CELL TRANSPORT

Homeostasis

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

Cell Membrane 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

Understanding Concentration

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 vs. Active Transport

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!!

Passive Transport

Three Types of Passive Transport:1. Diffusion - Transport of substances2. Osmosis – Transport of water3. Facilitative Diffusion – Transport with

the help of carrier proteins (for molecules too large to pass through the membrane without help)

Diffusion Diffusion - Process by

which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated when the concentration

of a solute is the same throughout a solution it has reached equilibrium

View Diffusion

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

Diffusion (Continued) Because diffusion depends upon random

particle movements, substances diffuse across membranes without requiring the cell to use energy.

Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions.

Particles are always in motion!

Some Membrane Terms

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.

Osmosis

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

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

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

Osmotic Pressure

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 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

Osmotic and Turgor Pressure Causes….

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

Hypertonic, Hypotonic, or Isotonic?

ISOTONIC ENVIRONMENT

HYPOTONIC ENVIRONMENT

HYPERTONIC ENVIRONMENT