Unit 1 key terms

Water molecule – A molecule (H₂O) consisting of two hydrogen atoms and one oxygen atom.
Polar covalent bond – A bond where electrons are unequally shared, creating partial charges.
Hydrogen bond – A weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen).
Cohesion – Water molecules sticking together due to hydrogen bonding.
Xylem – Plant tissue that transports water and minerals from roots to leaves.
Surface tension – The elastic-like force on a liquid's surface caused by cohesive forces.
Adhesion – Water molecules sticking to other surfaces due to hydrogen bonding.
Capillary action – Water moving up narrow spaces against gravity due to cohesion and adhesion.
Phloem – Plant tissue that transports sugars and nutrients from leaves to the rest of the plant.
Solvent – A substance that dissolves other substances to form a solution.
Polar/non-polar – Polar molecules have charged regions, while non-polar molecules do not.
Hydrophilic – Water-attracting substances that dissolve in water.
Hydrophobic – Water-repelling substances that do not dissolve in water.
Metabolism – The sum of all chemical reactions in an organism.
Buoyancy – The ability of an object to float in a fluid due to density differences.
Density – The mass per unit volume of a substance.
Viscosity – A fluid's resistance to flow.
Thermal conductivity – The ability of a substance to transfer heat.
Specific heat capacity – The amount of heat needed to raise the temperature of a substance by 1°C.
Extraplanetary origin – The hypothesis that life or its building blocks originated outside Earth.
Retaining – The ability to maintain or preserve genetic information across generations.
Extra-terrestrial life – Life that exists or has existed beyond Earth.
The Goldilocks zone – The habitable region around a star where conditions allow liquid water to exist.
Hereditary information – Genetic material (DNA/RNA) passed from parents to offspring.
Nucleic acids – Macromolecules (DNA & RNA) that store and transmit genetic information.
Polymer – A large molecule made up of repeating monomer units.
Monomer – A small molecule that binds with others to form a polymer.
Virus – A non-living infectious particle that requires a host cell to reproduce.
Pentose – A five-carbon sugar found in nucleotides (e.g., ribose and deoxyribose).
Phosphate – A chemical group in nucleotides that forms part of the sugar-phosphate backbone in DNA/RNA.
Nitrogenous base – A molecule (A, T, G, C, U) that stores genetic code in nucleic acids.
Sugar-phosphate backbone – The structural framework of DNA and RNA consisting of sugar and phosphate groups.
Covalent bond – A strong bond where atoms share electrons, found in the sugar-phosphate backbone.
Hydrogen bond – A weak bond between complementary nitrogenous bases in DNA (e.g., A-T, G-C).
Ribose – A five-carbon sugar in RNA nucleotides.
Deoxyribose – A five-carbon sugar in DNA nucleotides, lacking one oxygen atom compared to ribose.
Adenine – A nitrogenous base in DNA and RNA that pairs with thymine (T) in DNA and uracil (U) in RNA.
Thymine (T) – A nitrogenous base found only in DNA, pairing with adenine (A).
Guanine (G) – A nitrogenous base in DNA and RNA that pairs with cytosine (C).
Cytosine (C) – A nitrogenous base in DNA and RNA that pairs with guanine (G).
Uracil (U) – A nitrogenous base found only in RNA, replacing thymine and pairing with adenine (A).
DNA (Deoxyribonucleic acid) – The molecule carrying genetic instructions for life.
RNA (Ribonucleic acid) – A single-stranded molecule involved in protein synthesis and gene regulation.
Condensation reaction – A chemical reaction forming a bond between molecules, releasing water (e.g., in nucleic acid formation).
Double helix – The twisted-ladder shape of DNA formed by two antiparallel strands.
Complementary – The specific base-pairing rules in DNA (A-T, G-C) and RNA (A-U, G-C).
Antiparallel – The opposite orientation of DNA strands (5’ → 3’ and 3’ → 5’).
Strands – The two long chains of nucleotides in DNA or the single strand in RNA.
Base pairing – The hydrogen bonding between specific nitrogenous bases in DNA/RNA.
Replication – The process of copying DNA before cell division.
Gene – A segment of DNA that codes for a specific protein.
Gene expression – The process where genetic information is used to synthesize proteins.
Central dogma – The flow of genetic information: DNA → RNA → Protein.
Transcription – The process of copying a gene’s DNA sequence into RNA.
Translation – The process of converting mRNA into a polypeptide (protein) at the ribosome.
Codon – A sequence of three nucleotides in mRNA that codes for an amino acid.
Genetic information – The instructions in DNA/RNA that determine an organism’s traits.
Genetic code – The universal set of rules that translate nucleotide sequences into amino acids for protein synthesis.
5’ to 3’ – The direction in which DNA and RNA are synthesized, from the 5' (phosphate) end to the 3' (hydroxyl) end.
Purines – Nitrogenous bases (adenine and guanine) with a double-ring structure.
Pyrimidines – Nitrogenous bases (cytosine, thymine, and uracil) with a single-ring structure.
Tetranucleotide hypothesis – An early (incorrect) theory that DNA consists of repeating four-base units in equal amounts.
Histones – Proteins that DNA wraps around to form chromatin structure.
Nucleosome – A unit of DNA wrapped around histone proteins, forming chromatin.
Supercoil – The tightly packed and twisted structure of chromosomal DNA.
Chromosomes – Structures made of DNA and proteins that carry genetic information.
Centrifuged – A process using centrifugal force to separate components of a mixture.
Pellet – The solid mass of particles collected at the bottom after centrifugation.
Supernatant – The liquid remaining above the pellet after centrifugation.
Covalent bond – A strong chemical bond formed by the sharing of electrons.
Hydroxyl groups – Functional groups (-OH) found in sugars and alcohols.
Amine groups – Functional groups (-NH₂) found in amino acids and proteins.
Macromolecules – Large biological molecules such as carbohydrates, lipids, proteins, and nucleic acids.
ATP – Adenosine triphosphate, the main energy carrier in cells.
Monosaccharide – A single sugar unit, e.g., glucose or fructose.
Disaccharide – Two monosaccharides linked by a glycosidic bond, e.g., sucrose.
Oligosaccharide – A carbohydrate consisting of 3-10 monosaccharide units.
Polysaccharide – A complex carbohydrate made of many sugar units, e.g., starch or cellulose.

