Cell Cycle And Cell Division - Class 11 Medical Biology - Extra Questions
Why is meiosis essential in sexually reproducing organisms ?
Define : Mitosis Division
Write a neat labelled diagram of metaphasic chromosome.
In the course of cell division, chromatin starts condensing and reaches maximum condensation during metaphase. It is now called a 'metaphase chromosome'. At this juncture, each chromosome has been duplicated. This condensation is mainly due to the histone proteins on which the DNA tightly wraps around. Various structures such as a centromere, kinetochore, telomere etc. can be distinguished in a metaphase chromosome as seen in the figure.
What would have happened if meiosis not occur during the production of human sperm cell and egg cell?
Synapsis, Crossing over, Terminalisation and disjunction respectively take place in _______ , ___________. _____________ and ___________ stages of meosis.
What is the first phase of Mitiosis?Write the changes that take place in that stage.
The diagram given represents a certain stage of mitosis:
$$(i)$$ Identify the stage of cell division.
$$(ii)$$ Name the parts labelled $$A$$ And $$B$$.
$$(iii)$$ What is the unique feature observed in this stage?
$$(iv)$$ How many daughter cells formed from this type of cell division?
Why is mitosis called as equational division?
Name the stage of cell cycle at which one of the following events occur.
(i) Chromosomes are moved to spindle equator.
(ii) Centromere splits and chromatids separate.
(iii) Pairing between homologous chromosomes takes place.
(iv) Crossing over between homologous chromosomes takes place.
Short / Long Answer Type Questions :
Give a diagrammatic description of mitotic division of animal cell and write its significance.
Mitosis is the division of the cells in which the diploid number of the cell is maintained.
The cell division is used for growth, repair and replacement of worn-out tissues.
Find examples where the four daughter cells from meiosis are equal in size and where they are found unequal in size.
What are the causes of anaphasic movement ?
Anaphase movement is the movement of sister chromatids of each chromosome towards the pole during M phase of the cell cycle. It is caused by the attachment of spindle fibre to the kinetochores and then shortening of these spindle fibres that pulls these chromosomes to the opposite poles of cell.
Which type of cell division helps in regeneration ?
Fill in the blanks with appropriate words.
In meiotic division, prophase I is completed in five successive stages, viz .......... , .......... , .......... , .......... , and ..........
A parenchymatous cell has 20 units of DNA. It starts to divide mitotically. How many units of DNA would it have
during very late telophase
Very Short Answer Types :
Give a specific scientific term for each of the following.
Process of cell division by which the chromosome number is halved.
How many times will the process of mitosis occur in the formation of 256 cells in a root tip from a single cell?
Very Short Answer Types :
Who coined the term mitosis and in which year?
Fill in the blanks with appropriate words.
During cell division, disappearance of nuclear membrane and nucleolus marks the beginning of ..........
Short / Long Answer Type Questions :
Explain meiosis. Write the role of meiosis and sexual reproduction in producing genetic variability
In the prophase 1 of meiosis 1, crossing over takes place between the homologous chromosomes that result in the variability of the genome in the next generation.
Short / Long Answer Type Questions :
Make a neat and labelled diagram of metaphase stage of mitotic cell division
Diagram for metaphase in mitotic cell division.
Differentiate between :
Mitosis and.meiosis II
Value Based Questions :
Which of the following statements is associated with A. prophase, B. meraphase, C. anaphasc, D. telophase, and E. interphase of mitosis?
Chromosomes are thickest and shortest.
In a prokaryotic cell, cell division takes place by .......................... type of reproduction.
What is Totipotency?
Identify the stage of mitotic division. Give a reason to support your answer.
Define cell division ?
Value Based Questions :
Which of the following statements is associated with A. prophase, B. meraphase, C. anaphasc, D. telophase, and E. interphase of mitosis?
The nuclear membrane reappears.
The nuclear membrane reappears at the end of telophase.
So, the correct option is 'Telophase'.
Value Based Questions :
Which of the following statements is associated with A. prophase, B. meraphase, C. anaphasc, D. telophase, and E. interphase of mitosis?
Centromere divides into two.
Distinguish cytokinesis from karyokinesis.
Short / Long Answer Type Questions :
Draw and explain a series of diagrams that illustrate the stages of meiosis I.
R.E.F image
At the onset of meiosis, DNA strands thicken into chromosomes.
Homologous, or like chromosomes begin to approach each other.
R.E.F image
Homologous chromosomes pair to from bivalents.
The centrioles divide and move to opposite poles of the cell.
R.E.F image
The bivalents duplicates to from tetrads, or four-chromatid groups.
The nuclear membrane disntegrates.
Crossing over (recombination) occurs.
R.E.F image
In metaphase I, the tetrads, attached to spindle fibers at their centromere, line up at mid-cell.
R.E.F image
In early anaphase I, the tetrads separate, and the paired chromatids move along the spindle to their respective centrioles.
R.E.F image
In late anaphase I, the chromatides have almost reached the spindle poles. The cell membrane begins to constrict.
R.E.F image
In telophase I, nuclear membrans enclose the sparated chromatids.
The cell membrane completes its constriction.
R.E.F image
The first meiotic division ends.
There are now two cells each with the same number of
chromatids as the parent cell.
Very Short Answer Types :
Give a specific scientific term for each of the following.
Nuclear division.
Meiosis is an essential event in the sexual life cycle of an organism. Give the reasons.
