1. The Plasma Membrane and Homeostasis

2. Homeostasis – Maintaining a Balance
Cells must keep the proper concentration of nutrients and water and eliminate wastes. The plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things. This is also known as being partially permeable or semi-permeable.

3. Structure of the Plasma Membrane
Double phospholipid (phosphates and lipids - fats).
Double phospholipid membranes are found around the cell (plasma membrane), the nucleus, vacuoles, mitochondria, and chloroplasts.
Embedded with proteins and strengthened with cholesterol molecules.
This model of what the plasma membrane looks like is called the FLUID MOSAIC MODEL

4. What’s a Phospholipid?
It’s a pair of fatty acid chains and a phosphate group attached to a glycerol backbone.
Polar (water-soluble) heads face out and the nonpolar fatty acids hang inside.

5. Membrane Proteins
Determine what particles can pass through the membrane.
Serve as enzymes (may speed reactions).
Act as markers that are recognized by chemicals and molecules from the
inside and the outside of the cell (the
immune system).

7. Diagram representing the cell membrane.
The above image is from
But I found it at An On-Line Biology Book:

9. Movement in and out of the Cell (Cellular Transport)
Passive transport – no energy is needed to move particles across the plasma membrane.
There are three main types:
Simple diffusion
Facilitated diffusion
Osmosis

10. Passive Transport
Simple Diffusion – movement of particles from an area of high concentration to an area of low concentration.
Continues until an equilibrium is reached (no gradient).
Dynamic equilibrium – particles move freely and are evenly distributed.
Substances that dissolve in lipids (fats) will cross the plasma membrane easily as they are lipophilic (hydrophobic) e.g. alcohol and ether

11. Passive Transport cont...
Facilitated Diffusion – movement of particles is facilitated or assisted by carrier protein molecules in the plasma membrane.
The net direction of flow is also from
high concentration to low concentration
and therefore, requires no energy.
These are substances that do not
readily dissolve in the phospholipid
layer, e.g. glucose

13. Passive Transport cont...
c. Osmosis– Diffusion of water across a selectively permeable membrane. Occurs until water is balanced on both sides of the membrane.

14. Cell Concentrations
These refer to the comparison between the inside and outside of the cell
Hypertonic solutions – more dissolved solute.
Hypotonic solutions – less dissolved solute.
Isotonic solutions – the same dissolved solute.

16. (high solute, low water) (low solute, high water)
Hypertonic Solution
(high solute, low water)
Hypotonic Solution
(low solute, high water)

17. Overcoming Osmosis
Contractile vacuoles – expel excess water from bacterial cells that live in water.
Turgor pressure – water pressure in a plant cell. Loss of turgor pressure causes wilting (plasmolysis).

18. Cellular Transport
Active transport – energy is needed to move particles. It needs energy as it refers to the movement of substances AGAINST a concentration gradient
The energy is in the form of ATP – adenosine triphosphate. It requires a carrier protein to transfer the material across the plasma membrane.

19. Active Transport

20. Bulk Transport
Larger particles entering the cell – formation of vesicles around the material
Endocytosis – material moving INTO a cell
Phagocytosis – solids entering the cell
Pinocytosis – liquid entering the cell
Exocytosis – material moving OUT of the cell