Cell Cycle And Cell Division

Question 1

Why is mitosis known as equational division?

Answer 1

This type of cell division results in formation of daughter cells with the same chromosomal number as parent cell

Question 2

Gap 1 phase

Answer 2

Cell is metabolically active and enlarging in size

Question 3

S phase

Answer 3

DNA replication occurs (2C to 4C) and duplication of centrioles occur

Question 4

G2 phase

Answer 4

Proteins required for cell division are synthesized

Question 5

G0/quiescent phase

Answer 5

Certain cellls divide only when the need arises, hence, theyexit the G1 phase and enter this phase and remain metabolically active but temporsrily suspended from cell division unless required for example heart cells or those who only occasionally divide to replace other cells during cell injury or death

Question 6

Prophase M phase

Answer 6

Chromatid reticulum condenses to form distinct thread like chromosomes composed of sister chromatids held together by centromeres in the centre. Formation of spindle apparatus begins. Arrangement of centrioles in opposite poles. ER and Golgi complex disintegrate

Question 7

Metaphase

Answer 7

Formation of spindle apparatus ends, chromosomes get arranged in the equatorial plane of the spindle apparatus, nuclear membrane disintegrates, spindle fibres attach to kinetochores of chromosomes

Question 8

Anaphase

Answer 8

Spindle fibers contract leading to splitting of centromeres which in turn causes separation of sister chromatids (NOT CHROMOSOMES) towards opposite poles.

Question 9

Telophase

Answer 9

Decondensation of chromosomes occur, reforming of nuclear membrane, nucleolus, ER, Golgi complex occurs. Disintegration of spindle apparatus.

Question 10

How does cytokinesis take place in animals

Answer 10

Formation of cleavage furrow from outside to inside which deepens and join inthe centre which leads to formation of 2 daughter cells, the furrow is created due to a constriction in the contractile ring made up of actin and myosin filaments

Question 11

How does cytokinesis take place in plants

Answer 11

begins by formation of a precursor of the new cell wall, called the cell plate which represents the middle lamella between 2 adjacent cells. This wall grows to meet the lateral walls.

Question 12

Significance of mitosis points

Answer 12

1.Helps in the growth of an organism
2. Replaces damaged cells, helps in cell repair.
3. When the cell increases in size, the nucelo-cytoplasmic ration which is altered is restored by giving rise to daughter cells
4. Itcan produce copies of the parent.

Question 13

What is Interkinesis

Answer 13

Itis the internal gap between meiosis 1 and meiosis 2.

Question 14

What are homologous chromosomes

Answer 14

Homologous chromosomes are a pair of chromosomes which bear the same set of genes in the same position and are derived from parental origins.

Question 15

Prophase 1 consists of

Answer 15

Leptotene, zygotene, pachytene,diplotene, diakinesis

Question 16

Leptotene?

Answer 16

Compaction of chromosomes

Question 17

Zygotene

Answer 17

Synapsis-pairing of homologous chromosomes. Formation of complex structure called
synaptonemal complex. The complex formed by a pair of synapsed
homologous chromosomes is called a bivalent or a tetrad. The complex is a proteinaceous network which holds the pair of homologous chromosomes tgt

Question 18

Pachytene

Answer 18

appearance of recombination nodules, the sites
at which crossing over occurs between non-sister chromatids of the
homologous chromosomes. Crossing over is exhnage of genetic material between sister chromatids which is catalysed by enzyme recombinase

Question 19

Diplotene+ funfact about some vertebrates

Answer 19

Characterized by disintegration of the synaptonemal complex and homologous chromosomes separate from each other except at the sites of crossovers, these x shaped structures are called chiasmata. In some vertebrates, oocytes remained arrested in diplotene stage for months or years.

Question 20

Diakinesis

Answer 20

Terminalization of chiasmata, chromosomes are fully condensed, spindle formation begins, nucleolus and nuclear envelope disintegrate

Question 21

Which stage is Dyad of cells

Answer 21

Telophase I stage

Question 22

Significance of meiosis

Answer 22

1. Production of haploid gametes so original chromosomes number is maintained i.e., conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms.
2. Involves variation, therefore, can help the organism to survive in changing conditions i.e., increases genetic variability from oine geenration to the next, which are very important for evolution