What are the sub stages prophase $$1$$ of Meiosis $$1$$? Explain briefly
How many mitotic divisions cell needed for a single cell to make $$128$$ cells?
What is synapsis?
Why Mitosis is significant?
The stage through which change in chromosomes numbers occurs is called?
Name one structure that is associated with meiosis of an animal cells but not seen in plant cells.
How many linkage groups are represented in the diagram?
How many chromosomes each daughter cell will have at the end of meiosis, according to the diagram?
How does cytokinesis in plant cells differ from that in animal cells?
List the main differences between mitosis and meiosis?
The exchange of chromatid parts between the maternal and the paternal chromatids of a pair of homologous chromosomes during meiosis.
There are two homologous chromosomes one from the father which is known as paternal chromosome and one from the mother which is known as maternal chromosome. During the metaphase of meiosis, there is exchange of chromatid parts between the maternal and the paternal chromatids of a pair of homologous chromosomes during meiosis. This phenomenon is known as crossing over. The site at which the genetic material is exchanged is called as chiasmata.
Name the types of cell division that occurs during the following cellular activity.
A. Growth of a shoot.
B. Formation of pollen grains.
In Meiosis, the chromosome number in the daughter cells are reduced to half that of their parent cells. Guess, what would happen, if the reduction of chromosome number is not done?
The diagram given represents a certain stage of mitosis.
$$(i)$$ Identify the stage of cell division.
$$(ii)$$ Name the parts labelled $$A$$ and $$B$$.
$$(iii)$$ What is the unique feature observed in this stage?
$$(iv)$$ How many daughter cells formed from this type of cell division?
Mention the stages of Mitosis with the help of diagrams. Explain the changes that takes place in Prophase.
The diagram represents the type of cell division mitosis. There are four phases of mitosis. In the interphase, there is the duplication of the genetic material. The prophase is the first phase of mitosis, followed by metaphase, anaphase and telophase.
The chromatin fibres start to condense in the early prophase forming the chromosomes. The nucleolus and the nuclear membrane disappears. There is the orientation of the centrioles in the opposite poles. The mitotic spindle formation starts in the late prophase.
Pick out the item which has sequential arrangement.
i) $$Zygotene \rightarrow Leptotene \rightarrow Pachytene \rightarrow Diplotene \rightarrow Diakinesis$$.
ii)$$Diakinesis \rightarrow Zygotene \rightarrow Leptotene \rightarrow Pachytene\rightarrow Diplotene$$.
iii)$$Leptotene \rightarrow Zygotene \rightarrow Pachytene\rightarrow Diplotene \rightarrow Diakinesis.$$
Match the items in Column-I with those in Column-II, and choose the CORRECT answer
If the number of chromosomes in a nucleus is 24, how many finger-like structures will you be able to see during the metaphase. Why?
Define cell cycle?
In which sub-stages of meiosis-I do the following events occur?
i) pairing of homologous chromosomes
ii) terminalization
ii) crossing over
iv) formation of spindle apparatus.
Look at the given picture. Describe the changes in the nuclear material from stage A to stage B.
Why is meiosis called reduction division? Describe the various stages with relevant diagrams. Add a note on significance of meiosis.
Meiosis is called reduction division because the number of chromosomes in the daughter cells are half that of the parent cell.
Significance of Meiosis:
1. Meiosis reduces the chromosome number to half in the daughter cells of the gamete forming cells. This helps maintains a constant chromosome number for a species when zygote is formed
2. During meiotic division variations occur due to crossing over between maternal and paternal chromosomes or the homologous pair during Prophase I of meiosis I.
3. Further the random combinations of maternal and paternal chromosomes during Anaphase I leads to a distinct chromosomal composition in all the 4 daughter cells.
4. The variations thus produced leads to evolution
Explain cell cycle ?
Cell Cycle: It is a sequence of events which occur between the formation of the cell and its division into the daughter cell.
Describe mitosis. Add a note on its significance ?
Describe the following : (a) Synapsis (b) Bivalent (c) Chiasmata. Draw a diagram to illustrate your answer.
a) Synapsis:- Synapsis is basically pairing of two homologous chromosomes that occurs during meiosis.
b) Bivalent:- Bivalent is the association of a pair of homologous chromosomes held together by atleast one DNA crossover.
c) Chiasmata:- Chiasmata is point of attachment at which chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.
What is Leptotene stage ?
Describe the changes occurring in the nucleus during prophase of mitosis.
- In prophase, the condensation of chromosomal material. The chromosomal material becomes untangled during the process of chromatin condensation.
- Chromosomes are seen to be composed of two chromatids attached together at the centromere.
- There is the initiation of assembly of the mitotic spindle, the microtubules the proteinaceous component of the cell cytoplasm help in the process.
- The cell at the end of this phase, has no golgi complex, endoplasmic reticulum, nucleolus, and nuclear envelope.
Name the two types of cytokinesis.
Study the diagram given below which represents a stage during the mitotic cell division and answer the questions that follow:
Which is the cell division that results in half the number of chromosomes in daughter cells?
Study the diagram given below which represents a stage during the mitotic cell division and answer the questions that follow:
What is the technical term for the division of nucleus?
Study the diagram given below which represents a stage during the mitotic cell division and answer the questions that follow:
Identify the stage giving suitable reasons.
Study the diagram given below which represents a stage during the mitotic cell division and answer the questions that follow:
Mention the stage that comes before the stage shown in the diagram. Draw a neat labelled diagram of the stage mentioned.