Glycosidic bond – A covalent bond linking monosaccharides in carbohydrates.
- 1 → 4 – A glycosidic bond between carbon 1 and carbon 4 in a sugar molecule.
- 1 → 6 – A glycosidic bond between carbon 1 and carbon 6, forming branching points.
α-glucose – A glucose isomer where the -OH on carbon 1 is below the ring.
β-glucose – A glucose isomer where the -OH on carbon 1 is above the ring.
Ribose – A five-carbon (pentose) sugar found in RNA.
Deoxyribose – A five-carbon sugar found in DNA, lacking one oxygen atom.
Hydrolysis reaction – A chemical reaction breaking down molecules by adding water.
Pentose – A sugar with five carbon atoms, e.g., ribose.
Hexose – A sugar with six carbon atoms, e.g., glucose.
Sugar – A general term for carbohydrates, including mono-, di-, and polysaccharides.
Starch – A storage polysaccharide in plants, made of amylose and amylopectin.
Amylose – A linear, unbranched form of starch with 1→4 glycosidic bonds.
Amylopectin – A branched form of starch with both 1→4 and 1→6 bonds.
Glycogen – A highly branched storage polysaccharide in animals.
Cellulose – A structural polysaccharide in plant cell walls, made of β-glucose.
Fibrils – Bundles of cellulose fibers providing strength to plant cell walls.
Cell wall – A rigid structure surrounding plant cells, composed of cellulose.
Glycoproteins – Proteins with attached carbohydrate chains, important for cell signaling.
Oligosaccharides – Short carbohydrate chains involved in cell recognition.
Cell-to-cell recognition – The process where cells identify and communicate using glycoproteins.
ABO-system – A classification of blood types based on antigen presence.
Antigen – A molecule, usually a protein or polysaccharide, that triggers an immune response by binding to specific antibodies or immune receptors.

