Cell Membranes and Transport Processes

Students are instructed to discuss scenarios involving human cells with neighbors:
- Scenario 1: A cell in very salty water.
- Scenario 2: A cell in pure water (with no salt).
- Important Note: Human cells contain a certain amount of salt.

Definition: A hypertonic solution is one where the concentration of solute is higher than that inside the cell.
Impact on Cell:
- Water molecules (H2O) move out of the cell.
- Result: The cell shrinks due to loss of water.
Diagram Annotations:
- [c] denotes concentration of solute (water, solute).

Definition: A hypotonic solution has a lower concentration of solute compared to the inside of the cell.
Impact on Cell:
- Water molecules (H2O) move into the cell.
- Result: The cell enlarges or swells.
Diagram Annotations:
- [c] denotes concentration of solute (water, solute).

Definition: An isotonic solution has an equal concentration of solute compared to the inside of the cell.
Impact on Cell:
- Water molecules (H2O) move in both directions at equal rates.
- Result: The cell remains the same size.
Diagram Annotations:
- [c] denotes concentration of solute (water, solute).

Structure or Process	Energy Required?	[c] Gradient Used?	Active or Passive Transport?	Other Notes
Diffusion	No	Yes	Passive	Movement down a concentration gradient.
Facilitated Diffusion	No	Yes	Passive	Assisted by proteins.
Osmosis	No	Yes	Passive	Special case of diffusion for water.
Channel Proteins	No	Yes	Passive	Allow specific solutes through.
Carrier Proteins (Facilitated)	No	Yes	Passive	Bind specific substances.
Carrier Proteins (Active)	Yes	Yes	Active	Move against concentration gradient.
Coupled Transport	Yes	Yes	Active	Combines movement with energy.

Definition: ATP is the main energy currency in biological systems.
Conversion:
- ATP = Adenosine triphosphate
- ATP can be converted to ADP (Adenosine diphosphate) by losing a phosphate group.
Cycle:
- Energy is absorbed from food to synthesize ATP.
- Energy is released from ATP when a phosphate group is dropped.

Function: Transports sodium (Na+) and potassium (K+) ions across the cell membrane.
Process Steps:
1. Pump binds Na+ from inside the cell.
2. ATP donates a phosphate, providing energy.
3. Pump changes shape, releasing Na+ outside the cell.
4. Pump binds K+ from outside the cell.
5. Phosphate is released, the pump returns to its original shape.
6. K+ is released inside the cell.
Final Note: This pump creates an unequal charge across the cell membrane, with a net loss of positive charge outside.

Definition: Membrane potential refers to the voltage difference across the membrane due to unequal transport of ions.
Implications: Can be used to drive other cellular processes and can be essential in nerve impulses and muscle contractions.

Mechanism: One protein establishes a gradient using ATP, while a second protein transports another molecule (e.g., glucose) along with an ion moving down its concentration gradient.

Definition: The process of the cell taking in large particles through the plasma membrane.
- Types:
- Phagocytosis: For taking in solid particles.
- Pinocytosis: For taking in liquid.
- Receptor-mediated Endocytosis: Targets specific molecules by binding to receptors.

Definition: The process by which materials are expelled from the cell through the fusion of vesicles with the plasma membrane.

If a cell needs to move molecules up the concentration gradient, what must it do?
- Answer: Use energy (D).
If a large polar molecule needs to cross the membrane against its concentration gradient, what transport mechanism would it use?
- Answer: Carrier protein and active transport (C).

Students should draw examples of diffusion, facilitated diffusion, osmosis, and describe associated proteins in small groups.
Focus on identifying whether the process is active or passive and which proteins are involved in each case.