1. Daily Science
Which cell has more surface area compared to volume (left/right)?
Why is having more surface area and smaller cells important for our bodies?
What makes up the cell membrane? (hint: it’s a macromolecule)
Which part of the molecule to the right is hydrophobic the head or tail?
What does the cell membrane do?
The cell on the right
More efficient/faster transport of nutrients, water, oxygen.
Lipids
Tails are phobic
Gives cell shape, protects inside from outside

2. Processes of the Cell Membrane
Biology I

3. The Cell Membrane The cell membrane has two functions:
Regulate what enters and leaves the cell.
Provide support and protection.

4. The Cell Membrane Phospholipids: Hydrophilic heads on the outside.
Hydrophobic tails on the inside.
When put into water, phospholipids naturally arrange themselves into a sphere to keep the tails completely protected from water.

5. The Cell Membrane
The cell membrane is very fluid, meaning that it has the ability to bend and stretch without breaking.
There is a limit to this – if the cell membrane is stretched too far, it will break.

6. The Cell Membrane
The cell membrane is a phospholipid bilayer that has proteins and carbohydrates inserted into it.
Outside
of cell
Inside
(cytoplasm)
Cell
membrane
Proteins
Protein
channel
Lipid bilayer
Carbohydrate
chains

7. Concentration Every living cell is surrounded by liquid.
The cell membrane regulates the movement of materials from one side of the lipid bilayer to the other side.
Has to control materials moving from outside to inside and from inside to outside.

8. Concentration Liquids have a concentration.
Concentration – the mass of solute in the solution.
Equals mass divided by volume (mass/volume).
Solution – a mixture of two or more substances.
Example: salt water
Solute – the substance dissolved in the solution.
Example: salt
Solvent – the dissolving agent.
Example: water

9. Concentration Solutions are classified in three ways:
Hypertonic – above strength (more solute, less solvent)
Hypotonic – below strength (less solute, more solvent)
Isotonic – same strength (equal amounts of solute and solvent)
Hypertonic
Hypotonic

10. Concentration Practice Problems
If you dissolve 12g of salt in 3L of water, what is the concentration?
12g/3L = 4g/L
If you dissolve 12g of salt in 6L of water, what is the concentration?
12g/6L = 2g/L
Which has the higher concentration?
The solution with a concentration of 4g/L.

11. Passive Transport
The cell membrane is responsible for moving materials in and out of the cell.
Passive transport – when materials move across the cell membrane without using energy.
Three Types:
Diffusion
Osmosis
Facilitated Diffusion

12. Passive Transport Membranes have three classifications:
Permeable – substances can move across the membrane.
Impermeable – substances cannot move across the membrane.
Selectively Impermeable – some substances can move across the membrane and some cannot.
The majority of cell membranes are selectively impermeable.

13. Diffusion Particles move constantly when in solution.
These particles often collide with one another and spread out randomly.
Particles tend to move from high concentration to low concentration because they want all areas of a solution to be equal.
Diffusion – the movement of particles from high to low concentration.

14. Diffusion Which side has a higher concentration?
Which side has a lower concentration?
Which direction will the solute move?
Lower Concentration
Higher Concentration

15. Diffusion
When the concentration of solute is the same on both sides of the membrane, the system is in equilibrium.
Remember: particles always move in solution. When in equilibrium, there are equal numbers of particles moving in both directions.
Because diffusion is the result of random particle movements, it does not require the cell to use energy.

16. Osmosis Osmosis – the diffusion of water across a cell membrane.
Just like particles, water moves from areas of high concentration to low concentration.
The higher the concentration of solutes, the lower the concentration of water, and vice versa.
Draw example with Miss Hager below!

17. Osmosis