· Antibody – A Y-shaped protein produced by B-cells that binds to specific antigens to help neutralize pathogens.

· Blood type – A classification of blood based on the presence or absence of specific antigens (A and B) on red blood cells and antibodies in the plasma, determining compatibility for transfusions (e.g., A, B, AB, O).

Lipid – A group of hydrophobic organic molecules, including fats, oils, and steroids, that serve as energy storage, structural components of membranes, and signaling molecules.
Hydrophobic – A property of molecules that repel water due to being nonpolar, preventing their dissolution in aqueous environments.
Hydrophilic – A property of molecules that attract and interact with water due to being polar, allowing them to dissolve in aqueous environments.
Oils – Liquid lipids at room temperature, composed mainly of unsaturated fatty acids, commonly found in plants and fish.
Fats – Solid lipids at room temperature, composed mainly of saturated fatty acids, serving as long-term energy storage in animals.
Waxes – Lipids with long-chain fatty acids linked to alcohols, providing waterproofing and protection in plants and animals.
Phospholipids – A type of lipid with a hydrophilic phosphate head and two hydrophobic fatty acid tails, forming the bilayer structure of cell membranes.
Steroids – Lipids with a characteristic four-ring structure, including cholesterol and hormones like testosterone and estrogen.
Triglycerides – Lipids composed of one glycerol molecule and three fatty acids, serving as energy storage molecules in adipose tissue.
Glycerol – A three-carbon alcohol that serves as the backbone of triglycerides and phospholipids.
Fatty acid – A long hydrocarbon chain with a carboxyl group at one end, forming the building blocks of lipids.
Phosphate – A charged molecule containing phosphorus and oxygen, essential for nucleotides, ATP, and the hydrophilic head of phospholipids.
Here are short definitions for your IB Biology HL key terms:
Condensation reaction – A reaction where two molecules join, releasing water.
Ester bond – The bond formed between a glycerol and fatty acid in lipids.
Carboxyl group – A functional group (-COOH) found in amino acids and fatty acids.
Covalent bond – A strong bond where atoms share electrons.
Single bond – A covalent bond where two atoms share one pair of electrons.
Double bond – A covalent bond where two atoms share two pairs of electrons.
Cis / trans – Isomers of molecules with different spatial arrangements around a double bond.
Saturated – A fatty acid with only single bonds between carbon atoms.
Monounsaturated – A fatty acid with one double bond in its carbon chain.
Polyunsaturated – A fatty acid with two or more double bonds in its carbon chain.
Essential fatty acid – Fatty acids that must be obtained from the diet because the body cannot synthesize them.
Endotherms – Organisms that regulate their body temperature internally.
Adipose tissue – Fat-storing tissue that provides insulation and energy storage.
Phospholipid bilayer – The structure of cell membranes, consisting of two layers of phospholipids.
Amphipathic – A molecule with both hydrophilic and hydrophobic regions.
Hydrophilic head – The water-attracting part of a phospholipid.
Hydrophobic tails – The water-repelling part of a phospholipid.
Testosterone – A steroid hormone that regulates male development and reproduction.

· · Amino acid – The building blocks of proteins, consisting of an amino group, carboxyl group, hydrogen atom, and variable side chain (R-group).

· · Protein – A macromolecule made of one or more polypeptides folded into a specific three-dimensional structure, performing various biological functions.

· · Alpha carbon (α-carbon) – The central carbon in an amino acid to which the amino group, carboxyl group, hydrogen atom, and side chain (R-group) are attached.

· · Amino group – A functional group (-NH₂) in amino acids that acts as a base and participates in peptide bond formation.

· · Carboxyl group – A functional group (-COOH) in amino acids that acts as an acid and participates in peptide bond formation.

· · Side chain (R-group) – The variable group in an amino acid that determines its properties and function.

· · Amphiprotic – A molecule that can act as both an acid and a base, such as amino acids due to their amino and carboxyl groups.

· · Peptide – A short chain of amino acids linked by peptide bonds.

· · Dipeptide – A molecule consisting of two amino acids joined by a single peptide bond.

· · Oligopeptide – A peptide composed of a few amino acids (usually fewer than 20).

