1. Maintaining a Constant Cell Environment
Chapter 5-3
Maintaining a Constant Cell Environment

2. CELL MEMBRANE
“Gate-keeper”- helps regulate what enters and leaves the cell
__________ process by which a stable internal environment is kept

3. Balloon Demonstration
Smell the balloon- what do you observe?
Why is this possible?

4. Cell Membranes
Cell membranes are selectively permeable- some things pass through easily and others do slowly or not at all

5. Particles are always moving
Move in straight lines in all directions
Collide with each other

6. Diffusion: movement of molecules or particles from an area of high concentration to an area of lower concentration
Concentration gradient: difference in concentration between two areas

8. Osmosis
OSMOSIS: diffusion of water across selectively permeable membrane from high water concentration to low water concentration
Osmosis Animation

9. 100 mL of pure water or 100 mL saltwater?
Osmosis
Which has a higher water concentration?
100 mL of pure water or 100 mL saltwater?
ANSWER: There are more water molecules in pure water because salt takes up volume

11. Three types of solutions:
Hypertonic solution: higher concentration of solutes than the cell
Hypotonic solution: lower concentration of solutes than the cell
Isotonic solution: same concentration of solutes as the cell

12. Effects of Osmosis
Effects of Osmosis

14. Turgor Pressure
Turgor (osmotic) pressure- Force exerted outward by the water contained in the cell.
All cells experience this

15. Effects of Osmosis
Plasmolysis- shrinking of cytoplasm caused by osmosis
What type of solution causes this?
Cytolysis- cell bursts due to too much caused by osmosis

16. PLASMOLYSIS
CYTOLYSIS

19. Cell membrane Composed of lipids, proteins and carbohydrates
Made up of two layers sandwiched together
Parts of the membrane are actually “fluid” and move

20. Functions of proteins
Transport proteins- allow materials that can’t directly go through membrane to get into the cell
Receptor- communication for the cell
Enzymes
Structural – connect to other cells or to structures inside cell

22. Selective permeability
Lipid molecules
Small molecules- water glucose, amino acids, CO2, oxygen
What passes through is based on chemical properties of membrane and substance trying to get in

23. Facilitated Diffusion
Facilitated Diffusion- transport of substances across membrane through transport proteins
Specific to substate

24. Facilitated Diffusion
High Concentration of substance
Low Concentration of substance

25. Passive and Active Transport
Passive transport – diffusion down a concentration gradient without using energy from cell
EXAMPLE: Like riding the bike down the hills
high concentration
Low concentration

26. high concentration Low concentration
Active Transport- movement of materials against a concentration gradient
Riding a bike up a hill
high concentration
Low concentration

27. Why do cells need active transport?
Maintain different internal conditions than would occur naturally
Creating a large gradient can use this for work
Use to generate energy
Conduct nerve impulses
Concentrate substances

28. Two forms of active transport