7. Transport through membranes SC: Compare passive with active transport. Define osmosis, diffusion, facilitated diffusion, active transport, concentration gradient

What happens when you spray perfume into a corner of a room?

Diffusion : Occurs in a fluid (liquid or gas) where particles are constantly moving Is the movement of particles from an area of high concentration to an area of low concentration until the concentrations are equal. (Note: Particles move in both directions)

Cell Membrane Forms a barrier through which molecules must pass to enter or exit the cell. Recap: Phospholipid bilayer has hydrophilic heads facing ___________ and hydrophobic _________ facing ____________. What particles will be able to pass through this layer? How do other particles get through?

Types of Passive Transport (no energy required) __________ diffusion - some molecules pass through the lipid bilayer without assistance eg: water, CO2, O2, lipids. http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works. html __________ diffusion – large molecules and charged molecules require carrier proteins or channel proteins to pass through the lipid bilayer. http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_ diffusion_works.html O________ – diffusion of water molecules across a selectively permeable membrane to an area of lower concentration of water. http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

More about Osmosis This is the movement of water molecules from low concentration of water to high concentration of water Experiment Recap: How did you measure concentration of water in yesterdays experiment? Experiment # Concentration of sucrose solution in beaker Concentration of sucrose solution in tubing Mass change A 50% 5% B C 0%

Osmosis continued Water molecules are small so they easily diffused through the membrane and moved from the area where there are lots of water molecules compared with solute molecules (sugar). Definitions: Hypotonic = low concentration of water Hypertonic = high concentration of water Isotonic = balanced concentration of water on each side of membrane

Pg 71 in your books has this diagram

Define: Turgid: Plasmolysed: Flaccid: Lysed: These words are used to describe animal and plant cells with different water potentials.

What do you think isotonic sports drinks do? What would happen if you drunk water only during sport? Or very sugary drinks?

Isotonic sports drinks Contain a similar concentration of ions as is found inside the cells of your body. Contain carbohydrates, water and essential ions such as Na+ and K+ Hydrate the cells without bloating them or removing excess water. Sugary drinks can remove water from the cells and cause excess sweating and urination. Drinking water only can cause bloating and water retention. Isotonic drinks maintain the natural cell balance during sustained exercise.

Kidney dialysis

Why should you not drink seawater if stuck on a desert island? Seawater has a lower concentration of water than our cells (and a higher concentration of ions). Drinking it would cause water to diffuse from our cells and be lost from the body by urination. Low water concentration in the cells would cause a change in cell reactions. The facts: Seawater has an average salinity of 35 g/L whereas our cells have a salinity of 9 g/L. Seawater is a hypertonic solution.

Active Transport Cells sometimes need to transport against a concentration gradient (from low to high). This can only be achieved by using energy in the form of ATP and specific membrane proteins. This use of energy is about ¼ of all the energy used by our bodies. The sodium potassium pump is the most common example of active transport. http://highered.mcgraw- hill.com/olc/dl/120068/bio03.swf

Recap What is the main difference between passive and active transport? Active uses energy to go up a gradient, passive – diffusion down a concentrationgradient. What molecules can diffuse though the phospholipid layer? CO2, H2O, O2, lipids Does water travel towards or away from a high concentration of sugar? Towards because the molecules are actually diffusing towards a low concentration of water molecules.