· · Polypeptide – A long chain of amino acids linked by peptide bonds that can fold into a functional protein.

· · Conformation – The three-dimensional shape of a protein, essential for its function.

· · Peptide bond – A covalent bond formed between the amino group of one amino acid and the carboxyl group of another during protein synthesis.

· · Catalysed – A reaction that is sped up by an enzyme.

· · Condensation reaction – A chemical reaction in which two molecules are joined together with the loss of a water molecule, as in peptide bond formation.

· · Ribosome – The cellular organelle that synthesizes proteins by translating mRNA into polypeptide chains.

· · Essential amino acid – An amino acid that cannot be synthesized by the body and must be obtained from the diet.

· · α-amylase – An enzyme that catalyzes the hydrolysis of starch into smaller carbohydrate molecules.

· · Insulin – A peptide hormone that regulates blood glucose levels by promoting glucose uptake into cells.

· · Denaturation – The loss of a protein’s three-dimensional structure due to external factors like heat or pH changes, leading to loss of function.

· · Primary protein structure – The sequence of amino acids in a polypeptide chain.

· · Secondary protein structure – Local folding patterns in a protein, including α-helices and β-pleated sheets, stabilized by hydrogen bonds.

· · Tertiary protein structure – The overall three-dimensional shape of a polypeptide due to interactions among R-groups.

· · Quaternary protein structure – The arrangement of multiple polypeptide chains in a multi-subunit protein.

· · α-helix – A right-handed coiled structure in proteins stabilized by hydrogen bonds.

· · β-pleated sheets – A secondary structure in proteins where polypeptide chains are linked side by side by hydrogen bonds.

· · Intramolecular forces – Forces within a molecule that help stabilize protein structure, such as hydrogen bonds, ionic bonds, and disulfide bridges.

· · Globular protein – A protein with a compact, spherical shape, often soluble in water and involved in metabolic functions (e.g., enzymes and hormones).

· · Denatured – A protein that has lost its functional shape due to structural disruption.

· · Disulfide bonds – Strong covalent bonds between sulfur atoms in cysteine residues, stabilizing protein structure.

· · Hydrophobic interactions – Nonpolar interactions that cause hydrophobic amino acids to cluster inside proteins, stabilizing their structure.

· · Ionic bonds – Electrostatic attractions between charged amino acid side chains, contributing to protein stability.

· · Prosthetic group – A non-protein component tightly bound to a protein, necessary for its function (e.g., heme in hemoglobin).

· · Conjugated protein – A protein that contains a prosthetic group in addition to polypeptides (e.g., hemoglobin with its heme group).

· · Fibrous proteins – Structural proteins with elongated, insoluble fibers that provide support and strength (e.g., collagen and keratin).

· Plasma membrane – A selective barrier that surrounds cells, controlling the movement of substances in and out.

· Fluid mosaic model – A model describing the membrane as a flexible structure with embedded proteins and lipids.

· Phospholipid bilayer – A double layer of phospholipids forming the main structure of the plasma membrane.

· Amphipathic phospholipids – Phospholipids with both hydrophilic and hydrophobic regions.

· Polar/hydrophilic head – The water-attracting part of a phospholipid.

· Non-polar/hydrophobic tails – The water-repelling part of a phospholipid.

· Cholesterol – A lipid in the membrane that helps regulate fluidity and stability.

· Integral protein – A protein embedded in the membrane, spanning across it.

· Peripheral protein – A protein attached to the membrane surface, involved in signaling or support.

· Glycolipids – Lipids with attached carbohydrates, important for cell recognition.

· Glycoproteins – Proteins with attached carbohydrates, involved in cell signaling and recognition.

· Vesicles – Small membrane-bound sacs that transport substances within or outside the cell.

· Permeability – The ability of a membrane to allow substances to pass through.

· Diffusion – The passive movement of particles from high to low concentration.

· Concentration – The amount of a substance in a given space.

· Concentration gradient – The difference in concentration of a substance across a space.

· Simple diffusion – The passive movement of molecules directly through the membrane.

· Passive transport – Movement of molecules across a membrane without energy input.

