Solved Exercise, Bio-11, Ch-02

FILL IN THE BLANKS

(i) The sum of all the chemical reactions taking place within a cell is called ________. (metabolism)

(ii) _________ is the basic element of organic compounds. (Carbon)

(iii) All the amino acids have an amino group and a carboxyl group attached to the same _________ atom. (alpha)

(iv) _________ is the most abundant carbohydrate in nature. (cellulose)

(v) Adenine and guanine are double ringed bases and are called _________. (pyrimidines)

TRUE/FALSE

(i) A small proportion of water molecules are in ionized form. (TRUE)

(ii) The covalent bond among two monosaccharides is called a peptide bond. (FALSE)

CORRECT: The covalent bond among two monosaccharides is called a glycosidic bond.

(iii) Glycogen is also called plant starch. (FALSE)

CORRECT: Glycogen is also called animal starch.

(iv) Adenine is always opposite to guanine, cytosine and thymine are opposite to each other in DNA molecule. (FALSE)

CORRECT: Adenine is always opposite to thymine, cytosine and guanine are opposite to each other in DNA molecule.

(v) DNA molecule is made of two polynucleotide strands. (TRUE)

MULTIPLE CHOICE QUESTIONS

(i) Animals obtain carbohydrates mainly from:

(a)   Glucose

(b)   Starch

(c)   Sucrose

(d)   Glycogen

EXPLANATION: Animals obtain starch mainly from plant sources and digest it into glucose.

(ii) Peptide bond is a:

(a)   C–N link

(b)   C–O link

(c)   N–H link

(d)   C–H link

EXPLANATION: Peptide bond is formed between the amino group of one amino acid and the carboxyl group of other amino acid to form a dipeptide.

(iii) Globular proteins differ from fibrous proteins in:

(a)   Having amino acids

(b)   Their repeating units joined by peptide bonds

(c)   Being soluble in aqueous medium

(d)   Being non-crystalline

EXPLANATION: Globular proteins are soluble in aqueous medium primarily due to their three-dimensional, compact folding that results in a hydrophilic exterior, composed of polar and charged amino acid residues, which readily interact with water molecules.

(iv) Which of the following amounts of bases are more likely to be found in an organism?

(a)   Adenine 30.9% & cytosine 30.7%

(b)   Guanine 27.5% & adenine 27.8%

(c)   Cytosine 19.8% & thymine 20.0%

(d)   Adenine 32% & thymine 31.9%

EXPLANATION: In a double stranded DNA molecule, adenine of one strand is always paired with thymine on the other strand. Thus, their percentages must be almost equal.

(v) Amino acids are arranged in proper sequence during protein synthesis according to the instructions transcribed on:

(a)   Transfer RNA

(b)   Ribosomal RNA

(c)   Messenger RNA

(d)   DNA

EXPLANATION: Information about the specific sequence of amino acids in a polypeptide chain is transcribed from DNA to mRNA in nucleus. From mRNA, this information is translated into specific protein in the cytoplasm with the help of ribosomes.

SHORT QUESTIONS

(i) Name the carbohydrates suitable as food for man.

ANSWER:

The carbohydrates suitable as food for man are:

1) Starches ­(in cereals, potatoes & sugar beets)

2) Sucrose ­(in sugar cane)

3) Lactose (in milk)

4) Glucose ­(in fruits like grapes, figs etc.)

(ii) Why are fats considered as high energy compounds?

ANSWER:

Fats are considered as high energy compounds because they have higher proportion of C—H bonds and very low proportion of oxygen. The C—H bonds are a potential source of energy. So, lipids store double amount of energy as compared to the same amount of any carbohydrate.

(iii) What is the function of mRNA?

ANSWER:

Function of Messenger RNA:

Messenger RNA carries the genetic information from DNA to ribosomes, where amino acids are arranged according to the information in mRNA to form specific protein molecules.

(iv) What is the general formula for amino acids?

ANSWER:

General Formula of an Amino Acid:

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