The stage shown in the diagram is telophase as the the mitotic spindle disappears, the two sets of daughter chromosomes reach opposite poles and the nuclear envelope reforms. The stage that comes before telophase is anaphase.
Anaphase- The centromeres separate, and one of each pair of sister chromatids migrates to each end of the spindle as the microtubules that form the mitotic spindle contract.
Hence, the stage that comes before the stage shown in the diagram is Anaphase.
Study the diagram given below which represents a stage during the mitotic cell division and answer the questions that follow:
Name the parts numbered $$1$$ and $$2$$.
The diagram given represents a stage during cell division.
Study the same and answer the question that follow.
Name the type of cell division that occurs during.
$$1$$. Replacement of old leaves by new ones.
$$2$$. Formation of gametes.
The diagram given represents a stage during cell division. Study the same and answer the question that follow.
Name the stage depicted in the diagram. What is the unique feature observed in this stage?
The diagram given represents a stage during cell division. Study the same and answer the question that follows. Identify whether it is a plant cell or an animal cell. Give a reason in support of your answer.
Short / Long Answer Type Questions :
During mitosis sister chromatids separate and migrate to opposite poles. Why does this- not occur during meiosis I ?
Match the events given in column A with the phase in mitotic cell division in column B
| Column 'A' | Column 'B' |
| (a) Chromosomes get arranged in a horizontal plane at the equator. | 1.Anaphase |
| (b) Daughter chromosomes move to the opposite poles of a spindle. | Prophase |
| (c) Chromosomes become visible as fine long threads. | Telophase |
| (d) Chromosomes lose their distinctiveness and gradually become transformed into a chromatin network | Metaphase |
The diagram given represents a stage during cell division.
Study the same and answer the question that follow.
What is the stage that comes before the stage shown in the diagram?
"First meiotic division is the reduction division". What does the word 'reduction' refer to in this statement?
The diagram given represents a stage during cell division.
Study the same and answer the question that follows.
Draw a neat labeled diagram of the stage that comes before the stage shown in the diagram, keeping the chromosome number constant.
Fill in the blanks with appropriate words.
In .......... every DNA replication of chromosome duplication is followed by two nuclear divisions.
Fill in the blanks with appropriate words.
In .......... division chromosome number in daughter cells remains the same as in parent cell.
Fill in the blanks with appropriate words.
Mitosis results in the formation of nuclei having .......... number of chromosomes.
Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. It is an equational division.
So, the correct answer is 'same or equal'.
Fill in the blanks with appropriate words.
The morphology of chromosomes can be best studied during .......... stage of mitosis when they are .......... and arranged along the ..........
Fill in the blanks with appropriate words.
In meiosis, resultant daughter cells are genetically .......... to each other and to the parent cell.
In meiosis, the resultant daughter cells only carry a haploid number of chromosomes and are different as they carry only one set.
So, the correct word is 'dissimilar'.
Fill in the blanks with appropriate words.
In mitotic metaphase centromeres of chromosomes remain directed towards the .......... and the arms of chromosomes remain directed towards the ..........
The centromeres of the chromosomes are aligned towards the spindle axis pointing towards the pole and the arms(chromatids) are aligned to the equatorial plane.
So, the correct statement is 'In mitotic metaphase centromeres of chromosomes remain directed towards the poles and the arms of chromosomes remain directed towards the equatorial plane'
Fill in the blanks with appropriate words.
The cell cycle is divisible into two main phases .......... and ..........
Fill in the blanks with appropriate words.
Exchange of sections of chromatids of synapsing chromosomes during meiosis I is termed ..........
Fill in the blanks with appropriate words.
Synapsis, chiasma formation and crossing over occur between homologous chromosomes in .......... of meiosis.
Short / Long Answer Type Questions :
When and where does meiotic division take place in cells? What is the significance of this type of cell division in the animals life?
Value Based Questions :
Which of the following statements is associated with A. prophase, B. meraphase, C. anaphasc, D. telophase, and E. interphase of mitosis?
Each chromosome consists of two chromatids.
Differentiate between :
Metaphase and anaphase of mitosis
Value Based Questions :
Which of the following statements is associated with A. prophase, B. meraphase, C. anaphasc, D. telophase, and E. interphase of mitosis?
Followed by cytokinesis.
Match the terms to these definitions.
Centromere, centrosome, chromatin, chromosome, spindle, cell cycle, karyotype, meiosis, mitosis, sister chromatids, interphase, metaphase
.......... The period from the end of one division of a, cell to the end of the next division.
Match the terms to these definitions.
Centromere, centrosome, chromatin, chromosome, spindle, cell cycle, karyotype, meiosis, mitosis, sister chromatids, interphase, metaphase
.......... A type of cell division where chromosome number in daughter cells remains the same as in parent cell.
What is cell division? Write two types of cell division?
- The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells. In eukaryotes, the cell cycle is divided into three periods which are interphase, the mitotic phase, and cytokinesis.
- During interphase, the cell grows, accumulates nutrients needed for mitosis, preparing it for cell division and duplicating its DNA. During the mitotic phase, the chromosomes separate. During cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells.
- Cell division is the process by which a parent cell divides into two or more daughter cells. The primary concern of cell division is the maintenance of the original cell's genome.
- Before division can occur, the genomic information that is stored in chromosomes must be replicated, and the duplicated genome must be separated cleanly between cells.
- In eukaryotes, there are two types of cell division. One is a vegetative division where two daughter cells are formed and each daughter cell is genetically identical to the parent cell. This type of division is called as mitosis.
