Cell Boundaries Essential Question: How do the materials needed for life get in and out of cells?

Warm Up: What’s the difference between diffusion and osmosis?

How does osmosis affect movement of water in and out of cells? Water tends to move in or out of cells by osmosis in such a way as to reach equilibrium (equal concentrations inside and outside)

OrganelleFunctionsAnalogy cell membrane Outer covering of cell, controls what goes in and out. Your skin Animal CellPlant Cell

OrganelleFunctionsAnalogy cell wall Thick outer wall of plant cells. Provides protection and support. Brick wall, Cereal box Animal CellPlant Cell Cell wall Cell membrane

Close-up of Cell Membrane

Osmosis & Diffusion hill.com/sites/ /student_view0/chapter2/animation_ _how_osmosis_works.html

5. How is osmosis related to diffusion? Diffusion = movement of molecules from area of high concentration to low. Osmosis = diffusion of water molecules across a membrane. Red food coloring diffuses through a glass of water Water moves by osmosis from left to right Equilibrium (equally spread out)

80% water 6. A red blood cell is 80% water. What would happen if red blood cells were put into each of the three beakers shown below? Label the appropriate solutions as hypotonic, hypertonic, or isotonic. Then describe how osmotic pressure would affect the blood cells placed in each. 100% water 80% water 20% salt 65% water 35% salt Hypotonic Hypertonic Isotonic 80% water More water moves into cell than out, Making it swell More water moves out of cell than in, Making it shrink Water moves in & out of cell at same rate, So cell stays same size

Maintaining water balance Sea water Fresh water

A C B corn syrup (hypertonic) More water diffused out of egg pure water (hypotonic) More water diffused into egg salt water (isotonic) Water diffused in and out of egg equally. Which jar contains pure water? Salt water? Corn syrup?

7. What is facilitated diffusion? Copy the diagram in Figure 7-17 and use it to explain how facilitated diffusion is used to move glucose into cells. Facilitated diffusion = Protein channels help molecules diffuse into or out of cell

8. Given that a starch molecule can be hundreds of times bigger than a glucose molecule, would it be easy or difficult for starch in your bloodstream to get inside your cells? Explain. Difficult. Starch molecule too big to get through holes in cell membrane.

starch Glucose (sugar)

How is a colander like a cell membrane? Both are selectively permeable; they let small things through, but not big things.

9. What’s the difference between active and passive transport in cells?

Active or passive? Active: requires energy Passive: does not require energy

9. What’s the difference between active and passive transport in cells? Active requires energy from cells. Moving materials from area of low concentration to high. Passive requires no energy from cells, happens by itself. Moving materials from high concentration to low.

10. Apply what you’ve learned here to explain why you shouldn’t drink sea water if you’re stranded on a raft in the middle of the ocean. Cells will lose water and shrink, you will get dehydrated.

What do you think caused the elodea cells to change as they did after adding salt water? Cells became dehydrated, water moved out of cells. Cell membrane contracted around chloroplasts. Before adding salt water After

Questions?

Video: Active & Passive Transport

More videos Diffusion & osmosis Active & passive transport