CBSE Questions for Class 11 Medical Biology Cell Cycle And Cell Division Quiz 10 - MCQExams.com

Formation of four unidentical daughter cells from a parent cell is called Meiosis. The four daughter cells formed in meiosis are unidentical to the parent cells because of the occurrence of crossing over and independent assortment. During meiosis, chromosomes in a pair are segregate or separate from one another, move into a gamete. Simultaneously, a character or trait separate from its pair and move into a gamete. So, each gamete receive one allele in a pair.

• To produce 200 pea seeds 200 pollen grains and 200 eggs are required.
• To produce 200 pollen grains 50 meiotic divisions are required. 
• Whereas, to produce 200 eggs from mother cells 200 meiotic division are required.
• Therefore, a total of 250 meiotic divisions are required to produce 200 seeds of the pea.
  
• The correct answer is $$250/500$$
  

$$\textbf{Correct option: C}$$

$$\textbf{Solution:}$$

Option C:

$$\bullet$$ Spindle fibres form a protein structure that divides a cell's genetic material or chromosomes during cell division.

$$\bullet$$ During both types of nuclear division (mitosis and meiosis) the spindle is required to evenly divide the chromosomes in a parental cell into two daughter cells. 

$$\bullet$$ Formation of spindle fibers occur in prophase of the cell cycle from centrioles present at opposite ends of dividing cell.

$$\bullet$$ Spindle fibers get attached to the kinetochores of the chromosomes and pull the sister chromatids toward opposite ends to separate them.

$$\bullet$$ The spindle fibres are referred to as the mitotic spindle during mitosis.

$$\bullet$$ Spindle fibers are made up of tubulin protein and RNA.

Hence the correct option is option C.

• The synaptonemal complex forms during the early stages of meiotic prophase I zygotene, when it mediates the pairing of homologous chromosomes. 
• Synaptonemal complex in chromosome synapsis and genetic recombination plan an important role. The synaptonemal complex is a proteinaceous structure and is thought to mediate synapsis and recombination during meiosis I of eukaryotic cell division.

• Five stages of prophase include:-

• Cyclin-dependent kinases, through phosphorylation,  signal the cell that it is ready to pass into the next stage of the cell cycle. As their name suggests, Cyclin-Dependent Protein Kinases are dependent on cyclins, another class of regulatory proteins. Cyclins bind to Cdks, activating the Cdks to phosphorylate other molecules.

• Zygotene is the second stage of the prophase 1 of meiosis 1 
• The chromosomes of the cell starts to pair during the prophase. During this phase the homologous chromosomes pair with each other this is called synapsis, the chromosomes pair in a zipper fashion.
• These form bivalents where the 2 pairs of sister chromatid are paired together.
• Leptotene is the first stage of prophase 1 where the chromosome condense and form thread like structures.
• Pachytene is the 3rd stage followed by zygotene, here crossing over of the non sister chromosomes takes place where the genetic material is exchanged at the site of formation of chiasmata.
• diplotene is the 4th stage where the non sister chromosomes where they have crossed over starts to move away from each other but remain connected at the site of chiasmata.
• Diakinesis is the last phase of prophase 1 where the chromosome tetrad is clearly visible with chiasmata and the overlapping chromosomes. At the end of this phase the nuclear membrane has disappeared and the cell is ready to enter the metaphase 1.
• Therefore the correct answer is option 'zygotene'.

• During the leptotene stage of the prophase 1 of the meiosis 1 the chromosomes are condensed and they start to form pairs.
• The homologous chromosomes that pair are called sister chromatids.
• Each pair of chromosomes have 2 chromosomes which are similar to each other. They are connected to each other by the means of centromere which is present in the middle of the chromosomes and are also called primary constriction.
• Bivalents mean that structure has 2 pairs of homologous chromosomes. Which means that each pair has 2 sister chromatids which is each connected by a centromere.
• Therefore the whole structure is made up of 4 chromatids ( 2 pair of sister chromatids) and 2 centromere each present in 1 pair.
• Therefore the correct answer is option 'four chromatids and two centromere'.

