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Frank ICSE Class 10 Biology Solutions – Structure of Chromosomes

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Frank ICSE Class 10 Biology Solutions – Structure of Chromosomes

PAGE NO-20:
Solution 1:
Chromatin is an extremely thin, long nuclear fibre occurring in the nucleus before cell division.

Solution 2:
In interphase, the chromatin appears as a network of long, extremely thin fibres.

Solution 3:
During prophase of mitosis, the chromatin fibres shorten and become thick to form chromosomes.
During metaphase, the chromosomes appear more distinct and clear and each consists of two parallel strands called chromatids joined by a centromere.

Solution 4:
Chromosomes are the thread like structures or chromatin material present inside the nucleus.
Chromosomes are so called because they take up certain basic dye and stain very rapidly. The word chromosome comes from two words “chromos” meaning colour and “soma” meaning body.

Solution 5:

  1. Strasburger – He observed thread like structures during cell division.
  2. Balbiani – Described rod like structures in nucleus before cell division.
  3. Waldeyer – Coined the term ‘chromosomes’.
  4. Sutton and Boveri – They described chromosomes as physical structures and transmitters of hereditary traits.

Solution 6:
Chromosomes are the thread like structures present in the nucleus of the cell. They are covered with a sheath made up of proteins and filled with granular matter called matrix. Inside the matrix, there are two threads called chromonemata.
The chromosome consists of two symmetrical strands called chromatids. Each chromosome consists of a distinct constriction called centromere which gets attached to the spindle network.
Frank ICSE Class 10 Biology Solutions - Structure of Chromosomes 1

Solution 7:

  1. Sheath – It is a proteinaeous covering present around the chromosomes.
  2. Matrix – It is a granular matter present inside the sheath.
  3. Chromonemata – They are the subunits of chromatids.
  4. Centromere – A constriction in the chromosome is called centromere.
  5. Secondary Constriction – A constriction other than primary constriction is called a secondary constriction.
  6. Telomere – The ends of the chromosomes is termed as telomere.

Solution 8:
Chromosomes are best observed at metaphase

Solution 9:
The chromosomes other than sex chromosomes present in the human body are called autosomes.
22 pairs of autosomes are present in man.

Solution 10:
The chromosomes which determine the sex of an individual are called sex chromosomes.

Solution 11:
Sex chromosomes are significant as they determine the sex of an individual.

Solution 12:
In man, there is a pair of sex chromosomes. In males, it is X and Y while in female, the sex chromosomes are X and X which are identical to each other.

Solution 13:
Chromosomes are the main source of chemical information which determines that the cell should become like its parent cell.

During the developmental stage they also determine that the cells of the organism will give the animal or the plant, the characteristic features of its species.

Solution 14:
DNA and RNA are the two nucleic acids.
Frederick Miescher discovered DNA

Solution 15:
Nucleic acids are made up of three types of molecules:

  1. a pentose sugar,
  2. nitrogenous bases
  3. a phosphate

Solution 16:
The chemical composition of chromosome consists of:

  1. Approximately 40% of DNA
  2. 50% of Histone proteins
  3. 8.5% Non histone proteins
  4. Metallic ions like magnesium and calcium in traces.

Solution 17:
Two nitrogenous bases present in DNA are:

  1. Purines – Adenine and Guanine.
  2. Pyrimidines – Cytosine and Thymine.

Solution 18:
Frank ICSE Class 10 Biology Solutions - Structure of Chromosomes 2

Solution 19:
Features of DNA:

  1. DNA consists of two strands which are spirally arranged around an axis. This is called a double helical arrangement.
  2. Each DNA strand is made up of nitrogenous bases, pentose sugar and phosphate.
  3. Sugars are pentose type; bases are adenine, guanine, cytosine and thymine.
  4. Both strands are connected with hydrogen bonds. There are two bonds between adenine and thymine and three bonds between guanine and cytosine.
  5. In the DNA, bases are inside and sugars are outside and two sugars are connected with phosphoric acid.
  6. Each DNA strand replicates and from each replicated DNA a new DNA is formed. This is called replication of DNA.

