In IB Biology Human Physiology (B3.2 / C3.2), compare the structure and function of Phagocytes, B-Lymphocytes, Helper T-Cells, and Memory Cells, and explain how Monoclonal Antibodies are produced via hybridomas.

Phagocytes provide non-specific innate immunity via endocytosis and antigen presentation on MHC-II. Helper T-cells bind antigen-MHC, releasing cytokines to activate B-cells whose surface antibodies match the antigen (clonal selection). Activated B-cells divide by mitosis into antibody-secreting Plasma cells and long-lived Memory cells (secondary immunity). Monoclonal antibodies: inject a mouse with target antigen → isolate spleen B-lymphocytes producing the specific antibody → fuse them with endlessly dividing myeloma (cancer) cells to form hybridoma cells → screen via ELISA and culture in fermenters (used in hCG pregnancy tests and targeted cancer therapy).

Explain how Leptin, Melatonin, and Thyroxin act as hormones regulating appetite, circadian rhythms, and metabolic rate (C3.1).

1) Thyroxin (secreted by thyroid gland, contains 4 iodine atoms): targets almost all body cells to increase basal metabolic rate and heat production (thermogenesis); iodine deficiency prevents thyroxin synthesis, causing goitre. 2) Leptin (secreted by adipose/fat tissue): binds to receptors in the hypothalamus to inhibit appetite; ob/ob mice lack leptin and become obese. 3) Melatonin (secreted by the pineal gland in darkness, inhibited by light via retinal ganglion cells and the suprachiasmatic nucleus SCN): regulates circadian sleep–wake rhythms and alleviates jet lag.

Compare Brønsted–Lowry, Lewis, and Arrhenius definitions of acids and bases, and explain why transition metal hexaaqua complex ions act as Lewis acid–base adducts (HL Reactivity 3.1 / 3.4).

Brønsted–Lowry: Acid = proton (H⁺) donor; Base = proton (H⁺) acceptor. Lewis: Acid = electron pair ACCEPTOR (electrophile with an empty orbital); Base = electron pair DONOR (nucleophile with a lone pair). Every Brønsted–Lowry base is also a Lewis base, but Lewis acids include species without H⁺ (e.g., BF3, AlCl3, and transition metal cations like Cu²⁺ or Fe³⁺). When [Fe(H2O)6]³⁺ forms, H2O ligands act as Lewis bases donating lone pairs into empty d/s/p orbitals of the Fe³⁺ Lewis acid.

In HL Electrochemistry, state the 3 factors that determine which ions are selectively discharged during the electrolysis of aqueous solutions (e.g., dilute vs concentrated NaCl(aq) and CuSO4(aq) with Cu vs Pt electrodes).

Selective discharge depends on: 1) Relative Standard Electrode Potentials (E°: at the cathode, the species with the MORE POSITIVE E° is reduced preferentially; at the anode, the species with the MORE NEGATIVE E° is oxidised); 2) Concentration effect (in concentrated NaCl brine, Cl⁻ is oxidised to Cl2 gas at the anode instead of H2O → O2 due to overpotential and high [Cl⁻]); 3) Nature of the electrodes (in CuSO4(aq) with inert Pt/C electrodes, H2O is oxidised at the anode to O2 + 4H⁺; with active copper electrodes, the copper anode itself oxidises: Cu(s) → Cu²⁺(aq) + 2e⁻, used in electrorefining copper).

In HL Chemistry Spectroscopy, what causes X-ray Crystallography diffraction patterns and how does it complement Mass Spectrometry, IR, and ¹H NMR?

X-rays have wavelengths (~0.1 nm) comparable to interatomic bond lengths in crystals. When a monochromatic X-ray beam strikes a crystalline solid, X-rays scatter off the electron clouds of atoms and constructively interfere according to Bragg's Law (nλ = 2d sin θ), producing an electron density map that reveals exact 3D bond lengths and bond angles (hydrogen atoms are hardest to detect because they have only 1 electron).

How do you calculate the Standard Gibbs Free Energy Change (ΔG°) of a redox reaction from Standard Electrode Potentials (E°cell) and Equilibrium Constant (K)?

IB Data Booklet equations: ΔG° = −nFE°cell = −RT ln K, where n = number of moles of electrons transferred in the balanced redox equation, F = 96,500 C mol⁻¹ (Faraday's constant), and E°cell is in Volts (J C⁻¹) (divide by 1000 to convert J mol⁻¹ to kJ mol⁻¹). Thus: E°cell > 0 V ⇔ ΔG° 1 (spontaneous forward reaction).

How do you identify the number of peaks, chemical shifts, integration trace, and multiplicity in ¹H NMR of isomers like C3H6O2 (propanoic acid, methyl ethanoate, ethyl methanoate)?

All three have Mr = 74 and 3 proton environments: 1) Propanoic acid (CH3–CH2–COOH): 3 signals with integration 3:2:1 — triplet (3H, CH3), quartet (2H, CH2), and downfield singlet at δ = 11.5 ppm (1H, –COOH). 2) Methyl ethanoate (CH3–COO–CH3): 2 signals with integration 3:3 — two singlets (one at δ ~ 2.0 ppm for CH3C=O, one at δ ~ 3.7 ppm for –OCH3). 3) Ethyl methanoate (H–COO–CH2–CH3): 3 signals with integration 1:2:3 — singlet at δ ~ 8.0 ppm (1H, H–C=O), quartet at δ ~ 4.1 ppm (2H, –OCH2–), and triplet at δ ~ 1.3 ppm (3H, –CH3).

In HL Biology Reproduction (D3.1), compare Spermatogenesis and Oogenesis in terms of timing, cell numbers, and unequal cytokinesis.

Both involve germinal epithelium mitosis, cell growth, two meiotic divisions, and differentiation. Spermatogenesis (in seminiferous tubules, aided by Sertoli nurse cells and interstitial Leydig cells secreting testosterone): begins at puberty, continuous throughout life, produces millions of sperm daily, with 4 equal haploid spermatozoa per primary spermatocyte. Oogenesis (in ovarian follicles): begins in the female fetus (arrested in Prophase I until puberty, then Metaphase II until fertilisation), cyclical (1 per month, ends at menopause), and unequal cytokinesis produces 1 large ovum (retaining cytoplasm/organelles/yolk) plus 2–3 degenerating polar bodies.

