GATE XL0 Chemistry: How Biology Students Can Score the Compulsory 25
The compulsory Chemistry section of GATE Life Sciences 2027 — all ten sections, the formulas that recur, a study order built for biology graduates, and the negative-marking maths.
Updated : 43 minutes ago
View Complete ArticleChecked 25 September 2026. Syllabus and marking scheme are official and fixed for GATE 2027. The formulas are standard chemistry and do not change.
Every GATE Life Sciences candidate writes the same Chemistry section. In 2027 it is called XL0 (it was XL-P), it carries 25 of the 100 marks across 17 questions, and for most people who studied biology it is the hardest part of the paper — not because it is advanced, but because it is the part their degree did not teach.
The good news is in the syllabus itself. Of XL0's ten sections, four are really biology written in chemical language, and the physical-chemistry sections recycle a small set of equations. This guide takes the sections in the order a biology graduate should learn them.
The shape of XL0
| Item | Value |
|---|---|
| Questions | 17 (9 one-mark, 8 two-mark) |
| Marks | 25 |
| Compulsory? | Yes, for every XL candidate |
| Question types | MCQ, MSQ (one or more correct) and NAT (typed numerical answer) |
| Negative marking | MCQ only: −1/3 (1-mark), −2/3 (2-mark). None for MSQ or NAT |
| Calculator | On-screen virtual calculator only |
Counted from the official answer keys (IIT Roorkee 2025, IIT Guwahati 2026). The same split two years running: more than half of the Chemistry section carried no negative marking.
That split is worth absorbing before you plan a single chapter. Nine of the seventeen Chemistry questions in each of the last two papers were multiple-select or numerical-answer, where a wrong answer costs nothing. Four were numerical — you type a number, so there are no options to eliminate and no way to recognise the answer; you have to compute it. That is why the formula list below matters more than any amount of theory reading.
The ten sections, in the order to learn them
Group 1 is the closest to biology and should come first; Group 3 is pure chemistry and comes last. The section numbers are the official 2027 ones.
Group 1 — biology in chemical language (start here)
XL0.10 Chemistry of Biomolecules
- Amino acids, proteins, nucleic acids and nucleotides; carbohydrates up to hexoses; lipids (triglycerides only).
- Peptide sequencing (chemical and enzymatic) and DNA sequencing (chemical and enzymatic).
- Purification by ion-exchange and gel-filtration chromatography; absorption and fluorescence spectroscopy for identifying biomolecules.
XL0.7 Reaction Kinetics
- Rate constant, order and molecularity, zero/first/second-order kinetics, activation energy, catalysis.
- Elementary enzyme reactions and reversible and irreversible inhibition — the same ideas as enzyme kinetics in Biochemistry.
XL0.4 Bioinorganic Chemistry (new in 2027)
- Oxygen transport and storage: haemoglobin, myoglobin and haemocyanin.
- Electron-transport iron–sulphur proteins; carbonic anhydrase; Cu–Zn superoxide dismutase.
- Because it is new, no recent paper covers it. Learn the metal, its coordination and what it does, for each of the six proteins named.
XL0.5 Chemical Equilibria
- pH, buffers and their applications, ionic equilibria, solubility product, common-ion effect, hydrolysis of salts.
- Colligative properties: osmotic pressure, boiling-point elevation, freezing-point depression.
- Kc, Kp and Kx for homogeneous reactions.
Group 2 — the physical chemistry that is mostly equations
XL0.8 Thermodynamics and XL0.6 Electrochemistry
- State and path functions, first and second laws, enthalpy, Hess's law, Kirchhoff equation, entropy and free energy, Gibbs–Helmholtz, free energy from the equilibrium constant.
- Conductance, Kohlrausch's law, cell potentials, EMF, the Nernst equation and its thermodynamic link.
Group 3 — pure chemistry (learn last, but do not skip)
XL0.1, XL0.2, XL0.3 and XL0.9
- XL0.1 Atomic structure and periodicity; XL0.2 bonding (MO/VB, VSEPR, hybridisation, lattice energy, HSAB); XL0.3 s, p and d-block elements and coordination complexes (crystal field theory, colour, magnetism, isomerism).
- XL0.9 Organic mechanisms: acids and bases, stereochemistry, SN1/SN2/E1/E2, Markovnikov and Kharasch, hydroboration, Grignard reagents, electrophilic and (new in 2027) nucleophilic aromatic substitution, functional-group tests.
