Download Chapter 5 - Marissa Junior/Senior High School

CHAPTER 5
Cell Homeostasis
Section 1: Passive Transport


Cell membranes: controls what enters and leaves
the cell
Sometimes it takes energy to do this.
Sometimes it does not!
TRANSPORT: movement across the cell
membrane

2 types of transport:
 Active
 Energy
from the cell is required
 Passive
 No
energy is required
Passive Transport

Types of Passive Transport
 Diffusion
 Osmosis
 Facilitated
Diffusion
Diffusion



Diffusion is the SIMPLEST type of passive transport.
Diffusion: the movement of molecules from an area
of higher concentration to an area of lower
concentration
Concentration Gradient: the difference in the
concentration of molecules across a distance
Example of Diffusion

Sugar water/food coloring example

Goal of diffusion:
EQUILIBRIUM
 Equilibrium:
the concentration of molecules becoming
the same throughout the space they occupy
Sugar water has reached equilibrium when the sugar is
equally distributed throughout the water
REMEMBER

Do not forget…..even at equilibrium, molecules still
continue to move
OSMOSIS


Osmosis: the process by which WATER moves across
a cell membrane from an area of higher
concentration to an area of lower concentration
NO ENERGY REQUIRED!!!
Osmosis, con’t

Solution: made up of 2 parts
 SOLUTE
& SOLVENT
SOLUTE: what will be dissolved
SOLVENT: what will do the dissolving
In the sugar and water example
Solute: sugar
Solvent: water ***WATER is the universal solvent
3 types of Osmotic Solutions

1. Hypotonic Solution

2. Hypertonic Solution

3. Isotonic Solution
Hypotonic Solution

Osmosis depends upon the direction of the solute!

Table 5-1 on page 99

HYPOTONIC SOLUTION: when the concentration of
solute molecules outside the cell are LOWER than
the concentration of solute molecule inside the cell



Water will naturally move into the cell
Result: cell will enlarge
Cytolysis can occur: bursting
Hypertonic Solution

Hypertonic: when the concentration of solute
molecules outside the cell is HIGHER than the
concentration of solute molecules inside the cell

Water will naturally move OUT!!

Result: cell will SHRINK!
 Dehydration
Isotonic


Isotonic: when the concentration of solutes outside
the cell equal the concentration of solutes inside the
cell
Result: EQUILIBRIUM
Osmosis: CONTRACTILE
VACUOLES
Turgor Pressure


Found in Hypotonic
solutions:
It is the pressure that
water molecules exert
against a cell wall
Plasmolysis



Found in Hypertonic
solution:
Cells shrink from the
cell wall
Loss of turgor pressure
Different cells: RBC


Some cells do not have a contractile vacuole and
cell wall
Therefore: the normal shape changes
Page 100: picture of RBC
Facilitated Diffusion

Used for molecules too big to cross the membrane

Uses transport proteins!


Still moves molecules from area of high
concentration to an area of low concentration
Example: glucose
Facilitated diffusion



Can also move molecules OUT of the cell
If sugar concentration gets too high inside the cell, it
can transport those sugar molecules to the outside
of the cell
SPECIFIC transport proteins are used for SPECIFIC
molecules
Section 2: Active Transport



In many cases, a cell MUST move materials from an
area of LOWER concentration to an area of
HIGHER concentration.
Therefore: it is UP the concentration gradient, not
down.
It requires ENERGY
Transport Proteins


Also called “carrier” proteins: called “pumps”
They move substances from lower to higher
concentration
Carrier Protien
Sodium-Potassium Pump
Sodium-Potassium Pump



Transports Na+ and K+ ions UP the concentration
gradient
Some cells need a higher concentration of Na+
outside and K+ inside the cell
This pump MAINTAINS this concentration
STEPS: page 104



1. 3 Na+ ions bind to the carrier protein on the
inside (cytosol) side of the cell
2. A phosphate group binds to use its energy to
fulfill this process
3. This takes energy! ATP becomes ADP: a
phosphate is used to do this!

4. This allows the carrier protein to have the shape
it needs to bind with 2 K+ ions from the outside of
the cell

5. The phosphate is released

6. The 2 K+ are released inside the cell

The process begins again!
Sodium-Potassium Pump

THIS CREATES AN ELECTRICAL GRADIENT!

Outside: becomes + charged relative to the inside


Inside: becomes - charged relative to the outside
Therefore: like a battery!
Movement in Vesicles
Some substances are too large to pass through the cell
membrane through diffusion or facilitated diffusion.
A carrier protein is too small for the object.
To transport LARGE quantitites of molecules:
1.
Endocytosis
2.
Exocytosis
Endocytosis




Steps:
1. cell membrane forms a pouch
2. materials flow into pouch
3. pouch pinches off from the cell membrane and
becomes a membrane bound organelle:
 VESICLE


4. vesicle fuses with lysosomes
5. contents digested
Endocytosis


2 types:
1. Phagocytosis
 Large

particles
2. Pinocytosis
 Large
amt. of fluid
Exocytosis:

Process in which
substances from the
cell through a vesicle
are transported OUT
of the cell

It is the
REVERSE of
endocytosis!

1.
2.
3.
Removes:
waste, proteins,
toxins, etc.
These products
placed in vesicles
Vesicles fuse with cell
membrane
Substances are
released