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?