In HL Chemistry Kinetics (Reactivity 2.2), how do you use the Arrhenius Equation in linear form to find Activation Energy (Ea) from experimental rate constants at different temperatures?

The logarithmic Arrhenius equation is ln k = −(Ea / R)(1 / T) + ln A, where R = 8.31 J K⁻¹ mol⁻¹ and T is in Kelvin. Plot ln k on the vertical y-axis against (1 / T) in K⁻¹ on the horizontal x-axis to get a straight line with a negative gradient m = −Ea / R and y-intercept = ln A. Therefore, Ea = −m × R (in J mol⁻¹; divide by 1000 for kJ mol⁻¹). Alternatively, for two temperatures T₁ and T₂: ln(k₂ / k₁) = (Ea / R)(1/T₁ − 1/T₂).

Compare Voltaic (Galvanic) Cells and Electrolytic Cells in terms of spontaneity (ΔG°), anode/cathode signs, and electron/ion flow (Reactivity 3.2).

In BOTH cells, Oxidation ALWAYS occurs at the Anode and Reduction ALWAYS occurs at the Cathode ('AN OIL RIG CAT'), and electrons flow through the external wire from Anode to Cathode. 1) Voltaic cell: spontaneous exothermic redox reaction converts chemical energy to electrical energy (E°cell > 0, ΔG° = −nFE°cell 0); Anode is POSITIVE and Cathode is NEGATIVE.

Compare SN1 and SN2 Nucleophilic Substitution mechanisms of halogenoalkanes in IB HL Chemistry (Reactivity 3.4).

SN2 (Bimolecular, favoured by PRIMARY halogenoalkanes and polar aprotic solvents like propanone/DMSO): concerted 1-step mechanism with rate = k[RX][Nu⁻]; nucleophile attacks from the opposite side (backside attack) through a trigonal bipyramidal pentavalent transition state, causing WALDEN INVERSION of stereochemical configuration. SN1 (Unimolecular, favoured by TERTIARY halogenoalkanes and polar protic solvents like water/ethanol): 2-step mechanism with rate = k[RX]; rate-determining heterolytic C–X fission forms a trigonal planar carbocation intermediate, attacked from either side to form a RACEMIC mixture.

Compare the environmental and thermodynamic properties of Biofuels (bioethanol, biodiesel) vs Fossil Fuels and Hydrogen in IB Chemistry Reactivity 1.

Specific Energy (kJ g⁻¹) = ΔcH° ÷ Mr; Energy Density (kJ cm⁻³) = Specific Energy × Density. Hydrogen (H2) has the highest Specific Energy (142 kJ g⁻¹) and zero CO2 emissions at point of use, but very low volumetric Energy Density as a gas (requiring high-pressure storage). Bioethanol (from fermentation of plant starch/cellulose) is theoretically carbon-neutral (CO2 released on combustion equals CO2 absorbed by crops during photosynthesis, ignoring farming/distillation energy) and renewable, but has lower specific energy than petrol/octane because ethanol is already partially oxidised.

How do you apply Faraday's Laws of Electrolysis (Q = It = n(e⁻)F) to calculate the mass of metal electroplated at a cathode (HL)?

1) Calculate total charge passed in Coulombs: Q = I × t (Current in Amps × Time in seconds); 2) Convert charge into moles of electrons using Faraday's constant (F = 96,500 C mol⁻¹): n(e⁻) = Q / F = (It) / 96500; 3) Use the cathode half-equation stoichiometry (M^(z+) + z e⁻ → M(s)) to find moles of metal deposited: n(M) = n(e⁻) / z. Thus Mass of metal plated = (I × t × Ar) ÷ (z × 96500).

Outline the 3-step Retro-Synthetic Pathway in HL Organic Chemistry to convert Ethene into Propanoic Acid.

Since ethene has 2 carbons (C2H4) and propanoic acid has 3 carbons (CH3CH2COOH), the chain must be extended via nucleophilic substitution with cyanide: Step 1: Ethene + HBr → Bromoethane (electrophilic addition at room temperature). Step 2: Bromoethane + KCN in warm aqueous ethanol under reflux → Propanenitrile (CH3CH2CN) + KBr (SN2 nucleophilic substitution). Step 3: Propanenitrile + dilute HCl/H2SO4 heated under reflux → Propanoic acid (CH3CH2COOH) + NH4⁺.

Explain the hormonal roles of hCG, Progesterone, Oestrogen, and Oxytocin in Placental Maintenance and the Positive Feedback Loop of Parturition (Childbirth).

The early blastocyst secretes human chorionic gonadotropin (hCG) to maintain the corpus luteum so it continues secreting progesterone until the placenta takes over at ~10–12 weeks (progesterone inhibits myometrial contractions and oxytocin receptors). At full term (~40 weeks), fetal growth stretches the cervix and placental progesterone drops while oestrogen rises (upregulating uterine oxytocin receptors): 1) Cervical stretch receptors signal the maternal posterior pituitary to secrete oxytocin; 2) Oxytocin stimulates stronger uterine myometrial contractions; 3) Contractions push the baby's head harder against the cervix, triggering even more oxytocin release (positive feedback) until birth.

In HL Chemistry, explain why 1-chlorobutane, 2-chlorobutane, and 2-chloro-2-methylpropane have different rates and mechanisms of nucleophilic substitution with OH⁻.

1) 1-chlorobutane (primary): undergoes concerted 1-step SN2 because the α-carbon is sterically unhindered and a primary carbocation is too unstable to form. 2) 2-chloro-2-methylpropane (tertiary): undergoes 2-step SN1 (much faster overall!) because three bulky methyl groups cause severe steric hindrance blocking backside SN2 attack, while strongly stabilising the tertiary carbocation intermediate via the +I inductive effect. 3) 2-chlorobutane (secondary): can undergo a mixture of both SN1 and SN2 pathways.

