H20 IS LOWER
INSIDE OF THE CELL; NET MOVEMENT OF H20 INTO THE
CELL; ANIMAL CELLS WILL SWELL AND BURST WHILE
PLANT CELLS WILL SWELL AND HAVE INCREASED
TURGOR PRESSURE
3. HYPERTONIC SOLUTION:CONC’N OF H20 IS HIGHER
INSIDE OF THE CELL;
NET MOVEMENT OF H20
OUT OF THE CELL;
ANIMAL CELLS WILL
SHRINK WHILE IN
PLANT CELLS THE
CYTOPLASM WILL
SHRINK (PLASMOLYSIS)
B. OTHER TYPES OF ABSORPTION
I. Active Transport
•PROBLEM: Some needed substances are
needed in HIGHER concentration inside the
cell.
•This means that after equilibrium is reached,
these substances must move AGAINST their
CONCENTRATION GRADIENT and move
from an area of LOW concentration to HIGH
concentration
SOLUTION: Pumps  Active Transport
• HOMEOSTASIS makes it possible for a
cell to maintain a stable internal
environment that is chemically different
from its surroundings.
• The plasma membrane is be involved in
active transport through the use of
PROTEIN RECEPTORS
Active and Passive Transport have
often been compared to rolling a ball up
and down a hill:
It requires no energy or ATP to
roll a ball down a hill. It
happens naturally just like
diffusion. However, pushing
the ball up the hill, against the
gradient, requires the input of
energy/ATP.
Selectively permeable membrane
C. GETTING THE BIG STUFF IN AND OUT
A. MOVEMENT OUT  EXOCYTOSIS
• Exocytosis involves THE MOVEMENT OF LARGE
MATERIALS OUT OF THE CELL
B. MOVEMENT IN  ENDOCYTOSIS
• Endocytosis involves THE MOVEMENT OF LARGE
MATERIALS INTO A CELL
• There are 2 types of endocytosis, and they both
require energy so they are also forms of ACTIVE
TRANSPORT
1. PINOCYTOSIS = CELL DRINKING
• This involves the absorption of SMALL
molecules that still too big to diffuse
through the cell membrane
2. PHAGOCYTOSIS = CELL EATING
• This involves the absorption of
molecules much TOO BIG to diffuse
through the cell membrane and structures
called PSEUDOPODS
• The term “ENGULF” is commonly used
when describing phagocytosis
An Ameba engulfing a Paramecium.
SUMMARY: Methods of Transport
Across a Cell Membrane
CELL TRANSPORT REVIEW
1. T
is the life process that involves the
A
and C
materials throughout a cell or organism.
2. P
of
transport does NOT require E
or
.
3. D
of passive transport.
4. D
H
and O
are
forms
is the movement of molecules from an area of
concentration to L
concentration.
5. O
is the diffusion of W
6. A
.
transport DOES require E
or
.
7. Two types of E
or “cell drinking” and P
“cell eating”.
include P
or