Chapter 10: Biomolecules Application Questions | chemistry Class 12 CBSE

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Chapter 10: Biomolecules Application Questions | chemistry Class 12 CBSE | ByteNotes.in

Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 1

Applied Concept

A food scientist tests two sugar solutions with Fehling's solution. Solution A gives a brick-red precipitate while Solution B gives no colour change. With reference to the chapter, identify the type of sugar in each solution and explain the chemical basis for this difference.

Solution A contains a reducing sugar — a carbohydrate with a free aldehyde or ketone group that reduces Cu2+ ions in Fehling's solution to Cu2O (brick-red precipitate); all monosaccharides (aldose or ketose) and some disaccharides like maltose and lactose are reducing sugars.
Solution B likely contains a non-reducing sugar such as sucrose, where the glycosidic bond involves both reducing groups (C1 of glucose and C2 of fructose), leaving no free carbonyl group to act as a reducing agent.
This distinction is chemically significant because reducing sugars can exist partially in open-chain form with a free –CHO or keto group, while non-reducing sugars like sucrose have all such groups locked in glycosidic linkages and cannot open to a free carbonyl form.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 2

Applied Concept

A child is diagnosed with rickets and a doctor recommends dietary changes. With reference to vitamins discussed in the chapter, identify the deficient vitamin, its food sources, and explain how its deficiency causes rickets.

Rickets (bone deformities in children) is caused by deficiency of Vitamin D, a fat-soluble vitamin; in adults the same deficiency causes osteomalacia (soft bones and joint pain).
Natural sources of Vitamin D include exposure to sunlight (which triggers its synthesis in skin), fish, and egg yolk; the doctor would recommend these in the child's diet and outdoor activity.
Vitamin D is essential for calcium and phosphorus absorption and bone mineralisation; its deficiency leads to inadequate mineralisation of bones, causing the softening and deformity characteristic of rickets.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 3

Applied Concept

In a forensic investigation, DNA from a crime scene is compared with that of a suspect. With reference to the chapter, explain the principle behind DNA fingerprinting and why it is considered more reliable than traditional fingerprinting.

DNA fingerprinting is based on the unique sequence of bases in every individual's DNA; this sequence is the same in every cell of that person's body and cannot be altered by any known treatment, unlike physical fingerprints which can be changed by surgery.
By identifying specific base sequences (using restriction enzymes and gel electrophoresis), investigators can generate a unique pattern (the DNA fingerprint) that can be compared between the crime scene sample and the suspect's DNA.
If the patterns match, it provides strong evidence of identity; the technique is used in forensic labs for criminal identification, determining paternity, and identifying accident victims, making it far more reliable and tamper-proof than traditional fingerprint evidence.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 4

Applied Concept

A diabetic patient is found to have abnormally high blood glucose levels. With reference to hormones discussed in the chapter, explain which hormones regulate blood glucose and what happens when their balance is disrupted.

Blood glucose is regulated by two antagonistic polypeptide hormones: insulin, which is released in response to a rapid rise in blood glucose and acts to lower it, and glucagon, which acts to increase blood glucose when levels fall too low.
In a diabetic patient, insufficient insulin production or action means that glucose cannot be efficiently taken up by cells after meals, causing blood glucose to remain abnormally elevated — a condition called hyperglycaemia.
Together, insulin and glucagon maintain blood glucose within a narrow physiological range; the imbalance in this system (particularly insulin deficiency) is the molecular basis of diabetes mellitus, illustrating the critical homeostatic role of hormones described in the chapter.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 5

Applied Concept

An athlete drinks a glucose energy drink before a race but also eats starchy food before a long training session. With reference to the chapter, explain the scientific basis for these choices, relating to how starch and glucose serve as energy sources.

Glucose is a monosaccharide (simple sugar) that is immediately available for cellular metabolism without requiring prior digestion; an energy drink provides instant energy, useful just before a sprint where quick energy is needed.
Starch is a complex polysaccharide polymer of alpha-D-glucose that must be hydrolysed by digestive enzymes to release glucose; this hydrolysis is gradual, providing a sustained and slow release of glucose into the bloodstream — ideal for endurance activities.
In the body, excess glucose from food is stored as glycogen (animal starch) in the liver and muscles; during prolonged exercise, enzymes break glycogen down to glucose, providing sustained fuel — which is why starchy meals are better for long training sessions.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 6

Applied Concept

A patient suffering from pernicious anaemia is found to have difficulty absorbing a specific vitamin. With reference to the chapter, identify the vitamin, explain why it cannot be easily replaced by diet alone in such patients, and name its food sources.

Pernicious anaemia is caused by deficiency of Vitamin B12, which leads to red blood cells being deficient in haemoglobin; it is unique among water-soluble vitamins in that it can be stored in the body.
Vitamin B12 deficiency in pernicious anaemia is often due to a lack of intrinsic factor (needed for absorption) rather than dietary deficiency, meaning simply increasing dietary intake may not correct the deficiency without addressing the absorption problem.
Food sources of Vitamin B12 include meat, fish, eggs, and curd; in cases where absorption is impaired, injections or high-dose supplements are typically required, unlike other water-soluble vitamins that are simply lost in urine if taken in excess.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 7

Applied Concept

When an egg is boiled, the egg white (albumin protein) becomes firm and opaque and cannot be reversed to its original liquid state. With reference to the chapter, explain the molecular changes occurring during this process.

