Cell Cycle And Cell Division
Class 11th Biology NCERT Exemplar Solution
- Meiosis results in diploid organisms
- At which stage of meiosis does the genetic constitution of gametes is finally decided…
- Meiosis occurs in organisms during
- During anaphase-I of meiosis
- Mitosis is characterised by
- A bivalent of meiosis-I consists of
- Cells which are not dividing are likely to be at
- Which of the events listed below is not observed during mitosis?
- Identify the wrong statement about meiosis
- Select the correct statement about G1 phase
- Between a prokaryote and a eukaryote, which cell has a shorter cell division time?…
- Which of the phases of cell cycle is of longest duration?
- Name a stain commonly used to colour chromosomes.
- Which tissue of animals and plants exhibits meiosis?
- Given that the average duplication time of E.coli is 20 minutes, how much time will two…
- Which part of the human body should one use to demonstrate stages in mitosis?…
- What attributes does a chromatid require to be classified as a chromosome?…
- The diagram shows a bivalent at prophase-I of meiosis. Which of the four chromatids can…
- If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original…
- An anther has 1200 pollen grains. How many pollen mother cells must have been there to…
- At what stage of cell cycle does DNA synthesis take place?
- It is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24…
- It is observed that heart cells do not exhibit cell division. Such cells do not divide…
- In which phase of meiosis are the following formed? Choose the answers from hint points…
- State the role of centrioles other than spindle formation.
- Mitochondria and plastids have their own DNA (genetic material). What is known about their…
- Label the diagram and also determine the stage at which this structure is visible.…
- A cell has 32 chromosomes. It undergoes mitotic division. What will be the chromosome…
- While examining the mitotic stage in a tissue, one finds some cells with 16 chromosomes…
- The following events occur during the various phases of the cell cycle, Name the phase…
- Mitosis results in producing two cells which are similar to each other. What would be the…
- Both unicellular and multicellular organisms undergo mitosis. What are the differences, if…
- Name the pathological condition when uncontrolled cell division occurs.…
- Two key events take place, during S phase in animal cells, DNA replication and duplication…
- Comment on the statement – Meiosis enables the conservation of specific chromosome number…
- Name a cell that is found arrested in diplotene stage for months and years. Comment in 2-3…
- How does cytokinesis in plant cells differ from that in animal cells?…
- Comment on the statement – Telophase is reverse of prophase.
- What are the various stages of meiotic prophase-I? Enumerate the chromosomal events during…
- Differentiate between the events of mitosis and meiosis .
- Write brief note on the followinga. Synaptonemal complexb. Metaphase plate…
- Write briefly the significance of mitosis and meiosis in multicellular organism.…
- An organism has two pair of chromosomes (i.e., chromosome number = 4). Diagrammatically…
Multiple Choice Questions
Question 1.Meiosis results in diploid organisms
A. Production of gametes
B. Reduction in the number of chromosomes
C. Introduction of variation
D. all of the above
Answer:
Meiotic division leads to formation of four gameteic cells.
Meiosis is also known as reductional division as it results in reduction in number of cells.
Due to crossing over, it leads to accumulation of variation.
Question 2.
At which stage of meiosis does the genetic constitution of gametes is finally decided
A. Metaphase I
B. Anaphase II
C. Metaphase II
D. Anaphase I
Answer:
In this stage the homologous chromosome separates from each other therefore genetic constitution is finally decided.
Question 3.
Meiosis occurs in organisms during
A. Sexual reproduction
B. Vegetative reproduction
C. Both sexual and vegetative reproduction
D. None of the above
Answer:
In vegetative reproduction there is no need of reduction division, as no recombination takes place.
Question 4.
During anaphase-I of meiosis
A. Homologous chromosomes separate
B. Non-homologous chromosomes separate
C. Sister chromatids separate
D. Non-sister chromatids separate
Answer:
During anaphase I, as the spindle fibre contracts homologous chromosomes separate to opposite poles.
Question 5.
Mitosis is characterised by
A. Reduction division
B. Equal division
C. Both reduction and equal division
D. Paining of homologous chromosomes
Answer:
It is the equational division i.e. the no. of chromosomes remain the same in the somatic cells.
Question 6.
A bivalent of meiosis-I consists of
A. Two chromatids and one centromere
B. Two chromatids and two centromere
C. Four chromatids and two centromere
D. Four chromatids and four centromere
Answer:
Two homologous chromosomes come together to form bivalent.
Question 7.
Cells which are not dividing are likely to be at
A. G1
B. G2
C. Go
D. S phase
Answer:
Also called the quiescent stage, in this stage the cell becomes inactive.
Question 8.
Which of the events listed below is not observed during mitosis?
A. Chromatin condensation
B. Movement of centrioles to opposite poles
C. Appearance of chromosomes with two chromatids joined together at the centromere.
D. Crossing over
Answer:
It is observed during the pachytene, sub stage of prophase I.
Question 9.
Identify the wrong statement about meiosis
A. Pairing of homologous chromosomes
B. Four haploid cells are formed
C. At the end of meiosis the number of chromosomes are reduced to half
D. Two cycle of DNA replication occurs
Answer:
In meiosis haploid set of chromosomes are produced, therefore one cycle of DNA replication occurs.