The formulas that carry the numerical questions
XL0 numericals come overwhelmingly from a short list of standard relationships. Learn these until you can use them without looking.
| Topic | Relationship | Use it for |
|---|---|---|
| Buffers | pH = pKa + log([A⁻]/[HA]) | Buffer pH, ratio of salt to acid |
| First-order kinetics | ln([A]₀/[A]) = kt; t½ = 0.693/k | Half-life, rate constant, time to a given fraction |
| Arrhenius | k = A·e^(−Ea/RT); ln(k₂/k₁) = (Ea/R)(1/T₁ − 1/T₂) | Activation energy from two temperatures |
| Enzyme kinetics | v = Vmax[S]/(Km + [S]) | Velocity at a given substrate; Km from data |
| Free energy | ΔG = ΔH − TΔS; ΔG° = −RT ln K | Spontaneity; equilibrium constant from ΔG° |
| Electrochemistry | E = E° − (RT/nF) ln Q; ΔG° = −nFE° | Cell EMF at non-standard concentration |
| Gas equilibria | Kp = Kc(RT)^Δn, Δn = gaseous product moles − gaseous reactant moles | Converting Kp ↔ Kc for ideal-gas reactions only (not Kx or solutions) |
| Colligative | π = iCRT; ΔTf = i·Kf·m | Osmotic pressure; freezing-point depression |
| Absorbance | A = εcl | Concentration from absorbance |
| Kirchhoff | ΔH(T₂) = ΔH(T₁) + ΔCp(T₂ − T₁) | Reaction enthalpy at another temperature |
The new section, at a glance
Bioinorganic Chemistry (XL0.4) is new in 2027, so no previous paper covers it. The syllabus names six systems. For each, know the metal, what it is bound to, and what it does — that is the level a one-mark question will test.
| Protein | Metal centre | Job | Remember |
|---|---|---|---|
| Haemoglobin | Fe(II) in haem | O₂ transport in blood | Tetramer; cooperative (sigmoidal) O₂ binding |
| Myoglobin | Fe(II) in haem | O₂ storage in muscle | Monomer; hyperbolic binding, higher O₂ affinity |
| Haemocyanin | Two Cu per O₂ site (no haem) | O₂ transport in molluscs and arthropods | Colourless when deoxygenated, blue when oxygenated |
| Fe–S proteins (e.g. ferredoxins) | Fe bound to sulphide and cysteine (2Fe–2S, 4Fe–4S) | Electron transfer | Iron cycles between Fe(II) and Fe(III) |
| Carbonic anhydrase | Zn(II) | CO₂ + H₂O ⇌ HCO₃⁻ + H⁺ | Zinc-bound hydroxide attacks CO₂ |
| Cu–Zn superoxide dismutase | Cu (redox) and Zn (structural) | 2 O₂⁻ + 2 H⁺ → O₂ + H₂O₂ | Copper does the chemistry; zinc holds the shape |
Five worked numericals
Each of these uses one formula from the table above and is the kind of calculation that appears as a numerical-answer question. Work them before reading the answer.
1. Buffer pH
- A buffer contains 0.10 M acetic acid and 0.20 M sodium acetate. pKa of acetic acid = 4.76. Find the pH.
- pH = pKa + log([A⁻]/[HA]) = 4.76 + log(0.20/0.10) = 4.76 + 0.301 = 5.06.
2. First-order half-life
- A first-order reaction has k = 0.0231 min⁻¹. Find its half-life, and the time for 87.5% of the reactant to be used up.
- t½ = 0.693/k = 0.693/0.0231 = 30 min. 87.5% used means 12.5% left = (½)³, i.e. three half-lives = 90 min.
3. Cell EMF at non-standard concentration
- For Zn | Zn²⁺(0.10 M) || Cu²⁺(1.0 M) | Cu at 298 K, E° = 1.10 V and n = 2. Find E.
- E = E° − (0.0592/n) log([Zn²⁺]/[Cu²⁺]) = 1.10 − 0.0296 × log(0.10) = 1.10 + 0.0296 = 1.13 V.
4. Free energy from an equilibrium constant
- A reaction has K = 10 at 298 K. Find ΔG°.
- ΔG° = −RT ln K = −(8.314)(298)(2.303) J mol⁻¹ = −5.7 kJ mol⁻¹. Negative ΔG° ⇔ K > 1.
5. Michaelis–Menten
- An enzyme has Km = 2 mM. What fraction of Vmax is reached at [S] = 2 mM, and at [S] = 6 mM?
- v/Vmax = [S]/(Km + [S]). At 2 mM: 2/4 = 0.50. At 6 mM: 6/8 = 0.75. Tripling [S] from Km adds only half as much again.
All five use standard textbook values; they are illustrations of the formula list, not questions from a GATE paper.
The negative-marking maths — when to guess
Only MCQs carry negative marks. A wrong 1-mark MCQ costs 1/3 mark and a wrong 2-mark MCQ costs 2/3. MSQ and NAT questions carry no negative marking at all.
What that means in practice
- Blind guess on an MCQ (four options): expected score = ¼ × 1 − ¾ × ⅓ = 0. A pure guess neither helps nor hurts on average — it only adds risk.