- The other type of cell division is a reproductive cell division where four daughter cells are formed and the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes. This type of cell division is called as meiosis.
How many chromosomes will be present in a diploid cell at mitotic anaphase, if its egg cell has ten chromosomes?
In multicellular organism, all the cells present in the body divide by
Human being are different in their colour size etc but yet they belong to same species. Explain.
Explain the stages of prophase I of meiosis.
The prophase I of meiosis occurs in the following stages:
1. Leptotene- This phase is the start of prophase-I. It is marked by the condensation of the chromosomes.
2. Zygotene- In this phase the homologous chromosomes start pairing up, called the synapsis. The synaptonemal complex starts building up. This complex is required to hold the homologous chromosomes at a place close to each other. Bivalent chromosomes are visible at this stage.
3. Pachytene- In this stage, this non-sister chromatids of homologous chromosomes exchange their parts, the process is called the crossing over. The attachment point of the crossing-over of the non-sister chromatids is called chiasma.
4. Diplotene- The crossing-over process is completed by this stage. The homologous chromosomes remain attched at the point of chiasma.
5. Diakinesis- The homologous chromosomes start to separate and synaptonemal complex disappears. The nuclear membrane also disappears.
What is the significance of meiosis?
Name the type of cell division observed in foetal cells and mega nucleus of
Paramecium.
In this stage of mitosis, the daughter chromosomes appear like bunch of bananas.
Due to mitosis the number of chromosomes in the cell ........... therefore the division occurs in ........... cell
If a back cell take $$20 $$ min to divide & if with this rate it take $$10 hrs$$ . To fill a cup of cells. What time it will take to fill it half?
Name the tissue whose cells divide throughout life
Give an account of somatic cell division.
Explain the process of meiosis - I
Calculate the total number of meiosis to produce $$100$$ seeds.
The term mitosis and meiosis are coined respectively by ________________ and __________.
What is the importance of Meiosis?
What is the importance of Mitosis ?
Mitosis occurs in?
Explanation:
Mitosis is the process of cell division where a haploid cell has the ability to divide and form two daughter cells.
In mitosis, the cell phases are interphase, prophase, metaphase, anaphase, and telophase.
Mitosis occurs in all types of cells that are somatic cells but doesn’t occur in gamete cells.
The number of meiosis to produce 35 wheat grains is:
What is Meiosis?
Explanation:
Meiosis is a process where the single cell divides twice to produce four cells.
It produces half the amount of genetic information from parental chromosomes.
There are two cell phases which are meiosis I and meiosis II.
Meiosis is an important process because it ensures that all organisms produced via sexual reproduction contain the correct number of chromosomes
Meiosis is important to bring genetic variation by way of the process of recombination.
It increases the survival chances.
Cytokinesis?
Explanation:
Cytokinesis is the process of the formation of two daughter cells by the division of the cytoplasm.
During cytokinesis, the cytoplasm splits.
It splits and forms two daughter cells.
In animal cells, the membrane of pasma of the parent cell is moved towards inside of cell along the cell's equator until two daughter cells form.
In the plant cells, along the equator of the parent cell, the cell plate is formed.
What would have been happened if any of the cells in nature had not been divided by meiosis?
Give brief account of somatic cell division.
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.
Distinguish between cytokinesis in plant and animal cell.
Mitosis usually results in the production of diploid daughter cells with identical genetic complement.
Cell division is the division of the cell into two daughter cells, it is an important process for the continuation of life. It is of two types:
- Mitosis (Equational division)
- Meiosis (Reductional division)
Mention the significance of mitosis.
Give significance of mitosis.
Answer in details.
With the help of suitable diagrams, explain the mitosis in detail.
With the help of suitable diagrams, explain the mitosis in detail.
Mitosis is the process of equational cell division where daughter cells, so produced, contain an equal number of chromosomes as that in the parent cell. The various stages of mitosis in an animal cell are as follows:
(i) Prophase: It is the first stage of mitosis that is marked by the initiation of the condensation of chromosomal material. Each chromosome is composed of two chromatids, which are attached by the centromere. At the end of prophase, the mitotic spindle begins to form from the centrioles. The nuclear membrane and the nucleolus disappear completely by the end of this stage.
(ii) Metaphase: It is the second stage of mitosis in which the condensation of the chromosomal material and the spindle formation gets complete. The spindle fibres get attached to the kinetochores of the chromosomes and the chromosomes get aligned along the metaphase plate
(iii) Anaphase: It is the stage of mitosis where the centromere of the chromosomes split and the chromatids get separated. The contraction of the spindle fibres moves the sister chromatid apart, towards the two opposite poles.
(iv) Telophase: It is the last stage of mitosis. In this stage, chromosomes finally reach their respective poles. The spindle fibres disappear and the nuclear envelope reappears around the chromosome cluster. Also, the nucleolus, Golgi complex, endoplasmic reticulum, and other cell organelles re-appear.
(i) Prophase: It is the first stage of mitosis that is marked by the initiation of the condensation of chromosomal material. Each chromosome is composed of two chromatids, which are attached by the centromere. At the end of prophase, the mitotic spindle begins to form from the centrioles. The nuclear membrane and the nucleolus disappear completely by the end of this stage.
(ii) Metaphase: It is the second stage of mitosis in which the condensation of the chromosomal material and the spindle formation gets complete. The spindle fibres get attached to the kinetochores of the chromosomes and the chromosomes get aligned along the metaphase plate
(iii) Anaphase: It is the stage of mitosis where the centromere of the chromosomes split and the chromatids get separated. The contraction of the spindle fibres moves the sister chromatid apart, towards the two opposite poles.