Question 10.
Select the correct statement about G1 phase
A. Cell is metabolically inactive
B. DNA in the cell does not replicate
C. It is not a phase of synthesis of macromolecules
D. Cell stops growing
Answer:
DNA replication occur during S-phase of cell cycle.
Very Short Answer Type
Question 1.Between a prokaryote and a eukaryote, which cell has a shorter cell division time?
Answer:
Prokaryotes take less time for cell division.
Question 2.
Which of the phases of cell cycle is of longest duration?
Answer:
Interphase.
In a 24 hour cell cycle, 23 hour are for I-phase and 1 hour for M phase.
Question 3.
Name a stain commonly used to colour chromosomes.
Answer:
To make the chromosomes visible the cell are stained with Acetocarmine and mounted in acetocarmine only.
Question 4.
Which tissue of animals and plants exhibits meiosis?
Answer:
Germ cells present in the reproductive tract undergo meiosis to produce gametes.
Question 5.
Given that the average duplication time of E.coli is 20 minutes, how much time will two E.coli cells take to become 32 cells?
Answer:
2 →4 →8 →16 →32
It takes 80 mins.
Question 6.
Which part of the human body should one use to demonstrate stages in mitosis?
Answer:
Any somatic tissue can be taken, for example tissues near to the cheeks.
Question 7.
What attributes does a chromatid require to be classified as a chromosome?
Answer:
When chromatids are attached to the centromere it is termed as chromosome.
Question 8.
The diagram shows a bivalent at prophase-I of meiosis. Which of the four chromatids can cross over?
Answer:
Crossing over takes place only between non sister chromatids.
Question 9.
If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?
Answer:
2x=1024
X=10
Therefore, parent will undergo 10 rounds of mitosis.
Question 10.
An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them?
Answer:
1 pollen mother cell →4 pollen grain
Therefore, no. of PMC = 1200/4
= 300 pollen grains
Question 11.
At what stage of cell cycle does DNA synthesis take place?
Answer:
S-phase of cell cycle .
Question 12.
It is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?
Answer:
Interphase takes 23 hours out of 24 hours.
Question 13.
It is observed that heart cells do not exhibit cell division. Such cells do not divide further and exit ___________ phase to enter an inactive stage called ___________ of cell cycle. Fill in the blanks.
Answer:
G1 phase, G0 phase.
Question 14.
In which phase of meiosis are the following formed? Choose the answers from hint points given below.
a. Synaptonemal complex ____________________________
b. Recombination nodules ____________________________
c. Appearance/activation of ____________________________
enzyme recombinase
d. Termination of chiasmata _ ___________________________
e. Interkinesis ____________________________
f. Formation of dyad of cells _ ___________________________
Hints : 1) Zygotene, 2) Pachytene, 3) Pachytene, 4) Diakinesis, 5) After Telophase-I /before Meosis-II, 6) Telophase-I /After Meiosis-I.
Answer:
a. Zygotene
b. Zygotene
c. Pachytene
d. Diakinesis
e. After telophase I/before meiosis
f. After Telophase I/after meiosis I
Short Answer Type
Question 1.State the role of centrioles other than spindle formation.
Answer:
Centriole forms microtubule and forms basal body of flagella.
Question 2.
Mitochondria and plastids have their own DNA (genetic material). What is known about their fate during nuclear division like mitosis?
Answer:
DNApresent in mitochondria in plastids are called the extra chromosomal DNA.
They are independent of the nuclear division of the nuclear DNA. Hence, no effect of mitosis is seen on extra chromosomal DNA.
Question 3.
Label the diagram and also determine the stage at which this structure is visible.
Answer:
It indicates the early Metaphase stage.
Question 4.
A cell has 32 chromosomes. It undergoes mitotic division. What will be the chromosome number (N) during metaphase? What would be the DNA content (C) during anaphase?
Answer:
Both N and C will be 32.
This is due the fact that DNA is replicated during S phase, after that it would remain the same during equational division.
Question 5.
While examining the mitotic stage in a tissue, one finds some cells with 16 chromosomes and some with 32 chromosomes. What possible reasons could you assign to this difference in chromosome number. Do you think cells with 16 chromosomes could have arisen from cells with 32 chromosomes or vice versa?
Answer:
• The phenomenon of existence of two types of chromosome no. in different cell of the body is called mosaicism.
• This may arise due to non disjunction of chromosomes or lag of anaphase.
Question 6.
The following events occur during the various phases of the cell cycle, Name the phase against each of the events.
a. Disintegration of nuclear membrane _________________________
b. Appearance of nucleolus _________________________
c. Division of centromere _________________________
d. Replication of DNA _________________________
Answer:
a. Early Prophase
b. Late Telophase
c. Anaphase
d. S phase
Question 7.
