Homeostasis – Process by which organisms maintain a relatively stable internal environment; All organisms have ranges that are tolerated (i.e. pH and temperature)

Example - Paramecium contain contractile vacuoles that collect and remove excess water, thereby helping to achieve homeostasis

Composed of a double-layered sheet called the lipid bilayer which includes:

1. Two layers of lipids (phosphate group + two fatty acids)

Creates a strong barrier that is flexible

2. Proteins that are embedded in the bilayer

Some form channels and pumps that help to move material across the cell membrane

3. Carbohydrate molecules that are attached to the proteins

Allows individual cells to identify one another

Many substances can diffuse across biological membranes, but some are too large or too strongly charged to cross the lipid bilayer.

If a substance is able to diffuse across a membrane, the membrane is said to be permeable to it.

A membrane is impermeable to substances that cannot pass across it.

Most biological membranes are selectively permeable, meaning that some substances can pass across them and others cannot.

Concentration - the mass of solute in a given volume of solution, or mass/volume

Example: 12 grams of salt in 3 liters of water

Concentration = 12 g/3 L (4 g/L)

If you had 12 grams of salt in 6 liters of water concentration = 12 g/6 L (2 g/L)

***The 1st solution is

2X as concentrated

as the 2nd.

Passive transport –Transport of materials from a higher to lower concentration. Energy is not required for this to occur.

Active transport –Transport of materials from a lower to higher concentration. Energy is needed for this to occur.

high

low

Weeee!!!

high

low

This is gonna

be hard work!!

Three Types of Passive Transport:

1. Diffusion - Transport of substances

2. Osmosis – Transport of water

3. Facilitative Diffusion – Transport with the help of carrier proteins (for molecules too large to pass through the membrane without help)

Diffusion

• Diffusion - Movement of molecules from an area of HIGH concentration to an area of LOW concentration• when the concentration of a

solute is the same throughout a solution it has reached equilibrium (particles never stop once this is reached – ALWAYS in MOTION!)

Diffusion (Continued)

•DOES NOT require the cell to use energy.

Examples…..

View Diffusion

• http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html

OSMOSIS

Water passes easily across most membranes, but most solute does not.

Osmosis - Diffusion of water through a selectively permeable membraneHigh to low concentration

NO ENERGY required by the cell

There are more sugar molecules on the right. That means that the concentration of water is lower on the right than the left.

The membrane is permeable to water but not to sugar. As a result, there is a net movement of water from the area of high concentration to the area of low concentration.

OSMOSIS TERMS

Water will tend to move across the membrane to the left until equilibrium is reached.

IsOtonic - when the concentration of two solutions is the same

Hypotonic - when comparing two solutions, the solution with the lesser concentration of solutes

Hypertonic - when comparing two solutions, the solution with the greater concentration of solutes

Facilitated Diffusion•Facilitated Diffusion -Movement of specific molecules across cell membranes through protein channels•Each protein channel only allows a particular substances to cross.

•The protein facilitates (helps) the diffusion across the membrane

Facilitated Diffusion and Energy• Occurs with the following:

1. Charged molecules (ions)

2. When molecules are too large

• HIGH concentration → LOW concentration.

• DOES NOT require energy.

Passive transport –Transport of materials from a higher to lower concentration. Energy is not required for this to occur.

Active transport –Transport of materials from a lower to higher concentration. Energy is needed for this to occur.

high

low

Weeee!!!

high

low

This is gonna

be hard work!!

Active Transport - Energy-requiring process that moves material across a cell membrane against a concentration difference.

Move materials in the opposite direction—against a concentration difference.

Requires:

1. Energy

2. Transport proteins

1. Endocytosis

2. Exocytosis

Endocytosis - Process by which a cell takes material into the cell by infoldings or pockets of the cell membrane; Low → high concentration

Transports:

1. Larger molecules

2. Solid clumps of material

1. Pinocytosis –

For fluids, cell

“drinking”

2. Phagocytosis –

For solids, cell

“eating”

3. Using vesicles

Macrophage (white blood cell)

engulfing bacteriaAmoeba engulfing food.

Exocytosis - Process by which a cell releases large amounts of material; Low → high concentration

Vacuole fuses with cell membrane

Transports:1. Larger molecules 2. Solid clumps of

material

For organisms to survive, they must have a way to balance the intake and loss of water.

Osmosis exerts a pressure known as osmotic pressure on the hypertonic side of a selectively permeable membrane.

Osmotic Pressure - The force exerted by osmosis that “pushes” water through a selectively permeable membrane to make the concentration of solutes the same on both sides.

Turgor Pressure - The force behind the cell walls of plants, which allows them to keep their shape.

Very similar to osmotic pressure, but occurs in plants.

When the cells contents press the plasma membrane against the cell wall and the cell wall in turn presses against the membrane

The cell is filled with salts, sugars, proteins, and other molecules.

If placed in a hypertonic solution.

Cell will shrink or become shriveled (plasmolysis)

Water moves out of cell.

If placed in a hypotonic solution

Cell will be swell or become enlarged.

Cytolysis occurs when a cell ruptures or lyses.

Water moves into the cell.

Plasmolysis occurs

as the cell shrinks.

Cytolysis occurs when

the cell bursts

ISOTONIC ENVIRONMENT

HYPOTONIC ENVIRONMENT

HYPERTONIC ENVIRONMENT