CHROMOSOMES

Question 1

Define the term chromosome

Answer 1

Chromosomes are highly coiled, ribbon like structures formed by the condensation of chromatin fibres during cell divison

Question 2

Who discovered chromosomes?

Answer 2

Walther Flemming

Question 3

Who first studies the structure of chromosomes?

Answer 3

Rosalind Franklin

Question 4

Who proposed the double helical structure of DNA?

Answer 4

Watson and Crick

Question 5

What is the composition of chromatin fibre?

Answer 5

DNA - 40%
Histones - 60%

Question 6

What is the structure of DNA?

Answer 6

Double helical macromolecule

Question 7

What are nucleotides?

Answer 7

Nucleotide is the structural and functional unit of DNA.
DNA is composed of repeating nucleotides.

Question 8

What are nucleotides made up of?

Answer 8

pentose sugars, nitrogenous bases, phosphate and hydrogen bonds

Question 9

What are the 4 types of nitrogenous bases in DNA?

Answer 9

Adenine, guanine, thymine and cytosine

Question 10

What are the different types of nitrogenous bases in RNA?

Answer 10

Adenine, guanine, cytosine and uracil

Question 11

Define the term histone

Answer 11

Histones are proteins which help in the coiling and packaging of DNA into structural units called nucleosome

Question 12

What are nucleosomes?

Answer 12

1 strand of DNA winds around a core of 8 histone proteins and is called histone octamer or nucleosomes

Question 13

What are the structural and functional units of chromosomes?

Answer 13

Nucleosomes

Question 14

What are the 2 types of nucleic acids?

Answer 14

DNA & RNA

Question 15

Define centromere

Answer 15

Centromere is the point of attachment of 2 sister chromatids that appears as a small constricted region

Question 16

What are the functions of centromere?

Answer 16

1. Centromere helps in attaching the sister chromatids to the spindle fibres
2. they help in the detaching of the sister chromatids during the anaphase stage

Question 17

What is the structure of a chromosome?

Answer 17

A chromosome is composed of 2 sister chromatids that are joined at the centromere

Question 18

Define the term chromatid

Answer 18

Chromatid is one vertical half of a duplicated chromosome

Question 19

What are sister chromatids?

Answer 19

Sister chromatids are two identical chromatids joined at the centromere

Question 20

What are genes?

Answer 20

Genes are specific sequences of nucleotides on a chromosome that encode particular proteins and are expressed in the form of some particular feature on the body

Question 21

What is the need for new cells?

Answer 21

1. growth
2. repair
3. replacement
4. reproduction

Question 22

Define cell cycle

Answer 22

Cell cycle is a series of events leading to the duplication of DNA and division of the cell to produce two daughter cells

Question 23

What are the 2 phases of the cell cycle?

Answer 23

1. interphase
2. mitosis

Question 24

What is the interphase?

Answer 24

The interphase is a non dividing phase of the cell where the relatively small daughter cells prepare for the next cell division and grow to the same size as the mother cell

Question 25

What are the 3 phases of the interphase?

Answer 25

1. Growth phase 1 2. Synthesis phase 3. Growth phase 2

Question 26

What are the 2 paths that a cell may follow in Growth phase 1?

Answer 26

The cell may withdraw from the cell cycle during Growth phase 1 and enter into a Resting phase or continue to the Synthesis phase

Question 27

What are the changes in the cell during Growth phase 1?

Answer 27

1. RNA and proteins are synthesized 2. Chloroplasts or mitochondria duplicate 3. Cytoplasm increases

Question 28

What is synthesized in the Synthesis phase?

Answer 28

DNA is synthesized chromosomes are duplicated

Question 29

What is synthesized during Growth phase 2?

Answer 29

RNA and proteins

Question 30

How does DNA duplicate?

Answer 30

The DNA opens at one end, making the 2 strands free, to which new strands form

Question 31

What are the 2 types of cell division?

Answer 31

1. Mitosis 2. Meiosis

Question 32

What is mitosis?

Answer 32

Mitosis is the cell division leading to the production of diploid cells - one parent cell divides into 2 identical daughter cells

Question 33

What are the 2 phases of mitosis?

Answer 33

1. Karyokinesis 2. Cytokinesis

Question 34

What is karyokinesis?

Answer 34

Karyokinesis is the division of the nucleus of the cell All the nuclear changes that take place in the cell during cell division can be called karyokinesis

Question 35

What are the 4 phases of karyokinesis?