Mitosis results in producing two cells which are similar to each other. What would be the consequence if each of the following irregularities occur during mitosis?
a. Nuclear membrane fails to disintegrate
b. Duplication of DNA does not occur
c. Centromeres do not divide
d. Cytokinesis does not occur
Answer:
a. Nuclear membrane fails to disintegrate, if it happens then the spindle fibre would not reach the chromosomes.
b. Duplication of DNA does not occur,
If it would happen then the whole cell cycle would get arrested and will enter an inactive stage called the G0 stage.
c. Centromeres do not divide- Sister chromatids would not split to opposite poles and one daughter cell would get two sister chromatids whereas the other will get none.
d. Cytokinesis does not occur- It will result in polyploidy.
Question 8.
Both unicellular and multicellular organisms undergo mitosis. What are the differences, if any, observed in the process between the two?
Answer:
• In prokaryotes amitosis takes place, the cell directly divides into two daughter cells.
• Whereas in multicellular organisms, proper steps of cell division occurs; first the karyokinesis takes place then cytokinesis occurs.
Question 9.
Name the pathological condition when uncontrolled cell division occurs.
Answer:
This is called malignancy caused due to cancer.
Question 10.
Two key events take place, during S phase in animal cells, DNA replication and duplication of centriole. In which parts of the cell do events occur?
Answer:
DNA replication occur in nucleus and centriole duplicates in the cytoplasm.
Question 11.
Comment on the statement – Meiosis enables the conservation of specific chromosome number of each species even though the process per se, results in reduction of chromosome number.
Answer:
During fertilisation two haploid cells called the gametes fuse to form diploid zygote.
If meiosis is absent , than two diploid gamete would be produced which will result in formation of tetraploid zygote.
Therefore, it can be said that in order to conserve the chromosome number meiosis is very important.
Question 12.
Name a cell that is found arrested in diplotene stage for months and years. Comment in 2-3 lines how it completes cell cycle?
Answer:
The oocyte of mammalian females get arrested in diplotene stage.
Process of oogenesis in females of mammal starts with their own embryogenesis.
The oocyte grows and forms secondary follicle and then it gets arrested at the diplotene stage.
As the woman attains the sexual maturity first meiosis gets completed.
Meiosis occurs one by one in the egg, which is released from the ovary.
Question 13.
How does cytokinesis in plant cells differ from that in animal cells?
Answer:
Cytokinesis in plants occur by cell plate formation.
Cell plate formation starts from the centre and grows to the periphery.
In animals furrow is formed, from the periphery of the cell to the centre.
Long Answer Type
Question 1.Comment on the statement – Telophase is reverse of prophase.
Answer:
Prophase-
• Chromosome condenses.
• Nuclear membrane disintegrates
• Organelles like mitochondria, endoplasmic reticulum, golgi apparatus disappears.
Telophase-
• Chromosome decondenses
• Nuclear membrane again gets formed
• Organelles reappear.
Question 2.
What are the various stages of meiotic prophase-I? Enumerate the chromosomal events during each stage?
Answer:
Prophase I-
a. Leptotene stage:
• Nuclear membrane starts to disappear.
• Chromatin material starts condensing.
• Centriole reaches opposite poles.
• In some members of lileaceae chromosomes remain attached to the nuclear membrane – bouquet stage.
b. Zygotene:
• Pairing of homologous chromosomes start.
• To hold these homologous chromosomes a protein called synoptonemal complex develops.
c. Pachytene
• Biavalent [homologous chromosomes] or tetrad becomes clearly visible.
• Crossing over takes place resulting in genetic recombination.
• The enzyme recombinase, for crossing over comes from the recombination nodule of the synoptonemal complex.
d. Diplotene
• Synoptenemal complex dissolves
• But homologous chromosomes are still held by a X like structure called the chiasma.
• Chiasmata develops at the point of crossing over.
e. Diakinesis
• Terminalisation of chiasmata: Chiasmata starts opening in a zipper like fashion towards the periphery.
• Nuclear membrane and nucleolus nearly disappears.
Question 3.
Differentiate between the events of mitosis and meiosis .
Answer:
Question 4.
Write brief note on the following
a. Synaptonemal complex
b. Metaphase plate
Answer:
a. Synaptonemal complex
• Formed during zygotene a sub stage of Prophase I.
• Made up of protein, formed between two homologous chromosomes.
• It contains a recombination nodule which consists of enzyme recombinase involved in crossing over.
b. Metaphase plate
• It is an imaginary line, located in the centre of the cell.
• Formed during metaphase.
• The chromosomes gets attached to the spindle fibre and aligns themselves on the plate.
• The movement of chromosomes toward the metaphasic plate is called congression.
Question 5.
Write briefly the significance of mitosis and meiosis in multicellular organism.
Answer:
• Mitosis creates the cells necessary to add more mass to the body, as well as more cells to cope with the growth, such as new blood cells. In case of injury mitosis is involved in healing of the tissues.
• Meiosis also produces genetic variation by way of the process of recombination.
It helps to conserve the no. of chromosomes in a species.
Question 6.
An organism has two pair of chromosomes (i.e., chromosome number = 4). Diagrammatically represent the chromosomal arrangement during different phases of meiosis-II.
Answer:
