Lesson 1 of 13 · 6 min
What is a cell, and the cell theory
NCERT §8.1–§8.2
Riya's teacher starts with one question before any slide goes under the lens: what is the smallest thing that still counts as fully alive?
The story this chapter follows: Riya's Saturday lab practical
The lesson in notes
In short
The cell is the basic structural and functional unit of all living things. A unicellular organism lives on its own and performs every essential life function, but nothing short of a complete cell can support independent life.
Leeuwenhoek was the first person to observe and describe a live cell; the nucleus was discovered later by Robert Brown.
Matthias Schleiden, a German botanist, studied many plants and concluded in 1838 that all plants are made of different kinds of cells that together form tissues.
Theodore Schwann, a zoologist, reported in 1839 that animal cells are bounded by a thin outer layer (what we now call the plasma membrane), and from his work on plant tissues he concluded that a cell wall is peculiar to plant cells.
Schwann proposed that plant and animal bodies are made of cells and cell products; Schleiden and Schwann together are credited with the cell theory.
Their theory could not explain where new cells come from. Rudolf Virchow in 1855 filled this gap by stating that cells divide and that new cells arise only from pre-existing cells, summed up as 'Omnis cellula-e cellula'.
The modern cell theory therefore has two parts: all living organisms are made of cells and their products, and all cells come from pre-existing cells.