1. As you grow from childhood to adulthood, your skin cells divide only to replace such cells that are lost from the surface.
2. Cell cycle goes endlessly in every cell.
3. Genes are specific sequence of nucleotides that encode particular glucose.
4. DNA has a single helical structure.
5. If you have 46 DNA molecules in the nucleus of a cell, then the no. Of chromosomes in your cell is 23 pairs.
6. Unit of DNA is called a Nucleosome.
7. Chromatin Fibres has constitution of 40% DNA and 60% Histone proteins.
8. Centromere serves to attach to the spindle fibres during the cell division.
9. All cell division helps in reproduction.
10. G1 Phase is the longest phase of Interphase.
11. After G1 Phase, Cell have two choices. Either they can enter S Phase or G2 Phase.
12. G2 Phase is the shortest phase of Interphase.
13. Mitochondria and Chloroplast divides in the S Phase of Cell Cycle.
14. In G2 Phase, RNA and proteins necessary for cell division are synthesised.
15. After the replication of a DNA molecule, each daughter DNA molecules has two new strands.
16. DNA replication is semi-conservative in nature.
17. Karyokinesis is the process of division of nucleus which includes mitosis and cytokinesis.
18. Cytokinesis means division of Chloroplasts.
19. In between two nitrogenous bases, hydrogen bonds are present.
20. Cytosine combines with Guanine with three hydrogen bonds.
21. Adenine belongs to Pyrimidine base.
22. Every cell which undergoes G1 Phase, must undergo S Phase.
23. Interphase has five stages.
24. First Growth Phase is followed by Second Growth Phase.
25. In G1 Phase, RNA and proteins are synthesised and the volume of cytoplasm increases.
26. In Synthesis Phase, more DNA is synthesised.
27. Replacement of cell occurs in every part of body cells.
28. DNA is described as a micromolecular structure because it is a very large single molecule.
29. Adenine, Cytosine and Guanine belongs to Nitrogenous bases but Thymine do not belongs to Nitrogenous base.
30. Centromere can be present anywhere in the whole length of the chromosome.
Answers -
1. False. Cells also divides for the purpose of Growth and Repair.
2. False. At some places it stops permanently, at some places temporarily and at others till it is needed. Brain and other nerve cells, once formed in the embryo do not divide further. Once dead, they are not replaced. Liver cells may divide only once every one or two years to replace damaged or destroyed cells.
3. False. Genes encode particular proteins.
4. False. DNA has a double helical structure.
5. True. 23 pairs = 23 × 2 = 46 no. Of chromosomes.
6. False. Unit of DNA is Nucleotide.
7. True.
8. True.
9. False. Only the cell division occuring in gametes ( Meiosis ) helps in reproduction.
10. True.
11. False. After G1 Phase, the cell enters either "Resting phase" or "Synthesis (S) Phase".
12. True.
13. False. Mitochondria and Chloroplast divides in the "G1 Phase" of cell cycle.
14. True.
15. False. After the replication of DNA, each daughter molecule has one new strand and one old ( parental ) strand.
16. True.
17. False. Karyokinesis is the division of nucleus; but Mitosis includes Karyokinesis and Cytokinesis.
18. False. Cytokinesis means division of Cytoplasm.
19. True.
20. True.
21. False. Adenine is a Purine base
22. False. After G1 Phase, the cell may enter S Phase or may not enter it by entering into a Resting Phase.
23. False. Interphase has three phases, G1, S, and G2 Phase. ( More accurately it has four phases. A very short G0 phase is present after G2 Phase which you is not included in your syllabus ).
24. False. G1 Phase is followed by Synthesis (S) Phase.
25. True.
26. True.
27. False. Cells of the eye lens, nerve cells of the cerebral cortex and most muscle cells last a lifetime but once dead are not replaced.
28. False. DNA is a "Macromolecular" structure due to it's being a very large single molecule.
29. False. All the four bases Adenine, Guanine, Cytosine, and Thymine belongs to Nitrogenous base.
30. True.
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