Answer 35

1. prophase 2. metaphase 3. anaphase 4. telophase

Question 36

What is cytokinesis?

Answer 36

The division of cytoplasm is called cytokinesis

Question 37

What changes take place during prophase?

Answer 37

1. The nuclear membrane disappears 2. nucleolus dissapears 3. centrioles move towards opposite poles (animal cell) 4. spindle fibres are formed 5. chromosomes become distinct

Question 38

What is an Aster?

Answer 38

Centrioles are surrounded by radiating rays and are termed as aster

Question 39

What changes take place in the cell during metaphase?

Answer 39

1. chromosomes line up in one plane on the equator 2. chromosomes attach to the spindle fibres with the help of their centromeres

Question 40

What changes take place in the cell during anaphase?

Answer 40

1. centromere splits 2. sister chromatids separate 3. sister chromatids move to opposite poles 4. a furrow starts developing ( animal cell )

Question 41

What changes take place in the cell during telophase?

Answer 41

1. 2 nucleus form 2. spindle fibres disappear 3. nuclear membrane forms 4. chromatids thin out to become chromatin fibres 5. furrow deepens ( animal cell ) cell plate is laid down ( plant cell )

Question 42

Asters are formed in which cell? (a) animal cell (b) plant cell

Answer 42

(a) animal cell

Question 43

How are spindle fibres formed in animal cells?

Answer 43

with the help of centrioles and asters

Question 44

How are spindle fibres formed in plant cells?

Answer 44

with the help of microtubules

Question 45

How does cytokinesis occur in animal cell?

Answer 45

By furrowing of cytoplasm

Question 46

How does cytokinesis occur in plant cell?

Answer 46

By formation of cell plate

Question 47

What is the significance of mitosis?

Answer 47

1. growth 2. repair 3. replacement 4. asexual reproduction 5. same number of chromosomes is maintained in the daughter cells

Question 48

Why do mitochondria and chloroplasts divide on their own?

Answer 48

Mitochondria and chloroplasts have their own DNA and ribosomes which help them produce particular proteins. They divide by simple fission.

Question 49

What is meiosis?

Answer 49

Meiosis is the cell division leading to the production of haploid cells or gametes - sperms and eggs

Question 50

What is the significance of meiosis?

Answer 50

1. number of chromosomes are halved - haploid 2. mixing up of genes occurs

Question 51

How does mixing up of genes take place during meiosis?

Answer 51

1. during the first reduction division, due to the separation of the chromosomes from the homologous pairs 2. by crossing over 3. random assortment of chromosomes between the gametes

Question 52

Why is the chromosome number halved during meiosis?

Answer 52

As the diploid (2n) number of chromosomes will be restored on fertilization

Question 53

What is crossing over?

Answer 53

The exchange of genetic material during meiosis between a pair of non sister chromatids from a homologous pair of chromosomes

Question 54

What is chiasma?

Answer 54

The point of attachment between 2 non sister chromatids of a pair of homologous chromosomes during meiosis

Question 55

Where does mitosis occur?

Answer 55

Vegetative or somatic parts of the plant

Question 56

Where does meiosis occur?

Answer 56

In the reproductive cells

Question 57

Why does meiosis occur?

Answer 57

To form gametes

Question 58

How many daughter cells are formed in mitosis?

Answer 58

2 daughter cells

Question 59

How many daughter cells are formed in meiosis?

Answer 59

4 daughter cells

Question 60

How many divisions occur in a) mitosis b) meiosis

Answer 60

a) 1 division b) 2 divisions

Question 61

How many chromosomes are passed on in a) mitosis b) meiosis

Answer 61

a) 2n - diploid b) n - haploid

Question 62

When does it occur? a) mitosis b) meiosis

Answer 62

a) throughout life b) only during reproductively active age

Question 63

How are the daughter cells with respect to their parent cells after mitosis?

Answer 63

daughter cells are identical to parent cells

Question 64

What are homologous chromosomes?

Answer 64

Homologous chromosomes are chromosomes that are of the same length and centromere positioning. One chromosome is inherited from each parent

Question 65

How many hydrogen bonds is adenine paired with thymine with?

Answer 65

2 hydrogen bonds

Question 66

How many hydrogen bonds is guanine paired with cytosine with?

Answer 66

3 hydrogen bonds