1. How do cells maintain homeostasis
Cell Membrane and Solutions
How do cells maintain homeostasis
Homeostasis – the process by which living things maintain a stable internal environment.
Can everything go in and out of a cell?
The Cell membrane regulates what enters and leave the cell.

2. What is the cell membrane made of?
The cell membrane is a phospholipid bilayer.
Phosphate head
2 Lipid tails 2

3. Semi- Permeable Membrane
This cell membrane is semi – permeable.
Some substances can pass across and others cannot.
What other things that you know of are semi-permeable?

4. Diffusion
Diffusion: process by which molecules move from an area that is more concentrated to an area that is less concentrated.
They constantly move, collide and spread out randomly.
No ENERGY is required.
More concentration
Less concentration

5. Osmosis
Osmosis: the diffusion of water through a selectively permeable membrane.
Water moves from an area of greater water concentration (more pressure) to an area of lesser water concentration (less pressure).
Water passes across the membrane easily, but some solute molecules are too big to cross.

6. Osmosis
Isotonic

7. High to Low
Particles will move from an area of high (more) concentration to an area of low (less) concentration until EQUILIBRIUM is reached.

8. Equilibrium Equal amounts of solute on both sides of a membrane.
Even when equilibrium is reached, particles will continue to diffuse in both directions, but the concentration won’t change.

9. What is it called when stuff dissolves in water?
Solute = Stuff that dissolves (Sugar)
Gasses: oxygen, carbon dioxide
Solids: Salts, sugars, amino acids, proteins
Solvent = What it dissolves in (Water)
A “Solution” is when the solute is evenly distributed throughout the solvent.
A “Suspension” is when the substance doesn’t dissolve.
Example –oil in water, salt in water 9

10. Measuring Concentration
The cytoplasm of cells is a solution of many things dissolved in water. Cytoplasm is mostly WATER!
The concentration of a solution is the mass of solute in a given volume of solvent. (mass/volume)
What is the concentration of 12 grams of salt in 3 liters of water?
12 g/3 L = 4 g/L 10

11. Types of Solutions Isotonic solution: Same strength
The solute concentration is the same inside and outside the cell.
Hypertonic solution: Above strength
The solute concentration is higher in in the solution surrounding the cell than inside.
Hypotonic solution: Below strength
The solute concentration is lower in the solution surrounding the cell than inside.

12. pH pH is a measure of how acidic or basic a solution is.
The higher the concentration H+ ions the more acidic the solution is
We measure this using the pH scale
Low pH means more acidic (less basic)
High pH means more basic (less acidic)
pH =7 is neutral

13. Why does only one move through the baggie?
Starch
Mass: >360g/mol
Iodine
Mass: 127g/mol I