(iv) Telophase: It is the last stage of mitosis. In this stage, chromosomes finally reach their respective poles. The spindle fibres disappear and the nuclear envelope reappears around the chromosome cluster. Also, the nucleolus, Golgi complex, endoplasmic reticulum, and other cell organelles re-appear.
"First meiotic division (reduction or heterotypic division) " What does the word 'reduction' refer to in this statement?
Define Karyokinesis.
What do you understand by cell cycle?
Fill in the blank and explain the statement.
Genetic recombination occurs in ______ phase of prophase of meiosis-I.
Genetic recombination occurs in ______ phase of prophase of meiosis-I.
What is the importance of :
(a) Mitosis (b) Meiosis
At what stage does the meiosis occur in an organism exhibiting haploidic life cycle and mention the fate of the products thus produced.
Answer in details.
With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
Prophase I is the longest phase of meiosis and is further sub divided into 5 phases:
- Leptotene : Condensation makes chromosomes become distinct and compact.
- Zygotene : Homologous chromosome start pairing together by a process called synapsis to form a complex structure called synaptonemal complex. Two synapsed homologous chromosomes form a complex called bivalent or tetrad.
- Pachytene : Longest phase of prophase I
Recombination nodules appear in this stage at the sites where crossing over has to take place between non-sister chromatids of homologous chromosomes.
- Diplotene : Synaptonemal complex dissolves and recombinants separate from each other except at crossover sites to form X-shaped structure called chiasmata.
- Diakinesis : Chiasmata terminalises and chromosomes condense. Meiotic spindle assembles and nucleolus and nuclear envelope disappear.
Write the significance of Meiosis?
Why meiosis division is known as a reductional division?
Which part of the human body should one use to demonstrate stages in mitosis?
Describe Meiosis?
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?
Why does chromosomal number reduce to half in Meiosis?
What is Mitosis? Explain the different phases of mitosis division with a labelled diagram.
Mitosis: The term Mitosis was proposed by W. Fleming- It is a type of cell division during which a cell divides into two daughter cells. Each containing the similar and same number of chromosomes as present in the parent cell.
Interphase: During this phase doubling of DNA, synthesis of proteins and duplication of cellular organelles takes place. Interphase is the time between the end of telophase and the beginning of the next phase.
The process of mitosis is studied in two parts:
(1) Karyokinesis
(2) Cytokinesis.
(1) Karyokinesis: Division of the nucleus is called Karyokinesis. During this, many events take place.
$$*$$ Main stages are:
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
(a) Prophase: During prophase,
1. Chromosomes become very clear in the form of coiled threads.
2. Chromosomes shorten and become very thick.
3. The chromosomes are made of two identical filaments called chromatids. Both the chromatids of a chromosome are attached to a centromere,
4. The nuclear membrane and nucleolus dissolve away,
5. Spindle apparatus begins to form.
(b) Metaphase: All chromosomes arrange themselves on the equatorial plate.
(c) Anaphase: It is the third stage of nucleus division.
1.Each chromosome consists of two chromatids attached by centromere. The centromeres split. Separated chromatids are now called daughter chromosomes.
2. Daughter chromosomes move to the opposite poles, by the contraction of the spindle fibres.
(d) Telophase:
1. All the daughter chromosomes after reaching the poles uncoil and form the chromatin network.
2. The nuclear membrane is formed around the chromatin material.
3. Astral rays (animal cell) and spindle apparatus disintegrate.
4. Nucleus becomes very distinct and is known as the daughter nucleus,
5. Two daughter cells are formed.
(2) Cytokinesis: Division of the cytoplasm is known as Cytokinesis. After karyokinesis, the somatic cells divide by cell plate method. In a plant cell, minute cytoplasmic vesicles filled up with substances such as calcium and magnesium pectinate, are arranged in a line in the middle of the equatorial plane and divide the cytoplasm into two parts by progressing from middle to periphery. The cell wall is formed, due to a collection of cellulose on both sides of the plate.
A cleavage or furrow appears at the opposite cell membrane axes of the animal cell and deepens progressively, until the daughter cells separate.
Interphase: During this phase doubling of DNA, synthesis of proteins and duplication of cellular organelles takes place. Interphase is the time between the end of telophase and the beginning of the next phase.
The process of mitosis is studied in two parts:
(1) Karyokinesis
(2) Cytokinesis.
(1) Karyokinesis: Division of the nucleus is called Karyokinesis. During this, many events take place.
$$*$$ Main stages are:
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase
(a) Prophase: During prophase,
1. Chromosomes become very clear in the form of coiled threads.
2. Chromosomes shorten and become very thick.
3. The chromosomes are made of two identical filaments called chromatids. Both the chromatids of a chromosome are attached to a centromere,
4. The nuclear membrane and nucleolus dissolve away,
5. Spindle apparatus begins to form.
(b) Metaphase: All chromosomes arrange themselves on the equatorial plate.
(c) Anaphase: It is the third stage of nucleus division.
1.Each chromosome consists of two chromatids attached by centromere. The centromeres split. Separated chromatids are now called daughter chromosomes.