Boiling subjects albumin (a globular protein) to heat, a physical change that disrupts the hydrogen bonds stabilising its secondary (alpha-helix, beta-pleated sheet) and tertiary (three-dimensional folding) structures.
With the loss of secondary and tertiary structure, the polypeptide chains unfold (globules unfold and helices uncoil), exposing previously buried hydrophobic groups and causing the protein to aggregate and coagulate — this is denaturation.
The primary structure (sequence of amino acids linked by covalent peptide bonds) remains intact during denaturation; however, since the specific 3D shape required for biological activity is irreversibly lost at high temperature, the process is irreversible and the protein permanently loses its native properties.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 8

Applied Concept

A dairy technologist notices that fresh milk becomes curdled (solid, opaque) when left at room temperature for hours. With reference to proteins discussed in the chapter, explain the chemical process responsible for curdling.

Milk contains casein protein; curdling occurs because bacteria present in milk produce lactic acid through fermentation of lactose (milk sugar) at room temperature.
The lactic acid lowers the pH of the milk, causing a chemical change (change in pH) that disrupts the hydrogen bonds maintaining the secondary and tertiary structure of the casein protein molecules.
With the disruption of higher-order protein structures, the proteins denature, unfold, and aggregate to form the solid curd; this is a classic example of denaturation caused by a chemical change (pH change), as described in the chapter.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 9

Applied Concept

During digestion, a patient is found to be unable to digest maltose due to a deficiency of a specific enzyme. With reference to the chapter, identify the enzyme and explain the role of enzymes as biocatalysts in digestion.

The enzyme deficient in this patient is maltase, which specifically catalyses the hydrolysis of maltose into two molecules of glucose; enzymes are named after the substrate upon which they act, with the suffix '-ase'.
Enzymes are biocatalysts (nearly all globular proteins) that dramatically increase the rate of specific biochemical reactions under mild physiological conditions of temperature and pH that would otherwise proceed too slowly.
Enzymes reduce the activation energy of reactions — for example, sucrase reduces the activation energy for sucrose hydrolysis from 6.22 kJ/mol to 2.15 kJ/mol; their high substrate specificity (one enzyme, one substrate) means that absence of maltase specifically blocks maltose digestion without affecting other carbohydrates.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 10

Applied Concept

A person living in a region with very little sunlight and a diet lacking in fish and dairy is found to have weak bones. With reference to the chapter, explain the problem and suggest dietary changes.

The person is likely deficient in Vitamin D, which is a fat-soluble vitamin obtained from sunlight exposure (which triggers skin synthesis), fish, and egg yolk; in children this causes rickets (bone deformities) and in adults osteomalacia (soft bones and joint pain).
Vitamin D is stored in liver and adipose tissue (fat-soluble) and is not readily obtained from most plant foods; with minimal sun exposure and a diet low in fish and dairy, the person cannot synthesise or consume adequate amounts.
Dietary recommendations should include oily fish, egg yolk, and fortified foods; since fat-soluble vitamins are stored in the body, periodic high-dose supplements (under medical advice) can also correct the deficiency, unlike water-soluble vitamins which must be consumed daily.

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Chapter sections

Chapter 10: Biomolecules | Application Questions

A food scientist tests two sugar solutions with Fehling's solution. Solution A gives a brick-red precipitate while Solution B gives no colour change. With reference to the chapter, identify the type of sugar in each solution and explain the chemical basis for this difference.

A child is diagnosed with rickets and a doctor recommends dietary changes. With reference to vitamins discussed in the chapter, identify the deficient vitamin, its food sources, and explain how its deficiency causes rickets.

In a forensic investigation, DNA from a crime scene is compared with that of a suspect. With reference to the chapter, explain the principle behind DNA fingerprinting and why it is considered more reliable than traditional fingerprinting.

A diabetic patient is found to have abnormally high blood glucose levels. With reference to hormones discussed in the chapter, explain which hormones regulate blood glucose and what happens when their balance is disrupted.

An athlete drinks a glucose energy drink before a race but also eats starchy food before a long training session. With reference to the chapter, explain the scientific basis for these choices, relating to how starch and glucose serve as energy sources.

A patient suffering from pernicious anaemia is found to have difficulty absorbing a specific vitamin. With reference to the chapter, identify the vitamin, explain why it cannot be easily replaced by diet alone in such patients, and name its food sources.

When an egg is boiled, the egg white (albumin protein) becomes firm and opaque and cannot be reversed to its original liquid state. With reference to the chapter, explain the molecular changes occurring during this process.

A dairy technologist notices that fresh milk becomes curdled (solid, opaque) when left at room temperature for hours. With reference to proteins discussed in the chapter, explain the chemical process responsible for curdling.

During digestion, a patient is found to be unable to digest maltose due to a deficiency of a specific enzyme. With reference to the chapter, identify the enzyme and explain the role of enzymes as biocatalysts in digestion.

A person living in a region with very little sunlight and a diet lacking in fish and dairy is found to have weak bones. With reference to the chapter, explain the problem and suggest dietary changes.

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