Download Chapter 4 - Warren`s Science Page

Chapter 4
Cells and Their Environment
Section 1: Passive Transport
Cell need to maintain Homeostasis
 Controlling what moves across the
cell membrane
1) Energy is need to move
materials = ACTIVE TRANSPORT
2) Energy is NOT need to move
materials = PASSIVE TRANSPORT
Passive Transport
Molecules enter and exit an area
because of their own motion
Molecules will ALWAYS move from
areas of HIGH concentration to areas of
LOW concentration
A difference in concentration of
substances is called a CONCENTRATION
GRADIENT
Passive Transport
All cells strive for EQUILIBRIUM

Is a condition in which the concentration of
a substance is equal through a space
DIFFUSION is the movement of
molecules from an area of high
concentration to an of low
concentration
Small molecules or Nonpolar molecules
can diffuse across the cell membrane
Diffusion is the simplest type of Passive
Transport
Osmosis
Is the diffusion of WATER through the
cell membrane
Is a type of Passive Transport
Occurs as “free” water molecules move
into the solution with lower
concentration
3 possibilities for the direction of water
movement
Osmosis – Directions of
Movement
#1 – Water Moves Out (Hypertonic)
 Cell Shrinks
 Outside the cell = Lower Concentration
 Inside the cell = Higher Concentration
#2 – Water Moves In (Hypotonic)
 Cell Swells
 Outside the cell = Higher Concentration
 Inside the cell = Lower Concentration
Osmosis – Directions of
Movement
#3 –No Net Water Movement (Isotonic)



Cell Stays the same
Free water molecules inside & out are EQUAL
Cell is in a state of Equilibrium
Hypotonic solution could cause the cell to
burst

Cell walls in plants & fungi help prevent
bursting
Crossing the Cell Membrane
Most ions & polar molecules can NOT
cross the cell membrane
But CAN cross with the help of Channels
ION CHANNELS




Na, K, Ca, and Cl ions
Is a transport protein with a polar pore
through which ions can pass
Some channels are always open
Some channels have gates
Crossing the Cell Membrane
Diffusion of ions through ion channels is
a form of Passive Transport
No energy is used because ions move
down their concentration gradients
Movement of ions is influenced by their
charge


Inside the cell  Negatively Charged
“Opposites Attract”
Facilitated Diffusion
(Pg. 80 - Figure 4)
CARRIER PROTEINS – a kind of
transport protein that can bind to a
specific substance on one side and be
carried to the other side of a cell
Transport – Sugar & Amino Acids
When carrier proteins transport Sugar &
amino acid is is called FACILITATED
DIFFUSION
Facilitated diffusion is a type of Passive
Transport
Section 1 Review
1. What is the difference 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. How does facilitated diffusion work?
4. T/F Diffusion occurs as a result of
the random motion of substances.
4. Why are green leafy vegetables
sprayed with water at supermarkets?
Section 2: Active Transport
Moves substances AGAINST their
concentration gradients
From an area of LOW concentration to
an area of HIGH concentration
REQUIRES ENERGY
Energy comes from ATP
Membrane Pumps
Sodium-Potassium Pump
Transports 3 Na ion out & 2 K ions into
the cell
ATP supplies the energy to move the Na
and K ions
FIGURE 5 – page 82 – STUDY!
Important for 2 Reasons


#1 – Prevents Na from accumulating inside
 If accumulation occurs the cell could burst
#2 – Helps Maintain the concentration
gradient
Movement in Vesicles
Large molecules are moved across the
cell membrane by VESICLES

Proteins & Polysaccharides
Movement of substances into the cell by
vesicles is called ENDOCYTOSIS


Cell membrane forms a pouch around a
substance
Pinches off & forms a vesicle
Movement in Vesicles
The movement of substances outside of
a cell is called EXOCYTOSIS
 Vesicles fuse with the cell membrane
and expel their contents outside the
cell
Cells use exocytosis to transport
proteins that are modified by the Golgi
Apparatus
Membrane Receptor Proteins
Signal Molecules  Hormones
RECEPTOR PROTEINS – pick up these
signals and respond to the ones that
are important
Signal Molecules binding to a receptor
protein cause a change in receiving
cells
Changes in Receiving Cell
1) Change in Permeability
 Cause the ion channel to open
 Important in the nervous system
2) Second Messengers
 Act as a signal molecule in the
cytoplasm
 Activating enzymes, triggering
chemical reactions or change the
permeability of the cell
Changes in Receiving Cells
3) Enzyme Action




Receptor Protein may act as an Enzyme
Speeds up chemical reactions
Activate other enzymes
Drug affect the binding sites of molecules
to receptor proteins
Section 2 Review
1. What is the difference between passive
and active transport?
2. Which ion(s) move against a
concentration gradient in a sodium-potassium
pump?
3. What serves as an “escort” to enable
substances to move across a cell membrane
by active transport and by endocytosis or
exocytosis?
4. What are the 3 functions of receptor
proteins?