1. Cell Membrane & Cellular Transport

2. Homeostasis – the maintenance of internal stable conditions
The cell membrane keeps the cell in balance.

3. Membrane Functions
Provides a selectively permeable barrier around the cell.
Controls the passage of substances in and out of the cell.
Maintains homeostasis for the cell.

4. Membrane Structure Phospholipid bilayer (nonpolar)
Membrane proteins: act as transport channels.
Carbohydrate chains: act as “ID” tags for the cell.
Cholesterol: provides stability for the membrane.

5. Phospholipid Bilayer Phospholipid Bilayer
Phospholipids: phosphate head and lipid tail.
Phospholipid Bilayer: two layers.
Hydrophilic = attracts water
inside cell
outside cell
Phosphate
Head
Lipid Tails
Phospholipid Bilayer
Hydrophobic = repels water

6. So what needs to get across the membrane?
The cell membrane is semipermeable, which means only some material can get in or out.
So what needs to get across the membrane?
Sugar
Lipids
Amino
Acids O2
H2O
Salt
Waste

7. How do you build a semi-permeable cell membrane?
Channels are made of proteins.
Proteins act as doors in the membrane.
Bilipid
Membrane
Protein Channels in Bilipid Membrane

8. Diffusion Molecules move from HIGH to LOW concentration; this continues until equilibrium is reached.
Simple diffusion: directly through membrane.
Facilitated diffusion: help through a protein channel.
NO energy needed!!
HIGH
LOW

9. Active Transport
Cells use energy to move against concentration gradient - from LOW to HIGH.
Particles that are polar (charged) must move through a protein channel.
Use protein pump
requires energy (ATP)
Plants have nitrate & phosphate pumps in their roots.
Why?
Nitrate for amino acids
Phosphate for DNA & membranes
Not coincidentally these are the main constituents of fertilizer.
ATP

10. Transport of Molecules
Endocytosis: takes material into cell by cell membrane making pockets.
Phagocytosis – “cell eating”; cell engulfs particles
Pinocytosis – cell takes in liquid from surrounding environment.
Exocytosis: process forcing contents out of the cell.

11. Endocytosis
PHAGOCYTOSIS
PINOCYTOSIS

12. Exocytosis

13. Transport Summary simple diffusion facilitated diffusion
(Smaller molecules)
facilitated diffusion
ATP
active transport
(Larger molecules)

14. Types of Cellular Transport
PASSIVE
Does NOT require energy
Goes with the concentration gradient (high to low)
Simple Diffusion, Facilitated Diffusion
ACTIVE
Requires energy from ATP
Goes against the concentration gradient (low to high)
Active Transport, Endocytosis, Exocytosis

15. Osmosis movement of water across cell membrane.
HIGH H2O
LOW H2O

16. Effects of Osmosis on Cells (osmotic pressure)
Hypertonic: higher concentrations of solute; less H2O.
Isotonic: equal concentrations of solute.
Hypotonic: lower concentrations of solute; more H2O.