Contrast Antibiotics (e.g., Penicillin discovered by Florey & Chain) with Antivirals, and explain how HIV destroys the immune system.

Antibiotics block prokaryotic metabolic pathways (e.g., penicillin inhibits transpeptidase enzymes that cross-link peptidoglycan bacterial cell walls, causing osmotic lysis; others target 70S ribosomes) without harming eukaryotic cells. Viruses lack their own metabolism or cell walls and replicate inside host cells, so antibiotics are completely ineffective against viruses. HIV (a retrovirus using reverse transcriptase) specifically infects and lyses CD4⁺ Helper T-lymphocytes, eventually preventing B-cell activation and antibody production (AIDS).

Explain why aqueous solutions of NaCl, NH4Cl, CH3COONa, and [Fe(H2O)6]Cl3 are neutral, acidic, or basic (Salt Hydrolysis in HL Chemistry).

1) Strong acid + Strong base salt (NaCl): neither Na⁺ nor Cl⁻ hydrolyses water → neutral (pH = 7). 2) Strong acid + Weak base salt (NH4Cl): NH4⁺ is the conjugate acid of weak base NH3 and donates H⁺ to water (NH4⁺ + H2O ⇌ NH3 + H3O⁺) → acidic (pH 7). 4) Small, high-charge cations like Fe³⁺ or Al³⁺ polarise O–H bonds in coordinated H2O ligands, releasing H⁺ → strongly acidic (pH ~2–3).

Explain why Tertiary Carbocations are more stable than Secondary and Primary Carbocations in both SN1 and Markovnikov Electrophilic Addition.

Carbocation stability follows the order: Tertiary (R3C⁺) > Secondary (R2CH⁺) > Primary (RCH2⁺) > Methyl (CH3⁺). Alkyl groups (–R) have a positive inductive effect (+I) and hyperconjugation, donating electron density towards the positively charged carbon atom. Three electron-releasing alkyl groups delocalise and spread out the positive charge much more effectively than one, lowering the activation energy for forming the tertiary carbocation intermediate.

In HL Chemistry, how do you calculate the pH of a solution at any point along a Strong Acid–Strong Base vs Weak Acid–Strong Base titration curve?

1) Initial pH of weak acid: [H⁺] = √(Ka × [HA]_0). 2) Buffer region (before equivalence): calculate moles of HA remaining and moles of A⁻ formed by OH⁻ neutralisation, then use pH = pKa + log₁₀(n(A⁻) / n(HA)). 3) Half-equivalence point (V = ½ V_eq): [HA] = [A⁻], so pH = pKa. 4) Equivalence point (V = V_eq): for Weak Acid + Strong Base, all HA has been converted into conjugate base A⁻, which hydrolyses water (A⁻ + H2O ⇌ HA + OH⁻ with [OH⁻] = √(Kb × [A⁻])), so pH > 7. 5) Beyond equivalence: calculate excess moles of OH⁻ divided by total volume V_total.

Explain how the structure of the Placenta facilitates exchange of materials between maternal and fetal blood (HL Biology D3.1).

Chorionic villi provide a huge, highly branched surface area projecting into the intervillous spaces filled with maternal blood, separated by a very thin placental barrier (fetal capillary endothelium + trophoblast cells). Maternal and fetal blood never mix (preventing maternal blood pressure from damaging fetal capillaries and avoiding immune rejection). O2, glucose, amino acids, lipids, water, vitamins, and maternal IgG antibodies cross to the fetus via diffusion, facilitated diffusion, active transport, and endocytosis; CO2 and urea diffuse back into maternal blood.

In HL Biology Gene Expression (D1.2 / D2.2), how do Transcription Factors, Enhancers, Silencers, and Promoter-Proximal Elements regulate eukaryotic transcription?

Unlike prokaryotes (which use operons like the lac operon where lactose binds the repressor protein), eukaryotic genes are regulated individually: 1) General transcription factors bind to the TATA box in the promoter so RNA polymerase II can attach; 2) Activator proteins bind to distal Enhancer DNA sequences, while Repressor proteins bind to Silencer sequences; 3) DNA bending proteins loop the chromatin so distant enhancer-bound activators physically contact the mediator complex and RNA polymerase at the promoter, dramatically increasing transcription rate.

Explain the cascade of Blood Clotting (Hemostasis) and why coronary thrombosis causes Myocardial Infarction.

When a blood vessel is damaged, exposed collagen fibres cause platelets to adhere and release clotting factors. Clotting factors trigger a cascade that converts the inactive zymogen prothrombin into the active enzyme thrombin; thrombin then catalyses the conversion of soluble plasma protein fibrinogen into insoluble fibrous strands of fibrin, which form a mesh trapping red blood cells to form a clot. If an atherosclerotic plaque ruptures inside a coronary artery, a thrombus (clot) occludes blood flow, depriving cardiac muscle of O2 and ATP (myocardial infarction).

How do Kangaroo Rats (desert mammals) adapt their kidney nephron structure compared to Beavers (freshwater mammals)?

The maximum hypertonicity of the renal medulla—and therefore the maximum concentration of urine produced—is directly proportional to the relative length of the Loop of Henle and thickness of the medulla. Desert kangaroo rats have a very thick renal medulla and extremely long Loops of Henle (juxtamedullary nephrons) to generate a steep medullary osmotic gradient and reabsorb almost all water, whereas semi-aquatic beavers have thin medullas and short Loops of Henle, producing large volumes of dilute urine.

Explain the mechanism of Electrophilic Addition of interhalogens (e.g., I–Cl or Br–Cl) to unsymmetrical alkenes in HL Chemistry.

In an interhalogen molecule like I–Cl, chlorine is more electronegative than iodine, creating a permanent dipole (I^(δ+)–Cl^(δ−)). Therefore, I^(δ+) acts as the electrophile attacked by the π-electrons of the alkene double bond. By Markovnikov's rule, the I atom attaches to the carbon atom with more hydrogens so as to generate the more stable secondary/tertiary carbocation intermediate, which is then attacked by the :Cl⁻ nucleophile.

