IB Biology SL Unit 1 – Flashcard Summary Tables

A comprehensive vocabulary review of 177 flashcards covering water properties, organic chemistry basics, nucleic acids, carbohydrates, lipids, proteins, enzymes, membrane structure, transport mechanisms, and cellular osmosis for IB Biology SL Unit 1.

Water as the Medium for Life (A1.1.1)

Water gives an aqueous environment where most metabolic reactions happen and carries dissolved substances (nutrients, ions, wastes). Medium = the environment in which something happens.

Examples of Water as a Medium

Cytoplasm (aqueous; molecules move and meet enzymes); blood plasma (transports nutrients, hormones, ions, wastes); xylem (transports dissolved mineral ions from roots upwards).

Structure of a Water Molecule (A1.1.2)

$1$ oxygen + $2$ hydrogen atoms joined by polar covalent bonds.

Covalent Bond

Intramolecular force (within a molecule) formed when atoms share pairs of electrons. In water, O shares one pair with each H, but unequally.

Electronegativity

The ability of an atom to attract shared electrons in a covalent bond. O has higher electronegativity than H, so it pulls the electrons closer.

Polarity Formation in Water

O is more electronegative than H $\rightarrow$ unequal sharing of electrons $\rightarrow$ O is slightly negative ($\delta^-$), H slightly positive ($\delta^+$) $\rightarrow$ bent shape means charges do not cancel $\rightarrow$ polar molecule.

Polarity

Uneven distribution of electrical charge in a molecule, giving a slightly positive end and a slightly negative end.

Bent Shape of Water ($104.5^\circ$)

O has $2$ bonding pairs and $2$ lone pairs of electrons. The electron pairs repel, pushing the H atoms closer and making a bent shape, so the partial charges do not cancel.

Hydrogen Bond Formation in Water

The $\delta^+$ hydrogen of one water molecule is attracted to the $\delta^-$ oxygen of another (opposite partial charges attract). Weak intermolecular force.

Covalent Bond vs. Hydrogen Bond

Covalent: intramolecular, within a molecule (O–H in one $H_2O$), stronger. Hydrogen: intermolecular, between separate molecules, weaker.

Intramolecular vs. Intermolecular Forces

Intra = within a molecule (covalent bonds). Inter = between molecules (hydrogen bonds).

Importance of Hydrogen Bonds in Water

Huge numbers of them give cohesion, surface tension, high specific heat capacity and a relatively high boiling point.

Cohesion (A1.1.3)

Attraction between molecules of the same substance. In water, caused by hydrogen bonds (water sticks to water). E.g. droplets on a leaf; dome of water on a coin.

Surface Tension

Resistance of a liquid's surface to being broken, due to cohesion. Surface molecules have net inward attraction (fewer molecules above), so the surface acts like an elastic film.

Biological Use of Surface Tension

Water striders walk on water without sinking: hydrogen bonds $\rightarrow$ cohesion $\rightarrow$ surface tension supports their light body; hydrophobic legs spread weight and avoid breaking the surface.

Cohesion-Tension Mechanism in Xylem

$1$) Transpiration: water evaporates from mesophyll cells and leaves through stomata. $2$) This creates tension (pull) in the xylem. $3$) Cohesion (hydrogen bonds) keeps water in a continuous column. $4$) Column is pulled up from roots to leaves. Adhesion to xylem walls helps resist gravity.

Transpiration

Loss of water vapour from a plant, mainly through stomata in the leaves.

Role of Cohesion in Xylem Transport

Cohesion does not push water up the xylem. Cohesion keeps the water column continuous so transpiration pull can move it.

Adhesion (A1.1.4)

Attraction between molecules of different substances. Water is attracted to polar or charged surfaces (cellulose in cell walls, glass).

Cohesion vs. Adhesion

CO-hesion: water sticks to its own kind (hydrogen bonds between water molecules). AD-hesion: water attaches to something different (polar/charged surfaces).

Capillary Action

Movement of water through narrow spaces due to adhesion + cohesion. $1$) Adhesion: water sticks to polar walls of tube. $2$) Cohesion: those molecules pull neighbouring water molecules along. $3$) Water rises against gravity. Narrower tube = higher rise. Adhesive + cohesive forces $>$ gravity.

Importance of Capillary Action in Plants

Helps water move up narrow xylem vessels (cellulose walls are polar). Not the main explanation for long-distance movement in tall plants; that is cohesion-tension driven by transpiration.

Water as a Good Solvent (A1.1.5)

It is polar: $\delta^+$ H and $\delta^-$ O attract charged and polar substances, so many dissolve. Links to its role as a medium for metabolism and transport.

