important terms

Negative feedback

A control mechanism that reverses a change to maintain stability.

Positive feedback

A mechanism that amplifies a change.

Eukarya

Domain of life containing all organisms with eukaryotic cells.

Inductive reasoning

Using specific observations to form a general conclusion.

Deductive reasoning

Using a general principle to predict specific results.

Theory

A broad, well-supported explanation of natural phenomena.

Technology

Application of scientific knowledge for practical use.

Element

A substance made of one type of atom.

Compound

A substance made of two or more different elements bonded.

Atom

The smallest unit of matter that retains element properties.

Atomic number

Number of protons.

Atomic mass

Protons + neutrons.

Isotope

Atoms of the same element with different neutron numbers.

Polar covalent bond

Unequal sharing of electrons.

Nonpolar covalent bond

Equal sharing of electrons.

Ionic bond

Transfer of electrons; attraction between charged ions.

Ion

A charged atom or molecule.

Hydrogen bond

Weak attraction between polar molecules.

Cohesion

Water sticking to itself.

Adhesion

Water sticking to other surfaces.

Surface tension

Difficulty of breaking the surface of water.

Specific heat

Amount of heat needed to change temperature.

Solvent

Substance that dissolves other substances.

Solute

Substance dissolved in a solvent.

Hydrophilic

Water-loving; mixes with water.

Hydrophobic

Water-fearing; does not mix with water.

pH scale

Measures acidity/basicity (0–14).

Acid

Adds H⁺ ions to a solution

Base

Removes H⁺ ions / adds OH⁻.

Buffer

Resists changes in pH.

Hydrocarbon

Molecule made only of hydrogen and carbon.

Isomer

Same formula, different structure.

Structural isomer

Different arrangement of atoms.

Enantiomer

Mirror-image molecules.

Functional group

Chemical groups giving molecules their properties.

ATP

Main energy molecule of the cell.

Monomer

Small building block of polymers.

Polymer

Chain of monomers.

Dehydration reaction

Builds polymers by removing water.

Hydrolysis

Breaks polymers by adding water.

Monosaccharide

Simple sugar.

Polysaccharide

Chain of sugars (starch, glycogen).

Triacylglycerol

Fat molecule; glycerol + 3 fatty acids.

Steroid

Lipids with 4 fused rings.

Protein

Polymer of amino acids; performs most cell functions.

DNA

Hereditary genetic material.

RNA

Helps make proteins from DNA instructions.

Cell fractionation

Technique to separate cell parts.

Plasma membrane

Selective barrier around cells.

Prokaryotic cell

Cell without a nucleus.

Eukaryotic cell

Cell with a nucleus and organelles.

Organelle

Specialized internal cell structure.

Cytoskeleton

Protein network giving shape/support.

Cilia

Short, hairlike movement structures.

Flagella

Long, whip-like movement structures.

Cell wall

Rigid outer layer in plants, fungi, bacteria.

Extracellular matrix (ECM)

Outside network supporting animal cells.

Amphipathic

Having both hydrophilic and hydrophobic parts.

Selective permeability

Membrane allowing some substances through.

Concentration gradient

Difference in concentration across space.

Hypertonic

Higher solute; water moves out of cell.

Hypotonic

Lower solute; water moves into cell.

Isotonic

Equal solute; no net water movement.

Diffusion

Movement from high to low concentration.

Facilitated diffusion

Passive transport using proteins.

Sodium–potassium pump

Protein using ATP to move Na⁺ out, K⁺ in.

Exocytosis

Vesicles releasing materials out of the cell.

Endocytosis

Cell taking in materials via vesicles.

Oxidation

Loss of electrons.

Reduction

Gain of electrons.

Fermentation

ATP production without oxygen.

Electron transport chain (ETC)

Series of proteins transferring electrons to make ATP.

Glycolysis

Breaks glucose into pyruvate; makes small ATP.

Citric acid cycle

Breaks down Acetyl-CoA; releases electrons/CO₂.

Oxidative phosphorylation

Making ATP using ETC + chemiosmosis.

Acetyl CoA

Molecule that enters the citric acid cycle.

Proton-motive force

H⁺ gradient powering ATP synthase.

Chemiosmosis

Flow of H⁺ through ATP synthase to make ATP.

Autotrophic

Makes its own food (like plants).

Chloroplasts

Organelles where photosynthesis happens.

Thylakoids

Membranous structures where light reactions occur.

Photosynthesis

Process converting light into chemical energy.

Light reactions

First stage; produce ATP and NADPH.

NADPH

Electron carrier used in photosynthesis.

Stroma

Fluid around thylakoids; where Calvin cycle occurs.

Visible light

Part of electromagnetic spectrum we see.

Wavelengths

Distance between light wave peaks.

Chlorophylla

Main pigment used in photosynthesis.

Catabolic

Breaks down molecules to release energy.

Anabolic

Builds larger molecules using energy.

Energy

Capacity to cause change or do work.

Free energy

Energy available to do work.

Exergonic

Releases energy; spontaneous

Endergonic

Requires energy input

Energy coupling

Using energy from one reaction to power another.

Substrate

Molecule an enzyme acts on.

Active site

Region of an enzyme where the substrate binds.

Competitive inhibitor

Blocks the active site, preventing enzyme action.

Signal transduction pathway

Process by which a cell responds to a signal

Local regulator

Chemical signaling that affects nearby cells.