2. Daughter chromosomes move to the opposite poles, by the contraction of the spindle fibres.
(d) Telophase:
1. All the daughter chromosomes after reaching the poles uncoil and form the chromatin network.
2. The nuclear membrane is formed around the chromatin material.
3. Astral rays (animal cell) and spindle apparatus disintegrate.
4. Nucleus becomes very distinct and is known as the daughter nucleus,
5. Two daughter cells are formed.
(2) Cytokinesis: Division of the cytoplasm is known as Cytokinesis. After karyokinesis, the somatic cells divide by cell plate method. In a plant cell, minute cytoplasmic vesicles filled up with substances such as calcium and magnesium pectinate, are arranged in a line in the middle of the equatorial plane and divide the cytoplasm into two parts by progressing from middle to periphery. The cell wall is formed, due to a collection of cellulose on both sides of the plate.
A cleavage or furrow appears at the opposite cell membrane axes of the animal cell and deepens progressively, until the daughter cells separate.
Which tissue of animals and plants exhibits meiosis?
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?
If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?
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.
Synaptonemal complex
How many pollen tetrads will be formed by the meiotic division of 16 pollen mother cells?
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?
Short Answer.
With which type of reproduction do we associate the reduction division ? Analyse the reasons for it.
Comment on the statement - Telophase is reverse of prophase.
Following contrasting features of prophase and telophase show that telophase is reverse of prophase.
| Prophase | Telophase |
| (i) Mitochondria. ER. Golgi Complex, etc. disappear. | (i) Mitochondria. ER. Golgi Complex, etc. reappear. |
| (ii) Nuclear membrane disintegrates. | (ii) Nuclear membrane gets formed. |
| (iii) Chromosomes become clearly visible. | (iii) Chromosomes lose their visible identity. |
How many megaspores are formed from the meiotic division of one megaspore mother cells?
The amount of DNA per cell of a particular species is measured in cells found at various stages of meiosis, and the following amounts are obtained. Match the amounts of DNA on the left with the corresponding stages of the cell cycle on the right. You may use more than one stage for each amount of DNA.
Stage of Mitosis $$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;$$ Amount of DNA per cell
Stage of Mitosis $$\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;$$ Amount of DNA per cell
Describe the following : (a) Synapsis (b) Bivalent (c) ChiasmataDraw a diagram to illustrate your answer.
(a) Synapsis : The pairing of homologous chromosomes is called as synapsis. This occurs during the second stage of prophase I or zygotene.
(b) Bivalent : Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis.
(c) Chiasmata : Chiasmata is the site where two non-sister chromatids have crossed over. It represents the site of cross-over. It is formed during the diplotene stage of prophase I of meiosis.
(i) Draw a well-labelled diagram to show the anaphase stage of mitosis in a cell having four chromosomes.
(ii) State any two harmful effects of acid rain.
(iii) Expand the following biological abbreviations.
(1) NADP (2) ACT
(ii) Acid rain is caused by emissions of sulphur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. It corrodes buildings and metal structures. It also makes soil acidic which becomes unsuitable for cultivation.
(iii) (1) NADP: Nicotinamide Adenine Dinucleotide Phosphate. It acts as a cofactor in anabolic reaction.
(2) ACT: Adrenocorticotropin. It is a hormone which stimulates the production and release of cortisol from the cortex of the adrenal gland.
Here are some statements about meiosis. State whether each of them is true or false:
i) It takes place in somatic cells.
ii) Meiosis is also called reduction division.
iii) Pairing of homologous chromosomes is called crossing over.
iv) Meiosis leads to variations which form the raw material for evolution.
Write notes on significance of mitosis/ significance of meiosis ?
i) Draw a well-labelled diagram to show the metaphase stage of mitosis in an animal cell having four chromosomes.
ii) Mention any two reasons for the population explosion in India.
iii) Give biological reasons for the following.
1) The pituitary gland is also known as the master gland.
2) Gametes have a haploid number of chromosomes.
ii) The reason for population control is as followed
1. The desire for a male child.
2. Lack of awareness about birth control measures.
iii) 1. The pituitary gland secretes hormones that regulate all other endocrine glands so it is called the master gland.
2. Gametes are produced by meiosis in which the number of chromosomes gets reduced to half. So they are haploid. During fertilisation, the zygote has a diploid number of chromosomes.
2. Lack of awareness about birth control measures.
iii) 1. The pituitary gland secretes hormones that regulate all other endocrine glands so it is called the master gland.
2. Gametes are produced by meiosis in which the number of chromosomes gets reduced to half. So they are haploid. During fertilisation, the zygote has a diploid number of chromosomes.
Pick out the item which has sequential arrangements.
a) Zygotene $$\rightarrow$$ Leptotene $$\rightarrow$$ Pachytene $$\rightarrow$$ Diplotene $$\rightarrow$$ Diakinesis.
b) Diakinesis $$\rightarrow$$ Zygotene $$\rightarrow$$ Leptotene $$\rightarrow$$ Pachytene $$\rightarrow$$ Diplotene
c) Leptotene $$\rightarrow$$ Zygotene $$\rightarrow$$ Pachytene $$\rightarrow$$ Diplotene $$\rightarrow$$ Diakinesis.
"Gametes must be produced by meiosis for sexual reproduction". Why is it so?
Ascus, mycelium, basidium, mycorrhiza, budding, conidiospore, rhizomorph, stroma, fruiting body, sporangium, fungus, hypha, spore, lichen, zygospore, apothecium.
.......... Club like structure in which nuclear fusion and meiosis occur during sexual reproduction of club fungi.
A parenchymatous cell has 20 units of DNA. It starts to divide mitotically. How many units of DNA would it have
during anaphase, and
What would have happened if meiosis does not occur during the production of human sperm cell and egg cell?