Trace the Acrosome Reaction, Cortical Reaction, and blocks to polyspermy during mammalian Internal Fertilisation (HL D3.1).

1) Sperm chemoattraction & Binding: capacitated sperm swim through the corona radiata (follicle cells) and bind to specific ZP3 glycoprotein receptors on the zona pellucida; 2) Acrosome Reaction: hydrolytic enzymes released from the sperm acrosomal vesicle digest a path through the zona pellucida; 3) Membrane Fusion: sperm and egg plasma membranes fuse, triggering completion of Meiosis II; 4) Cortical Reaction (slow block to polyspermy): Ca²⁺ wave triggers cortical granules in the egg cytoplasm to release enzymes by exocytosis that cross-link and harden the zona pellucida and destroy ZP3 receptors so no second sperm can enter.

In HL Biology Plant Reproduction & Growth (C3.1 / D3.1), how does Phytochrome (Pr ↔ Pfr) control photoperiodic flowering in Short-Day vs Long-Day plants?

Phytochrome is a photoreceptor pigment existing in two interconvertible forms: inactive Pr absorbs red light (660 nm) and rapidly converts to active Pfr; Pfr absorbs far-red light (730 nm) in sunlight or slowly reverts back to Pr in darkness (night). Thus, the length of the uninterrupted DARK period determines remaining Pfr at dawn: 1) In Long-Day Plants (short-night plants, e.g., spinach/iris), high remaining Pfr acts as a promoter to activate the flowering gene (FT); 2) In Short-Day Plants (long-night plants, e.g., chrysanthemum), Pfr acts as an inhibitor of flowering, so a long night is needed to lower Pfr below a threshold.

In HL Biology Muscle Contraction (B3.3), compare Striated Skeletal Muscle Fibres with Cardiac and Smooth Muscle, and distinguish Slow-Twitch vs Fast-Twitch fibres.

Skeletal muscle fibres are multinucleate syncytia (formed by fusion of embryonic myoblasts) surrounded by the sarcolemma (with T-tubules) and packed with myofibrils, mitochondria, and sarcoplasmic reticulum. Slow-twitch (Type I) fibres contract more slowly over long endurance periods via aerobic respiration (dense capillaries, lots of mitochondria, high myoglobin content → dark red). Fast-twitch (Type II) fibres contract rapidly and powerfully for short sprints via anaerobic glycolysis and phosphocreatine (fewer mitochondria/myoglobin, large glycogen stores → pale, fatigue rapidly due to lactate).

Compare LithiumAlH4 (LiAlH4) and NaBH4 as reducing agents in HL Organic Chemistry.

Sodium borohydride (NaBH4, in aqueous/methanolic solution with heat) is a milder, safer reducing agent that reduces Aldehydes (to primary alcohols) and Ketones (to secondary alcohols), but CANNOT reduce carboxylic acids. Lithium aluminium hydride (LiAlH4, in anhydrous ethoxyethane / dry ether followed by dilute acid H⁺ workup, because it reacts violently with water) is a much stronger reducing agent that reduces Carboxylic Acids all the way to Primary Alcohols (as well as aldehydes and ketones).

State the HL Acid–Base equations connecting Ka, Kb, Kw, pKa, pKb, pKw, and the Henderson–Hasselbalch Buffer equation.

For any conjugate acid–base pair: Ka × Kb = Kw (1.0 × 10⁻¹⁴ at 298 K), and pKa + pKb = pKw = 14.00 (at 298 K), where pH + pOH = pKw. Henderson–Hasselbalch equation for an acidic buffer: pH = pKa + log₁₀([Conjugate Base A⁻] / [Weak Acid HA]); for a basic buffer: pOH = pKb + log₁₀([BH⁺] / [B]). At the half-equivalence point of a weak acid–strong base titration (where [HA] = [A⁻]), pH = pKa (region of maximum buffering capacity).

How do you interpret an Oscilloscope trace of a neurone Action Potential, and how do Neonicotinoid pesticides disrupt cholinergic synapses?

Oscilloscope trace: Resting potential at −70 mV → threshold at −55 mV → rapid upward spike of depolarisation to +30/+40 mV (voltage-gated Na⁺ channels open) → rapid downward repolarisation (Na⁺ channels inactivate, voltage-gated K⁺ channels open) → undershoot hyperpolarisation to −80 mV → Na⁺/K⁺ pump restores −70 mV. Neonicotinoids bind irreversibly to nicotinic acetylcholine receptors in insect CNS synapses and cannot be broken down by acetylcholinesterase, blocking synaptic transmission and causing paralysis and death (harming honeybee pollinators).

In HL Biology Kidney Osmoregulation (B3.3 / D3.3), compare the composition of blood in the Renal Artery vs Renal Vein and glomerular filtrate vs urine.

Renal vein vs Renal artery: Renal vein has much lower urea concentration, lower O2 and higher CO2 (kidney cells respire actively to make ATP for Na⁺ pumps), slightly lower glucose, and regulated optimal ion/water concentrations. Proteins and blood cells are present in blood but ABSENT in both glomerular filtrate and urine (stopped by the basement membrane). Glucose is present in glomerular filtrate at the same concentration as plasma, but 100% reabsorbed in the Proximal Convoluted Tubule (absent in healthy urine).

IB Biology & Chemistry HL: Human Physiology, Neurobiology, Chemical Kinetics, Acids/Bases, Redox & Organic Pathways

Higher Level (HL) IBDP Biology and Chemistry integration: nephron osmoregulation, sarcomere contraction, antibody/vaccine immunity, menstrual/fertilisation hormones, SN1 vs SN2 stereochemistry, Lewis acids/bases, pKa/pKb buffers, Voltaic/Electrolytic cells, and HL Organic Synthesis.

