Chapter 5 – The Working Cell: Membrane Structure and Function

This set of flashcards covers vocabulary and key concepts from Chapter 5 regarding cell membranes, transport mechanisms, energy in cells, and enzyme function.

Diffusion

The movement of particles from an area of higher concentration to an area of lower concentration.

Concentration Gradient

A difference in the concentration of a substance across a space or membrane.

Passive Transport

The movement of molecules across a membrane without using energy (ATP).

Active Transport

The movement of molecules across a membrane using energy (ATP), often against a concentration gradient.

Osmosis

The diffusion of water across a selectively permeable membrane.

Semipermeable Membrane

A membrane that allows certain molecules (like water) to pass but not others.

Hypotonic Solution

A solution with a lower solute concentration than inside the cell — water moves into the cell.

Hypertonic Solution

A solution with a higher solute concentration than inside the cell — water moves out of the cell.

Isotonic Solution

A solution with equal solute concentration inside and outside the cell — no net water movement.

Transport Proteins

They help specific molecules cross the membrane, either passively (channels) or actively (pumps).

Exocytosis

The process of exporting large molecules out of the cell via vesicles.

Endocytosis

The process of importing large molecules into the cell via vesicles.

Laws of Thermodynamics

1. Energy cannot be created or destroyed, only transformed. 2. Energy transformations increase disorder (entropy).

Kinetic Energy

Energy of motion.

Thermal Energy

Energy from the movement of particles — heat.

Potential Energy

Stored energy based on position or structure.

Chemical Energy

Potential energy stored in chemical bonds.

Metabolism

All chemical reactions in a cell.

Metabolic Pathway

A series of enzyme-catalyzed reactions that build or break down molecules.

Energy Coupling

Using energy released from exergonic reactions to drive endergonic reactions.

ATP (adenosine triphosphate)

The main energy currency of the cell.

Enzymes

Biological catalysts that speed up chemical reactions by lowering activation energy.

Substrate

The reactant molecule that an enzyme acts on.

Active Site

The region on the enzyme where the substrate binds.

Activation Energy

The amount of energy required to start a reaction.

Catalyst

A substance that speeds up a reaction without being consumed.

Cofactors

Inorganic helpers (e.g., metal ions).

Coenzymes

Organic molecule helpers (e.g., vitamins).

Competitive Inhibitors

Substances that bind to the enzyme’s active site, blocking the substrate.

Noncompetitive Inhibitors

Substances that bind elsewhere, changing the enzyme’s shape so the substrate can’t bind.

Feedback Inhibition

When the product of a metabolic pathway inhibits an earlier enzyme in the pathway to regulate activity.