Q.Briefly give the contributions of the following scientists in formulating the cell theory
a. Robert Virchow
b. Schielden and Schwann

Rudolf Virchow and the pair Schleiden and Schwann each contributed a distinct piece of the cell theory.

• Schleiden, a botanist, studied many plants and concluded that all plants are built from different kinds of cells forming their tissues; Schwann, a zoologist, studied animal cells, noted the plasma membrane as their boundary and the cell wall as a feature special to plants, and together they proposed that both plant and animal bodies are made of cells and cell products.
• Their combined theory, however, did not explain how new cells actually arise. …

Matthias Schleiden, a German botanist, examined a great many plants and concluded that they are all built from different kinds of cells, which together make up the plant's tissues. Around the same period, Theodore Schwann, a German zoologist, studied a wide range of animal cells and noticed that they are bounded by a thin outer layer, the plasma membrane; from his parallel look at plant tissue, he also recognised the cell wall as a feature special to plant cells. Bringing their findings together, Schleiden and Schwann proposed that the bodies of both animals and plants are made up of cells and the products of cells, and jointly formulated the cell theory in this early form. …

Method: Answer in the Order the Theory Actually Developed

When a question asks for "the contribution of" more than one scientist to a single theory, resist the urge to answer them in the order they're listed in the question and instead answer in the order their ideas actually built on each other — this naturally produces a coherent narrative instead of two disconnected trivia facts.

Here, Schleiden and Schwann's joint contribution came first historically: one studied plant tissue, the other animal tissue, and by comparing notes they arrived at the general claim that all living bodies — plant and animal alike — are built from cells and cell-derived material. State what each of them specifically observed (plant cell walls and tissue organisation for Schleiden; the plasma membrane boundary in animal cells for Schwann) before merging their conclusion into one sentence, since a shared credit answer that skips what each person individually saw reads as guesswork rather than knowledge. …