Level: intermediate
Languages: en → en
Cards: 32
Markdown: IB Biology & Chemistry HL: Human Physiology, Neurobiology, Chemical Kinetics, Acids/Bases, Redox & Organic Pathways (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	In IB Biology Human Physiology (B3.2 / C3.2), compare the structure and function of Phagocytes, B-Lymphocytes, Helper T-Cells, and Memory Cells, and explain how Monoclonal Antibodies are produced via hybridomas.	Phagocytes provide non-specific innate immunity via endocytosis and antigen presentation on MHC-II. Helper T-cells bind antigen-MHC, releasing cytokines to activate B-cells whose surface antibodies match the antigen (clonal selection). Activated B-cells divide by mitosis into antibody-secreting Plasma cells and long-lived Memory cells (secondary immunity). Monoclonal antibodies: inject a mouse with target antigen → isolate spleen B-lymphocytes producing the specific antibody → fuse them with endlessly dividing myeloma (cancer) cells to form hybridoma cells → screen via ELISA and culture in fermenters (used in hCG pregnancy tests and targeted cancer therapy).
2	Explain how Leptin, Melatonin, and Thyroxin act as hormones regulating appetite, circadian rhythms, and metabolic rate (C3.1).	1) Thyroxin (secreted by thyroid gland, contains 4 iodine atoms): targets almost all body cells to increase basal metabolic rate and heat production (thermogenesis); iodine deficiency prevents thyroxin synthesis, causing goitre. 2) Leptin (secreted by adipose/fat tissue): binds to receptors in the hypothalamus to inhibit appetite; ob/ob mice lack leptin and become obese. 3) Melatonin (secreted by the pineal gland in darkness, inhibited by light via retinal ganglion cells and the suprachiasmatic nucleus SCN): regulates circadian sleep–wake rhythms and alleviates jet lag.
3	Compare Brønsted–Lowry, Lewis, and Arrhenius definitions of acids and bases, and explain why transition metal hexaaqua complex ions act as Lewis acid–base adducts (HL Reactivity 3.1 / 3.4).	Brønsted–Lowry: Acid = proton (H⁺) donor; Base = proton (H⁺) acceptor. Lewis: Acid = electron pair ACCEPTOR (electrophile with an empty orbital); Base = electron pair DONOR (nucleophile with a lone pair). Every Brønsted–Lowry base is also a Lewis base, but Lewis acids include species without H⁺ (e.g., BF3, AlCl3, and transition metal cations like Cu²⁺ or Fe³⁺). When [Fe(H2O)6]³⁺ forms, H2O ligands act as Lewis bases donating lone pairs into empty d/s/p orbitals of the Fe³⁺ Lewis acid.
4	In HL Electrochemistry, state the 3 factors that determine which ions are selectively discharged during the electrolysis of aqueous solutions (e.g., dilute vs concentrated NaCl(aq) and CuSO4(aq) with Cu vs Pt electrodes).	Selective discharge depends on: 1) Relative Standard Electrode Potentials (E°: at the cathode, the species with the MORE POSITIVE E° is reduced preferentially; at the anode, the species with the MORE NEGATIVE E° is oxidised); 2) Concentration effect (in concentrated NaCl brine, Cl⁻ is oxidised to Cl2 gas at the anode instead of H2O → O2 due to overpotential and high [Cl⁻]); 3) Nature of the electrodes (in CuSO4(aq) with inert Pt/C electrodes, H2O is oxidised at the anode to O2 + 4H⁺; with active copper electrodes, the copper anode itself oxidises: Cu(s) → Cu²⁺(aq) + 2e⁻, used in electrorefining copper).
5	In HL Chemistry Spectroscopy, what causes X-ray Crystallography diffraction patterns and how does it complement Mass Spectrometry, IR, and ¹H NMR?	X-rays have wavelengths (~0.1 nm) comparable to interatomic bond lengths in crystals. When a monochromatic X-ray beam strikes a crystalline solid, X-rays scatter off the electron clouds of atoms and constructively interfere according to Bragg's Law (nλ = 2d sin θ), producing an electron density map that reveals exact 3D bond lengths and bond angles (hydrogen atoms are hardest to detect because they have only 1 electron).
6	How do you calculate the Standard Gibbs Free Energy Change (ΔG°) of a redox reaction from Standard Electrode Potentials (E°cell) and Equilibrium Constant (K)?	IB Data Booklet equations: ΔG° = −nFE°cell = −RT ln K, where n = number of moles of electrons transferred in the balanced redox equation, F = 96,500 C mol⁻¹ (Faraday's constant), and E°cell is in Volts (J C⁻¹) (divide by 1000 to convert J mol⁻¹ to kJ mol⁻¹). Thus: E°cell > 0 V ⇔ ΔG° < 0 kJ mol⁻¹ ⇔ K > 1 (spontaneous forward reaction).
7	How do you identify the number of peaks, chemical shifts, integration trace, and multiplicity in ¹H NMR of isomers like C3H6O2 (propanoic acid, methyl ethanoate, ethyl methanoate)?	All three have Mr = 74 and 3 proton environments: 1) Propanoic acid (CH3–CH2–COOH): 3 signals with integration 3:2:1 — triplet (3H, CH3), quartet (2H, CH2), and downfield singlet at δ = 11.5 ppm (1H, –COOH). 2) Methyl ethanoate (CH3–COO–CH3): 2 signals with integration 3:3 — two singlets (one at δ ~ 2.0 ppm for CH3C=O, one at δ ~ 3.7 ppm for –OCH3). 3) Ethyl methanoate (H–COO–CH2–CH3): 3 signals with integration 1:2:3 — singlet at δ ~ 8.0 ppm (1H, H–C=O), quartet at δ ~ 4.1 ppm (2H, –OCH2–), and triplet at δ ~ 1.3 ppm (3H, –CH3).
8	In HL Biology Reproduction (D3.1), compare Spermatogenesis and Oogenesis in terms of timing, cell numbers, and unequal cytokinesis.	Both involve germinal epithelium mitosis, cell growth, two meiotic divisions, and differentiation. Spermatogenesis (in seminiferous tubules, aided by Sertoli nurse cells and interstitial Leydig cells secreting testosterone): begins at puberty, continuous throughout life, produces millions of sperm daily, with 4 equal haploid spermatozoa per primary spermatocyte. Oogenesis (in ovarian follicles): begins in the female fetus (arrested in Prophase I until puberty, then Metaphase II until fertilisation), cyclical (1 per month, ends at menopause), and unequal cytokinesis produces 1 large ovum (retaining cytoplasm/organelles/yolk) plus 2–3 degenerating polar bodies.
