Cell MembranesOsmosis and Diffusion

Functions of Membranes

1. Protect cell

2. Control incoming and outgoing substances

3. Maintain ion concentrations of various substances

4. Selectively permeable - allows some molecules in, others are kept out

Phospholipid Bilayer

Fluid Mosaic Model

Blood-Brain Barrier• Allows some substances into the

brain, but screens out toxins and bacteria

• Substances allowed to cross include: water, CO2, Glucose, O2, Amino Acids,

Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.

Solutions

• Solutions are made of solute and a solvent

• Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today.

• Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.

Methods of Transport Across Membranes

1. Diffusion

2. Osmosis

3. Facilitated Diffusion

4. Active Transport

Methods of Transport Across Membranes

1. Diffusion -passive transport - no energy expended

2. Osmosis - Passive transport of water across membrane

3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across

4. Active Transport- requires energy to transportmolecules against a concentration

gradient – energy is in the form of ATP

Diffusion

• Movement of molecules from an area of high concentration to an area of low concentration.

• Movement from one side of a membrane to another, un-facilitated

Diffusion

Osmosis

Tonicity is a relative term

• Hypotonic SolutionHypotonic Solution - One solution has a lower concentration of solute than another.

• Hypertonic SolutionHypertonic Solution - one solution has a higher concentration of solute than another.

• Isotonic SolutionIsotonic Solution - both solutions have same concentrations of solute.

Plant and Animal Cells put into various solutions

Types of Transport

OSMOSIS

• We will make an osmo meter to observe osmosis.

• We use 2 chicken eggs

• Place them in vinegar over night to remove the shell.

• Now each egg behaves as a single cell

Procedure

Weigh each egg on an electronic scale

Egg # 1 weight in grams 70.4 grams

Egg # 2 weight in grams 58.7 grams

Place egg # 1 in distilled water

Place egg # 2 in corn syrup

HYPOTHESIS

• Write a hypothesis for the two eggs

• Which egg will shrink and which egg will become turgid (swollen)?

• Make an initial diagram and observations.

• Is the egg firm or flaccid?

• What is the color and size estimate today?

Elmhurst College Website

Final observations the next day

After incubation of eggs overnight write your final observations.

Which egg is swollen and why?

Which egg has shrunk and why?

Give reasons for each answer.

Which solution was hypertonic and which one was hypotonic?

More questions

• Which egg had endocytosis

• Which egg had exocytosis and how did you know that these procedures took place in the eggs.

Final observations

What was the colour of the eggs?

Draw the final pictures of the two eggs.

Osmosis