1. Cells and Their environment
Chapter 4 Notes
Cells and Their environment

2. Section 1 – Passive Transport
Cells maintain homeostasis by – controlling the movement of substances across the cell membrane.
Phospholipid Bilayer – double layer of phospholipids
Proteins are embedded in the cell membrane:
Marker proteins
Receptor proteins
Transport proteins

3. Section 1 – Passive Transport
Marker Proteins - advertise cell type; protein with a carbohydrate attached
Receptor Proteins – recognizes & binds to substances outside of the cell
Transport Proteins - helps substances move across the cell membrane (like a gate)
Marker Protein

4. Section 1 – Passive Transport
Substances that CAN move in and out freely: H2O, O2, & CO2
Substances that CANNOT move in and out freely: large sugars (carbohydrates), amino acids (proteins), & ions

5. Section 1 – Passive Transport
Passive Transport – movement across the cell membrane that does NOT require energy
Concentration gradient – difference in the concentration of a substance across a space
Equilibrium – a condition in which the concentration is equal throughout a space

6. Section 1 – Passive Transport
DIFFUSION
Movement from an area of high concentration to an area of low concentration
Type of passive transport
If allowed to continue, equilibrium eventually results
Solution = Solute + Solvent
Solute – a dissolved substance
Solvent – substance doing the dissolving

7. Section 1 – Passive Transport
To diffuse “down” a concentration gradient (high conc. -> low conc.) a substance must be able to pass through the cell membrane
The rate of diffusion depends on temperature, size of molecules, and type of molecule.
Down hill = down a concentration gradient = NO ENERGY

8. Section 1 – Passive Transport
OSMOSIS
Diffusion of water through a selectively permeable membrane
Type of passive transport
The direction of water movement across a cell membrane depends on the relative concentration of “free” water molecules in the cytoplasm and in the fluid outside of the cell.

9. Section 1 – Passive Transport
Three possible directions of water movement:
Hypertonic solution – having more solute outside of the cell and “free” water is forced out
Water moves out & cell shrinks

10. Section 1 – Passive Transport
Hypotonic solution – having a high solute concentration inside the cell and water is forced inside.
Water moves in & the cell swells.

11. Section 1 – Passive Transport
Isotonic solution – “free” water concentration is the same inside & outside of the cell. No net movement of water.
Cell stays the same size; equal amounts of water moving in and out

12. Section 1 – Passive Transport
Transport proteins called channels provide polar passageways that allow ions & polar molecules to move across the cell membrane.
Ion channels – transport protein with a polar core through which ions can pass
Passive transport
Ions pass through the membrane without contacting the interior of the cell membrane

13. Section 1 – Passive Transport
The movement of a charged particle (ion) across the cell membrane is influenced by the particle’s positive or negative electrical charge.
The inside of a typical cell is negatively charged compared to the outside. Because opposites attract, more positive ions outside the cell are more likely to diffuse into the cell.

14. Section 1 – Passive Transport
Carrier proteins – a protein that transports substances across a cell membrane
FACILITATED DIFFUSION
Passive transport
Moves substances down their concentration gradient without energy
Involves a carrier protein
Moves small sugars across the cell membrane

15. Section 1 – Passive Transport
3 steps of Facilitated Diffusion:
A molecule binds to the carrier protein on the outside of the cell.
Carrier protein changes shape & exposes the molecule to the interior of the cell.
Molecule is released from the carrier protein inside the cell.

16. Section 2 – Active Transport
Active transport – transport of a substance against its concentration gradient
Move from low concentration to high concentration
Requires the use of energy (ATP)
Some processes involve a carrier protein that functions as a pump.

17. Section 2 – Active Transport
SODIUM-POTASSIUM PUMP
3 sodium ions (Na+) are pumped out of a cell & 2 potassium ions (K+) are pumped into the cell.
Prevents Na+ from building up inside the cell that would force water into the cell bursting!

18. Section 2 – Active Transport
Proteins and polysaccharides are too large to be transported by carrier proteins.
Instead, they are moved across the cell membrane by vesicles.

19. Section 2 – Active Transport
ENDOCYTOSIS
Movement of a substance into a cell by a vesicle
Phagocytosis – engulfing solid particles; “cell eating”
Pinocytosis – engulfing of liquids; “cell drinking”

20. Section 2 – Active Transport
EXOCYTOSIS
Movement of a substance by a vesicle to the outside of the cell.
Used to export proteins.

21. Section 2 – Active Transport
Your body’s cells must communicate with each other to coordinate your growth, metabolism, and other activities. Some cells have to release signal molecules that carry information to cells throughout the body (Ex: hormones)

22. Section 2 – Active Transport
The binding of a signal molecule to a receptor protein causes a change in the receiving cell.
Change in permeability – the receiving of a signal molecule can cause an ion channel to open and allow ions to move in
Second Messenger – amplifies the signal of the 1st messenger; acts as a signal molecule in the cytoplasm
Enzyme Action – may speed up chemical reactions inside the cell

23. Section 2 – Active Transport
Illegal drugs, such as heroin, imitate signal molecules by binding to receptor proteins and altering the function of the cell. Other drugs block receptor proteins from binding with signal molecules. Ex: People taking beta-blockers for rapid heart beat, the medicine will interfere and prevent the heart rate from increasing too rapidly.