Explain the mitosis in detail with the help of diagram.
- Mitotic division is also called somatic division or equational division.
- It occurs in two steps- karyokinesis ( nuclear division), cytokinesis (a division of cytoplasm).
- Four stages of karyokinesis are:-
- Longest phase
- Chromatin fibres condense to form elongated chromosomes.
- Centrosome divides and daughter centrosome begin to move away from each other.
- Chromosomes shorten, centrosomes develop asters and develop spindle fibres.
- Nucleolus degenerates and nuclear envelope breaks.
- Chromosomes are shortest and thickest at this stage.
- Each chromosome gets attached to 2 spindle fibres from each pole in the region of kinetochores.
- The kinetochore fibres contract and bring chromosomes over the equator.
- The apparent plate formed is called equatorial or metaphase plate.
- Shortest duration phase.
- Anaphase-promoting complex develops.
- It degenerates protein binding the 2 chromatids in the region of the centromere.
- As a result centromere of each chromosome divides.
- Chromosomes move to the poles with centromeres projecting towards the poles and limbs trailing behind.
- Stage of reconstitution of nuclei.
- Chromosomes uncoil, elongate, lose their stainability and form chromatin fibres.
- Nucleolar organisers form nucleoli in one or more pairs of chromosomes.
- Nucleoplasm and nuclear membrane appear forming 2 daughter nuclei.
- Cytokinesis:- It begins towards the middle of anaphase and completed simultaneously with completion of telophase.
- It brings the equitable distribution of cells organelles.
In which stage of Meiosis I does synapsis occurs?
Onion root tip cells have 16 chromosomes in each cell. How many chromosomes will the cell have at $$G_1$$ phase, after S phase, and after M phase?Also, what will be the DNA content of the cells at $$G_1$$, after S and at $$G_2$$, if the content after M phase is 2C?
State whether the following statement is true or false. A haploid parent produces gametes by mitotic division. Justify your answer.
Describe prophase-I of meiosis.
Give an account of prophase - 1 of meiosis.
The first phase of Meiosis is Prophase I. This phase is more complicated and prolonged as compared to the similar stage of mitosis.
Prophase I is divided into five sub-phases: leptotene, zygotene, pachytene, diplotene and diakinesis. Another sub-phase called pre-leptonema is sometimes recognized prior to leptonema. Chromosomes are not distinguishable because of their thinness. Sex chromosomes are often seen in heterochromatic bodies.
At the start of prophase I, the chromosomes have already duplicated. During prophase I, they coil and become shorter and thicker and visible under the light microscope.
The duplicated homologous chromosomes pair and crossing-over (the physical exchange of chromosome parts) occurs. Crossing-over is the process that can give rise to genetic recombination. At this point, each homologous chromosome pair is visible as a bivalent (tetrad), a tight grouping of two chromosomes, each consisting of two sister chromatids. The sites of crossing-over are seen as crisscrossed non-sister chromatids and are called chiasmata (singular: chiasma).
The nucleolus disappears during prophase I.
In the cytoplasm, the meiotic spindle, consisting of microtubules and other proteins, forms between the two pairs of centrioles as they migrate to opposite poles of the cell.
The nuclear envelope disappears at the end of prophase I, allowing the spindle to enter the nucleus.
Prophase I is the longest phase of meiosis, typically consuming 90% of the time for the two divisions.
What happen if meiosis does not occur in the organisms?
In what way does mitotic division help the living organism?
Name the process where cytoplasmic material is divided into daughter cells.
Describe meiosis. Draw labelled diagram of any two phases.
The term 'Meiosis' was proposed by Farmer and Moore. Meiosis is important for organisms which reproduce sexually. It is a special type of cell division, in which cell undergoes two successive divisions, producing four daughter cells, each containing half the number of chromosomes as compared to the parent cell.
The reduction takes place because the gametes are diploid (2n). They will produce a zygote after fertilisation, with double the number of diploid chromosomes (4n). To avoid this, reduction takes place and cell become haploid from diploid, before fertilisation. So, after the fusion of gametes, the zygote has 2n-diploid chromosome number. Meiosis involves two separate cell divisions, called Meiosis I and Meiosis II.
(1) Meiosis I:
Reductional division: Meiosis I results in a reduction of chromosomes to half with the formation of two haploid cells. It takes place in four phases, i.e., Prophase, Metaphase, Anaphase and Telophase.
$$*$$ Prophase-I. In this phase, the nucleus increases in size. Centrosome separates and moves toward the poles. Chromatin network converts into chromosomes. Chromosomes are present in the form of fine threads. Attraction occurs in homologous chromosomes which arrange in pairs. This is known as synapsis or pairing. The two non-sister homologous chromatids break apart (separate) at corresponding points, due to repulsion. They remain in contact with each other at many points, which are termed as chiasmata. By the formation of chiasmata a piece of a chromatid, bearing genes get transferred from one to another chromatid and vice versa. It is known as a crossover.
$$*$$ Metaphase I - Centrioles form the spindle apparatus. The pairs of homologous chromosomes arrange on the equatorial plate in such a way that centromeres are towards the poles, but their arms are towards mid-line.
$$*$$ Anaphase I - The two partners of homologous chromosomes completely separate from each other and start migrating towards the opposite poles of the spindle. In this way, two sets are formed. Each set is at a pole. Now, the number of chromosomes becomes haploid.
$$*$$ Telophase I - Nuclear membrane reappears. Thus, a nucleus is reformed at each pole. Nucleolus also again appears. The division of cytoplasm (cytokinesis) by cleavage, results in the two haploid daughter cells.
