Q.Which of the following is not correct?

The statement that is not correct is (a) — "Robert Brown discovered the cell."

• Robert Brown did not discover the cell; his contribution was the discovery of the nucleus inside the cell. The first person to see and describe a living cell was Antonie von Leeuwenhoek.
• Statement (b) is correct: Schleiden (studying plants) and Schwann (studying animals) together framed the cell theory.
• Statement (c) is correct: Virchow explained that every cell arises from a pre-existing cell (Omnis cellula-e cellula).
• Statement (d) is correct: a single-celled organism is able to carry out all its life activities on its own within one cell.

This question tests how well the milestones in the study of the cell are remembered, so it helps to place each name against what that scientist actually contributed.

Our knowledge of the cell grew hand in hand with the tools used to look at it. Antonie von Leeuwenhoek was the first to see and describe a living cell. Later, Robert Brown examined cells and identified the dense, membrane-bound body sitting inside them — the nucleus. So Brown's name belongs to the nucleus, not to the cell as a whole, which makes statement (a) the incorrect one.

The remaining options are all sound:

• (b) The cell theory was not the work of one person. Matthias Schleiden studied many plants and concluded that all plants are built from cells, while Theodore Schwann examined animal cells and recognised that cells are bounded by a thin outer plasma membrane. Working together, the two formulated the cell theory.
• (c) Schleiden and Schwann's version had a gap — it did not explain how new cells arise. Rudolf Virchow filled this by showing that cells divide and that every cell comes from a pre-existing cell, giving the theory its final form.
• (d) A unicellular organism is a complete cell that leads an independent existence and performs all the essential functions of life by itself, which is exactly why the cell is called the fundamental unit of life.

Method: Elimination by Matching Each Name to Its Real Contribution

A "which statement is NOT correct" question about the history of cell biology is best solved by building a small mental timeline of scientist-to-discovery pairs first, then checking each option against that timeline rather than judging the options in isolation.

The timeline to hold in your head: Robert Hooke first observed cell-like compartments in dead cork tissue and coined the term "cell"; Antonie von Leeuwenhoek was the first to see and describe a genuinely living, free cell; Robert Brown later identified the dense body inside cells that we now call the nucleus; Matthias Schleiden and Theodor Schwann, working on plants and animals respectively, jointly proposed that all living bodies are made of cells; and Rudolf Virchow completed the theory by showing cells arise only from pre-existing cells through division.

Once that sequence is fixed, run each option against it: does the name match the achievement claimed? Statement (a) attributes cell discovery to Brown, but Brown's real legacy is the nucleus — that mismatch is what makes it the false statement, and no other option shows a similar name/achievement mismatch.

This matching approach is more reliable than trying to recall the exemplar answer directly, because the same pool of names and discoveries gets recombined into many differently-worded MCQs — the underlying skill being tested is whether you know who did what, not whether you've memorised one particular sentence.