SUMMARY: The chapter "Biomolecules" in Class 11 Biology explores the chemical constituents of living cells and the roles they play in biological processes. KEY TOPICS: carbohydrates, proteins, lipids, nucleic acids, enzymes, structure of biomolecules, metabolism, biomolecular interactions, water as a solvent, macromolecules.
ACarboxyl group of one amino acid and amino group of another
BTwo carboxyl groups
CTwo amino groups
DTwo side chains
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Correct answer: Option 1 — Carboxyl group of one amino acid and amino group of another
Q41 Mark
Enzymes are mostly:
ACarbohydrates
BLipids
CProteins
DNucleic acids
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Correct answer: Option 3 — Proteins
Q51 Mark
Which of the following is a nucleotide?
AAdenine
BAdenosine
CAMP
DRibose
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Correct answer: Option 3 — AMP
Q61 Mark
Which of the following is a characteristic of lipids?
ASoluble in water
BStore genetic information
CInsoluble in water
DForm peptide bonds
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Correct answer: Option 3 — Insoluble in water
Q71 Mark
What type of bond links monosaccharides to form polysaccharides?
AIonic bond
BHydrogen bond
CGlycosidic bond
DPeptide bond
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Correct answer: Option 3 — Glycosidic bond
Q81 Mark
Which of the following biomolecules is primarily responsible for catalyzing biochemical reactions?
ACarbohydrates
BProteins
CLipids
DNucleic acids
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Correct answer: Option 2 — Proteins
Q91 Mark
Which macromolecule is composed of amino acids?
ACarbohydrates
BProteins
CLipids
DNucleic acids
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Correct answer: Option 2 — Proteins
Q101 Mark
What is the primary function of nucleic acids in cells?
AEnergy storage
BStructural support
CInformation storage and transfer
DCatalysis
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Correct answer: Option 3 — Information storage and transfer
Q111 Mark
Which of the following is a disaccharide?
AGlucose
BFructose
CSucrose
DCellulose
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Correct answer: Option 3 — Sucrose
Q121 Mark
What role does water play in biological systems?
AIt is a source of energy
BIt acts as a solvent
CIt forms proteins
DIt stores genetic information
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Correct answer: Option 2 — It acts as a solvent
Q131 Mark
Which of the following statements about enzymes is true?
AThey are consumed in reactions
BThey lower activation energy
CThey are only proteins
DThey function at any temperature
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Correct answer: Option 2 — They lower activation energy
Q141 Mark
What type of structure do enzymes have that is crucial for their function?
APrimary structure
BSecondary structure
CTertiary structure
DQuaternary structure
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Correct answer: Option 3 — Tertiary structure
Q151 Mark
Which of the following is NOT a function of carbohydrates?
AEnergy source
BStructural component
CHormone production
DCell recognition
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Correct answer: Option 3 — Hormone production
Short Answer Questions10 questions
Q163 Marks
Differentiate between primary, secondary, tertiary and quaternary structures of proteins.
Q173 Marks
What are the factors affecting enzyme activity?
Q183 Marks
Explain the structure of a nucleotide.
Q193 Marks
Differentiate between essential and non-essential amino acids.
Q203 Marks
Distinguish between starch and cellulose.
Q213 Marks
What are the main functions of carbohydrates in living organisms?
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Carbohydrates serve as a primary energy source, provide structural support in cell walls of plants (e.g., cellulose), and play roles in cell recognition and signaling processes.
Q223 Marks
Describe the role of lipids in biological membranes.
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Lipids, particularly phospholipids, form the bilayer structure of biological membranes, providing fluidity and flexibility while also acting as barriers to protect cellular contents.
Q233 Marks
What is the significance of water as a solvent in biological systems?
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Water's polarity allows it to dissolve a wide range of substances, facilitating biochemical reactions and transport of nutrients and waste products in living organisms.
Q243 Marks
Explain the term 'macromolecule' and give two examples.
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Macromolecules are large, complex molecules that are essential for life, including proteins and nucleic acids, which play critical roles in structure and function of cells.
Q253 Marks
What is the role of enzymes in metabolic processes?
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Enzymes act as biological catalysts that speed up chemical reactions in metabolic pathways by lowering the activation energy required for the reactions to occur.
Long Answer Questions6 questions
Q266 Marks
Describe the structure of proteins at primary, secondary, tertiary, and quaternary levels.
Q276 Marks
Discuss the mechanism of enzyme action and the factors affecting enzyme activity.
