Text Book Back Questions and Answers - Chapter 7 Cell Cycle 11th Biology Botany Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated By SaraNextGen

On April 24, 2024, 11:35 AM

Cell Cycle
Text Book Back Questions and Answers
I. Multiple Choice Questions
Choose the correct answer
Question 1.
The correct sequence in cell cycle is
(a) S-M-G1-G2
(b) S-G1-G2-M
(c) G1-S-G2-M
(d) M-G-G2-S
Answer:
(c) G1-S-G2-M
Question 2.
If mitotic division is restricted in $\mathrm{G} 1$ phase of the cell cycle then the condition is known as
(a) S Phase
(b) G2 Phase
(c) M Phase
(d) $G_0$ Phase

Answer:
(d) $\mathrm{G}_0$ Phase
Question 3.
Anaphase promoting complex APC is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in human cell, which of the following is expected to occur?
(a) Chromosomes will be fragmented
(b) Chromosomes will not condense
(c) Chromosomes will not segregate
(d) Recombination of chromosomes will occur
Answer:
(b) Chromosomes will not condense

Question 4.
In $S$ phase of the cell cycle
(a) Amount of DNA doubles in each cell
(b) Amount of DNA remains same in each cell
(c) Chromosome number is increased
(d) Amount of DNA is reduced to half in each cell
Answer:
(a) Amount of DNA doubles in each cell
Question 5.
Centromere is required for
(a) Transcription
(b) Crossing over
(c) Cytoplasmic cleavage
(d) Movement of chromosome towards pole
Answer:
(d) Movement of chromosome towards pole
Question 6.
Synapsis occur between
(a) mRNA and ribosomes
(b) Spindle fibres and centromeres
(c) Two homologous chromosomes
(d) A male and a female gamete
Answer:
(c) Two homologous chromosomes

Question 7.
In meiosis crossing over is initiated at
(a) Diplotene
(b) Pachytene
(c) Leptotene
(d) Zygotene
Answer:
(b) Pachytene
Question 8.
Colchicine prevents the mitosis of the cells at which of the following stage
(a) Anaphase
(b) Metaphase
(c) Prophase
(d) Interphase

Answer:
(b) Metaphase
Question 9.
The paring of homologous chromosomes on meiosis is known as
(a) Bivalent
(b) Synapsis
(c) Disjunction
(d) Synergids
Answer:
(b) Synapsis
Question 10.
Anastral mitosis is the characteristic feature of
(a) Lower animals
(b) Higher animals
(c) Higher plants
(d) All living organisms
Answer:
(c) Higher plants
Question 11.
Write any three significance of mitosis.
Answer:
Exact copy of the parent cell is produced by mitosis (genetically identical).

1. Genetic stability - daughter cells are genetically identical to parent cells.
2. Repair of tissues - damaged cells must be replaced by identical new cells by mitosis.
3. Regeneration - Arms of star fish.
Question 12.
Differentiate between Mitosis and Meiosis.
Answer:
Difference Between Mitosis and Meiosis:

Question 13.
Given an account of $\mathrm{G}_0$ phase.
Answer:
Some cells exit $\mathrm{G}_1$ and enters a quiescent stage called $\mathrm{G}_0$, where the cells remain metabolically active without proliferation. Cells can exist for long periods in $\mathrm{G}_0$ phase. In $\mathrm{G}_0$ cells cease growth with reduced rate of RNA and protein synthesis. The $\mathrm{G}_0$ phase is not permanent. Mature neuron and skeletal muscle cell remain permanently in $\mathrm{G}_0$. Many cells in animals remains in $\mathrm{G}_0$ unless called onto proliferate by appropriate growth factors or other extracellular signals. $\mathrm{G}_0$ cells are not dormant.
Question 14.
Differentiate Cytokinesis in plant cells and animal cells.
Answer:

1. Cytokinesis in Plant Cells:
Division of the cytoplasm often starts during telophase. In plants, cytokinesis cell plate grows from centre towards lateral walls centrifugal manner of cell plate formation. Phragmoplast contains microtubules, actin filaments and vesicles from golgi apparatus and ER. The golgi vesicles contains carbohydrates such as pectin, hemicellulose which move along the microtubule of the pharagmoplast to the equator fuse, forming a new plasma membrane and the materials which are placed their becomes new cell wall.
The first stage of cell wall construction is a line dividing the newly forming cells called a cell plate. The cell plate eventually stretches right across the cell forming the middle lamella. Cellulose builds up on each side of the middle lamella to form the cell walls of two new plant cells.
2. Cytokinesis in Animal Cells:
It is a contractile process. The contractile mechanism contained in contractile ring located inside the plasma membrane. The ring consists of a bundle of microfilaments assembled from actin and myosin. This fibril helps for the generation of a contractile force. This force draws the contractile ring inward forming a cleavage furrow in the cell surface dividing the cell into two.
Question 15.
Write about Pachytene and Diplotene of Prophase I.
Answer:
1. Pachytene: At this stage bivalent chromosomes are clearly visible as tetrads.

Bivalent of meiosis I consists of 4 chromatids and 2 centromeres. Synapsis is completed and recombination nodules appear at a site where crossing over takes place between non - sister chromatids of homologous chromosome. Recombination of homologous chromosomes is completed by the end of the stage but the chromosomes are linked at the sites of crossing over. This is mediated by the enzyme recombinase.
2. Diplotene: Synaptonemal complex disassembled and dissolves. The homologous chromosomes remain attached at one or more points where crossing over has taken place. These points of attachment where ' $\mathrm{X}$ ' shaped structures occur at the sites of crossing over is called Chiasmata. Chiasmata
are chromatin structures at sites where recombination has been taken place. They are specialised chromosomal structures that hold the homologous chromosomes together.Sister chromatids remain closely associated whereas the homologous chromosomes tend to separate from each other but are held together by chiasmata. This substage may last for days or years depending on the sex and organism. The chromosomes are very actively transcribed in females as the egg stores up materials for use during embryonic development. In animals, the chromosomes have prominent loops called lampbrush chromosome.