the cell and its environment. homeostasis homeostasis- “ steady state” or balance cells...
TRANSCRIPT
THE CELL AND ITS ENVIRONMENT
HOMEOSTASISHomeostasis- “ steady state” or
balancecells constantly seek homeostasis
The Cell Membrane is responsible for maintaining the steady state within cells. Most cells live in some kind of fluidSingle celled organisms – ponds, oceans,
other bodies!?!Multicellular organism cells are surrounded
by body fluid
HOMEOSTASIS CONTINUED:
Cells have limits to the changes they can survive:TemperatureSalt concentrations in waterInterstitial fluid – body fluid between cells
DIFFUSION
Molecules move from a area of high concentration to an area of low concentrationTakes place in both solutions and airGradual spreading out of the
moleculesThe spread out until the reach
equilibriumREQUIRES NO ENERGY!
DIFFUSION THROUGH MEMBRANES
Permeablewhen membranes allow all substances to
pass through
Selectively Permeablewhen membranes allow some substances
to pass through, & others not
CELL MEMBRANES ARE SELECTIVELY PERMEABLE!
Osmosis- diffusion of water through a
selectively permeable membrane
Remember from high concentrations to low concentrations or…
“HIGH to LOW”
Q?:What decides what moves into the
cell???
A:Compare the solution outside the cell to
the solution inside the cell.
Hypotonic- a solution having a lower concentration of solutes than the cell
Hypertonic- a solution having a higher concentration of solutes than the cell
Isotonic- a solution having the same
concentration of solutes as the cell
RULES FOR DECIDING WHAT WILL HAPPEN TO CELLS…
1. look at the solute concentrations to set up the picture puzzle
2. water moves first and fastest….so3. look at the water concentrations to decide
what will happen to the cell…try some problems
…OR “Water Follows Solute”
TURGOR PRESSURE-
term used to describe water pressure within a cell, (usually plant cells)
will continue to build up until equilibrium is reached
Even if that means EXPLODING! This doesn’t happen often – plant cells are protected by their cell wall
PLASMOLYSIS
water diffuses out of a cell and turgor pressure is lost
plants “wilt” cells shrink
CYTOLYSIS
when cells burst because water pressure inside the cell is too great
This is why sea animals can not live in fresh water (lakes).
They are not built to pump out the extra water
2 WAYS SUBSTANCES ARE TRANSPORTED THROUGH MEMBRANES
PASSIVE TRANSPORT- the movement of substances through the cell membrane when NO ENERGY taken from the cell
Osmosis Diffusion Facilitated Diffusion
Has the help of a protein channel
These both happen “naturally”
SUBSTANCES THAT USE PASSIVE TRANSPORT
Water Carbon Dioxide Oxygen Steroids Alcohol Glucose
ACTIVE TRANSPORT
Transporting substances across membranes USING ENERGY from the cell
Examples: Sodium (Na+) Potassium (K+)
The cells have high needs of these ions
Active Transport moves against natural diffusion Plants have the ability to absorb Na
and K when concentrations are higher inside the cell than outside the cell
ACTIVE TRANSPORT (CONT.)
Endocytosis- taking into a cell Exocytosis- putting out of a cell Phagocytosis- taking in large solid Pinocytosis- taking in or putting out fluid
drops excrete or secrete (like sweat!)
Cells reach around the particle to be taken in and form a pouch!
REVIEW QUESTIONS!
Describe the functions of the cell membrane and cell wall.
What happens during diffusion? Describe how water moves during osmosis. What is the basic structure of a cell
membrane? What is the difference between phagocytosis
and pinocytosis? Critical Thinking Comparing and Contrasting
What is the main way that active transport differs from diffusion?