Q286 Marks
Describe different classes of enzymes with one example each.
Q296 Marks
Explain the structure of polysaccharides with examples (starch, cellulose, glycogen).
Q306 Marks
Describe the various types of lipids and their biological importance.
Q316 Marks
Compare DNA and RNA with the help of a table on at least five points.
Assertion–Reason Questions8 questions
Q321 Mark
Assertion (A): Enzymes lower the activation energy of reactions.
Reason (R): They provide an alternative pathway with a lower energy barrier.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q331 Mark
Assertion (A): Proteins are polymers of amino acids.
Reason (R): Amino acids are joined by peptide bonds in proteins.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q341 Mark
Assertion (A): Glycogen is the storage carbohydrate in animals.
Reason (R): It is a highly branched polymer of glucose.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q351 Mark
Assertion (A): Lipids are not strictly biomacromolecules.
Reason (R): Their molecular weights do not exceed 800 Daltons.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q361 Mark
Assertion (A): DNA is a double helix.
Reason (R): The two strands are held together by hydrogen bonds between complementary bases.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q371 Mark
Assertion (A): Carbohydrates are primarily used for energy storage in living organisms.
Reason (R): Carbohydrates can be broken down into glucose, which is a primary energy source for cells.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Q381 Mark
Assertion (A): All lipids are soluble in water.
Reason (R): Lipids are hydrophobic and do not mix well with water.
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Correct answer: Option 4 —
A is false, but R is true.
Q391 Mark
Assertion (A): Nucleic acids are responsible for the storage and transmission of genetic information.
Reason (R): Nucleic acids like DNA and RNA play critical roles in heredity and protein synthesis.
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Correct answer: Option 1 —
Both A and R are true, and R is the correct explanation of A.
Statement-Based Questions8 questions
Q401 Mark
Statement 1: Enzymes are biological catalysts.
Statement 2: They speed up biochemical reactions without being consumed.
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Correct answer: Option 1 —
Both statements are true.
Q411 Mark
Statement 1: Cellulose is the most abundant organic compound on Earth.
Statement 2: It is the chief structural component of plant cell walls.
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Correct answer: Option 1 —
Both statements are true.
Q421 Mark
Statement 1: All amino acids contain an amino group and a carboxyl group.
Statement 2: They differ in their side chain (R group).
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Correct answer: Option 1 —
Both statements are true.
Q431 Mark
Statement 1: RNA contains uracil instead of thymine.
Statement 2: RNA is single-stranded while DNA is double-stranded.
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Correct answer: Option 1 —
Both statements are true.
Q441 Mark
Statement 1: Cofactors are non-protein components needed for enzyme activity.
Statement 2: They may be metal ions or organic molecules called coenzymes.
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Correct answer: Option 1 —
Both statements are true.
Q451 Mark
Statement 1: Carbohydrates are primarily composed of carbon, hydrogen, and nitrogen.
Statement 2: Lipids are insoluble in water due to their hydrophobic nature.
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Correct answer: Option 3 —
Only Statement 2 is true.
Q461 Mark
Statement 1: Proteins are made up of long chains of nucleotides.
Statement 2: Enzymes can be denatured by changes in temperature and pH.
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Correct answer: Option 2 —
Only Statement 1 is true.
Q471 Mark
Statement 1: Nucleic acids are responsible for the storage and transmission of genetic information.
Statement 2: All lipids are soluble in water.
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Correct answer: Option 3 —
Only Statement 2 is true.
Case Study / Passage Questions4 questions
Q483 Marks
A school laboratory studies the action of salivary amylase on starch. The enzyme is incubated at 37 degrees C with starch solution and the product is tested with iodine at intervals. The blue colour of starch fades and a brick red colour appears with Benedict's reagent indicating the formation of reducing sugars.
Salivary amylase is an example of a/an:
ACarbohydrates
BLipids
CProteins
DNucleic acids
The product of starch digestion by amylase is:
AGlucose
BMaltose
CSucrose
DLactose
Discuss the factors that affect enzyme activity.
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1. Option 3 — Proteins
2. Option 2 — Maltose
3. Enzyme activity depends on temperature, pH, substrate concentration and enzyme concentration. Each enzyme has an optimum temperature and pH at which it is most active. At very high temperatures the enzyme is denatured because its three-dimensional structure unfolds and the active site loses its specific shape. Cofactors and coenzymes may also be required for activity.
