Note

If you cannot find what you are looking for. Please visit our sitemap

Thursday, 31 March 2016

FSc Notes Biology Part 2 Chapter 21 Cell Cycle Short Questions

FSc Notes Biology Part 2 Chapter 21 Cell Cycle Short Questions


Q 1. Define cell cycle?
Ans.
The cell under goes a sequence of changes, which involve period of growth, replication of DNA followed by cell division. This sequence of changes is called cell cycle.

Q 2. How much time is required for cell cycle in case of human?
Ans.
In the case of human cell, average cell cycle is about 24 hours.

Q 3. What does you know about chromatin?
Ans.
Chromatin is a network of very fine threads which can be visualized but using histologic stains of DNA.

Q 4. In higher plants instead of visible centriole what is present?
Ans.
Higher plants lack visible centrioles, instead they have its analogous region from which the spindle microtubules radiate.

Q 5. What is metastasis?
Ans.
The cell composing a malignant tumor or cancer, divide more rapidly, mostly invade surrounding tissues, get into the body circulatory system, and set up areas of proliferation, away from their site of original appearance. This spread of tumor cells and establishment of secondary areas of growth is called metastasis.

Q 6. When in plants and animals the meiosis takes place?
Ans.
Meiosis takes place in diploid cells only, in animals at the time of gamete formation, while in plants when spores are produced.

Q 7. Define crossing over?
Ans.
It is the exchange of segments between non-sister chromatids of homologous chromosomes due to chiasmata formation.

Q 8. What are the two significant happenings of meiosis?
Ans.
Crossing over and random assortment of chromosomes are two significant happening of meiosis.

Q 9. How many chromosomes do occur in male affected by Klinefelter's syndrome?
Ans.
Males with 48 chromosomes (44 autosomes + XXXY), with 49 chromosomes (44 autosomes + XXXXY) and male with 47 chromosomes (44 autosomes + XYY) are also observed.

Q 10. What are symptoms of Turner's syndrome?
Ans.
The affected individuals have one missing X chromosome with only 45 chromosomes (44 autosomes + Y). Individuals have female appearance with short stature, webbed neck, without ovaries and complete absence of germ cells.

Q 11. What is apoptosis?
Ans.
Internal programme of events and sequence of morphological changes by which cell commits suicide is collectively called apoptosis (Greek word that means dropping off or falling off).

Q 12. Name the different stages of interphase?
Ans.
Interphase can further e divided into G1-phase, S-phase and G2-phase.

Q 13. What is G1-phase?
Ans.
G1 (Gap 1) is the period of extensive metabolic activity, in which cell normally grows in size, specific enzymes, are synthesized and DNA base units are accumulated for the DNA synthesis.

Q 14. What is G0?
Ans.
Post-mitotic cell can exit the cell cycle during G1 entering phase called G0, and remain for days, weeks, or in some cases even the life time of the organism without proliferation further.

Q 15. What is S-phase of cell cycle?
Ans.
Following the G1 is the S-phase (synthesis phase) during which the DNA is synthesized and chromosomes number doubled.

Q 16. What happens in G2-phase (pre-mitotic phase)?
Ans.
In G2 phase (pre-mitotic phase) the cell prepares for division i.e., energy storage for chromosome movements, mitosis specific proteins, RNA and microtubule subunits (for spindle fibres) synthesis are accomplished.

Q 17. Define mitosis?
Ans.
It is the type of cell division, which ensures the same number of chromosomes in the  daughter cells as that in the parent cells.

Q 18. What are two conventional phases of Mitosis?
Ans.
Conventional phases of Mitosis
  1. Karyokinesis, which involves the division of nucleus.
  2. Cytokinesis that refers to the division of the whole cell.

Q 19. What is Mitotic apparatus?
Ans.
The specialized micro-tubule structure including aster and spindle is called mitotic apparatus.

Q 20. Name the microtubules which originate from centrioles?
Ans.
Three sets of microtubules (fibres) originate from each pair of centrioles ie.e, astral microtubules, kinetochore microtubules and polar microtubules.

Q 21. What events occur in Prophase of mitosis?
Ans.
Each chromosome is visible having two sister chromatids, attached at centromere. Towards the end of prophase nuclear envelope disappears and nuclear material is released in the cytoplasm, nucleoli disappear. Mitotic apparatus is organized. Cytoplasm becomes more viscous.

Q 22. What is kinetochore?
Ans.
The centromere has special area the kinetochore, with specific base arrangement and special proteins where kinetochore fibres of mitotic apparatus attach.

Q 23. What happens in Telophase of mitosis?
Ans.
The chromosomes decondense, due to unfolding, ultimately disappear as chromatin. Mitotic apparatus disorganize, nuclear membrane and nucleoli reorganize, forming two nuclei  at two poles of the cell.

Q 24. What is Phragmoplast?
Ans.
At cytokinesis, in plants, a membrane structure called phragmoplast is formed from vesicles of Golgi complex. These vesicles line up in the centre of the dividing cell, where they fuse to form phragmoplast at the end of telophase.

Q 25. Define cancer?
Ans.
Any malignant growth or tumour from an abnormal and uncontrolled division of body cells is known as cancer.