9	In HL Chemistry Kinetics (Reactivity 2.2), how do you use the Arrhenius Equation in linear form to find Activation Energy (Ea) from experimental rate constants at different temperatures?	The logarithmic Arrhenius equation is ln k = −(Ea / R)(1 / T) + ln A, where R = 8.31 J K⁻¹ mol⁻¹ and T is in Kelvin. Plot ln k on the vertical y-axis against (1 / T) in K⁻¹ on the horizontal x-axis to get a straight line with a negative gradient m = −Ea / R and y-intercept = ln A. Therefore, Ea = −m × R (in J mol⁻¹; divide by 1000 for kJ mol⁻¹). Alternatively, for two temperatures T₁ and T₂: ln(k₂ / k₁) = (Ea / R)(1/T₁ − 1/T₂).
10	Compare Voltaic (Galvanic) Cells and Electrolytic Cells in terms of spontaneity (ΔG°), anode/cathode signs, and electron/ion flow (Reactivity 3.2).	In BOTH cells, Oxidation ALWAYS occurs at the Anode and Reduction ALWAYS occurs at the Cathode ('AN OIL RIG CAT'), and electrons flow through the external wire from Anode to Cathode. 1) Voltaic cell: spontaneous exothermic redox reaction converts chemical energy to electrical energy (E°cell > 0, ΔG° = −nFE°cell < 0); Anode is NEGATIVE and Cathode is POSITIVE; salt bridge (KNO3/KCl) completes circuit by migrating anions to anode and cations to cathode. 2) Electrolytic cell: external DC power supply drives a non-spontaneous reaction (ΔG° > 0); Anode is POSITIVE and Cathode is NEGATIVE.
11	Compare SN1 and SN2 Nucleophilic Substitution mechanisms of halogenoalkanes in IB HL Chemistry (Reactivity 3.4).	SN2 (Bimolecular, favoured by PRIMARY halogenoalkanes and polar aprotic solvents like propanone/DMSO): concerted 1-step mechanism with rate = k[RX][Nu⁻]; nucleophile attacks from the opposite side (backside attack) through a trigonal bipyramidal pentavalent transition state, causing WALDEN INVERSION of stereochemical configuration. SN1 (Unimolecular, favoured by TERTIARY halogenoalkanes and polar protic solvents like water/ethanol): 2-step mechanism with rate = k[RX]; rate-determining heterolytic C–X fission forms a trigonal planar carbocation intermediate, attacked from either side to form a RACEMIC mixture.
12	Compare the environmental and thermodynamic properties of Biofuels (bioethanol, biodiesel) vs Fossil Fuels and Hydrogen in IB Chemistry Reactivity 1.	Specific Energy (kJ g⁻¹) = ΔcH° ÷ Mr; Energy Density (kJ cm⁻³) = Specific Energy × Density. Hydrogen (H2) has the highest Specific Energy (142 kJ g⁻¹) and zero CO2 emissions at point of use, but very low volumetric Energy Density as a gas (requiring high-pressure storage). Bioethanol (from fermentation of plant starch/cellulose) is theoretically carbon-neutral (CO2 released on combustion equals CO2 absorbed by crops during photosynthesis, ignoring farming/distillation energy) and renewable, but has lower specific energy than petrol/octane because ethanol is already partially oxidised.
13	How do you apply Faraday's Laws of Electrolysis (Q = It = n(e⁻)F) to calculate the mass of metal electroplated at a cathode (HL)?	1) Calculate total charge passed in Coulombs: Q = I × t (Current in Amps × Time in seconds); 2) Convert charge into moles of electrons using Faraday's constant (F = 96,500 C mol⁻¹): n(e⁻) = Q / F = (It) / 96500; 3) Use the cathode half-equation stoichiometry (M^(z+) + z e⁻ → M(s)) to find moles of metal deposited: n(M) = n(e⁻) / z. Thus Mass of metal plated = (I × t × Ar) ÷ (z × 96500).
14	Outline the 3-step Retro-Synthetic Pathway in HL Organic Chemistry to convert Ethene into Propanoic Acid.	Since ethene has 2 carbons (C2H4) and propanoic acid has 3 carbons (CH3CH2COOH), the chain must be extended via nucleophilic substitution with cyanide: Step 1: Ethene + HBr → Bromoethane (electrophilic addition at room temperature). Step 2: Bromoethane + KCN in warm aqueous ethanol under reflux → Propanenitrile (CH3CH2CN) + KBr (SN2 nucleophilic substitution). Step 3: Propanenitrile + dilute HCl/H2SO4 heated under reflux → Propanoic acid (CH3CH2COOH) + NH4⁺.
15	Explain the hormonal roles of hCG, Progesterone, Oestrogen, and Oxytocin in Placental Maintenance and the Positive Feedback Loop of Parturition (Childbirth).	The early blastocyst secretes human chorionic gonadotropin (hCG) to maintain the corpus luteum so it continues secreting progesterone until the placenta takes over at ~10–12 weeks (progesterone inhibits myometrial contractions and oxytocin receptors). At full term (~40 weeks), fetal growth stretches the cervix and placental progesterone drops while oestrogen rises (upregulating uterine oxytocin receptors): 1) Cervical stretch receptors signal the maternal posterior pituitary to secrete oxytocin; 2) Oxytocin stimulates stronger uterine myometrial contractions; 3) Contractions push the baby's head harder against the cervix, triggering even more oxytocin release (positive feedback) until birth.
16	In HL Chemistry, explain why 1-chlorobutane, 2-chlorobutane, and 2-chloro-2-methylpropane have different rates and mechanisms of nucleophilic substitution with OH⁻.	1) 1-chlorobutane (primary): undergoes concerted 1-step SN2 because the α-carbon is sterically unhindered and a primary carbocation is too unstable to form. 2) 2-chloro-2-methylpropane (tertiary): undergoes 2-step SN1 (much faster overall!) because three bulky methyl groups cause severe steric hindrance blocking backside SN2 attack, while strongly stabilising the tertiary carbocation intermediate via the +I inductive effect. 3) 2-chlorobutane (secondary): can undergo a mixture of both SN1 and SN2 pathways.
