Plasma Membrane and Transport Systems

Practice questions covering plasma membrane permeability, diffusion, osmosis, tonicity, and the various forms of passive and active transport.

What is the primary objective for studying the plasma membrane according to the lecture?

To understand why the plasma membrane is selectively permeable.

How is diffusion defined in the context of concentration?

The movement of something from a region of greater concentration to a region of lower concentration.

What is the ultimate driving force behind diffusion?

The concentration gradient.

What occurs when a system reaches dynamic equilibrium?

Solutes or water move in opposite directions at about the same rate, resulting in no net change.

What is Brownian movement?

The random movement of molecules in either a fluid or a gas.

What is absolute zero and its significance in molecular movement?

Absolute zero is $0\,K$ (Kelvin), the coldest measurable state in the universe where all molecular vibration stops.

Define osmosis as described in the lecture.

A special form of diffusion that involves water.

What is the difference between a solute and a solvent?

A solute is the thing being dissolved (e.g., salt or sugar), and a solvent is the thing doing the dissolving (e.g., water).

What is tonicity?

A measurement of osmotic pressure against a permeable membrane.

What do the prefixes hyper, hypo, and iso mean in relation to tonicity?

Hyper means more or greater, hypo means less, and iso means the same or equal to.

What happens to animal cells in a hypertonic solution versus a hypotonic solution?

In a hypertonic solution, the cell shrivels as water leaves; in a hypotonic solution, the cell may burst (undergo lysis) as water rushes in.

Why do plant cells prefer hypotonic solutions?

The cell wall maintains rigidity and prevents the cell from bursting despite the high intake of water.

What are the two main categories of cellular transport?

Passive transport (requires no energy) and active transport (requires energy).

How do simple diffusion and facilitated diffusion differ?

Simple diffusion involves substances crossing the membrane directly, while facilitated diffusion requires a specialized protein channel.

What types of molecules can easily cross the plasma membrane via simple diffusion?

Small, nonpolar, hydrophobic molecules such as $O_2$ and $CO_2$.

What molecule is required for active transport to perform cellular work?

$$ATP$$

What is the function and ratio of the sodium-potassium pump?

It is an active transport pump that cycles constantly to move three sodium ions ($3Na^+$) out of the cell and two potassium ions ($2K^+$) into the cell.

What does it mean to move against the concentration gradient?

Moving substances from a region of low concentration to high concentration, which requires energy.

Define exocytosis.

The process of transport vesicles fusing with the plasma membrane to move large molecules outside the cell.

Which organelle typically generates the transport vesicles used in exocytosis?

The Golgi complex.

What is the difference between phagocytosis and pinocytosis?

Phagocytosis (cell eating) uses pseudopodia to engulf large particles, while pinocytosis (cell drinking) uses receptors to take in small ions or molecules in bulk.

Which organelle fuses with food vesicles created by endocytosis to digest their contents?

Lysosomes.