1. Chp 7.3:Cells and their Environments
Bio A

2. Cell Theory 1. All living things are made of one or more cells.
2. Cells are the basic units of structure and function in organisms.
3. All cells arise from existing cells.

3. Prokaryote vs. Eukaryote
Prokaryote- a single celled organism that lacks a nucleus and other internal compartments. The only organisms on Earth for 2 billion years.
Eukaryote- organism whose cells have a nucleus.

4. The Plasma Membrane -
Gateway to the Cell

5. Photograph of a Cell Membrane

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

7. Structure of the Cell Membrane

8. Passive Transport- Movement across cell membrane that does NOT require energy from the cell
Concentration Gradient- a difference in the concentration of a substance.
***Substances move from areas of high concentration to areas of low concentration.
Equilibrium- condition in which the concentration of a substance is equal throughout a space.

9. Diffusion
- the movement of high concentration to an area of low concentration caused by the random motion of particles of the substance.
Diffusion Animation- #2 #3

10. Diffusion of Liquids

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

12. Cell Membrane Allows Some Things to Pass Through…
Osmosis- the diffusion of water through a selectively permeable membrane. #2 Tutorial
Cell Membrane is selectively permeable to substances

13. Permeable- allows most all things to pass through
Semi permeable- allows some things to pass through
Impermeable- things can not pass through

14. Cell Membrane
Is a lipid bilayer…
Has polar heads and non-polar tails
Cell membrane Animation
The non polar part of the lipid bilayer repels most polar molecules, preventing these substances from passing (except water). So in contrast… very small, non polar substances, pass across cell membrane.
Diffusion of such molecules across the cell membrane is known as … Passive Transport.

15. Hyper, Hypo, Iso….Tonic Fluid outside cell Outside fluid considered…
#2 #3
Fluid outside cell
Outside fluid considered…
Water Diffuses
Effect on cell
Low water
High Solute.
Hypertonic *
Cell Shrinks
High water
Low Solute.
Hypotonic
Cell Swells
Same water and Solute
Isotonic
Stays same size

16. Cell Membrane Polar heads are hydrophilic “water loving”
Nonpolar tails are hydrophobic “water fearing”
Makes membrane “Selective” in what crosses

17. The Plasma Membrane
12/1/2018
G. Podgorski, Biol. 1010

18. Cells in Solutions

19. Osmosis in Red Blood Cells
Isotonic
Hypertonic
Hypotonic

20. hypotonic
hypertonic
isotonic
hypertonic
isotonic
hypotonic

21. Three Forms of Transport Across the Membrane
The Plasma Membrane
Three Forms of Transport Across the Membrane
12/1/2018
G. Podgorski, Biol. 1010