1. The Master of Homeostasis
The Cell Membrane
The Master of Homeostasis

2. Homeostasis
An organism’s regulation of its internal environment to maintain conditions suitable for survival is known as homeostasis
One of the main structures of a cell responsible for maintaining homeostasis is the cell membrane or (plasma membrane)

3. The Cell Membrane

4. The Cell Membrane
The cell membrane allows certain things in, such as water and nutrients, and other things out
This ability of the cell membrane to allow certain things in or out is referred to as selective permeability

5. Diffusion
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
Activity: in a beaker, fill with corn syrup and place a few drops of food coloring on the top of the syrup in one location. Discuss that the concentration of food coloring particles is very high where the drops are located and that the particles of corn syrup and food coloring are randomly moving, even though you cannot see the individual particles moving. Ask the students what will happen if you leave the mixture overnight. Discuss that because of the net movement of particles from an area of higher concentration to an area of lower concentration, the food coloring should distribute itself evenly throughout the mixture until it reaches equilibrium.

6. Diffusion
Particles are usually moving about randomly and changing directions as they bump into one another
In diffusion, the particles in high concentration will migrate to areas of lower concentration until they fill in all of the empty space

7. Diffusion in Cells
Movement of particles from areas of high concentration to low concentration are said to be moving with the “gradient”
The particles move until they are evenly distributed, which is called “dynamic equilibrium”
Substances in cells are in a water solution and constantly move by diffusion

8. Osmosis
The diffusion of water molecules across a selectively permeable membrane is known as osmosis
The direction of osmosis is determined by whether the concentration of dissolved substances is higher inside of or outside of a cell membrane

9. Osmosis
If a cell has more dissolved substances (like sugar) inside the cell than outside, the water is going to move INSIDE the cell with the gradient until dynamic equilibrium is reached
This cell is said to be in a hypotonic solution
You can remember this by using the word (HIPPO-Tonic) because the cell becomes fat and hippos are fat

10. Osmosis
If the concentration of dissolved substances is higher outside of a cell than inside, then the concentration of water is higher inside and the water will rush outside of the cell with the gradient until dynamic equilibrium is reached
This cell is said to be in a hypertonic solution
You may think of hyper students running outside of a classroom and the classroom, or (cell) shrinks in size

11. Osmosis
If the concentration of dissolved substances inside the cell are the same as the outside of a cell, there is no concentration gradient and water moves back and forth across the cell membrane at an equal rate
A cell in this case is said to be in an isotonic solution

12. Active Transport
Sometimes the cell needs to get things inside and outside of the cell against the concentration gradient
This requires energy from the cell and is called active transport- requires input of ATP