Question

objectives:

1. what is the difference between passive transport and active transport? which one requires energy (atp)?
2. which direction do molecules move in passive transport (down or up the concentration gradient)?
3. which direction do molecules move in active transport?
4. define diffusion and osmosis. are they active or passive?
5. explain what will happen to an animal cell when it is placed in each of the following solutions (where does water move, and what does the cell do?):

a. hypertonic solution:
b. hypotonic solution:
c. isotonic solution:

1. what is the sodium - potassium pump? is it an example of active or passive transport? why is it important for nerve impulses?
2. what is the difference between endocytosis and exocytosis? are they active or passive?

Explanation:

These questions are about cell transport mechanisms (passive, active, diffusion, osmosis, sodium - potassium pump, endo/exocytosis) and how cells respond to different solutions. This falls under Biology (a subfield of Natural Science) as it deals with cellular processes and biological concepts.

1. Difference between passive and active transport, energy requirement:

• Passive transport moves substances across the cell membrane without energy (ATP). It includes diffusion, osmosis, and facilitated diffusion, moving substances down the concentration gradient (from high to low concentration).
• Active transport requires energy (ATP) to move substances against the concentration gradient (from low to high concentration), e.g., sodium - potassium pump.

1. Direction in passive transport:

• In passive transport, molecules move down the concentration gradient (from an area of higher concentration to an area of lower concentration).

1. Direction in active transport:

• In active transport, molecules move up (against) the concentration gradient (from an area of lower concentration to an area of higher concentration).

1. Define diffusion and osmosis, active or passive:

• Diffusion: The movement of particles (e.g., solutes, gases) from an area of high concentration to an area of low concentration, no energy needed (passive).
• Osmosis: The diffusion of water across a selectively permeable membrane from an area of low solute concentration (high water) to high solute concentration (low water), passive.

1. Animal cell in different solutions:

• a. Hypertonic Solution: The solution has a higher solute concentration than the cell. Water moves out of the cell (from cell to solution) via osmosis. The cell shrinks (crenation).
• b. Hypotonic Solution: The solution has a lower solute concentration than the cell. Water moves into the cell (from solution to cell) via osmosis. The cell swells and may burst (lysis).
• c. Isotonic Solution: The solute concentration is equal inside and outside the cell. Water moves in and out of the cell at an equal rate, and the cell remains the same size.

1. Sodium - Potassium Pump:

• The sodium - potassium pump is a membrane protein that uses ATP to move 3 sodium ions out of the cell and 2 potassium ions into the cell, against their concentration gradients. It is active transport. It's important for nerve impulses as it helps maintain the resting membrane potential (negative inside, positive outside) and re - establishes it after an action potential.

1. Difference between endocytosis and exocytosis, active or passive:

• Endocytosis: The cell takes in substances (e.g., large molecules, cells) by engulfing them. The cell membrane folds around the substance, forming a vesicle. Requires energy (active), e.g., phagocytosis (cell eating), pinocytosis (cell drinking).
• Exocytosis: The cell releases substances (e.g., hormones, waste) by fusing a vesicle containing the substance with the cell membrane. Requires energy (active).

Answer:

1. Passive transport: no energy (ATP) needed, moves substances down concentration gradient. Active transport: needs ATP, moves substances against concentration gradient. Active transport requires energy.
2. Down the concentration gradient.
3. Up (against) the concentration gradient.
4. Diffusion: movement of particles from high to low concentration, passive. Osmosis: diffusion of water across a selectively permeable membrane from low solute to high solute concentration, passive.
5. a. Hypertonic Solution: Water moves out of the cell (cell to solution). Cell shrinks (crenation).

b. Hypotonic Solution: Water moves into the cell (solution to cell). Cell swells/bursts (lysis).
c. Isotonic Solution: Water moves in and out equally. Cell size remains same.

1. Sodium - Potassium Pump: moves 3 Na⁺ out, 2 K⁺ in, uses ATP, against gradients. Active transport. Important for nerve impulses as it maintains resting membrane potential.
2. Endocytosis: cell takes in substances (vesicle formation), active. Exocytosis: cell releases substances (vesicle fusion), active.