Solvent Properties: Metabolism and Transport

Metabolism: cytoplasm is aqueous so dissolved substances move and react. Animals: blood plasma transports dissolved nutrients etc. Plants: xylem carries mineral ions; phloem carries sugars.

Solvation (D2.3.1)

Solvent molecules surround solute particles so the solute dissolves. With water as solvent it is also called hydration.

Dissolution of NaCl in Water

$\delta^-$ O attracted to $Na^+$; $\delta^+$ H attracted to $Cl^-$. Water surrounds and separates the ions from the crystal and they disperse.

Water Solubility of Substances

Ionic substances (salt) and polar substances (glucose) dissolve. Non-polar substances (oil, wax) do not: they are hydrophobic.

Hydrophilic vs. Hydrophobic

Hydrophilic: attracted to water, usually polar or charged. Hydrophobic: does not interact favourably with water, usually non-polar.

Water's Action as a Solvent (Exam Answer)

Water is polar, with slightly positive and negative regions that attract charged and polar substances. Water molecules surround these particles and separate them, so they dissolve.

Density of Water (A1.1.6)

Ice is less dense than liquid water so it floats; water is densest at about $4\,^\circ\text{C}$. Ice forms an insulating surface layer, so water below stays liquid and organisms survive.

Specific Heat Capacity of Water

Water needs a lot of energy to heat up, so it heats and cools slowly. Aquatic habitats have stable temperatures.

Buoyancy

Upward force of water supports organisms, reducing the effect of gravity so less energy is needed to stay afloat.

Viscosity

Resistance to flow. Water is more viscous than air, so aquatic animals face more resistance and often have streamlined bodies.

Thermal Conductivity of Water

Water transfers heat better than air, so aquatic animals lose heat quickly. E.g. seals have thick blubber for insulation.

Animal Adaptations to Water's Physical Properties

Seals: blubber insulates against heat loss. Mallard ducks: oil glands waterproof feathers so they do not get soaked.

Specific Heat Capacity vs. Thermal Conductivity

Specific heat capacity: water heats and cools slowly. Thermal conductivity: water transfers heat quickly.

Carbon Atom Bonding Capacity (B1.1.1)

Four covalent bonds ($4$ electrons in outer shell). Strong, stable bonds allow large molecules.

Carbon Chains and Bond Types

Straight chains, branched chains and rings. Carbon can also form single, double and triple bonds.

Biological Importance of Carbon

Four bonds + bonding to other carbons gives huge variety: carbohydrates, lipids, proteins, nucleic acids.

Monomer vs. Polymer (B1.1.2)

Monomer: small building-block molecule. Polymer: large molecule made by joining many monomers with covalent bonds. E.g. starch = many glucose.

Condensation Reaction

Joins monomers into a polymer by removing water. An OH from one monomer and an H from the other form $H_2O$; a covalent bond forms between monomers.

Formation of Biological Macromolecules

All formed by condensation, releasing one water per bond. Polysaccharides: monosaccharides, glycosidic bonds. Polypeptides: amino acids (amino + carboxyl groups), peptide bonds. Nucleic acids: nucleotides, phosphodiester bonds (sugar of one + phosphate of next).

Macromolecule Monomers, Polymers, and Bonds

Carbohydrates: monosaccharide $\rightarrow$ polysaccharide, glycosidic bond. Proteins: amino acid $\rightarrow$ polypeptide, peptide bond. Nucleic acids: nucleotide $\rightarrow$ polynucleotide (DNA/RNA), phosphodiester bond.

Examples of Biological Polymers

Polysaccharides: starch, glycogen, cellulose. Polypeptides: insulin, haemoglobin. Nucleic acids: DNA, RNA.

Hydrolysis (B1.1.3)

Opposite of condensation: breaks polymers into monomers by adding water. Water splits into H and OH, which attach to the two parts as the covalent bond breaks.

Steps of Hydrolysis

$1$) Water added to a bond between two monomers. $2$) Bond breaks. $3$) H attaches to one monomer, OH to the other. $4$) Larger molecule separated into smaller ones.

Products of Hydrolysis

Polysaccharides $\rightarrow$ monosaccharides; polypeptides $\rightarrow$ amino acids; nucleic acids $\rightarrow$ nucleotides.

Condensation vs. Hydrolysis

Condensation: joins, forms a covalent bond, removes water, builds polymers. Hydrolysis: breaks, breaks a covalent bond, adds water, breaks polymers into smaller units.

Role of DNA (A1.2.1)

Stores genetic information for growth, development, functioning and reproduction. Information is in the sequence of nitrogenous bases. Contains instructions for making proteins. DNA is copied before a cell divides.

Viral Genetic Transmission

Genetic material is DNA or RNA (not both). They infect a host cell and use its enzymes/ribosomes (sometimes viral enzymes) to copy their nucleic acid and make viral proteins. These assemble into new viruses carrying copies of the genetic material.