· Osmosis – The diffusion of water across a semipermeable membrane.

· Solute – A substance dissolved in a solvent.

· Solvent – A liquid that dissolves a solute.

· Aquaporin – A membrane protein that facilitates water transport.

· Semipermeable – A membrane that allows some molecules to pass but not others.

· Facilitated diffusion – Passive transport using membrane proteins.

· Transport proteins – Proteins that help move substances across a membrane.

· Active transport – The movement of molecules against a gradient using energy.

· Protein pumps – Membrane proteins that use ATP to transport substances.

· ATP – A molecule that stores and provides energy for cellular processes.

· Selective membranes – Membranes that regulate what enters and exits the cell.

· Here are definitions for your IB Biology HL key terms related to nerve impulses and action potentials:

· Axon – A long, slender projection of a neuron that transmits electrical signals to other neurons, muscles, or glands.

· Nerve impulse – An electrical signal that travels along a neuron, allowing communication between different parts of the nervous system.

· Action potential – A rapid change in membrane potential due to the movement of ions across a neuron's membrane, leading to signal transmission.

· Electrical signal – A flow of ions across a neuron’s membrane that carries information along the nervous system.

· Movement of ions – The controlled flow of sodium (Na⁺) and potassium (K⁺) ions across the neuron membrane, essential for action potential generation and transmission.

· Sodium-potassium pump – A membrane protein that actively transports three sodium ions out and two potassium ions into the neuron, maintaining resting membrane potential.

· Concentration gradient – The difference in ion concentration across the neuron's membrane, driving passive ion movement during nerve impulses.

· Voltage-gated sodium and potassium channels – Protein channels in the neuron membrane that open and close in response to changes in membrane voltage, allowing Na⁺ and K⁺ ions to flow in and out, generating an action potential.

· Threshold of polarity – The minimum membrane potential (around -55mV) required to trigger an action potential by opening voltage-gated sodium channels.

· Synapse – The junction between two neurons where nerve signals are transmitted.

· Neurotransmitter – A chemical messenger that transmits signals across a synapse.

· Acetylcholine – A neurotransmitter involved in muscle contraction and nervous system signaling.

· Receptor protein – A protein that binds to specific molecules to trigger a response.

· Cotransporter – A membrane protein that moves two substances simultaneously.

· Sodium-dependent glucose cotransporter – A protein that transports glucose into cells using sodium ion gradients.

· Tissue – A group of similar cells performing a specific function.

· Solvent – A liquid that dissolves a solute to form a solution.

· Solute – A substance dissolved in a solvent.

· Dipole-ion bonds – Electrostatic attractions between polar molecules and ions.

· Precipitate – An insoluble solid that forms from a solution.

· Concentration – The amount of solute in a given volume of solvent.

· Hypotonic – A solution with a lower solute concentration than the cell, causing water to enter.

· Hypertonic – A solution with a higher solute concentration than the cell, causing water to leave.

· Isotonic – A solution with equal solute concentration inside and outside the cell.

· Equilibrium – A state where concentrations are balanced and no net movement occurs.

· Turgid – A swollen plant cell due to water intake in a hypotonic solution.

· Flaccid – A limp plant cell due to water loss in an isotonic solution.

· Wilting – The drooping of plant tissues due to water loss.

· Plasmolysis – The shrinkage of a plant cell’s cytoplasm in a hypertonic solution.

· Intravenous drip – A method of delivering fluids directly into a vein.

· Here are definitions for your IB Biology HL key terms related to water potential:

· Water potential (ψW) – The potential energy of water in a system, determining the direction of water movement. Water moves from areas of higher water potential to lower water potential. It is measured in megapascals (MPa).

· Hydrostatic pressure – The pressure exerted by a fluid in response to an external force, such as water pressure inside plant cells due to turgor pressure.

· Solute potential (ψS) – The component of water potential affected by dissolved solutes. Adding solutes lowers water potential (more negative ψS), causing water to move into a region by osmosis.

· Pressure potential (ψP) – The pressure exerted by the cell wall or membrane on the water inside a plant cell. A positive ψP contributes to overall water potential and maintains turgor pressure in plant cells.