Frank Solutions for Chapter 2 Structure of Chromosomes Class 10 Biology ICSE
Exercises
1. What is chromatin?
Answer
Answer
Chromatin is an extremely thin, long nuclear fibre occurring in the nucleus before cell division.
2. How is chromatin observed in an interphase cell?
Answer
In interphase, the chromatin appears as a network of long, extremely thin fibres.
3. What happens to chromatin during prophase and metaphase of mitosis?
Answer
Answer
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.
During metaphase, the chromosomes appear more distinct and clear and each consists of two parallel strands called chromatids joined by a centromere.
4. What are chromosomes? Why are they called so?
Answer
Answer
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 color and “soma” meaning body.
Chromosomes are so called because they take up certain basic dye and stain very rapidly. The word chromosome comes from two words “chromos” meaning color and “soma” meaning body.
5. Mention the contribution of the scientists given below in the study of chromosomes:
(i) Strasburger
(ii) Balbiani
(iii) Waldeyer
(iv) Sutton and Boveri
Answer
(i) Strasburger
(ii) Balbiani
(iii) Waldeyer
(iv) Sutton and Boveri
Answer
(i) Strasburger – He observed thread like structures during cell division.
(ii) Balbiani – Described rod like structures in nucleus before cell division.
(ii) Balbiani – Described rod like structures in nucleus before cell division.
(iii) Waldeyer – Coined the term ‘chromosomes’.
(iv) Sutton and Boveri – They described chromosomes as physical structures and transmitters of hereditary traits.
(iv) Sutton and Boveri – They described chromosomes as physical structures and transmitters of hereditary traits.
6. Briefly mention the structure of a typical chromosome.
Answer
Answer
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.
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.
7. Write a sentence about each of the following:
(i) Sheath
(ii) Matrix
(iii) Chromonemata
(iii) Centromere
(v) Secondary constriction
(iv) Telomere
Answer
(i) Sheath
(ii) Matrix
(iii) Chromonemata
(iii) Centromere
(v) Secondary constriction
(iv) Telomere
Answer
(i) Sheath – It is a proteinaeous covering present around the chromosomes.
(ii) Matrix – It is a granular matter present inside the sheath.
(iii) Chromonemata – They are the subunits of chromatids.
(iv) Centromere – A constriction in the chromosome is called centromere.
(v) Secondary Constriction – A constriction other than primary constriction is called a secondary constriction.
(vi) Telomere – The ends of the chromosomes is termed as telomere.
(ii) Matrix – It is a granular matter present inside the sheath.
(iii) Chromonemata – They are the subunits of chromatids.
(iv) Centromere – A constriction in the chromosome is called centromere.
(v) Secondary Constriction – A constriction other than primary constriction is called a secondary constriction.
(vi) Telomere – The ends of the chromosomes is termed as telomere.
8. At which stage are chromosomes best observed?
Answer
Answer
Chromosomes are best observed at metaphase
9. What are autosomes? How many are present in man?
Answer
Answer
The chromosomes other than sex chromosomes present in the human body are called autosomes.
22 pairs of autosomes are present in man.
22 pairs of autosomes are present in man.
10. What do you understand by sex chromosomes?
Answer
Answer
The chromosomes which determine the sex of an individual are called sex chromosomes.
11. How are sex chromosomes significant?
Answer
Answer
Sex chromosomes are significant as they determine the sex of an individual.
12. What are the sex chromosomes in man?
Answer
Answer
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.
chromosomes are X and X which are identical to each other.
13. Give the importance of chromosomes as hereditary material.
Answer
Answer
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.
14. Name the two nucleic acids. Who discovered them?
Answer
Answer
- DNA and RNA are the two nucleic acids.
- Frederick Miescher discovered DNA
15. What are nucleic acids made of?
Answer
Nucleic acids are made up of three types of molecules:
- a pentose sugar,
- nitrogenous bases
- a phosphate
16. What are the chemical composition of chromosome?
Answer
The chemical composition of chromosome consists of:
- Approximately 40% of DNA
- 50% of Histone proteins
- 8.5% Non histone proteins
- Metallic ions like magnesium and calcium in traces.