17	Contrast Antibiotics (e.g., Penicillin discovered by Florey & Chain) with Antivirals, and explain how HIV destroys the immune system.	Antibiotics block prokaryotic metabolic pathways (e.g., penicillin inhibits transpeptidase enzymes that cross-link peptidoglycan bacterial cell walls, causing osmotic lysis; others target 70S ribosomes) without harming eukaryotic cells. Viruses lack their own metabolism or cell walls and replicate inside host cells, so antibiotics are completely ineffective against viruses. HIV (a retrovirus using reverse transcriptase) specifically infects and lyses CD4⁺ Helper T-lymphocytes, eventually preventing B-cell activation and antibody production (AIDS).
18	Explain why aqueous solutions of NaCl, NH4Cl, CH3COONa, and [Fe(H2O)6]Cl3 are neutral, acidic, or basic (Salt Hydrolysis in HL Chemistry).	1) Strong acid + Strong base salt (NaCl): neither Na⁺ nor Cl⁻ hydrolyses water → neutral (pH = 7). 2) Strong acid + Weak base salt (NH4Cl): NH4⁺ is the conjugate acid of weak base NH3 and donates H⁺ to water (NH4⁺ + H2O ⇌ NH3 + H3O⁺) → acidic (pH < 7). 3) Weak acid + Strong base salt (CH3COONa): CH3COO⁻ is the conjugate base of weak acid CH3COOH and accepts H⁺ from water (CH3COO⁻ + H2O ⇌ CH3COOH + OH⁻) → basic (pH > 7). 4) Small, high-charge cations like Fe³⁺ or Al³⁺ polarise O–H bonds in coordinated H2O ligands, releasing H⁺ → strongly acidic (pH ~2–3).
19	Explain why Tertiary Carbocations are more stable than Secondary and Primary Carbocations in both SN1 and Markovnikov Electrophilic Addition.	Carbocation stability follows the order: Tertiary (R3C⁺) > Secondary (R2CH⁺) > Primary (RCH2⁺) > Methyl (CH3⁺). Alkyl groups (–R) have a positive inductive effect (+I) and hyperconjugation, donating electron density towards the positively charged carbon atom. Three electron-releasing alkyl groups delocalise and spread out the positive charge much more effectively than one, lowering the activation energy for forming the tertiary carbocation intermediate.
20	In HL Chemistry, how do you calculate the pH of a solution at any point along a Strong Acid–Strong Base vs Weak Acid–Strong Base titration curve?	1) Initial pH of weak acid: [H⁺] = √(Ka × [HA]_0). 2) Buffer region (before equivalence): calculate moles of HA remaining and moles of A⁻ formed by OH⁻ neutralisation, then use pH = pKa + log₁₀(n(A⁻) / n(HA)). 3) Half-equivalence point (V = ½ V_eq): [HA] = [A⁻], so pH = pKa. 4) Equivalence point (V = V_eq): for Weak Acid + Strong Base, all HA has been converted into conjugate base A⁻, which hydrolyses water (A⁻ + H2O ⇌ HA + OH⁻ with [OH⁻] = √(Kb × [A⁻])), so pH > 7. 5) Beyond equivalence: calculate excess moles of OH⁻ divided by total volume V_total.
21	Explain how the structure of the Placenta facilitates exchange of materials between maternal and fetal blood (HL Biology D3.1).	Chorionic villi provide a huge, highly branched surface area projecting into the intervillous spaces filled with maternal blood, separated by a very thin placental barrier (fetal capillary endothelium + trophoblast cells). Maternal and fetal blood never mix (preventing maternal blood pressure from damaging fetal capillaries and avoiding immune rejection). O2, glucose, amino acids, lipids, water, vitamins, and maternal IgG antibodies cross to the fetus via diffusion, facilitated diffusion, active transport, and endocytosis; CO2 and urea diffuse back into maternal blood.
22	In HL Biology Gene Expression (D1.2 / D2.2), how do Transcription Factors, Enhancers, Silencers, and Promoter-Proximal Elements regulate eukaryotic transcription?	Unlike prokaryotes (which use operons like the lac operon where lactose binds the repressor protein), eukaryotic genes are regulated individually: 1) General transcription factors bind to the TATA box in the promoter so RNA polymerase II can attach; 2) Activator proteins bind to distal Enhancer DNA sequences, while Repressor proteins bind to Silencer sequences; 3) DNA bending proteins loop the chromatin so distant enhancer-bound activators physically contact the mediator complex and RNA polymerase at the promoter, dramatically increasing transcription rate.
23	Explain the cascade of Blood Clotting (Hemostasis) and why coronary thrombosis causes Myocardial Infarction.	When a blood vessel is damaged, exposed collagen fibres cause platelets to adhere and release clotting factors. Clotting factors trigger a cascade that converts the inactive zymogen prothrombin into the active enzyme thrombin; thrombin then catalyses the conversion of soluble plasma protein fibrinogen into insoluble fibrous strands of fibrin, which form a mesh trapping red blood cells to form a clot. If an atherosclerotic plaque ruptures inside a coronary artery, a thrombus (clot) occludes blood flow, depriving cardiac muscle of O2 and ATP (myocardial infarction).
24	How do Kangaroo Rats (desert mammals) adapt their kidney nephron structure compared to Beavers (freshwater mammals)?	The maximum hypertonicity of the renal medulla—and therefore the maximum concentration of urine produced—is directly proportional to the relative length of the Loop of Henle and thickness of the medulla. Desert kangaroo rats have a very thick renal medulla and extremely long Loops of Henle (juxtamedullary nephrons) to generate a steep medullary osmotic gradient and reabsorb almost all water, whereas semi-aquatic beavers have thin medullas and short Loops of Henle, producing large volumes of dilute urine.
