CDS (I) 2021 General Knowledge · Question 104 of 120

Correct — C, 1 and 2 only. The word 'fission' means splitting, and it is used in two different sciences with the same core sense. Statement 1 gives the biological use: in single-celled organisms such as Amoeba and Paramecium the parent cell divides into two daughter cells in binary fission, and in the malarial parasite one cell breaks into many in multiple fission — new individuals produced by division of the cell. Statement 2 gives the nuclear use: a heavy nucleus such as uranium-235 splits into lighter nuclei with a release of energy, which is what powers a reactor and the uranium bomb. Statement 3 describes the opposite process. Building a heavier nucleus by combining lighter ones is fusion, the reaction that runs the Sun and the hydrogen bomb, and calling it fission inverts the meaning of the word.

• (a)1 only — Accepts the biological sense and rejects the nuclear one, but statement 2 is a plain description of nuclear fission — a heavy nucleus breaking into smaller ones.
• (b)2 only — Treats fission as a purely nuclear word. Binary fission and multiple fission are standard terms in biology for reproduction in unicellular organisms, so statement 1 stands.
• (d)1 and 3 only — Keeps the true first statement but swaps the true second for the false third. Combining nuclei to build a heavier one is fusion, and picking this option means accepting fusion under the name of fission.

Fission is splitting and fusion is joining. In biology, binary fission is the asexual reproduction of a single-celled organism by division into two, and multiple fission divides one cell into many at once. In physics, nuclear fission splits a heavy nucleus into lighter fragments, releasing energy because the fragments are more tightly bound; nuclear fusion joins light nuclei into a heavier one and releases energy for the same underlying reason at the other end of the mass scale.

This is a vocabulary item wearing a science costume. Statements 1 and 2 both hinge on splitting, and statement 3 is the mirror image, so a candidate who fixes on the meaning of the word can grade all three without recalling any specific reaction. One printed detail is worth pointing out because it changes nothing but reads oddly: statement 3 says a heavier nucleus is created 'by means of combining two higher nuclei', where the sense plainly requires lighter nuclei. The slip is the paper's own. It does not rescue the statement — under either reading, joining nuclei together is fusion.

• Binary fission divides a unicellular organism into two daughter cells; Amoeba and Paramecium are the standard examples.
• Multiple fission divides one parent cell into many daughters at once, as in the malarial parasite.
• Nuclear fission splits a heavy nucleus such as uranium-235 into lighter nuclei, releasing energy — the process used in a nuclear reactor.
• Nuclear fusion joins light nuclei into a heavier one and is the source of the Sun's energy and of the hydrogen bomb.
• The energy released in both comes from a loss of mass, related to the energy by E = mc².

• Treating fission as a nuclear-physics word alone and rejecting the biological statement.
• Accepting a statement about combining nuclei because it appears under the heading of fission.
• Confusing binary fission with mitosis; mitosis is nuclear division, binary fission is reproduction of the whole organism.

As a multi-statement item that mixes the biological and the nuclear sense of one term, with the opposite process slipped in as the false statement.

• practice — not a real PYQ

  Multiple fission, in which a single parent cell divides into many daughter cells at once, is seen in

  • (a)Amoeba
  • (b)Plasmodium
  • (c)Hydra
  • (d)Planaria

  Answer(b) Plasmodium — the malarial parasite multiplies inside the host by dividing into many daughter cells at a time, while Amoeba divides into two.

• practice — not a real PYQ

  The energy of the Sun is produced mainly by

  • (a)nuclear fission of uranium
  • (b)nuclear fusion of hydrogen nuclei
  • (c)chemical burning of hydrogen
  • (d)radioactive decay of thorium

  Answer(b) nuclear fusion of hydrogen nuclei — light nuclei join to form helium, and the small loss of mass appears as the energy the Sun radiates.