Class 10 Cell Cycle, Cell Division and Structure of Chromosomes Mock Test (ICSE)

Topics in Cell Cycle, Cell Division and Structure of Chromosomes

• Structure of chromosomes: chromatin, chromatid, centromere, DNA and genes
• Cell cycle and interphase
• Stages of mitosis
• Meiosis and its significance
• Mitosis and meiosis compared

Cell Cycle, Cell Division and Structure of Chromosomes practice questions with answers

1. Q1Multiple choice·1 mark
   In which stage of mitosis do the chromosomes become shortest and thickest, and are most distinct?

   1. (a)Anaphase
   2. (b)Prophase
   3. (c)Metaphase
   4. (d)Telophase
   Show answer and step marks

   1. Correct option: (c) Metaphase+1

   Answer: (c)
2. Q2Multiple choice·1 mark
   Crossing over between non-sister chromatids of homologous chromosomes occurs during:

   1. (a)Prophase I
   2. (b)Metaphase I
   3. (c)Anaphase I
   4. (d)Prophase of mitosis
   Show answer and step marks

   1. Correct option: (a) Prophase I+1

   Answer: (a)
3. Q3Multiple choice·1 mark
   The point of attachment of two sister chromatids in a duplicated chromosome is called:

   1. (a)Centrosome
   2. (b)Chiasmata
   3. (c)Centromere
   4. (d)Chromomere
   Show answer and step marks

   1. Correct option: (c) Centromere+1

   Answer: (c)
4. Q4Multiple choice·1 mark
   During which phase of the cell cycle does DNA replication take place?

   1. (a)M phase
   2. (b)$G_1$ phase
   3. (c)$S$ phase
   4. (d)$G_2$ phase
   Show answer and step marks

   1. Correct option: (c) $S$ phase+1

   Answer: (c)
5. Q5Long answer·4 marks
   (a) Define a gene and state its exact location within the nucleus of a cell. [2] (b) Differentiate between chromatin and chromatid on the basis of: (i) state of condensation, and (ii) visibility under a light microscope during interphase versus cell division. [2]
   Show answer and step marks

   1. Definition of gene: A specific segment of DNA located on a chromosome that codes for a specific polypeptide or protein.+1
   2. Exact location: Located on chromosomes within the nucleoplasm of the nucleus.+1
   3. State of condensation: Chromatin consists of loosely coiled, extended DNA-histone threads, whereas a chromatid is a tightly coiled, highly condensed identical half of a replicated chromosome.+1
   4. Visibility: Chromatin is not visible as distinct individual structures under a light microscope during interphase; chromatids are clearly visible as distinct longitudinal strands during nuclear division stages like prophase and metaphase.+1

   Answer: (a) A gene is a segment of DNA on a chromosome that codes for a specific protein; it is located on the chromosomes inside the nucleus. (b) (i) Chromatin is loosely coiled, extended DNA-protein thread, while a chromatid is a tightly coiled, condensed half of a replicated chromosome. (ii) Chromatin is not seen as distinct threads during interphase (it appears as a network), while chromatids are clearly visible during cell division (prophase and metaphase).
6. Q6Long answer·4 marks
   (a) Define a gene and state its chemical nature. (b) Differentiate between chromatin and chromosomes on the basis of: (i) state of coiling, (ii) visibility under a light microscope. (c) State the precise function of the centromere during cell division.
   Show answer and step marks

   1. (a) Gene: a specific segment (sequence of nucleotides) of DNA on a chromosome that codes for a protein and determines a hereditary trait.+0.5
   2. (a) Chemical nature: a gene is made of DNA (deoxyribonucleic acid).+0.5
   3. (b)(i) Coiling: chromatin is a loosely coiled, extended thread-like network of DNA and protein, while chromosomes are tightly coiled, condensed, thick rod-like structures.+1
   4. (b)(ii) Visibility: chromatin appears only as a diffuse network during interphase, while chromosomes are clearly visible as distinct structures under a light microscope during cell division.+1
   5. (c) Centromere function: It holds the two sister chromatids together and serves as the primary site for the attachment of spindle fibres during cell division.+1

   Answer: (a) A gene is a segment of DNA on a chromosome that codes for a protein and determines a trait; chemically it is DNA. (b) (i) Chromatin is loosely coiled and extended, while chromosomes are tightly coiled and condensed. (ii) Chromatin appears as a diffuse network in interphase, while chromosomes are clearly visible during cell division. (c) It holds the sister chromatids together and is where spindle fibres attach.

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