CBSE Class 9 Biology The Fundamental Unit of Life MCQs Set 04

Answer: (c) Maltose

Explanation:
1. Maltose is made of two glucose units joined by a glycosidic bond.
2. Galactose and fructose are monosaccharides; dextrin is a polysaccharide breakdown product of starch.

Teacher's Note:
1. Disaccharides: maltose, lactose, sucrose.
2. They yield two monosaccharide molecules on hydrolysis.

Answer: (d) nucleotides

Explanation:
1. Nucleic acids are long polymers whose repeating unit is a nucleotide (a nitrogenous base, a pentose sugar and a phosphate group).
2. Amino acids build proteins, not nucleic acids.

Teacher's Note:
1. Nucleotide = nucleoside + phosphate.
2. DNA and RNA are polynucleotides.

Answer: (c) Wax

Explanation:
1. Starch, glycogen and glucose are carbohydrates.
2. Wax is a lipid (an ester of a fatty acid with a long chain alcohol).

Teacher's Note:
1. Carbohydrates contain C, H and O in the ratio Cn(H₂O)n.
2. Waxes belong to the lipid group.

Answer: (a) carbohydrates

Explanation:
1. Carbohydrates are the most readily oxidised food and release energy quickly (about 4 kcal per gram).
2. Fats give more energy per gram but are used more slowly; vitamins do not supply energy.

Teacher's Note:
1. Glucose is the main immediate fuel of cells.
2. Fats are the long-term energy store.

Answer: (b) mitochondria

Explanation:
1. Mitochondria (and chloroplasts) have their own small circular double-stranded DNA, like bacteria.
2. Nuclear DNA is linear and the Golgi body and endoplasmic reticulum have no DNA.

Teacher's Note:
1. Mitochondria and chloroplasts are semi-autonomous organelles.
2. Their DNA resembles that of prokaryotes.

Answer: (a) collagen

Explanation:
1. Collagen is the main structural protein of skin, bone, tendons and connective tissue and makes up about a quarter of all body protein.

Teacher's Note:
1. Collagen holds tissues together.
2. Myosin and actin are the main proteins of muscle contraction.

Answer: (a) Sucrose

Explanation:
1. Starch, glycogen and cellulose are polymers of glucose.
2. Sucrose is a disaccharide of glucose and fructose.

Teacher's Note:
1. Poly means many sugar units; di means two.
2. Sucrose is table sugar.

Answer: (a) Purkinje

Explanation:
1. Purkinje introduced the term protoplasm (1839) for the living substance of the cell.
2. Schultze established the protoplasm theory, and Sutton and Boveri proposed the chromosome theory of inheritance.

Teacher's Note:
1. Protoplasm = living content of the cell.
2. Remember Purkinje with protoplasm.

Answer: (d) all of the above

Explanation:
1. Monosaccharides cannot be hydrolysed further. Pentoses (ribose), hexoses (glucose, fructose, galactose) are all monosaccharides.
2. Glucose itself is a hexose.

Teacher's Note:
1. Classify monosaccharides by the number of carbon atoms.
2. Pentoses have 5 carbons; hexoses have 6.

Answer: (b) transcription

Explanation:
1. Making RNA from a DNA template is transcription.
2. Translation is protein synthesis from m-RNA.

Teacher's Note:
1. Transcription: DNA to RNA.
2. Translation: RNA to protein.

Answer: (a) Glycine

Explanation:
1. Glycine can be made in the body, so it is non-essential.
2. Phenylalanine and methionine are essential amino acids, and arginine is semi-essential (needed in the diet by growing children).

Teacher's Note:
1. Essential amino acids must come from the diet.
2. Phenylalanine and methionine are among the essential ones.

Answer: (a) Watson and Crick

Explanation:
1. Watson and Crick proposed the double helix model of DNA in 1953.
2. Schleiden and Schwann gave the cell theory and Singer and Nicholson the fluid mosaic model.

Teacher's Note:
1. Match the scientist with the discovery.
2. Fluid mosaic model is for the cell membrane.

Answer: (d) Uracil

Explanation:
1. DNA contains adenine, guanine, cytosine and thymine.
2. Uracil replaces thymine in RNA.

Teacher's Note:
1. Uracil is the RNA base.
2. Thymine is the DNA base.

Answer: (d) polymer of glucose units

Explanation:
1. Glycogen is a branched polysaccharide made of many glucose units and is the stored carbohydrate of animals.

Teacher's Note:
1. It is called animal starch.
2. It is stored mainly in the liver and muscles.

Answer: (c) polyhydric aldehyde or ketone

Explanation:
1. Chemically, carbohydrates are polyhydroxy aldehydes or ketones (or substances that give them on hydrolysis).

Teacher's Note:
1. Aldose has an aldehyde group and ketose has a ketone group.
2. Glucose is an aldose; fructose is a ketose.

Answer: (b) Glycogen

Explanation:
1. Animals store carbohydrate as glycogen in the liver and muscles.
2. Cellulose is a plant material and ATP is the energy currency, not a store.

Teacher's Note:
1. Plants store starch; animals store glycogen.
2. Excess glucose is converted to glycogen.

Answer: (d) proteins

Explanation:
1. Enzymes are biological catalysts that are proteins (a few are RNA, the ribozymes).

Teacher's Note:
1. Enzymes have a specific three-dimensional protein structure.
2. Heat can denature them.

Answer: (a) polymerisation of two carbon compounds

Explanation:
1. Fatty acids are built up by repeatedly joining two-carbon units (acetyl groups), which gives long unbranched chains with an even number of carbons.

Teacher's Note:
1. Fatty acid chains grow two carbons at a time.
2. Most natural fatty acids have an even number of carbon atoms.

Answer: (b) essential

Explanation:
1. Amino acids that the body cannot make and must obtain from food are called essential amino acids.

Teacher's Note:
1. Essential means that they must be supplied by the diet.
2. There are nine essential amino acids for adults.

Answer: (c) extra glycogen storage in liver and muscles is stopped

Explanation:
1. Excess glucose is first stored as glycogen in the liver and muscles.
2. When the glycogen stores are full, additional glucose is converted into fat.
3. Only the third statement describes the stage at which fat formation begins.

Teacher's Note:
1. Fat is the overflow store of surplus carbohydrate.
2. Glycogen storage has a limit.

Answer: (d) Phosphorus

Explanation:
1. Nitrogen bases (purines and pyrimidines) contain C, H, N and O.
2. Phosphorus occurs in the phosphate group of the nucleotide, not in the base.

Teacher's Note:
1. Phosphate is a separate part of the nucleotide.
2. The bases are ring compounds of C, H, N and O.