Q493 Marks
A research student isolates DNA from onion cells and finds that 30 percent of the bases are adenine. She is asked to use Chargaff's rules to determine the percentages of the other three bases and to explain why these rules hold for double-stranded DNA.
The percentage of thymine in this DNA must be:
A30
B20
C40
D15
The percentage of cytosine equals:
A5
B10
C15
D20
State Chargaff's rules and explain how they support the double-helix model of DNA.
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1. Option 1 — 30
2. Option 4 — 20
3. Chargaff's rules state that in any double-stranded DNA the amount of adenine equals that of thymine and the amount of guanine equals that of cytosine. So if A = 30 percent then T = 30 percent. The remaining 40 percent is shared equally by G and C giving G = C = 20 percent. These rules arise because A pairs with T and G pairs with C in the double helix.
Q503 Marks
Carbohydrates are essential biomolecules that serve as a primary energy source for living organisms. They are composed of carbon, hydrogen, and oxygen, typically in a ratio of 1:2:1. Simple carbohydrates, or sugars, include monosaccharides like glucose and fructose, while complex carbohydrates consist of oligosaccharides and polysaccharides such as starch and cellulose. Starch, a storage form of energy in plants, is made up of long chains of glucose units. In contrast, cellulose provides structural support in plant cell walls. The digestion of carbohydrates begins in the mouth, where enzymes like salivary amylase break down starch into simpler sugars, facilitating their absorption in the intestines.
What are the primary components of carbohydrates?
ACarbon, hydrogen, and nitrogen
BCarbon, hydrogen, and oxygen
COxygen, nitrogen, and sulfur
DCarbon, hydrogen, and phosphorus
Explain the role of salivary amylase in carbohydrate digestion.
Which carbohydrate serves as a storage form of energy in plants?
ACellulose
BGlycogen
CStarch
DFructose
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1. Option 2 — Carbon, hydrogen, and oxygen
2. Salivary amylase initiates the breakdown of starch into simpler sugars in the mouth.
3. Option 3 — Starch
Q513 Marks
Proteins are macromolecules composed of amino acids linked by peptide bonds. They play crucial roles in biological processes, including catalyzing metabolic reactions as enzymes, providing structural support, and facilitating communication within and between cells. The sequence of amino acids determines the protein's structure and function, which can be categorized into four levels: primary, secondary, tertiary, and quaternary. Denaturation, a process where proteins lose their functional shape due to environmental changes, can affect their activity. Enzymes, a specific type of protein, are vital for speeding up biochemical reactions without being consumed in the process.
What are the building blocks of proteins?
ANucleotides
BFatty acids
CAmino acids
DMonosaccharides
Describe the effect of denaturation on proteins.
What is the role of enzymes in biological processes?
ATo provide energy
BTo catalyze biochemical reactions
CTo store genetic information
DTo transport molecules
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1. Option 3 — Amino acids
2. Denaturation causes proteins to lose their functional shape, affecting their activity.
3. Option 2 — To catalyze biochemical reactions
Table-Based Questions4 questions
Q523 Marks
Study the table of biomolecules and answer the questions:
Biomolecule
Monomer
Bond
Example
Protein
Amino acid
Peptide
Albumin
Polysaccharide
Monosaccharide
Glycosidic
Cellulose
Nucleic acid
Nucleotide
Phosphodiester
DNA
Lipid
Fatty acid + glycerol
Ester
Triglyceride
The bond between two amino acids is a/an:
AGlycosidic
BPeptide
CPhosphodiester
DEster
A polymer of glucose is:
ATriglyceride
BCellulose
CAlbumin
DDNA
Compare the structure of a protein and a polysaccharide on the basis of monomer and linkage.
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1. Option 2 — Peptide
2. Option 2 — Cellulose
3. Biomolecules are classified into four major groups — carbohydrates, lipids, proteins and nucleic acids. Each is built from specific monomers joined by characteristic bonds. Proteins are polymers of amino acids joined by peptide bonds. Polysaccharides are polymers of monosaccharides joined by glycosidic bonds. Nucleic acids are polymers of nucleotides joined by phosphodiester bonds. Lipids are not strictly polymers but are formed by ester linkages between fatty acids and glycerol.
Q536 Marks
Match each vitamin with its deficiency disease.
Vitamin
Deficiency disease
Vitamin A
?
Vitamin B1
?
Vitamin C
?
Vitamin D
?
Vitamin K
?
Q546 Marks
Match each enzyme class with the type of reaction it catalyses.