17. Mention the names of the nitrogen bases present in DNA.
Answer
Answer
Two nitrogenous bases present in DNA are:
- Purines – Adenine and Guanine.
- Pyrimidines – Cytosine and Thymine.
18. Difference between DNA and RNA.
Answer
|
DNA |
RNA |
|
1. The sugar present in DNA molecule is deoxyribose. |
1. The sugar present in RNA molecule is ribose. |
|
2. DNA is double stranded molecule. |
2. RNA is single stranded molecule. |
|
3. The four bases found in DNA are- Adenine, Guanine, Cytosine and Thymine. |
3. In RNA, in place of thymine another nitrogenous base called uracil is present. |
19. Write a short note on features of DNA.
Answer
Answer
Features of DNA:
- DNA consists of two strands which are spirally arranged around an axis. This is called a double helical arrangement.
- Each DNA strand is made up of nitrogenous bases, pentose sugar and phosphate.
- Sugars are pentose type; bases are adenine, guanine, cytosine and thymine.
- Both strands are connected with hydrogen bonds. There are two bonds between adenine and thymine and three bonds between guanine and cytosine.
- In the DNA, bases are inside and sugars are outside and two sugars are connected with phosphoric acid.
- Each DNA strand replicates and from each replicated DNA a new DNA is formed. This is called replication of DNA.
20. Who described the detailed structure of DNA?
Answer
Watson and Crick described the detailed structure of DNA.
Watson and Crick described the detailed structure of DNA.
21. What is the importance of DNA?
Answer
Importance of DNA:
Importance of DNA:
- DNA is most important because it is the hereditary material.
- It acts as the director of protein synthesis.
- Some DNA of chromosomes forms nucleolus.
- DNA in presence of enzymes forms mRNA which acts as messenger.
22. What are the rungs of the "DNA ladder" made of?
Answer
Answer
The rungs of “DNA ladder” are made up of two types of nitrogenous bases:
- Purines: Adenine and Guanine
- Pyrimidines: Cytosine and Thymine.
23. Name the repeating components of each DNA strand lengthwise.
Answer
Answer
Repeating components of each DNA strand length wise are pentose sugar and phosphate group.
24. Fill in the blanks:
(i) DNA replicates in the ______ of the cell cycle.
(ii) Chromatin fibre is made up of DNA and ______.
(iii) There are two nucleic acids ______ and ______.
(iv) DNA acts as director of ______ synthesis.
(v) DNA stands are made up of, pentose sugar and four types of ______ bases.
(i) DNA replicates in the ______ of the cell cycle.
(ii) Chromatin fibre is made up of DNA and ______.
(iii) There are two nucleic acids ______ and ______.
(iv) DNA acts as director of ______ synthesis.
(v) DNA stands are made up of, pentose sugar and four types of ______ bases.
Answer
(i) Interphase
(ii) histone proteins
(iii) RNA, DNA
(iv) Protein
(v) Nitrogen
(ii) histone proteins
(iii) RNA, DNA
(iv) Protein
(v) Nitrogen
25. State whether the following sentences are true or false:
(i) Each spiral of the DNA has 12 nucleotides.
(ii) The two DNA chains are parallel to each other.
(iii) Genes are arranged in a linear order on a chromosome.
(iv) In any specimen of DNA, the total molar amount of A + G = T+ C.
Answer
(i) Each spiral of the DNA has 12 nucleotides.
(ii) The two DNA chains are parallel to each other.
(iii) Genes are arranged in a linear order on a chromosome.
(iv) In any specimen of DNA, the total molar amount of A + G = T+ C.
Answer
(i) False
(ii) False
(iii) True
(iv) True
(ii) False
(iii) True
(iv) True
26. Label the lettered parts of the given figure and answer the following questions:
(i) What does this diagram represent?
(ii) What is the importance of 'd'?
(iii) What are the 'staining' properties of 'b' and 'c'?
(iv) Who gave the term used for this structure today?
(v) What is a?
(vi) Is 'e' present in all chromosomes?
(i) What does this diagram represent?
(ii) What is the importance of 'd'?
(iii) What are the 'staining' properties of 'b' and 'c'?
(iv) Who gave the term used for this structure today?