Q 26. What is Tumour?
Ans.
When such cells produce new cells which continue to proliferation in uncontrolled fashion, an unwanted clone of cells, called Tumour is formed, which can expand un-definitely.

Q 27. What are two basic types of tumour?
Ans.
Basic types of tumour
  • Benign tumours.
  • Malignant tumours.

Q 28. What is benign tumours?
Ans.
Benign tumours are of small size and localized (not transferred to other parts) called Benign. The cells in this type usually behave like the normal cells and have little deleterious (harmful) effects.

Q 29. What is malignant tumour?
Ans.
The cells composing a malignant tumour or cancer, divide more rapidly, mostly invade surrounding tissues, get into the body's circulatory system, and set up areas of proliferation, away from their site of original appearance.

Q 30. How can you distinguish cancer cells from normal cells?
Ans.
Cancer cells can be distinguished from normal cells because they are less differentiated than normal cells, exhibit the characteristics of rapidly growing cells, that is, high nucleus to cytoplasm ratio, prominent nucleoli and many mitosis.

Q 31. What main causes of cancer?
Ans.
Cancer is caused mainly by mutations in somatic cells. The cancer results from the accumulation of as few as three to as many as twenty mutations, in genes that regulate cell division.

Q 32. Define meiosis?
Ans.
Meiosis is the special type of cell division in which the number of chromosomes in daughter cells reduces to half, as compared to the parent cell.

Q 33. How prophase of meiosis differs from that of mitosis?
Ans.
This is very prolonged phase, and differs from the prophase of mitosis, because in this chromosomes behave as homologous pairs. Each diploid cell has two chromosomes of each type, one member from each parent.

Q 34. What are homologous chromosomes?
Ans.
The chromosomes which are similar but not necessarily identical are called as homologous chromosomes.

Q 35. Name the sub-stages of prophase I of meiosis?
Ans.
Leptotene, zygotene, diplotene and diakinesis.

Q 36. What is synapsis?
Ans. The pairing of homologous chromosomes during zygotene stage is called synapsis.

Q 37. What is bivalent or tetard?
Ans.
Each paired but not fused, complex structure of homologous chromosomes is called as bivalent or tetard.

Q 38. What is the duration of Pachytene, leptotene and zygotene?
Ans.
Pachytene may lasts for days, weeks or even years, whereas leptotene and zygotene can last only for few hours.

Q 39. What is chiasmata?
Ans.
The paired homologous chromosomes repel each other and begin to separate but still remain united by their point of interchange which is called chiasmata.

Q 40. What happens in Diakinesis?
Ans.
The condensation of chromosomes reaches to its maximum. At the same time separation of the homologous chromosomes is completed, but still they are united at one point, more oftenly at ends, Nucleoli disappear.

Q 41. What events occur in metaphase I of meiosis?
Ans.
Nuclear membrane disorganize at the beginning of this phase. Spindle fibres originate and the kinetochore fibres attached to the kinetochore o homologous chromosome from each pole and arrange bivalents at the equator.

Q 42. How does anaphase I of meiosis differs from that of mitosis?
Ans.
In anaphase I of meiosis the sister chromatids are not separated, only homologous chromosomes get separated. while anaphase of mitosis the sister chromatids are separated.

Q 43. How meiosis maintains chromosome number constant generation after generation?
Ans. Meiosis usually takes place at the time of sexual cells (gamete) formation, (spore formation in plants) thus reducing the number of chromosomes to half in each, which is restored after fertilization and maintains chromosome number constant generation after generation.

Q 44. Define non-disjunction?
Ans.
In non-disjunction chromosomes fail to segregate during Anaphase and Telophase and do not finish with equal distribution of chromosome among all the daughter nuclei. This results either increase (or decrease) in the number of chromosomes, causing serious physical, social and mental disorders.

Q 45. What is autosomal non-disjunction?
Ans.
The non-disjunction in which autosomal chromosomes fail to segregate is called autosomal non-disjunction.

Q 46. What is Downs Syndrome (Mongolism)?
Ans.
It occurs, in man, during which 21st chromosome fails to segregate, resulting gamete with 24 chromosomes. This gamete fertilizes normal gamete the new individual will have 47 (2n + 1) chromosomes.

Q 47. Does Downs syndrome is related to the age of mother?
Ans.
Yes, the chances of teenage mother having downs syndrome child is one in many thousands, forty years old mother one in hundred chance and by forty-five the risk is three times greater.

Q 48. What are apparent symptoms or effects of Downs syndrome?
Ans.
The affected individuals have flat, broad face, squint eyes with the skin fold in the inner corner, and protruding tongue, mental retardation and defective development of central nervous system.

Q 49. What is sex chromosomal non-disjunction?
Ans.
The non-disjunction in which sex chromosomes fails to segregate is called sex chromosomal non-disjunction.

Q 50. What is Necrosis?
Ans.
The cell death due to tissue damage is called necrosis, during which the typical cell swells and bursts, releasing the intracellular contents, which can damage neighboring cells and cause inflammation.

Written by: Usman Rashid & Asad Hussain

1 comment: