CBSE Class 11 Biology VBQs Cell Cycle

Question. The cellular structure which disappear during mitosis is
(a) plasma membrane
(b) spindle apparatus
(c) mitochondria
(d) nuclear membrane and nucleolus.

Answer : D

Question. Select the stage that begins with the simultaneous splitting of centromere of each chromosome.
(a) D
(b) A
(c) B
(d) C

Answer : A

Question. In which stage of cell division, the chromosomes are most condensed?
(a) Prophase
(b) Metaphase
(c) Anaphase
(d) Telophase

Answer : B

Question. Which of the following statements is true about mitosis?
(a) Daughter cells exhibit division of labour i.e., perform different functions.
(b) Daughter cells are exactly similar in all respects.
(c) Daughter cells have half the number of chromosomes as compared to mother cell.
(d) Daughter cells have differences in genetic characters.

Answer : B

Question. Select the correct statement with respect to mitosis.
(a) Chromatids separate but remain in the centre of the cell in anaphase.
(b) Chromatids start moving towards opposite poles in telophase.
(c) Golgi complex and endoplasmic reticulum are still visible at the end of prophase.
(d) Chromosomes move to the spindle equator and get aligned along equatorial plate in metaphase.

Answer : D

Question. Two sister chromatids are attached with
(a) spindle fibre
(b) chromocentre
(c) centromere
(d) chromatid.

Answer : C

Question. Division of centromere occurs in
(a) late prophase or early metaphase
(b) late metaphase or early anaphase
(c) late anaphase or early telophase
(d) late telophase.

Answer : B

Question. Genetic recombination consequent to crossing over is a significant feature of
(a) pachytene
(b) zygotene
(c) leptotene
(d) diplotene.

Answer : A

Question. Interphase is the period in which the cell
(a) has stopped all its metabolic activities
(b) is metabolically inactive but grows in size
(c) has kept up metabolic activities but not dividing
(d) is set to divide by stopping other metabolic activities.

Answer : C

Question. Synthesisor replication of DNA in interphase takes place in phase
(a) G1
(b) S
(c) G2
(d) M.

Answer : B

Question. Mitosis is the process by which eukaryotic cells
(a) grow
(b) expose genes for protein synthesis
(c) multiply
(d) become specialised in structure and function.

Answer : C

Question. In the somatic cell cycle
(a) DNA content in G1 phase is double the amount of DNA content in the original cell
(b) DNA replication takes place in S phase
(c) a short interphase is followed by a long mitotic phase
(d) G2 phase follows mitotic phase.

Answer : B

Question. At which stage of the cell cycle, histone proteins are synthesised in a eukaryotic cell?
(a) During Go phase
(b) During S-phase
(c) During entire prophase
(d) During telophase

Answer : B

Question. Mitotic phases are alphabetically arranged and numbered as follows :
Anaphase-1, Metaphase-2, Prophase-3 and Telophase-4
The correct sequence of occurrence in cell division is
(a) 1, 2, 3 and 4
(b) 3, 2, 1 and 4
(c) 4, 3, 2 and 1
(d) 2, 1, 4 and 3.

Answer : B

Question. Colchicine acts as a mitotic poison by
(a) causing fragmentation and agglutination of chromosomes
(b) inducing breakage at centromeric position of chromosomes
(c) inhibiting formation of mitotic spindle
(d) all of these.

Answer : C

Question. A study is done on a mammalian cell line that has a doubling of 24 hours. These cells are synchronised in G1 and then labelled for 2 days with BrdU (an analog of thymidine that increases the density of DNA into which it is incorporated). At the end of labelling period, chromosomal DNA is isolated from the cells and its density was analysed. Which of the patterns would be expected to be seen? (H = Heavy, L = Light).
(a) 100% H/H
(b) 100% H/L
(c) 50% H/H, 50% H/L
(d) 50% H/H, 50% L/L

Answer : C

Question. Enzyme responsible for fixing crossed over parts of non-sister chromatids is
(a) lipase
(b) enterokinase
(c) recombinase
(d) endonuclease.

