Cell Membrane
Made up of a Lipid bilayer
Lipids are fats, like oils. They are insoluble in water.
The heads of a lipid are hydrophilic - mix with water
The tail is hydrophobic - does not mix with water.
Semipermeable - controls what enters and leaves
the cell membrane
Diffusion
◻ Diffusion: The tendency for molecules in a fluid to move from a high
concentration to a low concentration due to random motion.
Diffusion
◻ Concentration: The concentration of a solution is the mass of solute in
a given volume of solution. Concentration = mass/volume
⬜ Ex.1) If I dissolve 12 g of salt in 3 L of water the concentration is
12g/3L or 4g/L
⬜ Ex 2) If I dissolve 12 g of salt in 6L of water what is my
concentration? Which solution has the higher concentration?
■ 12g/6L or 2g/L
■ Solution 1 has a greater concentration
How Osmosis Works
◻ Osmosis is the diffusion of
water.
◻ Water moves in the direction
of low concentration to high.
◻ Water will tend to move across
a membrane until equilibrium is
reached.
◻ Until the concentration on both
sides of the membrane is equal.
Osmosis
◻ Isotonic: When the concentration of two solutions is the same.
◻ Hypertonic: The solution with greater concentration of solutes.
◻ Hypotonic: The solution with the lesser concentration of solutes
Osmosis
Video - What happened to the egg?
https://www.youtube.com/watch?v=rIN-5Worgm0
Facilitated Diffusion
A few molecules like glucose are able to diffuse across the cell membrane even
though they are large.
These molecules diffuse across the cell membrane with the help of protein
channels.
Facilitated Diffusion
Facilitated Diffusion
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These cell membrane channels are said to facilitate or help the diffusion of
glucose and other similar molecules across the cell.
This process is called Facilitated Diffusion.
There must be a concentration gradient in order for Facilitated Diffusion to
occur.
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Moving from High Concentration to Low Concentration
Facilitated Diffusion
Diffusion through a lipid bilayer and
Facilitated Diffusion are examples of
Passive Transport.
In Passive Transport energy is not
required
Active Transport
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Cells sometimes must move materials in the opposite direction
From low concentration to high concentration.
This is called Active Transport.
Energy is required during Active Transport - movement of larger molecules
across cell membrane
Active Transport
● Endocytosis
a. Taking materials into the cell by infolding of the cell
membrane
b. Large molecules and clumps of food can be taken into
cells via endocytosis
● Phagocytosis
a. Means cell eating
b. The cytoplasm extends and engulfs particles and then it
digests the particle
● Phagocytosis
a. Means cell eating
b. The cytoplasm extends and engulfs particles.
Active Transport
● Exocytosis
a. The process cells use to release amounts of material
b. Membrane of the vacuole fuses with the cell membrane
and forces the contents out.
https://www.youtube.com/watch?v=DuDmvlbpjHQ
https://www.youtube.com/watch?v=Z_mXDvZQ6dU