25	Explain the mechanism of Electrophilic Addition of interhalogens (e.g., I–Cl or Br–Cl) to unsymmetrical alkenes in HL Chemistry.	In an interhalogen molecule like I–Cl, chlorine is more electronegative than iodine, creating a permanent dipole (I^(δ+)–Cl^(δ−)). Therefore, I^(δ+) acts as the electrophile attacked by the π-electrons of the alkene double bond. By Markovnikov's rule, the I atom attaches to the carbon atom with more hydrogens so as to generate the more stable secondary/tertiary carbocation intermediate, which is then attacked by the :Cl⁻ nucleophile.
26	Trace the Acrosome Reaction, Cortical Reaction, and blocks to polyspermy during mammalian Internal Fertilisation (HL D3.1).	1) Sperm chemoattraction & Binding: capacitated sperm swim through the corona radiata (follicle cells) and bind to specific ZP3 glycoprotein receptors on the zona pellucida; 2) Acrosome Reaction: hydrolytic enzymes released from the sperm acrosomal vesicle digest a path through the zona pellucida; 3) Membrane Fusion: sperm and egg plasma membranes fuse, triggering completion of Meiosis II; 4) Cortical Reaction (slow block to polyspermy): Ca²⁺ wave triggers cortical granules in the egg cytoplasm to release enzymes by exocytosis that cross-link and harden the zona pellucida and destroy ZP3 receptors so no second sperm can enter.
27	In HL Biology Plant Reproduction & Growth (C3.1 / D3.1), how does Phytochrome (Pr ↔ Pfr) control photoperiodic flowering in Short-Day vs Long-Day plants?	Phytochrome is a photoreceptor pigment existing in two interconvertible forms: inactive Pr absorbs red light (660 nm) and rapidly converts to active Pfr; Pfr absorbs far-red light (730 nm) in sunlight or slowly reverts back to Pr in darkness (night). Thus, the length of the uninterrupted DARK period determines remaining Pfr at dawn: 1) In Long-Day Plants (short-night plants, e.g., spinach/iris), high remaining Pfr acts as a promoter to activate the flowering gene (FT); 2) In Short-Day Plants (long-night plants, e.g., chrysanthemum), Pfr acts as an inhibitor of flowering, so a long night is needed to lower Pfr below a threshold.
28	In HL Biology Muscle Contraction (B3.3), compare Striated Skeletal Muscle Fibres with Cardiac and Smooth Muscle, and distinguish Slow-Twitch vs Fast-Twitch fibres.	Skeletal muscle fibres are multinucleate syncytia (formed by fusion of embryonic myoblasts) surrounded by the sarcolemma (with T-tubules) and packed with myofibrils, mitochondria, and sarcoplasmic reticulum. Slow-twitch (Type I) fibres contract more slowly over long endurance periods via aerobic respiration (dense capillaries, lots of mitochondria, high myoglobin content → dark red). Fast-twitch (Type II) fibres contract rapidly and powerfully for short sprints via anaerobic glycolysis and phosphocreatine (fewer mitochondria/myoglobin, large glycogen stores → pale, fatigue rapidly due to lactate).
29	Compare LithiumAlH4 (LiAlH4) and NaBH4 as reducing agents in HL Organic Chemistry.	Sodium borohydride (NaBH4, in aqueous/methanolic solution with heat) is a milder, safer reducing agent that reduces Aldehydes (to primary alcohols) and Ketones (to secondary alcohols), but CANNOT reduce carboxylic acids. Lithium aluminium hydride (LiAlH4, in anhydrous ethoxyethane / dry ether followed by dilute acid H⁺ workup, because it reacts violently with water) is a much stronger reducing agent that reduces Carboxylic Acids all the way to Primary Alcohols (as well as aldehydes and ketones).
30	State the HL Acid–Base equations connecting Ka, Kb, Kw, pKa, pKb, pKw, and the Henderson–Hasselbalch Buffer equation.	For any conjugate acid–base pair: Ka × Kb = Kw (1.0 × 10⁻¹⁴ at 298 K), and pKa + pKb = pKw = 14.00 (at 298 K), where pH + pOH = pKw. Henderson–Hasselbalch equation for an acidic buffer: pH = pKa + log₁₀([Conjugate Base A⁻] / [Weak Acid HA]); for a basic buffer: pOH = pKb + log₁₀([BH⁺] / [B]). At the half-equivalence point of a weak acid–strong base titration (where [HA] = [A⁻]), pH = pKa (region of maximum buffering capacity).
31	How do you interpret an Oscilloscope trace of a neurone Action Potential, and how do Neonicotinoid pesticides disrupt cholinergic synapses?	Oscilloscope trace: Resting potential at −70 mV → threshold at −55 mV → rapid upward spike of depolarisation to +30/+40 mV (voltage-gated Na⁺ channels open) → rapid downward repolarisation (Na⁺ channels inactivate, voltage-gated K⁺ channels open) → undershoot hyperpolarisation to −80 mV → Na⁺/K⁺ pump restores −70 mV. Neonicotinoids bind irreversibly to nicotinic acetylcholine receptors in insect CNS synapses and cannot be broken down by acetylcholinesterase, blocking synaptic transmission and causing paralysis and death (harming honeybee pollinators).
32	In HL Biology Kidney Osmoregulation (B3.3 / D3.3), compare the composition of blood in the Renal Artery vs Renal Vein and glomerular filtrate vs urine.	Renal vein vs Renal artery: Renal vein has much lower urea concentration, lower O2 and higher CO2 (kidney cells respire actively to make ATP for Na⁺ pumps), slightly lower glucose, and regulated optimal ion/water concentrations. Proteins and blood cells are present in blood but ABSENT in both glomerular filtrate and urine (stopped by the basement membrane). Glucose is present in glomerular filtrate at the same concentration as plasma, but 100% reabsorbed in the Proximal Convoluted Tubule (absent in healthy urine).