Structures of Chromosomes| Chapter 2 | ICSE Biology | Selina Solutions

 

Chapter 2

Structure of Chromosomes: Cell Cycle and Cell Division

 

Progress Check Page 11

Fill in the blanks.

1.   Chromatin fibre is made up of DNA and ……… .

Answer

Ans. Histones

 

2.   The two sister chromatids of a chromosome are attached to each other at ……….

Answer

Ans. Centromere

 

3.   The structure of DNA was first discovered by ………….

Answer

Ans. Rosalind Franklin

 

4.   The three components of a nucleotide are ………….. , …………. and ……………..

Answer

Ans. phosphate, sugar (pentose) and nitrogenous base

 

5.   DNA strand wound around a histone octamer forms a complex called a …………..

Answer

Ans. Nucleosome

 

6.   A specific sequence of nucleotides on a chromosome constitutes a ………….

Answer

Ans. Gene

 

 

Back Questions

Review Questions

A. MULTIPLE CHOICE TYPE

(Choose the best option out of the four alternatives a, b, c and d)

1.   The chromatin material is formed of

a.   DNA only

b.   DNA and Histones

c.    Histones only

d.   Nucleotides

Answer

Ans. b. DNA and Histones

 

2.   The term “chromosomes” literally means

a.   Inherited bodies

b.   Twisted threads

c.    Coloured bodies

d.   Shining threads

Answer

Ans. c. Coloured bodies

 

3.   The number of chromosomes in a certain type of cell division is halved. This kind of cell division occurs in

a.   only testis

b.   only ovary

c.    both ovary and testis

d.   all body cells

Answer

Ans. c. both ovary and testis

 

4.   In which one of the following options the stages of mitosis have been given in correct sequence?

a.   Prophase, metaphase, telophase, anaphase

b.   Prophase, metaphase, anaphase, telophase

c.    Anaphase, telophase, prophase, metaphase

d.   Telophase, anaphase, prophase, metaphase

Answer

Ans. b. Prophase, metaphase, anaphase, telophase

 

5.   Synthesis phase in the cell cycle is called so for the synthesis of more of

a.   RNA

b.   RNA and proteins

c.    DNA

d.   Glucose

Answer

c. DNA

 

B. VERY SHORT ANSWER TYPE

1. Name the following:

a. The repeating components of each DNA strand lengthwise.

Answer

Nucleotide

 

b. The complex structure consisting of DNA strand and a core of histones.

Answer

Ans. Nucleosome

 

c. The type of bond which joins the complementary nitrogenous bases.

Answer

Ans. Hydrogen bond

 

d. The three components of a nucleotide.

Answer

Ans. phosphate, sugar(pentose) and a nitrogenous base

 

2. Imagine one cell (A) has undergone one mitotic division and another cell (B) has completed its meiotic division. How many cells would the two produce?

Cell A: ……………………………

Cell B: ……………………………

Answer

Ans. Cell A:  2 daughter cells

Cell B: 4 daughter cells

 

3. Match the events given in column A with the phase in mitotic cell division in column B.

 

Column A	Column B
a.   Chromosomes get arranged in a horizontal plane at the equator	Anaphase
b.   Daughter chromosomes move to the opposite poles of a spindle.	Prophase
c.    Chromosomes become visible as fine long threads.	Telophase
d.   Chromosomes lose their distinctiveness and gradually become transformed into a chromatin network.	Metaphase

 

Answer

Ans.

Column A	Column B
a.   Chromosomes get arranged in a horizontal plane at the equator	Metaphase
b.   Daughter chromosomes move to the opposite poles of a spindle.	Anaphase
c.    Chromosomes become visible as fine long threads.	Prophase
d.   Chromosomes lose their distinctiveness and gradually become transformed into a chromatin network.	Telophase

 

4. Fill in the blanks.

a. DNA replicates in the ……….. phase of the cell cycle.

Answer

Ans. synthesis

 

b. Mitosis occurs in our ………. cells.

Answer

Ans. somatic(body)

 

c. Meiosis occurs only in ……….. cells.

Answer

Ans. sex

 

d. Modern humans have 46 chromosomes. Their sperms and eggs will have ………… chromosomes each.

Answer

Ans. 23

 

e. During the pairing of chromosomes in meiosis, the …………. chromosomes come to lie side by side.

Answer

Ans. homologous

 

f. The two non-sister chromatids of a paired chromosome are attached to each other at …………. during the process of crossing over.

Answer

Ans. chiasmata / chiasma

 

 

C. SHORT ANSWER TYPE

1. What is the difference between chromatin fibre and chromosome?

Answer

Ans. Chromatin fibres are very long and thin, thread like structures made up of DNA and histones whereas chromosomes are highly coiled and condensed chromatin fibres.

 

2. What are the rungs of the “DNA ladder” made of?

Answer

Ans. The rungs of the “DNA ladder” are made up of two complementary nitrogenous bases joined by hydrogen bonds.

 

3. Correct the following statements for mistakes, if any.

a. The four nitrogenous bases in the DNA are Guanine, Thiamine, Adrenaline and Cytosine.

Answer

Ans. The four nitrogenous bases in the DNA are Guanine, Thiamine, Adenine and Cytosine.

 

b. Genes are specific sequences of bases on a chromosome.

Answer

Ans. Genes are specific sequences of nucleotides on a chromosome.

 

c. A nucleotide is composed of a sulphate, a sugar(pentose) and a nitrogenous base.

Answer

Ans. A nucleotide is composed of a phosphate, a sugar(pentose) and a nitrogenous base.

 

d. Nucleosomes are groups of cysteine molecules surrounded by DNA strands.

Answer

Ans. Nucleosomes are groups of histone molecules surrounded by DNA strands.

 

e. If there are 46 chromosomes in a cell, there will be 23 chromatin fibres inside the nucleus during interphase.

Answer

Ans. If there are 46 chromosomes in a cell, there will be 46 chromatin fibres inside the nucleus during interphase.