(2) Meiosis II: Equational Division: The two daughter cells then undergo Meiosis II which is exactly like mitosis. Meiosis II, is an equational division, resulting in four daughter cells with half the number of chromosomes.
$$*$$ This is also completed in two stages.
(A) Karyokinesis.
(B) Cytokinesis.
(A) Karyokinesis-
In this, four stages take place:
(i) Prophase II
(ii) Metaphase II
(iii) Anaphase II
(iv) Telophase II
(i) Prophase II - Two asters are formed, moving towards the opposite poles. Spindle fibres develop for chromosomes to get attached.
(ii) Metaphase II - Chromosomes get arranged on the equatorial plane for the sister chromatids to separate. Spindle fibres attach to the centromeres of the chromosomes at the kinetochores.
(iii) Anaphase II - Centromere of each chromosome splits, the two sister chromatids of the chromosome now separate and move towards opposite poles.
(iv) Telophase II - All of the four nuclei has one chromatid and each nucleus has a haploid number of chromosomes, as well as DNA, as compared to the parent cell.
(B) Cytokinesis-
The karyokinesis of the second meiotic division is followed by cytokinesis. Which results in division of the cytoplasm and formation of four daughter cells.
The reduction takes place because the gametes are diploid (2n). They will produce a zygote after fertilisation, with double the number of diploid chromosomes (4n). To avoid this, reduction takes place and cell become haploid from diploid, before fertilisation. So, after the fusion of gametes, the zygote has 2n-diploid chromosome number. Meiosis involves two separate cell divisions, called Meiosis I and Meiosis II.
(1) Meiosis I:
Reductional division: Meiosis I results in a reduction of chromosomes to half with the formation of two haploid cells. It takes place in four phases, i.e., Prophase, Metaphase, Anaphase and Telophase.
$$*$$ Prophase-I. In this phase, the nucleus increases in size. Centrosome separates and moves toward the poles. Chromatin network converts into chromosomes. Chromosomes are present in the form of fine threads. Attraction occurs in homologous chromosomes which arrange in pairs. This is known as synapsis or pairing. The two non-sister homologous chromatids break apart (separate) at corresponding points, due to repulsion. They remain in contact with each other at many points, which are termed as chiasmata. By the formation of chiasmata a piece of a chromatid, bearing genes get transferred from one to another chromatid and vice versa. It is known as a crossover.
$$*$$ Metaphase I - Centrioles form the spindle apparatus. The pairs of homologous chromosomes arrange on the equatorial plate in such a way that centromeres are towards the poles, but their arms are towards mid-line.
$$*$$ Anaphase I - The two partners of homologous chromosomes completely separate from each other and start migrating towards the opposite poles of the spindle. In this way, two sets are formed. Each set is at a pole. Now, the number of chromosomes becomes haploid.
$$*$$ Telophase I - Nuclear membrane reappears. Thus, a nucleus is reformed at each pole. Nucleolus also again appears. The division of cytoplasm (cytokinesis) by cleavage, results in the two haploid daughter cells.
(2) Meiosis II: Equational Division: The two daughter cells then undergo Meiosis II which is exactly like mitosis. Meiosis II, is an equational division, resulting in four daughter cells with half the number of chromosomes.
$$*$$ This is also completed in two stages.
(A) Karyokinesis.
(B) Cytokinesis.
(A) Karyokinesis-
In this, four stages take place:
(i) Prophase II
(ii) Metaphase II
(iii) Anaphase II
(iv) Telophase II
(i) Prophase II - Two asters are formed, moving towards the opposite poles. Spindle fibres develop for chromosomes to get attached.
(ii) Metaphase II - Chromosomes get arranged on the equatorial plane for the sister chromatids to separate. Spindle fibres attach to the centromeres of the chromosomes at the kinetochores.
(iii) Anaphase II - Centromere of each chromosome splits, the two sister chromatids of the chromosome now separate and move towards opposite poles.
(iv) Telophase II - All of the four nuclei has one chromatid and each nucleus has a haploid number of chromosomes, as well as DNA, as compared to the parent cell.
(B) Cytokinesis-
The karyokinesis of the second meiotic division is followed by cytokinesis. Which results in division of the cytoplasm and formation of four daughter cells.
Long Answer.
Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give a suitable explanation.
Gamete formation happens after meiosis. During the Pachytene stage of Prophase I in meiosis, crossing over takes place. Crossing over is an important steps of meiotic cell division. Non-sister chromatids of homologous chromosomes exchange genetic material during crossing over. This leads to recombination of various genes.
Secondly, during Anaphase I of Prophase I, the maternal and paternal chromosomes undergo independent assortment.
Thus,the daughter cells produced after meiosis has a different genotype compared to the mother cell.
In the context of above facts about meiosis, it is clear that the gametes do not have the same genetic composition as the parental genome.
Thus,the daughter cells produced after meiosis has a different genotype compared to the mother cell.
In the context of above facts about meiosis, it is clear that the gametes do not have the same genetic composition as the parental genome.
Difference
Karyokinesis and cytokinesis
2. Interphase and M-phase
Match the following column-A with column-B
| Column-A (phases) | Column-B (Their events) |
| a. Leptotene | Crossing over |
| b. Zygotene | Desynapsis |
| c. Pachytene | Synapsis |
| d. Diplotene | Bouquet stage |
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