Which of the following statements are correct about the cell theory of Schleiden and Schwann ?
(a) All living things are composed of one or more cells.
(b) New cells are formed from the pre-existing c

Question

Which of the following statements are correct about the cell theory of Schleiden and Schwann ?
(a) All living things are composed of one or more cells.
(b) New cells are formed from the pre-existing cells.
(c) There are basic similarities in chemical composition and metabolic functions of cells.
(d) The activity of an organism is collective activities and interactions of its cellular structures.
Answer options :

UnlockIAS · Accepted Answer

Correct — option (4), All of the above. The stem asks which of the printed statements are correct about the cell theory — the word 'correct' is emphasised in bold in the paper — and every one of the four is a proposition of that theory as it now stands. Statement (a) is its founding claim, put forward by Matthias Schleiden for plants in 1838 and extended to animals by Theodor Schwann in 1839: every living thing is composed of one or more cells, so the cell is the universal unit of life. Statement (b) states that new cells arise only from cells already in existence, the principle summed up in the Latin tag omnis cellula e cellula; it belongs to the theory as taught today, although the credit for establishing it goes to Rudolf Virchow in 1855 rather than to Schleiden and Schwann themselves, who had left the question of how new cells appear unresolved. Statements (c) and (d) are the two propositions usually listed as the modern extensions of the theory. Statement (c) records that cells are fundamentally alike in chemical composition and in the metabolic work they do — the same nucleic acids, proteins, sugars and lipids, and the same core reactions of energy release and biosynthesis in a bacterium as in a human liver cell — which is the biochemical unity that makes a single science of cells possible. Statement (d) records that the activity of a whole organism is the sum of the activities and the interactions of its cells, which is what makes the cell the functional as well as the structural unit and what justifies studying organs and organisms by studying the cells that compose them. With four correct statements and no exception among them, the inclusive option is the answer.

Why the other options are wrong — (a) Taking statements (a) and (b) alone gives the two classical propositions of the theory — that all living things are made of cells, and that cells come only from pre-existing cells — and stops there. That is a defensible summary of the theory in its nineteenth-century form, which is exactly why the choice is tempting, but it discards the two statements that carry the theory's modern content. Statements (c) and (d) are not optional additions: the chemical and metabolic similarity of cells and the derivation of an organism's activity from its cells are standard propositions of the theory as it is now stated, and the question asks which statements are correct rather than which two are the oldest.  (b) This takes statements (a), (b) and (c) and drops only statement (d), leaving out the proposition that the activity of an organism is the collective activity and interaction of its cells. That omission removes the functional half of the theory. The cell is described as the basic unit of both structure and function, and the second half of that formula is precisely what statement (d) expresses — it is why the behaviour of a tissue, an organ or a whole animal can be explained in terms of what its cells are doing, and why cell biology has explanatory reach beyond mere description of parts.  (c) This takes statements (a), (c) and (d) and drops statement (b) — the proposition that new cells arise from pre-existing cells. The likely reason a candidate would drop it is a good one historically: that principle was established by Rudolf Virchow in 1855, whereas Schleiden and Schwann had not solved the problem of how new cells form, and the stem names those two. But the stem asks which statements are correct about the cell theory, not which propositions the two men personally originated, and statement (b) is unquestionably a correct proposition of that theory — indeed the one that finally displaced the idea of spontaneous generation. Dropping a true statement on a question that asks for the correct ones leaves the answer incomplete.

Concept: Cell theory is the organising generalisation of biology, and it was assembled in stages. Robert Hooke gave the cell its name in 1665, describing the empty chambers he saw in a slice of cork, and Anton van Leeuwenhoek was the first to observe living single cells through his own lenses. The theory itself dates from the improvement of the microscope in the 1830s: Matthias Schleiden concluded in 1838 that all plant tissues are composed of cells, Theodor Schwann extended the conclusion to animals in 1839, and together they proposed that the cell is the elementary unit of all living things. Their formulation left one large gap, since neither could explain where new cells come from, and Schleiden's own suggestion of formation from a structureless matrix was mistaken; Rudolf Virchow closed the gap in 1855 with the principle that every cell arises from a pre-existing cell, which also disposed of spontaneous generation as an account of life's origin at that scale. The modern statement of the theory adds that cells are alike in chemical composition and metabolic activity, that they carry hereditary information passed on when they divide, and that the activity of an organism is the collective activity of its cells. The theory has one standing exception worth remembering: viruses are not cellular, and whether they count as living is disputed precisely because of it.

State PCS 2024 Q60 — Science & Technology PYQ with Answer

State PCS 2024 Q60 — Science & Technology PYQ with Answer