Solution 20:
Watson and Crick described the detailed structure of DNA.

Solution 21:
Importance of DNA:

  1. DNA is most important because it is the hereditary material.
  2. It acts as the director of protein synthesis.
  3. Some DNA of chromosomes forms nucleolus.
  4. DNA in presence of enzymes forms mRNA which acts as messenger.

Solution 22:
The rungs of “DNA ladder” are made up of two types of nitrogenous bases:

  1. Purines: Adenine and Guanine
  2. Pyrimidines: Cytosine and Thymine.

Solution 23:
Repeating components of each DNA strand length wise are pentose sugar and phosphate group

Solution 24:

  1. Interphase
  2. histone proteins
  3. RNA, DNA
  4. Protein
  5. Nitrogen

PAGE NO 21
Solution 25:

  1. False
  2. False
  3. True
  4. True

Solution 26:

  1. This diagram represents the structure of chromosome.
  2. ‘d’ is centromere which gets attached to the spindle fibres.
  3. ‘b’ is heterochromatin which is darkly stained region when stained with acetocarmine and ‘c’ is euchromatin which when stained with acetocarmine or felugen gets lightly stained.
  4. Waldeyer
  5. Matrix
  6. No, secondary constriction or ‘e’ is not present in all chromosomes.

Solution 27:

  1. (d) chromatin
  2. (c) Waldeyer
  3. (a) centromere
  4. (c) secondary constriction
  5. (a) interphase
  6. (d) prophase
  7. (a) DNA and histones
  8. (a) 46
  9. (a) I shaped
  10. (b) metacentric
  11. (c) XY
  12. (b) sex chromosomes
  13. (a) Watson and Crick
  14. (a) nitrogen base
  15. (c) Uracil
  16. (b) thymine
  17. (a) DNA

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Frank ICSE Class 10 Biology Solutions – Cell Division

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Frank ICSE Class 10 Biology Solutions – Cell Division

PAGE NO-11:
Solution 1:
Cell division is important for a variety of reasons. One reason is that cell division is important for the growth of an organism. It is also important for cells to divide so that they can remain efficient. As all the cells are produced by the division of pre-existing cells, so each organism needs new cells for growth, replacement, repair and reproduction.

Solution 2:
The cell cycle is a series of events that take place in a cell leading to its division and duplication

Solution 3:
Interphase is a long resting phase in the cell cycle during which the cell grows, multiplication of DNA, synthesis of RNA and proteins takes place. Thus interphase is important in the cell cycle as it allows the cell to grow and develop into a mature cell before it is able to reproduce.

Solution 4:
Meiosis results in the formation of ova.

Solution 5:
Frank ICSE Class 10 Biology Solutions - Cell Division 1

Solution 6:
In anaphase, the two chromatids separate at the centromere and begin to move in opposite direction towards either end of the spindle network called the poles. The chromosomes bend around the centromere showing a ‘V’ or ‘J’ or ‘L’ shaped structure based on the length of its arms.

Solution 7:
The different phases of mitosis are Prophase, Metaphase, Anaphase and Telophase.

Solution 8:
Mitosis takes place in the body cells or somatic cells of the organisms.

Solution 9:
Mitosis is important because:

  1. It helps in the growth of tissues, organs and thus the entire organism.
  2. It helps in the repair of damaged tissues and organs.
  3. It is the method by which lower organisms reproduce.
  4. It helps in the maintenance of the hereditary characters by the replication of chromosomes

Solution 10:
Some characteristic features of mitosis are:

  1. It takes place in somatic cells.
  2. Chromosome number is preserved.
  3. Daughter cells produced are identical to the parent cell.
  4. It results in increase in the number of cells.

Solution 11:
Few important characteristics of Meiosis are:

  1. Meiosis occurs in germ cells only.
  2. It results in the formation of gametes.
  3. Chromosome number of the parent cell is halved.
  4. Daughter cells differ from the parent cell.

