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Biomolecules
Biology · Class 11NCERT pp. 104–1182 sets × 25 questions
Key facts and formulas for Biomolecules, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Tissue analysis | Filtrate = acid-soluble pool; retentate = acid-insoluble fraction; burning leaves ash; fresh − water = dry weight |
| Cell composition | Water 70–90%, proteins 10–15%, nucleic acids 5–7%, carbohydrates 3%, lipids 2%, ions 1% |
| Peptide bonds | Chain of n amino acids has n − 1 peptide bonds and loses n − 1 water molecules |
| Nucleotides | Base + sugar = nucleoside; + phosphate = nucleotide; purines A, G; pyrimidines C, T, U; A = T, G = C |
| Carbohydrates | Cellulose β-1,4; amylose unbranched α-1,4; amylopectin and glycogen branched at α-1,6; sucrose = glucose + fructose |
| Protein levels | Primary = sequence; secondary = helix; tertiary = folded chain; quaternary = subunits; denaturation keeps primary |
| Enzyme basics | Enzymes are not used up; ES complex is short-lived; induced fit; cold inactivates temporarily, heat denatures |
| Enzyme rate | Rate changes about 2 times per 10 °C; Km low means high affinity; V = Vmax[S]/(Km + [S]) |
| Inhibition | Competitive inhibitor resembles substrate (malonate); more substrate overcomes it; feedback inhibition by end product |
| Co-factors | Haem in catalase; zinc in carboxypeptidase; niacin in NAD; riboflavin in FAD; thiamine in TPP; protein part = apoenzyme |
Three sample questions
Q1. Which statement about living matter and the earth's crust is correct?
- Living matter contains elements that are completely absent from the crust
- Every element found in the crust also occurs in living tissue, but carbon and hydrogen are relatively more abundant in living matter
- Carbon and hydrogen are less abundant in living matter than in the crust
- Silicon is the second most abundant element in the human body
Hint and solution
Hint: Compare proportions, not presence. Ask whether life uses special elements or just different amounts of the same ones.
- Same elements, different proportions — The question compares the elemental make-up of living tissue and the crust.
- No special elements for life — Analysis of both shows that every crustal element is also found in living tissue.
- C and H richer in living matter — The difference is quantity: carbon and hydrogen are relatively more abundant in living matter, while silicon is large in the crust but tiny in the body.
- Answer: Option B — So the statement that same elements occur but C and H are enriched in life is correct. Option B.
Answer: B. No special elements are needed for life. The difference is proportion: C and H are far higher in living matter. Silicon is large in the crust but negligible in the body.
Q2. Match the part of a tissue analysis with what it is.
a. Filtrate i. Acid-insoluble fraction
b. Retentate ii. Acid-soluble pool
c. Residue after complete burning iii. Ash
d. Fresh weight minus water iv. Dry weight
- a-ii, b-i, c-iii, d-iv
- a-i, b-ii, c-iii, d-iv
- a-ii, b-i, c-iv, d-iii
- a-iii, b-ii, c-i, d-iv
Hint and solution
Hint: The filtrate is what passes through the cheesecloth; the retentate stays behind. Burning leaves only minerals.
- Filtrate = acid-soluble pool — Grinding tissue in trichloroacetic acid and straining gives a filtrate, which is the acid-soluble pool.
- Retentate = acid-insoluble fraction — What stays on the cheesecloth is the retentate, the acid-insoluble fraction.
- Burning residue = ash; fresh − water = dry weight — Complete burning leaves ash with inorganic matter, and removing water from fresh weight gives dry weight.
- Pairing: a-ii, b-i, c-iii, d-iv — Only the first option has all four pairs right. Option A.
Answer: A. The filtrate is the acid-soluble pool and the retentate is the acid-insoluble fraction. Burning leaves ash; wet weight minus water gives dry weight.
Q3. A fresh tissue weighing 20 g is dried to 5 g and the dry tissue is then burnt completely, leaving 0.5 g of ash. The mass of carbon compounds that escaped as CO2 and water vapour is
- 15 g
- 0.5 g
- 19.5 g
- 4.5 g
Hint and solution
Hint: Water was lost earlier. Only what vanishes on burning, from the dry tissue, is carbon compounds.
- Fresh 20 g → dry 5 g — Drying removes water: 20 − 5 = 15 g of water. This is not part of the burning step.
- Dry 5 g → ash 0.5 g — On burning, carbon compounds go off as CO₂ and water vapour; only ash stays.
- lost = 5 − 0.5 = 4.5 g — The mass that escaped equals dry weight minus ash.
- Answer: 4.5 g — So 4.5 g of carbon compounds escaped. Option D.
Answer: D. Dry weight 5 g, ash 0.5 g. The carbon compounds that burnt off = 5 − 0.5 = 4.5 g. (The 15 g lost earlier was water.)
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.