Cell Cycle and Cell Division Class 11 Biology Exam Questions

Please refer to Cell Cycle and Cell Division Class 11 Biology Exam Questions provided below. These questions and answers for Class 11 Biology have been designed based on the past trend of questions and important topics in your class 11 Biology books. You should go through all Class 11 Biology Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 11 Biology Exam Questions Cell Cycle and Cell Division

Class 11 Biology students should read and understand the important questions and answers provided below for Cell Cycle and Cell Division which will help them to understand all important and difficult topics.

Very Short Answer Type Questions:

Question. Name a stain commonly used to colour chromosomes.
Ans. Acetocarmine and Giemsa stain can be used to stain the chromosomes.

Question. 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?
Ans. If a cell takes 24 hours to divide, it will have 18- 20 hours time to spend on interphase stage to prepare itself to undergo cell division.

Question. Between a prokaryote and a eukaryote, which cell has a shorter cell division time?
Ans. Prokaryotic cell has shorter cell cycle than the eukaryotic cell.

Question. Which tissue of animals and plants exhibits meiosis?
Ans. Meiosis is a special kind of cell division, also called as reduction division, which occurs in germ cells or sex cells of male and female reproductive organs of plants and animals. They

Question. Which part of the human body should one use to demonstrate stages in mitosis?
Ans. All the cells in the human body are somatic cells except germinal cells in the male and female reproductive organs. The somatic cells divide by mitotic cell division for growth
and regeneration.These can be used to demonstrate mitosis.

Question. What attributes does a chromatid require to be classified as a chromosome?
Ans. Chromatid is one copy of a duplicated chromosome, which is joined to the other copy centromere. The duplication of chromosome material takes place at synthetic phase of cell cycle.
During mitosis, late metaphase and early anaphase, there is longitudinal splitting of chromosomes and thus two chromosome get separated, to get divided into the daughter cells.

Question. At what stage of cell cycle does DNA synthesis take place?
Ans. Synthetic phase or S-phase of interphase, is the stage of cell cycle where DNA synthesis or replication takes place.

Question. If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?
Ans. The parental cell undergoes 10 divisions of mitotic cycle to give 1024 cells.

Question. 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 (a) Zygotene, (b) Pachytene,
(c) Pachytene, (d) Diakinesis,
(e) After Telophase-I/before prophase of meosis-II,
(f) Telophase-I/after meiosis-I.
Ans. (a) Synaptonemal complex zygotene.
(b) Recombination nodules pachytene.
(c) Appearance/activation of enzyme recombinase telophase-I/after, meiosis-I … .
(d) Termination of chiasmata diakinesis.
(e) Interkinesis after telophase-I/before prophase of meiosis-II.
(f) Formation of dyad of cells pachytene.

Question. An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them?
Ans. Three hundred pollen mother cells have to be there to produce 1200 pollen grains.
because one pollen mother cell will produce four pollen grains.

Question. 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.
Ans. It is observed that heart cells do not exhibit cell division. Such cells do not divide further and exit G₁ phase to enter an inactive stage called quiescent stage (G₀) of cell cycle.
Muscle cells when reach a level of maturity, no longer divide and just perform their function all through its life. Similar is the case with nerve cells too which are highly specific and lack the ability to divide once they get specialised. They remain in that state until they die.

Question. Which of the phases of cell cycle is of longest duration?
Ans. Interphase is of the longest duration. It has following events and is divided in the following phases
(a) G₁ phase (Gap 1) Corresponds to the interval between mitosis and initiation of DNA replication. Cell is metabolically active and continuously grows but does not replicate its DNA.
(b) S-phase (Synthesis phase) Marks the period during which DNA synthesis or replication takes place.
(i) Amount of DNA per cell doubles.
(ii) No increase in chromosome number.
(c) G₂ Phase (Gap 2) Proteins are synthesised for the preparation of cell division, while cell growth continues.

Question. 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?
Ans. 1 hour -20 minutes

These are the 4 subsequent cell divisions to produce 16 cells and each division takes =20 min
Total time = 20 × 4 = 80minutes or 1 hr 20 minutes
So, 1 cell produces 16 cells in 1 hour 20 minutes and
2 cells produces 32 cells in 1 hour 20 minutes.