Cellular vs. Viral Genetic Material

All cellular organisms use DNA; some viruses use RNA instead.

Components of a Nucleotide (A1.2.2)

Phosphate group (links adjacent nucleotides), pentose sugar ($5$-carbon; backbone), nitrogenous base (carries code in its sequence). Know how to draw it.

Two Pentose Sugars

Deoxyribose in DNA; ribose in RNA.

Joining of Nucleotides (A1.2.3)

Covalent phosphodiester bonds by condensation: phosphate of one nucleotide bonds to sugar of the next. Repeating sugar-phosphate = sugar-phosphate backbone; bases project from it. Forms a polynucleotide.

$5'$ and $3'$ Ends

$5'$ end: ends with a phosphate on carbon $5$ of the sugar. $3'$ end: ends with a hydroxyl (–OH) on carbon $3$ of the sugar. Strand runs $5' \rightarrow 3'$.

The Four Bases (A1.2.4)

DNA: A, T, C, G. RNA: A, U, C, G. Three shared (A, C, G); fourth differs: DNA has thymine, RNA has uracil.

Purines vs. Pyrimidines

Purines: A and G, two rings (six-membered + five-membered). Pyrimidines: C, T, U, one six-membered ring.

Complementary Base Pairing

DNA: A–T and C–G. RNA: A–U and C–G.

Bonding Between Nucleotides

Covalent (phosphodiester) bonds join nucleotides along one strand (backbone). Hydrogen bonds join complementary bases (between DNA strands; within a folded RNA strand).

RNA Structure (A1.2.5)

Single-stranded polynucleotide of nucleotides (phosphate, ribose, base A/U/C/G) joined by phosphodiester bonds via condensation. Can fold into shapes because complementary bases hydrogen-bond within the same strand.

Diagram Skills: Nucleotides and RNA

Identify phosphate group, ribose, base (A, U, C or G), sugar-phosphate backbone, phosphodiester bonds. DNA nucleotide: deoxyribose (H on carbon $2$, not OH), bases A, C, G, T.

DNA Structure (A1.2.6)

Double helix of two antiparallel polynucleotide strands. Sugar-phosphate backbones outside; bases face inwards and pair. Phosphodiester bonds (covalent) hold each strand together; hydrogen bonds hold the two strands together.

Antiparallel Strands

The two strands run in opposite directions: one $5' \rightarrow 3'$, the other $3' \rightarrow 5'$.

Hydrogen Bonds in Base Pairs

A–T: $2$ hydrogen bonds. C–G: $3$ hydrogen bonds.

Labels for DNA Molecule Drawing

Two sugar-phosphate backbones; bases A, T, C, G; hydrogen bonds between complementary bases; antiparallel strands with $5'$ and $3'$ ends; double helix.

DNA vs. RNA (A1.2.7)

Sugar: deoxyribose vs ribose. Strands: double vs usually single. Bases: A, T, C, G vs A, U, C, G. Shape: double helix vs can fold. Function: stores genetic info vs helps use it to make proteins.

Role of Complementary Base Pairing (A1.2.8)

Allows accurate DNA replication and allows information to be expressed (made into proteins).

Steps of DNA Replication

$1$) Strands separate as hydrogen bonds between bases break. $2$) Each strand is a template. $3$) Free nucleotides pair with exposed bases (A–T, C–G). $4$) Two identical DNA molecules, each with one old and one new strand = semi-conservative.

Gene Expression

Transcription: DNA used as template to make complementary mRNA (A–U, C–G). Translation: mRNA read in codons ($3$ bases), each codon specifies an amino acid; amino acids joined into a protein.

Diversity of DNA Sequences (A1.2.9)

Information is in the order of the $4$ bases. Same bases in a different order carry different information (e.g. ATGC vs ACTG). Very long sequences $\rightarrow$ enormous number of combinations $\rightarrow$ almost limitless storage capacity.

Conservation of the Genetic Code (A1.2.10)

Nearly all organisms use the same genetic code: codons of $3$ bases code for the same amino acids in bacteria, plants, animals, fungi.

Universal Genetic Code and Common Ancestry

All life uses the same four bases and (almost) the same code, suggesting these systems were inherited from a shared common ancestor.

Types of Carbohydrates

Monosaccharide = $1$ sugar unit; disaccharide = $2$ joined; polysaccharide = many joined.

Monosaccharides (B1.1.4)

Simplest carbohydrates (single sugar). Immediate energy source for cellular respiration; building blocks of larger carbohydrates. Small, soluble (easily transported), join by condensation.

Examples of Monosaccharides

Glucose: main respiration fuel. Fructose: in fruit, energy source. Galactose: joins glucose to form lactose. Ribose: $5$-carbon sugar in RNA.

