BIOLOGY HOMEWORK

Cell Membrane and Transport Below is a listing which will help you to prepare for the quiz and lab on this material.

CONTENT TO KNOW:

I.The Cell –

Molecules and ions must move into and out of cells in order for them to survive; therefore, it is important to understand what will happen when cells are placed in hypertonic, hypotonic or isotonic solutions

II. The Law of Diffusion -

This law states that particles will always move down a concentration gradient to try to reach equilibrium.

• This means that molecules move from areas of high concentration to areas of low concentration.

• Example: A drop of dye in a glass of water will immediately begin to spread evenly throughout the glass of water

Click HERE for a picture of Diffusion

III. OSMOSIS - This is the diffusion of WATER across a semi-permeable plasma membrane

• Selectively Permeable (Semi-Permeable) Membranes - these membranes allow some molecules to pass through, while selectively blocking others from passing

• PASSIVE TRANSPORT - both osmosis and diffusion are passive and do not require energy

• ACTIVE TRANSPORT - this type of movement requires ATP energy and proteins embedded in the plasma membrane, because it moves molecules AGAINST or UP the concentration gradient

IV. OSMOSIS & LIVING CELLS - Cells will either gain water or lose water if placed in solutions with lower or higher solute concentrations than inside themselves.

• Solute - the substance dissolved • Solvent - the substance doing the dissolving

o Example: Salt dissolved in a glass of water; salt is the SOLUTE, water is the SOLVENT

o Example: Glucose dissolved in water; Glucose is the SOLUTE, water is the SOLVENT

Note: The following terms only apply to solutions which are on either side of a semi-permeable plasma membrane, for instance, inside a cell and outside the cell (there are 2 different concentrations then)

• HYPERTONIC - the solution which has the GREATER AMOUNT OF SOLUTE • HYPOTONIC - the solution which has LESS SOLUTE • ISOTONIC - the solution which has an EQUAL SOLUTE CONCENTRATION to that of

the cell

V. APPLYING OSMOSIS TO LIVING CELLS -

Observe the cells in the beakers shown in the linked picture below; the "X" concentration is the same inside all 3 cells; only the solution out in the beaker is changing

Click HERE for a picture of the an Osmosis Problem

• ISOTONIC - The beaker "C" solution is said to be ISOTONIC to that of the cell because it has the same solute concentration as inside the cell

• HYPERTONIC Beaker Solution - The beaker solution in "A" is hypertonic to that of the cell because it has MORE solute (ie, 15 is greater than 5)

• HYPOTONIC Beaker Solution - the beaker solution in "B" is hypotonic to that of the cell because it has LESS solute (ie, 4 is less than 5)

• OSMOSIS - water will always MOVE INTO THE HYPERTONIC solution; therefore, beaker C does not change; the cell in beaker B gains water; and the cell in beaker A loses water

ANIMAL CELLS - will burst (lyse) when placed in a hypotonic solution, they swell and burst open PLANT CELLS - have a cell wall to prevent lysis; they swell and create pressure against the cell wall when placed in a hypotonic solution; or they shrivel inside the cell wall, when placed in a hypertonic solution

• Plasmolysis - the shrinking of the plasma membrane of a plant cell away from the cell wall when placed in a hypertonic solution

o Example: Celery becomes wilted when placed in a body of salt water

• Turgor Pressure - the pressure resulting on the cell wall when a plant cell gains water and becomes turgid due to being placed in a hypotonic solution

o Example: Celery becomes firm and crisp when placed in a hypotonic solution (fresh water)

DIALYSIS TUBING (or dialysis bags) & OSMOSIS - in lab you will use dialysis bags to mimic the plasma membrane; dialysis bags have very small holes in it which make it permeable to only small molecules; the starch starts out inside the bag; the iodine starts out in the beaker water

• Starch is a polysaccharide (a large molecule) -placed inside the bag at first • Iodine – IKI - (The test for Starch) - is very small; placed only out in the beaker at

first o Be sure you understand what happened to each item listed - clue: black color is

only INSIDE the bag over time.

o This is a picture of a dialysis bag used with starch inside the bag, IKI added out in the beaker; time has elapsed of at least 45 minutes

Click HERE for a picture of dialysis bags experiment