IB Biology Topic 1 Definitions

This page contains our IB Biology definitions for topic 1. By learning each one of these definitions, you will fully cover the content for IB Biology 'Molecules & Metabolism'.
0
absorption spectrum

It is the wavelengths of electromagnetic waves an atom can absorb

HL
acetylation

The addition of an acetyl group to histone N-terminal tails prevents the nucleosome from packing together and loosens the H1 protein to allow for DNA replication or transcription

HL
activation energy

The energy required to break the bonds in the reactants to convert them into products

HL
allosteric site

An alternate binding site on an enzyme

amino acid

The building block of proteins

anabolic reaction

A reaction that bonds monomers together to form a macromolecule

anaerobic respiration

The process by which a cell produces small amounts of ATP from organic compounds when no oxygen is present

anticodon

A base sequence complementary to a codon. Often found on tRNA, complementary to mRNA.

antiparallel

The property of DNA strands being next to each other but running in opposite directions

HL
Asteroid Theory

The hypothesis that Earth's water was delivered by water-rich asteroids that collided with the Earth during the early stages of its formation

catabolic reaction

A reaction that breaks a macromolecule down into monomers

chemiosmosis

The process by which proton pumps use the energy of electrons to pump protons from the matrix into the intermembrane space to build a concentration gradient

chemiosmosis in photosynthesis

The process by which proton pumps use the energy of electrons to pump protons from the stroma into the thylakoid space to build a concentration gradient

cis-unsaturated fatty acid

A fatty acid in which the double bond has hydrogens on the same side

codon

A sequence of three bases that codes for an amino acid

condensation reaction

A reaction that produces a disaccharide and water from two monosaccharides

HL
conjugated protein

Proteins with prosthetic groups, often a heme group

denature

The impairing of a protein's function by irreversibly changing its structure

dipole

The presence of positive and negative poles in a molecule due to unequal sharing of electrons between atoms

disaccharide

Two monosaccharides linked together by a condensation reaction

DNA profiling

The analysis of short tandem repeats unique to individuals to identify people

HL
end-product inhibition

A type of non-competitive inhibition whereby the last product of a chain or cycle inhibits the enzyme of the first reaction to control product formation

enzyme

A protein that speeds up and controls the rate of reactions of metabolism by lowering the activation energy required for a reaction to happen

enzyme catalysis

Breaking down of molecules by enzymes

HL
enzyme inhibitor

A substance that reduces or stops enzyme activity

HL
evaporation

A liquid absorbing heat to turn into a gas. Evaporation can occur randomly from a liquid's surface. Synonym for boiling and vaporization. 

HL
exon

A coding sequence

HL
Gas Giants

Large planets composed mostly of gases such as hydrogen and helium, found in the outer parts of the Solar System (e.g., Jupiter, Saturn, Uranus, Neptune)

gel electrophoresis

A method that separates proteins or DNA fragments by size

HL
Gene Knockout

A genetic engineering technique used to remove or inactivate specific genes in an organism

HL
genome

All the genes in an organism

glycolysis

The conversion of glucose to pyruvates in both aerobic and anaerobic respiration

HL
Goldilocks Zone

The region around a star where conditions are just right for liquid water to exist on a planet's surface, potentially allowing for life

hydrogen bonding

The strongest intermolecular force that only occurs between hydrogen and oxygen, nitrogen, or fluorine

hydrolysis reaction

A reaction that uses water to split a disaccharide into two monosaccharides

HL
hypercholesterolaemia

A genetic condition characterized by very high levels of cholesterol in the blood

immobilized enzyme

Enzymes attached to another material, such as beads, so they can be industrially recycled

HL
integral protein

A protein embedded in the plasma membrane

intermolecular forces

The forces between molecules

HL
intron

A non-coding sequence

HL
ionic bond

The electrostatic attraction between oppositely charged ions

HL
lagging strand

The strand that has the replication fork running in the 3' to 5' direction and replication in the 5' to 3' direction

HL
Lamarckism

The belief that acquired characteristics can be inherited

HL
leading strand

The strand that has the replication fork and replication both running in the 5' to 3' direction

macromolecule

A big molecule composed of two or more monomers

metabolism

The sum of all chemical reactions taking place within an organism

molecular biology

A study that explains the living processes in terms of the chemical processes involved

molecule

A group of two or more atoms held together by single, double, or triple covalent bonds

monomer

A small molecule

monosaccharide

The most basic unit of carbohydrates

monounsaturated fatty acid

A fatty acid with one double bond

mutagen

A substance capable of causing a mutation

mutation

A random change to the base sequence of a gene

HL
nucleosome

A complex composed of DNA bound to an eight-histone protein core and a linker histone protein

nucleotide

The most basic unit of a nucleic acid

oxidative phosphorylation

The process by which protons travel down the concentration gradient into the matrix via ATP synthase, which phosphorylates ADP into ATP

HL
peptide bond

The chemical bonds that link amino acids together in a polypeptide chain

HL
peristalsis

A wave of muscle contraction that passes along the entire digestive tract

photoactivation

The process by which chlorophyll reaction centers of photosystems absorb energy from light and their electrons become exited

photolysis

The process by which water is split into oxygen, protons, and electrons in the thylakoid space by an oxidized photosystem II after photoactivation

photophosphorylation

The process by which protons travel down the concentration gradient into the stroma via ATP synthase, which phosphorylates ADP into ATP

photosynthesis

The production of glucose and oxygen from light, CO2, and water, within the chloroplast

photosynthesis action spectrum

A spectrum that shows the rate of photosynthesis at different colors of light

polar molecule

A molecule with unequal covalent bonds between the atoms

polypeptide

A chain of many amino acids bound together by peptide bonds

polysaccharide

Many monosacchardies linked together by condensation reactions

polyunsaturated fatty acid

A fatty acid with two or more double bonds

HL
post-transcriptional modification

The process of splicing exons and removing introns from an mRNA strand after transcription to form mature mRNA for translation

proteome

The collection of proteins a cell produces

HL
Protoplanetary Disc

A rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, from which planets are formed

HL
Protostar

A young star still in the process of forming, gathering mass from its parent molecular cloud.

respiration

The production of ATP from organic compounds

HL
Sanger sequencing

A method of base sequencing that involves the use of ddNAs

saturated fatty acid

A fatty acid in which all carbon atoms are connected by single bonds

short tandem repeat

A repeating sequence present in an allele that is unique to an individual

HL
Solar Winds

Streams of charged particles released from the upper atmosphere of the Sun, which can influence planetary atmospheres and magnetic fields

HL
TALENs

Nucleases that bind to a DNA domain and cleave it to introduce a frameshift mutation and inactivate the gene

thin layer chromatography

A process that can separate xantophyll, carotene, and chlorophyll a and b by solubility

trans-unsaturated fatty acid

A fatty acid in which the double bond has hydrogen on opposite sides

tRNA

A single-stranded molecule that contains an anticodon and an associated amino acid

unsaturated fatty acid

A fatty acid that has one or more double bonds

Great Work!

You have now covered all of our topic 1 definitions for IB biology.
Now that you have completed these IB biology topic 1 definitions, dive into our topic 1 videos for the IB biology course.
IB biology topic 1 videos

Explored IB Biology?

Get stuck into one of our other subjects!
Join 85,000 students, across 130+ countries, in 500+ IB schools. That's half of the IB science graduates worldwide.
Start a 7d free trial