DIFFERENCES FROM PAST PAPERS (1998 & 99)

6. Isotopes & Isobars

Isotopes:
These are the elements having same atomic number but different mass number. They have the same atomic number because the number of protons inside their nuclei remains the same. The difference in their mass number is due to the difference in their number of neutrons.


Isobars
Where Isotopes are chemically the same and physically different, the converse is true in Isobars. That is isobars are elements, which are chemically different but physically the same. So, isobars are atoms of different elements having the same atomic mass but different atomic number. Since their number of electrons is different, their chemical properties are different. The light nuclei have unstable isobars. Heavy nuclei have stable isobars and these occur in pairs. Suppose the number of protons of one isobar matches with that of another they are called as mirror-nuclides of each other.

7. Autopsy & Biopsy

Autopsy:
i) An autopsy is the dissection and analysis of a dead subject.
ii) , autopsies are limited to the deceased and there are two kinds of autopsy; External examination and internal examination.
iii) Autopsy is performed for medico-legal purpose.

Biopsy:
i) A biopsy is a medical test in which cells, tissue, or fluid is removed for examination.
ii) Biopsy is not limited to only living people because they are routinely taken from organs that are going to be used for transplantation.
iii) Autopsy is performed for diagnosis purpose.

8. Mitosis & Meiosis

Mitosis:
i) Mitosis takes place within somatic cells (cells that make up the body).
ii) One single division of the mother cell results in two daughter cells.
iii) A mitotic mother cell can either be haploid or diploid.
iv) The number of chromosomes per nucleus remains the same after division.
v) It is preceded by a S-phase in which the amount of DNA is duplicated.
vi) In mitosis, there is no pairing of homologous chromosomes.
vii) There is no exchange of DNA (crossing-over) between chromosomes.
viii) The centromeres split during anaphase.
ix) The genotype of the daughter cells is identical to that of the mother cells.
x) After mitosis, each daughter cell has exactly same DNA strands.

Meiosis:
i) Meiosis takes place within gamete cells (sex cells).
ii) Two divisions of the mother cell result in four meiotic products or haploid gametes.
iii) A meiotic mother cell is always diploid.
iv) The meiotic products contain a haploid (n) number of chromosomes in contrast to the (2n) number of chromosomes in mother cell.
v) In meiosis, only meiosis I is preceded by a S-phase.
vi) During prophase I, complete pairing of all homologous chromosomes takes place.
vii) There is at least one crossing-over or DNA exchange per homologous pair of chromosomes.
viii) The centromeres do separate during anaphase II, but not during anaphase I.
ix) Meiotic products differ in their genotype from the mother cell.
x) After meiosis, each daughter cell has only half of the DNA strands.

9. Hard water & Heavy Water

Hard Water:
i) Hard water is that type of water which does not form lather easily.
ii) Its formula is H2O.
iii) Hard water is not used in nuclear power plants.

Heavy Water:
i) Heavy water is deuterium oxide in which hydrogen of water is replaced by its heavier isotope, Deuterium.
ii) The formula of heavy water is D2O.
iii) Heavy water is used in nuclear power plants.

10. Climate & Weather

Climate:
i) Climate is the normal weather conditions for an area during a season or a year.
ii) Climate of an area is described by means of an average means of an average of the statistics of the various weather factors over a period of time, normally 30-years.

Weather:
i) Weather is the condition of the atmosphere at any one place and time.
ii) Weather is described by air, temperature and humidity, wind speed and direction, cloud amount and precipitation, sunshine and visibility.