Chapter 5 - The Working Cell


the capacity to cause change

Potential energy

Energy that is stored and held in readiness

kinetic energy

Energy of motion

Conservative of energy

a principle stating that energy cannot be created or destroyed, but can be altered from one form to another.


The amount of kinetic energy contained in the movement of the atoms and molecules in a body of matter. (Heat is energy in its most random form).


A measure of disorder or randomness.

chemical energy

A form of potential energy that is stored in chemical bonds between atoms.

1. What aspect of the structure of ATP contributes to its potential energy?
2. Which component of ATP is transferred to make energy available to working cells?

1. The crowding of negative charge in the triphosphate tail contributes to the potential energy of ATP.
2. For ATP power, it is release of the phosphate tail that makes energy available to working cells.

ATP energy helps cells perform 3 types of work:

1. Motor protein performing mechanical work: ATP transfers phosphate groups to motor proteins. The proteins then change shape, causing the muscle cells to contract.
2. Transport protein performing transport work: ATP enables the transport of ions and othe


All of the chemical reactions that occur within an organism


Proteins that speed up chemical reactions by lowering activation energy

Activation energy

The energy that must be invested to start a reaction


A certain reactant molecule recognized by an enzyme

Active site

A pocket or groove on the surface of the enzyme where a substrate molecule attaches

Induced fit

The interaction between a substrate molecule and the active site of an enzyme, which changes shape slightly to embrace the substrate and catalyzed the reaction.

enzyme inhibitors

Molecules that inhibit a reaction by binding to an enzyme and disrupting its function


Movement of molecules across a membrane (down concentration gradient); does not require energy
Ex. Movement of O2 and CO2 into/out of cells

Traffic of large molecules: ENDOCYTOSIS

The movement of materials from the external environment into the cytoplasm of a cell via vesicles or vacuoles

Passive Transport (concentration gradient)

An increase or decrease in the density of a chemical substance within a given region. More to less.
Ex. Cells often maintain concentration gradients of hydrogen ions across their membranes

Passive transport (facilitated diffusion)

The passage of a substance across a biological membrane down its concentration gradient aided by specific transport proteins.
Ex. Water molecules move through the plasma membrane of some cells by transport proteins

active transport

The movement of a substance across a biological membrane against its concentration gradient aided by specific transport proteins and requiring the input of energy (often as ATP)
Ex. An animal nerve cell, the sodium phosphate pump

Traffic of larger molecules EXOCYTOSIS

The movement of materials out of the cytoplasm of a cell via vesicles or vacuoles
Ex. When you cry, cells in your tea or glands use exocytosis to export the salty tears

Isotonic (def, movement of water)

Has an equal concentration of solute as the cell.
- water molecules will move in and out of the cell at the same rate

Hypotonic (def, movement of water)

The solution with the lower solute concentration (higher water concentration)
- water molecules move into the cell


The solution with a higher concentration of solute (lower water concentration)
- water molecules move out of the cell


the control of solute concentrations and water balance