Question. The diagram shows a bivalent at prophase-I of meiosis. Which of the four chromatids can cross over?

Ans. The homologous chromosomes lie parallel to each other in leptotene stage. Each chromosome has four chromatids and are bivalent. The non-sister chromatids of homologous chromosomes cross over in pachytene stage of prophase- I.

Short Answer Type Questions:

Question. Label the diagram and also determine the stage at which this structure is visible.

Ans. The diagram shows the transition stage between prophase and metaphase stage of mitotic cell division.

Question. Both unicellular and multicellular organisms undergo mitosis. What are the differences, if any, observed in the process between the two?
Ans. In unicellular organisms, the type of cell division is known as amitosis in which somatic cell is divided into two parts directly. In multicellular organisms occurs which is an indirect process.
Both cell division in unicellular and multicellular organisms undergo mitosis have differences as below

Question. Name the pathological condition when uncontrolled cell division occurs.
Ans. Cancer is the pathological condition in which the cells loose control over cell division and this results into malformation of the organ in which such cell division occurs.

Question. 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?
Ans. The mitotic cell division occurs in somatic cells of an organism. The chromosome number in the daughter cells remain same as that of the parent (dividing) cell, so even at metaphase or anaphase, the chromosome number does not change.
The DNA content gets doubled at the synthetic phase of interphase and gets divided at anaphase but the chromosome number remains same.

Question. 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 ……… .
Ans. (a) Prophase (b) Telophase
(c) Anaphase (d) S-phase

Question. State the role of centrioles other than spindle formation.
Ans. The two centrioles in the centrosome lie perpendicular to each other. Each has organisation like a cart wheel. These form the basal body of cilia and flagella of plant/animal cells besides forming spindle fibre in animal cell division. It also helps in the formation of microtubuless and sperm tail.

Question. Mitochondria and plastids have their own DNA (genetic material). What is known about their fate during nuclear division like mitosis?
Ans. The DNA present in mitochondria and chloroplast is extrachromosomal DNA. It has nothing to do with the nuclear divisions. In mitosis, only nuclear DNA takes part.

Question. 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
Ans. (a) If nuclear membrane fails to disintegrate, the spindle fibres would not be able to reach chromosomes and they would not move towards opposite poles of the cell. In certain
protozoans, such as Amoeba, the spindle is formed within the nucleus and this is called intranuclear mitosis or pre-mitosis.
(b) If DNA duplication does not occur than cell might not be able to surposs S-phase of cell-cycle as no chromosome formation will take place, and will not be able to enter M-(mitotic phase) or if in case it enters mitosis the cycle will cease,
(c) If the centromeres do not divide,one of the daughter cell will receive a complete pair of chromosomes and other cell would not get any of them. This may result in trisomy.
(d) If cytokinesis does not occur, then multinucleate condition called coenocyte, syncytium is produced, as in Rhizopus and Vaucheria, etc.

Question. Two key events take place, during S-phase in animal cells, DNA replication and duplication of centriole. In which parts of the cell there events occur?
Ans. DNA replication takes place in nucleus and duplication of centriole occurs in the cytoplasm. Centriole forms spindle fibres during cell division in animal cells which direct the movement of chromosomes within the cell. The position of centriole determines the position of the nucleus and plays a crucial role in the spatial arrangement of the cell.

Question. 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?
Ans. Such a condition may arise in case of a mosaic or mosaicism, which denotes preserve of two or more populations of cells with different genotypes in one individual.
It can result from various mechanisms including non-disjunction, anaphase lagging and endoreplication. It may also result from a mutation during development which is propagated to only a subset of the adult cells.
In this case, cells with 16 chromosomes could have arisen from cells with 32 chromosomes.

Question. Name a cell that is found arrested in diplotene stage for months and years. Comment in 2-3 lines how it completes cell cycle?
Ans. Meiotic arrest at diplotene stage commonly occurs in mammalian occytes. In females, meiosis starts in the embryo and proceeds as for as diplotene, when the chromosomes become diffused and the cells are referred to as being in the dictuate stage. This arrest is under hormonal control.
In many amphibian oocytes binds and insects with a long period of immaturity, the oocyte may be arrested in the dictyate stage for many years and spend a prolonged period in diplotene.
This stage is characterised by formation of lampbrush chromosomes where intense RNA synthesis occurs and most of the genes in the DNA loops are actively transcribed and expressed.