(v) What is a?
(vi) Is 'e' present in all chromosomes?
Answer
(i) This diagram represents the structure of chromosome.
(ii) ‘d’ is centromere which gets attached to the spindle fibres.
(iii) ‘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.
(iv) Waldeyer
(v) Matrix
(vi) No, secondary constriction or ‘e’ is not present in all chromosomes.
(ii) ‘d’ is centromere which gets attached to the spindle fibres.
(iii) ‘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.
(iv) Waldeyer
(v) Matrix
(vi) No, secondary constriction or ‘e’ is not present in all chromosomes.
27. Choose the correct answer:
(i) The network of fine threads in nucleus is called
(a) chromosome
(a) chromosome
(b) chromonemata
(c) chromatid
(d) chromatin
Answer
(d) chromatin
(d) chromatin
(ii) The term 'chromosome' was coined by
(a) Balbiani
(a) Balbiani
(b) Darwin
(c) Waldeyer
(d) Sutton and Boveri
Answer
(c) Waldeyer
(iii) The primary constriction contains
(a) centromere
(a) centromere
(b) centriole
(c) chromatid
(d) telomere
Answer
(a) centromere
(iv) This structure is not present in all chromosomes
(a) centromere
(b) chromonemata
(c) secondary constriction
(d) telomere
(a) centromere
(b) chromonemata
(c) secondary constriction
(d) telomere
Answer
(c) secondary constriction
(v) Chromosomes are thin and thread like at
(a) interphase
(a) interphase
(b) metaphase
(c) anaphase
(d) pachytene
Answer
(a) interphase
(vi) Thick short chromosomes can be observed at (in mitosis)
(a) metaphase
(a) metaphase
(b) telophase
(c) anaphase
(d) prophase
Answer
(d) prophase
(vii) Chromosomes largely consist of
(a) DNA and histones
(b) DNA and RNA
(c) RNA and histones
(d) histones and ions
(a) DNA and histones
(b) DNA and RNA
(c) RNA and histones
(d) histones and ions
Answer
(a) DNA and histones
(viii) Chromosome number of man is
(a) 46
(b) 23
(c) 64
(d) 45
(a) 46
(b) 23
(c) 64
(d) 45
Answer
(a) 46
(ix) Telocentric chromosomes are
(a) I shaped
(a) I shaped
(b) V shaped
(c) J shaped
(d) L shaped
Answer
(a) I shaped
(x) A 'V' shaped chromosomes has to
(a) acrocentric
(b) metacentric
(c) telocentric
(d) sub-metacentric
(a) acrocentric
(b) metacentric
(c) telocentric
(d) sub-metacentric
Answer
(b) metacentric
(xi) Sex chromosomes in man are
(a) XX
(a) XX
(b) YY
(c) XY
(d) none of these
Answer
(c) XY
(xii) Sex of an individual is determined by
(a) autosomes
(b) sex chromosomes
(c) lampbrush
(d) polytene chromosomes
(a) autosomes
(b) sex chromosomes
(c) lampbrush
(d) polytene chromosomes
Answer
(b) sex chromosomes
(xiii) DNA model was given by
(a) Watson and Crick
(b) Sutton and Boveri
(c) Balbiani and Darwin
(d) Waldeyer and Carlson
(a) Watson and Crick
(b) Sutton and Boveri
(c) Balbiani and Darwin
(d) Waldeyer and Carlson
Answer
(a) Watson and Crick
(xiv) Adenine is a
(a) nitrogen base
(b) pentose sugar
(c) fatty acid
(d) enzyme
(a) nitrogen base
(b) pentose sugar
(c) fatty acid
(d) enzyme
Answer
(a) nitrogen base
(xv) Which of these is not present in DNA?
(a) Adenine
(a) Adenine
(b) Thymine
(c) Uracil
(d) Cytosine
Answer
(c) Uracil
(xvi) RNA has uracil instead of
(a) adenine
(a) adenine
(b) thymine
(c) guanine
(d) cytosine
Answer
(b) thymine
(xvii) Spirally coiled double strands are observed in
(a) DNA
(a) DNA
(b) chromosome
(c) RNA
(d) chromatin
Answer
(a) DNA