Download Chapter 5-3

Chapter 5-3
Maintaining a Constant Cell
Environment
CELL MEMBRANE
• “Gate-keeper”- helps regulate what enters
and leaves the cell
• __________ process by which a stable
internal environment is kept
Balloon Demonstration
• Smell the balloon- what do you observe?
• Why is this possible?
Cell Membranes
• Cell membranes are selectively
permeable- some things pass through
easily and others do slowly or not at all
• Particles are always moving
• Move in straight lines in all directions
• Collide with each other
• Diffusion: movement of molecules or
particles from an area of high
concentration to an area of lower
concentration
• Concentration gradient: difference in
concentration between two areas
Osmosis
• OSMOSIS: diffusion of water across
selectively permeable membrane from
high water concentration to low water
concentration
• Osmosis Animation
Osmosis
• Which has a higher water concentration?
100 mL of pure water or 100 mL saltwater?
ANSWER: There are more water molecules
in pure water because salt takes up
volume
Three types of solutions:
• Hypertonic solution: higher concentration
of solutes than the cell
• Hypotonic solution: lower concentration of
solutes than the cell
• Isotonic solution: same concentration of
solutes as the cell
Effects of Osmosis
• Effects of Osmosis
Turgor Pressure
Turgor (osmotic) pressure- Force exerted
outward by the water contained in the cell.
• All cells experience this
Effects of Osmosis
• Plasmolysis- shrinking of cytoplasm
caused by osmosis
– What type of solution causes this?
• Cytolysis- cell bursts due to too much
caused by osmosis
– What type of solution causes this?
PLASMOLYSIS
CYTOLYSIS
Cell membrane
• Composed of lipids, proteins and
carbohydrates
• Made up of two layers sandwiched
together
• Parts of the membrane are actually “fluid”
and move
Functions of proteins
• Transport proteins- allow materials that
can’t directly go through membrane to get
into the cell
• Receptor- communication for the cell
• Enzymes
• Structural – connect to other cells or to
structures inside cell
Selective permeability
• Lipid molecules
• Small molecules- water glucose, amino
acids, CO2, oxygen
• What passes through is based on
chemical properties of membrane and
substance trying to get in
Facilitated Diffusion
• Facilitated Diffusion- transport of
substances across membrane through
transport proteins
• Specific to substate
Facilitated Diffusion
High Concentration of
substance
Low Concentration
of substance
Passive and Active Transport
• Passive transport – diffusion down a
concentration gradient without using
energy from cell
– EXAMPLE: Like riding the bike down the hills
high concentration
Low
concentration
• Active Transport- movement of materials
against a concentration gradient
– Riding a bike up a hill
Low
concentration
high concentration
Why do cells need active
transport?
• Maintain different internal conditions than
would occur naturally
• Creating a large gradient can use this
for work
– Use to generate energy
– Conduct nerve impulses
– Concentrate substances
Two forms of active transport