Answer : C

Question. Homologous pair of chromosomes resemble each other except in the case of
(a) shape and size
(b) number of genes on them
(c) alleles on the same loci
(d) all of these.

Answer : C

Question. The stage of meiosis where centromere divides for the first and the only time, ensuring separation of daughter chromosomes, occur in
(a) anaphase- II
(b) telophase- I
(c) anaphase- I
(d) telophase- II.

Answer : A

Case Based Question

Study the figures given below and answer the questions.

Question. Identify the labelled figures A and B.
(a) Metaphase and Metaphase I
(b) Metaphase I and Anaphase I
(c) Metaphase II and Anaphase II
(d) Anaphase I and Anaphase II

Answer : B

Question. Which type of spindle is shown in the given cell?
(a) Anastral
(b) Amphiastral
(c) Both of these
(d) None of these

Answer : B

Question. Which of the following does not occur in anaphase-I but occurs in anaphase-II?
(a) Condensation of chromosomes
(b) Poleward movement of chromosomes
(c) Contraction of spindle fibres
(d) Splitting of centromere.

Answer : D

Question. Identify the meiotic stage in which the homologous chromosomes separate while the sister chromatids remain associated at their centromeres.
(a) A
(b) C
(c) B
(d) D

Answer : C

Assertion Reason

For question numbers 51-60, two statements are given-one labelled Assertion and the other labelled Reason.
Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Question. Assertion : Meiotic division results in the production of four dissimilar cells.
Reason : Synapsis occurs during zygotene of meiosis.

Answer : B

Question. Assertion : Meiosis II is similar to mitosis.
Reason : Meiosis I cannot occur in haploid cells.

Answer : B

Question. Assertion : Bivalents are formed during pachynema.
Reason : Bivalent and tetrad conditions of chromosomes are two different conditions.

Answer : C

Question. Assertion : Sexual reproduction always needs meiosis.
Reason : Gametes involved in sexual reproduction are always haploid.

Answer : A

Question. Assertion : Mitosis occurs in both unicellular and multicellular organisms.
Reason : Mitosis is a method of sexual reproduction in unicellular organisms.

Answer : C

Very Short Answer Type Questions

Question. Name the sub-stages of prophase of meiosis.

Answer. The various sub-stages of prophase occurs in meiosis are leptotene, zygotene, pachytene, diplotene and diakinesis.

Question. If a tissue has 1024 cell at a given time, how many cycles of mitosis had the original parental single cell undergone?

Answer. 10 (2n, where n = 10 generations).

Question. What happens during anaphase-I of meiosis?

Answer. During anaphase-I, homologous chromosomes separates from each other.

Question. Can there be mitosis without DNA replication in S-phase?

Answer. Mitosis cannot occurs without DNA replication in S-phase because the trigger for mitosis takes place due to the disturbance in nucleocytoplasmic ratio caused by DNA replication in S-phase.

Question. What does a bivalent of meiosis-I consists of ?

Answer. Bivalent of meiosis-I consists of four chromatids and two centromeres.

Short Answer Type Questions

Question. A cell having 32 chromosomes, undergoes mitotic divisions. What will be the chromosome number (n) during metaphase? What would be the DNA content (C) during anaphase?

Answer. The number of chromosome during metaphase will be 32. Also, the DNA content during anaphase will be same as in the parent cell.

Question. 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. Meiosis is reductional division which ensures production of haploid phase in life cycle of sexually reproducing organisms, but fertilisation restores the diploid phase, thus, enables conservation of specific chromosome number, e.g., gametes produced by 2n parents are haploid (n), but the zygote is diploid.

Question. Describe cell division. List various types of cell division. Also mention about the need of cell division.

Answer. Cell division, or cell multiplication is the process of formation of new daughter cell from the pre-existing cell or parent cell. It is of three types : (i) Amitosis (ii) Mitosis (iii) Meiosis. Cell division maintains continuity of living matter generation after generation.

Question. Give a specific scientific term for each of the following.
(i) The period between meiosis I and meiosis II.
(ii) Point at which two sister chromatids are held together.
(iii) Phase in the cell cycle when protein and RNA are synthesised.
(iv) Mitotic poison that does not allow the formation of spindle.