• Mitosis is the equational division where the mother cell is divided into 2 daughter cells.
• During the Sphase of the internphase the DNA or the genetic material of the cell is replicated and the amount of the genetic material is doubled in the mother cells.
• When the cell enters the cell division the cell will divided and the doubled genetic material during the Sphase will be equally distributed between the 2 daughter cells during the anaphase of mitosis.
• At the end of the telophase i.e. the last stage of mitosis the mother cell has divide to give rise to 2 daughter cells which each have a identical nucleus to the mother cell.
• Therefore at the end of mitosis 2 daughter cell each with  identical nucleus is formed.
• Therefore the correct options are 'two identical nuclei are formed' and 'two identical daughter cells are formed'.

Prophase is the first phase of both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase .so chromosomes are in the duplicated state during prophase. It is the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. During prophase, the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses. 

So, the correct answer is 'C'

• Meiosis is the reduction division where at the end of the division 4 daughter cells are formed each having half the genetic material compared to the mother cell.
• This division usually takes place in the cells which are engaged in the function of reproduction that is formation of gametes.
• All of the above options the root tips, stem tips and the leaf tips are just the regular organs of a plant which are engaged in other physiological functions such as absorption of water, food, preparation of food, oxygen and storage of food etc. They under go mitosis where the cells after dividing have the equal genetic material as the mother cell.
• Whereas the pollen mother cells are those that are present in the stamen of  flower which is involved in the reproduction process as the male reproductive organ. The cells of the stamen are known as pollen mother cell which give rise to pollen grains which are the plant male gametes.
• The gametes formed are to be haploid so the pollen mother cell undergoes meiosis where it forms 4 pollen cells at the end of the cycle each having half the genetic material as them mother cell.
• This haploid gamete will fuse with the female gamete and for a diploid zygote.
• Therefore the answer option 'pollen mother cells' is correct.
  

• In mitosis the genetic material is double during the S phase of the interphase and the genetic material or the chromosomes are equally divided between the daughter cells during the cell division.
• Therefore no tetrads are formed in the mitosis process.
  
• whereas meiosis the homologous  chromosomes pair with each other and form tetrads
• Therefore the answer option '0' is correct.
  

• In the mitosis the cells after the division retain the equal number of chromosome as the mother cell.
• During the S phase of cell cycle the genetic material is synthesized where the DNA is replication and the amount of the genetic material is doubled so when the cell enters the mitosis phases the chromosomes are condensed in prophase and then lined in the metaphase plate at the center of the cell after which they are moved to the poles of the dividing cells by the spindle fiber produced by the centrioles after this each of the dividing cell has the equal number of the chromosome as the mother cell as the chromes which were replicated during the S phase of the cell cycle are separated from each other and placed in different cells which is known as the anaphase.
• Which is followed by the telophase where the dividing cells undergo karyokinesis and finally separate.
• Therefore the answer option 'anaphase' is correct.
  

• Mitosis and cytoplasmic division is where the cell is divided into 2 daughter cells where the daughter cells are similar to that of the mother cell and have equal amount of genetic material.
• As most of the prokaryotes are very simple organisms with cellular level of organization they do not use sexual ways of reproduction and they reproduce by the act of simply dividing the cell body into 2 by methods such as binary fission, fragmentation or sporulation.
• In multicellular organisms reproduction usually takes place by the mode of sexual reproduction but the other cells of the body divide use mitosis for the function of growth, repair, wear and tear etc.
• But some unicellular eukaryotes such as yeast which reproduce by the method of budding which also takes place by the process of mitosis.
• And also some of the multicellular eukaryotes such as planaria which reproduce by fragmentation and some of the  plants that reproduce or are cultivated using fragmentation divide by the process of mitosis.
• Therefore options 'Growth, tissue repair, and sometimes asexual reproduction in many multicellular eukaryotes' and 'Asexual reproduction of single-celled eukaryotes' are correct.