Cell Membranes Osmosis and Diffusion Functions of Membranes

Cell Membranes Osmosis and Diffusion

Functions of Membranes 1. Protect cell 2. Maintain homeostasis 3. Selectively permeable - allows some molecules in, others are kept out

Homeostasis • Balanced internal condition of cells • Also called equilibrium • Maintained by cell membrane controlling what enters & leaves the cell

Phospholipid Bilayer Polar heads are hydrophilic “water loving” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” in what crosses

Fluid Mosaic Model: “Proteins floating in a sea of lipids”

Proteins Are Critical to Membrane Function

Blood-Brain Barrier • Allows some substances into the brain, but screens out toxins and bacteria • Substances allowed to cross include: water, CO 2, Glucose, O 2, 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 part. It does the dissolving. • Solute – The thing being dissolved. Salt and sugar are solutes.

Methods of Transport Across Membranes 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Active Transport

Diffusion • Movement of molecules from an area of high concentration to an area of low concentration. (Passive Transport) • Movement from one side of a membrane to another, without help.

Diffusion

Diffusion of Liquids

Diffusion through a Membrane Solute moves DOWN concentration gradient (HIGH to LOW) Cell membrane

Facilitated Diffusion • Does NOT require energy • Uses transport proteins to move things from high to low concentration Examples: Glucose or amino acids moving from blood into a cell.

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins.

Facilitated Diffusion • This is a helper.

Active Transport • Requires energy (ATP) • Moves materials from LOW to HIGH concentration AGAINST the concentration gradient.

Osmosis • Diffusion of water across a membrane. • Moves from HIGH water amount (low solute) to LOW water amount (high solute). Diffusion across a membrane Semipermeable membrane

• Hypertonic- more water EXITS a cell • Isotonic- Equal amounts of water enter and exits. • Hypotonic- more water ENTERS a cell

You could think of it this way… • In osmosis, water FOLLOWS salt!! This is sometimes an easier way to remember this concept.

Where is the water moving? • The water is moving out of the cell. • Why? • Remember wherever salt is water follows! Salt SALT

Light blue = Salt Dark blue = water

There is a lot of salt outside of the cell. What will happen? Why?

What will happen if there is a lot of salt inside of the cell?

• Normal Red Onion Cells • In Salt Water • What happened to the cytoplasm and cell membrane?

Diffusion of H 2 O Across A Membrane High H 2 O potential (amount) and Low solute concentration Low H 2 O potential (amount) and High solute concentration

Osmosis: Draw this

Three Forms of Transport Across the Membrane

Question • Why does eating popcorn make you thirsty? • Popcorn is very salty and may cause water to leave the cells of your mouth and through due to diffusion. This makes a person thirsty.

When a sea urchin egg is removed from the ocean and placed in freshwater, the egg swells and bursts. Which of these causes water to enter the egg? A. B. C. D. Coagulation Sodium Pump Active Transport Osmosis D

The picture shows a cell model and the solutions associated with it. In this situation the cell model will — A. Gain mass B. Shrink C. Increase in solute content D. Start to vibrate B

Which of these best explains why a freshwater aquarium would be a dangerous habitat for saltwater fish? A The tissues of the saltwater fish would absorb too much acid. B The cells of the saltwater fish would lose too much water. C The organ systems of the saltwater fish would consume too much energy. D The cells of the saltwater fish would gain too much water. D

On a hot summer day, a road-crew worker perspires and then feels thirsty as her body temperature increases. This response is an example of – A. B. C. D. Releasing enzymes Maintaining homeostasis Decreasing respiration Assimilating proteins B

Think/Pair/Share • Work with a partner to create different situations that can be classified as diffusion. • Do the same for osmosis.

Active Transport Video: http: //www. iteachbio. com/Life%20 Science/Life. Function sand. The. Cell/Active. Transport. mov Diffusion Video: http: //www. iteachbio. com/Life%20 Science/Life. Functio nsand. The. Cell/Diffusion. mov Another Video: http: //www. youtube. com/watch? v=ML-SWe 5 b. Ra. E