Answer. (i) Interkinesis (ii) Centromere (iii) G1-phase (iv) Colchicine

Question. Why is mitosis called equational division?

Answer. Mitosis is called an equational division because it divides the mother cell into two daughter cells, which are identical to each other and also to the original mother cell in every respect. In mitosis, the chromosomes of the mother cell are duplicated and distributed equally to the two daughter cells.

Question. The following statements describe the four main stages in the process of mitosis.
(i) The spindle fibres breakdown and the nuclear membrane forms.
(ii) The chromosomes arrange themselves on the equator of the cell.
(iii) The spindle forms and the nuclear membrane disintegrates.
(iv) The centromere splits and the sister chromatids migrate to the opposite poles of the cell.
Write the correct sequence of the stages in mitosis and also name the each stage.

Answer. III (prophase) → II (metaphse) → IV (anaphase) → I (telophase)

Question. The second meiotic division is similar to mitosis as it results in the separation of the sister chromatids. However, it also differs from mitosis. Explain how?

Answer. Though meiosis II is similar to mitosis, meiosis II is not mitosis because (i) it always occurs in haploid cells, (ii) it is not preceded by DNA replication, (iii) the two chromatids of a chromosome are often dissimilar, (iv) the daughter cells formed after meiosis II are neither similar to each other nor similar to the parent cell.

Question. Name three phases of interphase. Give one major event of each phase.

Answer. Three phases of interphase are G1-phase (post-mitotic or pre-synthetic phase), S-phase (synthesising phase) and G2-phase (post-synthetic or pre-mitotic phase). Major event of each phase is as follows : (i) G1-phase is the longest phase during which synthesis of RNA and DNA takes place. (ii) S-phase is the phase during which chromosomes replicate and prepare themselves for equal distribution. (iii) G2-phase is the phase in which synthesis of DNA gets stopped. However, formation of RNA takes place.

Long Answer Type Questions

Question. Briefly describe the significance of cell division.

Answer.  Cell division is significant in the following ways :
(i) Cell multiplication : Cell division is a means of cell multiplication or formation of new cells from pre-existing cells.
(ii) Continuity : It maintains continuity of living matter generation after generation.
(iii) Multicellular organisms : The body of a multicellular organism is formed of innumerable cells. They are formed by repeated divisions of a single cell or zygote. As the number of cells increases, many of them begin to differentiate, form tissues and organs.
(iv) Cell size : Cell division helps in maintenance of a particular cell size which is essential for efficiency and control of cell activities.
(v) Genetic similarity : The common type of cell division or mitosis maintains genetic similarity of all the cell in an individual despite being different structurally and functionally.

Question. Explain why a pair of homologous chromosomes are genetically different, but a pair of sister chromatids are genetically identical before crossing over in meiosis.

Answer. A pair of homologous chromosomes are genetically different because in a set of homologous chromosomes, one of the chromosome belongs to the male parent and the other come from the female parent. Therefore, one of a pair will contain paternal genes and the other will contain maternal genes. However, a pair of sister chromatids are genetically identical before crossing over as the chromatids are formed from the replication of DNA during the ‘S’ phase of interphase. DNA replication ensures that the DNA content is doubled with identical genes being copied from the original DNA. Therefore, there is no genetic variation because there is no exchange of genetic material between sister chromatids. If crossing over occurs, then it would be possible for some genes to be exchanged between the chromatids of homologous chromosomes that have chiasmata, thus leading to genetic variation.

Questions. A girl chased lizard. Due to fear lizard released its tail due to fear . Tail again grows after some time. Which kind of division is involved probably in this process? Whether this division is present in Human beings if yes then where .

Answer. Mitosis. This division is present in human beings in somatic cell.

Questions. A child ask her teacher that I am not similar to my sister. Though both of us are born from same parents why ? What could be the possible answer of teacher ?

Answer. Reason is meiosis is involved and there is recombination of gametes

Questions. Why we are not similar to our previous generations. What is the reason behind this change

Answer. Meiosis and recombination.