Chapter 4: Cells and Their Environment
Objectives for the Chapter:
1. Relate concentration gradi
equilibrium.
2. Predict the direction of wat
of cells.
3. Describe the importance o
transport.
4. Identify the role of carrier p
diffusion. 5. Compare active transport w
6. Describe the importance o
pump.
7. Distinguish between endoc
8. Identify 3 ways receptor pr
activity of a cell.
ient, diffusion, and
ter movement into and out
of ion channels in passive
proteins in facilitated
with passive transport.
of the sodium-potassium
cytosis and endocytosis. roteins can change the
Vocabulary
Passive transport
Concentration gradient
Equilibrium
Diffusion
Osmosis
Hypertonic solution
Hypotonic solution Isotonic solution
Ion channel
Carrier protein
Facilitated diffusion
Active transport
Sodium-potassium pump
Endocytosis
Exocytosis
Receptor protein
Second messenger Assignment:
Answer the following
question and submit answer
on MBC under Schoolwork.
It is called Chapter 4,
Assignment 1.
Using the figure on the
cover of this chapter,
hypothesize what this
chapter will cover. Why do
you think that?
10 points
Passive Transport
Movement across the cell membrane that does
not require any energy from the cell is called
passive transport. To better understand passive
transport, imagine 2 rooms of equal size
separated by a wall with a closed door. Suppose
you release 100 bouncy balls into the first room.
The balls move randomly, bouncing of the walls,
the floor, and the ceiling. Also suppose the balls
can bounce forever without slowing down.
Eventually the balls will become evenly
distributed in the first room. Now, open the door
to the second room. What happens? Some of
the balls from the first room bounce through the
doorway into the second room by the natural
bouncing motion of the balls. Occasionally a
ball will bounce back into the first room from the
second room. After a long while, both rooms
will reach equilibrium, meaning they will have
them same amount of bouncy balls in each room
bouncing back and forth between the two
rooms. In passive transport, molecules cross the cell
membrane randomly, without energy. The
movement of those molecules is always from a
higher concentration to a lower concentration,
passing through a barrier (the wall in the
example) which is known as the concentration
gradient.
Types of Passive Transport
Diffusion
The movement of any substance, except water,
from a high concentration to a low
concentration.
Osmosis
The movement of water from a high
concentration to a low concentration.
Types of Solutions
Isotonic solution - molecules move in and out of
the cell at the same rate causing the cell to stay
the same shape and size.
Hypertonic solution - molecules move from
inside the cell to the outside causing the cells to
shrink.
Hypotonic solution - molecules move from the
outside to the inside causing the cells to swell.
Diffusion through Ion Channels
Ions such as potassium, calcium, sodium, and
chloride play major roles in the functioning of
cells. In order to get those ions into the cell, ion
channels are used. An ion channel is a
transport protein, located within the cell
membrane, that opens and closes like a gate
allowing ions to pass. The gates of the ion
channel opens and closes in response to
chemical and electrical stimuli.
The movement of a substance across the cell
membrane is generally determined by the
concentration gradient. The movement of a
charged particle (ion) is also influenced by its
positive or negative charge. Typically, the
inside of a cell is negative. Thus, a positively
charged ion will be allowed to move into the cell
and negatively charged ions will be allowed to
move out of the cell.
Facilitated Diffusion
Most cells also have a kind of transport protein
that can bind to a specific substance on one side
of the cell membrane, carry the substance
across the cell membrane, and release it on the
other side. Such proteins are called carrier
proteins. When these proteins are used to
transport amino acids and sugars down the
concentration gradient (from high to low) then it
is called facilitated diffusion.
Assignment: Answer the following questions
and submit answers to MBC under
Schoolwork. It is called Chapter 4,
Assignment 2.
1. Distinguish between diffusion
and osmosis.
2. Describe how diffusion of ions
across a cell membrane differs
from the diffusion of nonpolar
molecules across the cell
membrane.
3. Explain how some substances
cross the cell membrane by
facilitated diffusion.
10 points
Active Transport
The transportation of a substance across a cell
membrane against (low to high) its
concentration gradient is called active
transport. Unlike passive transport which
requires no energy, active transport requires the
cell the give up ATP in order for the process to
occur. Some active transports will use carrier
proteins to "pump" the substances across the
cell membrane. For this reason, carrier proteins
are sometimes referred to as membrane pumps.
Active transport works much like this ball and
pump. As the air pump uses energy (from you)
the air is moved against the concentration
gradient into the ball.
Types of Active Transport
Sodium-Potassium Pump
One of the most important membrane pumps in
an animal cell is the sodium-potassium pump.
This is for 2 reasons: (1) prevents sodium ions
from building up in the cell which could cause a
hypotonic solution in our cells, (2) helps
maintain the concentration gradient.
Movement in Vesicles
Endocytosis
The movement into a cell by using a vesicle is
called endocytosis. Exocytosis
The movement out of a cell using vesicles is
called exocytosis.
Membrane Receptor Proteins
There is a vast amount of information In the
form of chemical signals coming into and out of
your cells at all times. Somehow, our cells have
to find a way to filter out the unimportant
information and respond to the important
information. They do this by using receptor
proteins. Receptor proteins are proteins,
imbedded in the cell membrane, that binds to a
specific signal molecule. Those signal
molecules are chemical messages. When a
receptor protein and it's complementary signal
molecule bind together, it causes a change in
the cell. The change can occur in one of three
ways. 1) change permeability of the cell
membrane, 2) triggering second messengers
inside the cell which amplifies the signal, 3)
activating enzymes within the cell.
Assignment: Answer the following questions and
submit answers to MBC under
Schoolwork. it is called Chapter 4,
Assignment 3.
1. Distinguish between active and
passive transport.
2. Describe how the sodiumpotassium pump helps prevent
animal cells from bursting.
3. List 3 ways that the binding of a
signal molecule to a receptor
protein causes change in the
receiving cell.
4. Compare endocytosis with
exocytosis. 10 points
End of Chapter 4