Biomolecule - JEE Main Previous Year Questions with Solutions
Biomolecules JEE Main Previous Year Questions covers important PYQs on carbohydrates, proteins, amino acids, vitamins, DNA, RNA, sugars, and biochemical processes, helping students strengthen conceptual understanding and exam preparation.
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Simulator Previous Years AIEEE/JEE Main Questions 
The Calvin cycle proceeds in three stages (1) carboxylation, during which $\mathrm{CO}_{2}$ combines with ribulose-1.5-bisphosphate (2) reduction, during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH and (3) regeneration during which the $\mathrm{CO}_{2}$ acceptor ribulose-1,5-bisphosphate is formed again so that the cylcle continues. It might help you to understand all of this if we look at what goes in and what comes out of the Calvin cycle. 
Vitamine C is soluble in water due to H-Bonding & all other vitamines given in question are fat soluble. 
The pI (isoelectric point) of aspartic acid is : (1) 1.88 (2) 2.77 (3) 3.65 (4) 5.74 JEE-Main(Online) - 2016 
JEE-Main 2017 
Frequently Asked Questions
Find answers to common questions.
How many questions from Biomolecules appear in JEE Main each year?
JEE Main typically includes 1 to 2 questions from the Biomolecules chapter per session. Since NTA conducts two sessions (January and April), you may see up to 4 questions across both. The questions are almost always factual or definition-based, making this one of the easier chapters to score in if NCERT is covered thoroughly.
What are the most important topics in Biomolecules for JEE Main?
The highest-frequency topics based on past papers are: (1) carbohydrates — functional groups, mutarotation, hydrolysis products; (2) proteins and amino acids — Biuret test, optical activity, isoelectric point; (3) nucleic acids — DNA vs RNA structural difference; (4) vitamins — fat-soluble vs water-soluble classification. These four areas have appeared every 2–3 years since AIEEE 2009.
What is the difference between Biuret test and Ninhydrin test?
The Biuret test detects peptide bonds using alkaline copper sulphate solution — it turns violet/purple with proteins and polypeptides. The Ninhydrin test detects free amino groups (–NH₂) and produces Rhumanns purple with amino acids and proteins. Carbohydrates give neither test positive. JEE Main has specifically tested both — know which detects what.
Why is glycine optically inactive while other amino acids are not?
Glycine (H₂N–CH₂–COOH) has two hydrogen atoms on its alpha carbon, making it achiral — no mirror image exists that is non-superimposable. All other standard amino acids have four different groups on their alpha carbon (amino, carboxyl, hydrogen, and a unique R-group), making them chiral and therefore optically active.
How do I calculate the isoelectric point (pI) of an amino acid?
The isoelectric point is the pH at which an amino acid carries zero net charge (exists as a zwitterion). For a dibasic amino acid like aspartic acid: pI = (pKa₁ + pKa₂) / 2 = (1.88 + 3.65) / 2 = 2.77. Always identify which two pKa values flank the neutral zwitterion form before calculating — this is where most students lose marks.