Question. Comment on the statement-meiosis enables the conservation of specific chromosome number of each species even through the process per se results in reduction of chromosome number.
Ans. Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms. Even though the process results in reduction of chromosome number by half, it is gradually conserved by union of male gamete (n) and female gamete (n) in next generation.
Meiosis also increases the genetic variability in the population of organisms from one generation to the next.

Question. How does cytokinesis in plant cells differ from that in animal cells?
Ans. Difference between cytokinesis in plant cell and animal cell is as follows

Long Answer Type Questions:

Question. Differentiate between the events of mitosis and meiosis.
Ans. Mitotic cell division results into the increase in the number of cells that have same genetic composition whereas meiosis has its importance in the life cycle of sexually reproducing
organisms.

Question. Comment on the statement- Telophase is reverse of prophase.
Ans. The following contrasting differences reveals that telophase is reverse of prophase, in cell division

Question. Write briefly the significance of mitosis and meiosis in multicellular organism.
Ans. Multicellular organisms grow and develop with the involvement of mitotic cell division.
Meiosis occurs in them to form gametes in their reproductive phase of life cycle.
Significance of Mitosis
(i) Multicellular plants and animals start life as single cells. The process of mitosis gives rise to many cells which differentiate to form tissues, organs and organ-systems of the organism.
(ii) It results in increase in size and growth of an organ.
(iii) Cell reproduction is used to form new cells to renew certain tissues and to replace worn out cells.
(iv) Mitosis is also involved in asexual reproduction in some organisms like in unicellular.
Amoeba and multicellular Hydra as well as in vegetative reproduction in plants.
Significance of Meiosis
(i) Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms.
(ii) Meiosis also increases the genetic variability in the population of organisms from one generation to the next. Variations are very important for the process of evolution.

Question. An organism has two pair of chromosomes (i.e., chromosome number= 4).
Diagrammatically represent the chromosomal arrangement during different phases of meiosis-II. 

Question. What are the various stages of meiotic prophase-I? Enumerate the chromosomal events during each stage?
Ans. Prophase-I occurs over a long duration and involves several complicated changes in meiotic cell division. It is important because genetic recombination and variation in sexually reproducing organism occurs due to the events of this phase.
Leptotene
(i) The chromatin network opens out and threads become clear.
(ii) The chromosomes are thin, slender and long.
(iii) Chromosome number is diploid.

Zygotene
(i) Corresponding chromosomes become intimately associated.
(ii) The process of pairing is known as synapse. It is so exact that pairing is not merely between corresponding chromosomes but between corresponding individual units.
(iii) The chromosomes become shorter and thicker.

Pachytene or Pachynema
(i) The synaptic chromosomes become very intimately associated.
(ii) The pair of chromosomes becomes short and thick.
(iii) Crossing over occurs at this stage. Chiasmata are clearly seen.

Diplotene
(i) Homologous chromosomes start separating from one another.
(ii) Chiasmata tend to slip out of the chromosomes. This is known as terminalisation of chiasmata.
(iii) Chromosomes start separating out but the separation is not complete.
(iv) Nuclear membrane and nucleolus start disappearing.

Diakinesis
(i) The bivalents condense further and get randomly distributed.
(ii) The separation of paired chromosomes is almost complete.
(iii) Terminalisation of chiasmata is almost complete.
(iv) Nuclear membrane and nucleolus disappear.

Question. Write brief note on the following
(a) Synaptonemal complex
(b) Metaphase plate
Ans. (a) Synaptonemal complexes are zipper-structures which are assembled between homologous chromosomes during the prophase of the first meiosis. Their asssembly and disassembly correlate with the successive chromatin rearrangements of meiotic prophase namely the condensation, pouring, recombination and dysfunction of homologous chromosomes.
They are considered to be the structures that control the number and distribution of reciprocal exchanges between homolgous chromosomes. They also are known to convert cross over into functional chiasmata .
(b) In metaphase, the centromeres of the chromosomes assemble themselves on the metaphase plate (equatorial plate), an imaginary line that is equidistant from two centrosome poles. This even alignment is due to the opposing kinetochore microtubules. At this plate, chromosomers, especially sister chromatids are attached to the bundle of four to eight spindle fibres.