Solution 12:
Frank ICSE Class 10 Biology Solutions - Cell Division 2

Solution 13:
In humans, meiosis occurs in testes producing sperms and in the ovaries resulting in ova.

Solution 14:
Significance of Meiosis:

  1. Due to meiosis, chromosome number is reduced to half in gametes and chromosome number of species is maintained.
  2. Genetic variations occur due to meiosis.
  3. The zygote on fertilization gets one maternal and one paternal chromosome in each homologous pair.

Solution 15:
Significance of Crossing over:

  1. As a result of crossing over, the paternal and maternal homologous chromosomes of an organism pair up and exchange certain portions of their chromatids which lead to genetic variations.
  2. It makes the genetic information in each haploid cell unique

Solution 16:
Frank ICSE Class 10 Biology Solutions - Cell Division 3

Solution 17:
No, cytokinesis is not necessary after karyokinesis in meiosis I. It generally takes place at the end of meiosis II when the four daughter cells are formed.

Solution 18:

  1. Karyokinesis – It is the nuclear division where nucleus divides into two.
  2. Cytokinesis – It is the division of cytoplasm in which the entire cell splits separating each nuclei.
  3. Chiasmata – is the point where two homologous non-sister chromatids exchange genetic material in chromosomal crossover during meiosis.

Solution 19:
In an animal cell, the cytoplasm between the two daughter nuclei constricts i.e. a furrow starts forming in the plasma membrane at the middle. This deepens towards the interior of the cell and the cytoplasm splits into two similar daughter cells.
In plant cells on the other hand, the constriction is not observed during cytokinesis. Instead a new cell wall is laid down along the equatorial region of the spindle network beginning at the centre. Thus, two distinct, daughter cells are cut off.

Solution 20:
Frank ICSE Class 10 Biology Solutions - Cell Division 4

Solution 21:
Meiosis is a reductional division as in meiosis the number of chromosomes of parent cell is reduced to half in the daughter cells. Now, this reductional division is significant because it restores the number of chromosomes in a species.

PAGE NO-12:
Solution 22:
Yes, meiosis is responsible for maintaining the chromosome number of a species as meiosis being a reductional division involves formation of daughter cells with half the number of chromosomes.

Solution 23:

  1. If four cells undergo mitosis, eight daughter cells will be produced.
  2. Sixteen daughter cells will be produced.
  3. Eight daughter cells will be produced if four cells undergo amitosis.

Solution 24:

  1. Mitosis
  2. ATP
  3. Homotypic
  4. Reduction
  5. Mitosis

Solution 25:

  1. Anaphase in a plant cell
  2. A – Spindle fibre
    B – Cell wall
  3. The homologous daughter chromatids or chromosomes begin to move towards opposite poles.
  4. This type of cell division occurs usually in the somatic cells.
  5. Two daughter cells are formed from this type of cell division.
  6. The dividing cell shown is a plant cell because of the presence of cell wall and the absence of centriole.

Solution 26:

  1. A – Duplicated chromosomes
    B – Centromere
  2. The structure C is Spindle fibre. Its function is to help in the movement of chromosomes.
  3. The type of cell division is mitosis because all chromosomes appear to be same as there is no crossing over.
  4. Metaphase.
  5. Prophase occurs before metaphase and after metaphase anaphase takes place

Solution 27:

  1. (c) Meiosis
  2. (a) Mitosis
  3. (c) Both of these
  4. (a) 1/2
  5. (b) Growth and repair
  6. (a) Movement of chromosomes
  7. (a) Meiosis
  8. (d) Both (a) and (c)
  9. (b) Chromatin
  10. (c) Both (a) and (b)
  11. (b) Metaphase
  12. (a) Meiosis I
  13. (d) One cell, two nuclei
  14. (a) Meiosis
  15. (d) Telophase
  16. (d) Prophase
  17. (c) Telophase

 

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