- Guess after eliminating one option: expected score = ⅓ × 1 − ⅔ × ⅓ = +1/9 of the question's marks. Once you can rule out one option, guessing is worth it on average.
- After eliminating two options: ½ × 1 − ½ × ⅓ = +⅓. Answer.
- MSQ and NAT: no penalty, so never leave one blank — even a rough numerical estimate is free.
The same arithmetic holds for 2-mark MCQs: every figure scales by two. All of it assumes your elimination is certain — if you are only leaning against an option, treat it as not eliminated. And an MSQ scores only when you pick exactly the full set of correct options, with no partial credit, so ticking MSQ options at random is almost worthless even though it costs nothing.
A six-week XL0 track you can run beside your optional sections
Run it at about 45 minutes a day — roughly a quarter of a three-hour study day, in line with Chemistry's 25 marks — with the rest of the day on your two optional sections. Keep Sunday's Chemistry slot for revision of the week, and from week 4 end each week with a timed set of five numerical-answer questions entered on an on-screen calculator.
| Week | Focus | Daily practice |
|---|---|---|
| 1 | XL0.10 Biomolecules | 8–10 past questions on biomolecules and chromatography |
| 2 | XL0.7 Kinetics + enzyme inhibition | Half-life and Arrhenius numericals |
| 3 | XL0.5 Equilibria + XL0.4 Bioinorganic | Buffer and colligative numericals |
| 4 | XL0.8 Thermodynamics + XL0.6 Electrochemistry | ΔG, K and Nernst problems |
| 5 | XL0.1–XL0.3 Atomic structure, bonding, inorganic | CFT, VSEPR and periodic-trend questions |
| 6 | XL0.9 Organic mechanisms | Mechanism and stereochemistry questions |
Practise it, don't just read it
Of the library, two quizzes are Chemistry-relevant: Enzyme Kinetics Parameters and Lineweaver–Burk Plot Analysis both drill XL0.7 (enzyme reactions and inhibition). The rest of XL0 is best practised from the past papers.
The ProSyllabus GATE XL library maps onto the 2027 syllabus like this: Enzyme Kinetics Parameters and Lineweaver–Burk Plot Analysis → XL1.2 and XL0.7; Cell Membrane Transport → XL1.5 and XL3.4; Operon Regulation Mechanisms → XL3.9; Mendelian Inheritance Patterns → XL2.5 and XL4.3. Ten questions each, a worked explanation for every option, and a free AI report on where you lost marks. Topics new in 2027 are not in the library yet — use the syllabus and your textbooks for those.
Is Chemistry compulsory in GATE Life Sciences?
Yes. XL0 Chemistry (called XL-P until 2026) is compulsory for every XL candidate and carries 25 of the 100 marks, from 17 questions.
What is new in the GATE XL Chemistry syllabus for 2027?
A new section on Bioinorganic Chemistry (haemoglobin, myoglobin, haemocyanin, iron-sulphur proteins, carbonic anhydrase and Cu-Zn superoxide dismutase), nucleophilic aromatic substitution in organic mechanisms, and fluorescence spectroscopy for identifying biomolecules. Absorption spectroscopy restates the old Beer-Lambert requirement.
Is there negative marking in GATE XL Chemistry?
Only for multiple-choice questions: a wrong 1-mark MCQ costs one third of a mark and a wrong 2-mark MCQ costs two thirds. Multiple-select and numerical-answer questions carry no negative marking.
Should I guess on GATE MCQs?
A blind guess among four options has an expected score of zero, so it only adds risk. Once you can eliminate at least one option the expected score becomes positive, so guessing is worthwhile. Never leave an MSQ or NAT blank, as they carry no penalty.
Which chemistry topics should a biology student start with for GATE XL?
Start with the sections closest to biology: Chemistry of Biomolecules, Reaction Kinetics (including enzyme inhibition), Chemical Equilibria (pH and buffers) and the new Bioinorganic Chemistry section. Then move to thermodynamics and electrochemistry, and finish with atomic structure, bonding, inorganic and organic chemistry.
More in this series
- GATE XL 2027 syllabus changes, section by section
- Which two GATE XL sections to choose
- GATE XL 2027 week-by-week plan, October to February
- GATE XL previous year papers 2019–2026, with answer keys
- GATE XL marks vs score vs rank, with calculator
- GATE XL vs GATE BT vs CSIR NET Life Sciences
- GATE Life Sciences cutoffs, top colleges and rank vs college
- GATE XL notice board — official updates
Sources
- official — GATE 2027 XL Life Sciences syllabus (IIT Madras)
- official — GATE 2027 question paper pattern
- official — GATE 2027 Information Brochure, revised 17 Sep 2026
- official — GATE 2026 XL combined syllabus (IIT Guwahati)
official = a document published by the conducting body. reported = a news or coaching site we could not check against an original. Where sources disagree this page says so rather than picking one.