Disaccharides

Two monosaccharides joined by condensation $\rightarrow$ glycosidic bond. Broken down to monosaccharides for energy.

Examples of Disaccharides

Maltose = glucose + glucose. Sucrose = glucose + fructose. Lactose = glucose + galactose.

Polysaccharides (B1.1.5)

Long chains of monosaccharides joined by glycosidic bonds. Used for energy storage (starch, glycogen) or structure (cellulose).

Starch vs. Glycogen

Starch: plants, stores glucose. Glycogen: animals (and fungi), stores glucose. Glycogen is more highly branched than starch, so glucose is released faster.

Two Types of Starch

Amylose: unbranched, coiled, compact. Amylopectin: branched, releases glucose more quickly.

Structural Features of Storage Polysaccharides

$1$) Compact (lots of energy in small space). $2$) Insoluble (do not diffuse out of cells). $3$) Do not affect osmosis/water potential significantly. $4$) Can be hydrolysed to glucose for respiration. $5$) Branching gives many ends for enzymes $\rightarrow$ fast glucose release.

Cellulose (B1.1.6)

Structural polysaccharide in plant cell walls; gives strength and support, helps cells keep shape. Made of beta-glucose.

Alpha-Glucose vs. Beta-Glucose

Same formula ($C_6H_{12}O_6$). Differ in the OH on carbon $1$: alpha = down, beta = up. Alpha $\rightarrow$ starch and glycogen; beta $\rightarrow$ cellulose.

Structure of Cellulose

Beta-glucose joined by $\beta\text{-}1,4$ glycosidic bonds; every other glucose is rotated $180^\circ \rightarrow$ long, straight, unbranched chains.

Tensile Strength of Cellulose

Straight parallel chains form hydrogen bonds with neighbours $\rightarrow$ bundles called microfibrils $\rightarrow$ high tensile strength, so cell walls resist stretching.

Cellulose Indigestibility in Humans

We do not make the enzyme cellulase, needed to break $\beta\text{-}1,4$ glycosidic bonds.

Starch vs. Cellulose

Starch: alpha-glucose, energy storage, coiled/branched, no strong microfibrils. Cellulose: beta-glucose, structure, straight/unbranched, strong microfibrils via hydrogen bonds.

Glycoproteins (B1.1.7)

Proteins with carbohydrate chains, on the outer surface of the cell membrane. Carbohydrate chains act as markers for cell-cell recognition.

ABO Antigens and Cell Recognition

ABO groups depend on carbohydrate markers (antigens) on red blood cell surfaces: A has A antigen, B has B, AB has both, O has neither. Immune system uses them to recognise own cells; if incompatible blood is given, antibodies attack the foreign red cells.

Lipids

Organic molecules of mainly C, H and O. Insoluble in water; used for long-term energy storage, insulation and cell membranes. NOT polymers of repeating monomers.

Hydrophobic Nature of Lipids (B1.1.8)

Most contain long non-polar hydrocarbon chains that cannot hydrogen-bond with water, so they separate from water (can be stored without dissolving in cytoplasm).

Examples of Lipids

Triglycerides (fats and oils; energy storage). Phospholipids (membrane structure). Steroids (e.g. cholesterol; membrane stability).

Triglyceride Formation (B1.1.9)

$1$ glycerol + $3$ fatty acids, joined by $3$ ester bonds through condensation (water released each time).

Phospholipid Formation

$1$ glycerol + $2$ fatty acids + $1$ phosphate-containing group, by condensation. Hydrophilic phosphate head, two hydrophobic fatty acid tails.

Saturated Fatty Acid (B1.1.10)

No $C=C$ double bonds, maximum hydrogen atoms. Straight chains pack closely, stronger forces between chains, higher melting point, usually solid fats.

Unsaturated Fatty Acid

One or more $C=C$ double bonds. Bends in chains stop close packing, weaker forces, lower melting point, usually liquid oils.

Monounsaturated vs. Polyunsaturated Fatty Acids

Mono = one $C=C$ double bond. Poly = two or more $C=C$ double bonds.

Effect of $C=C$ Double Bonds on Melting Point

$C=C$ creates bends $\rightarrow$ chains cannot pack closely $\rightarrow$ weaker forces between chains $\rightarrow$ lower melting point.

Fats and Oils in Plants and Endotherms

Saturated: pack closely, high melting point, solid fats. Unsaturated: pack less closely, low melting point, liquid oils. Plants often store energy as oils; endotherms store it as fats in adipose tissue.

Functions of Triglycerides in Adipose Tissue (B1.1.11)

Energy storage (many energy-rich C–H bonds), thermal insulation (fat under skin reduces heat loss), protection (cushions organs).