Biology 1st Paper (Botany) · Classes 11-12 · Chapter 1
The Cell, Cytology and Cell Theory.
Slice a bottle cork thin and put it under a microscope. What do you see? One man saw rows of tiny rooms and called them “cells”. The biggest word in biology was born that way. Let us follow it, and see who added what.
1. A small room called a cell
In 1665 Robert Hooke looked at a thin section of cork, the wood of a bottle stopper, under a microscope. He saw many small honeycomb-like chambers and named them cells. The Latin word Cellula means a small chamber. Hooke published what he saw in his book Micrographia.
There is a catch. What Hooke really saw were dead cells, just the empty chambers, which we now call cell walls. The first person to see living cells was the Dutch scientist Antony van Leeuwenhoek, in 1674. Inside the wall he saw the full cell contents too.
Look down the eyepiece three times: Hooke's cork, Leeuwenhoek's living cells, and what we see today.
under the lenspick a lens
Who saw what
2. What is a cell?
The structural and functional unit of a living body is the cell. It is the unit of structure, and the life activities needed for living all happen inside it.
Three scientists put it three ways. Jean Brachet (1961): the cell is the basic structural unit of an organism. Loewy and Siekevitz (1963): the cell is the unit of biological activity, bounded by a semipermeable membrane and able to reproduce itself without any other living medium. De Robertis (1979): the cell is the basic structural and functional unit of an organism. Now match them yourself.
match themtap a chip, then pick the scientist
Whose definition is it?
Pick up a definition, then drop it in a scientist's box. Notice whether it speaks of structure only, or of function too.
Right. Next one.
Not yet. Ask: does it mention self-reproduction? Structure alone, or structure and function both?
All in place. Brachet speaks of structure only, not function. Only Loewy and Siekevitz mention self-reproduction. De Robertis names both structure and function.
3. What a cell does, and what is inside
Keep the seven properties of a cell in mind. One, it holds every structural and molecular component life needs. Two, it takes in raw materials. Three, it harvests energy and synthesises its own molecules. Four, it grows in a controlled way. Five, it responds to stimuli. Six, it keeps a homeostatic state, holding its inside steady when the surroundings change. Seven, it adapts over time.
The cytoplasm of a cell holds living, working small parts without which the cell cannot survive. These are the cell organelles (meaning “small organs”). Examples: mitochondria, endoplasmic reticulum and ribosomes.
4. Cytology
The branch of biology that studies the kinds of cells, the physical and chemical structure of organelles, division, development, biological activities and growth is cytology. The word comes from the Greek Kytos (cell) and logos (discourse).
Robert Hooke is the father of cytology. The father of modern cytology is Carl P. Swanson (1911-1996).
5. The cell theory
The cell theory did not arrive in a day. Drag the year from 1665 to 1855 and watch the picture change at each step.
time scrubdrag the handle
From empty rooms to cells from cells
All these observations join up as the cell theory. It was proposed by the German botanist Schleiden and the zoologist Theodor Schwann (1838-1839), and later, in 1855, by Rudolf Virchow. See the whole story in one place.
along the linetap each year
Who saw what, and when?
1665, Hooke. Honeycomb-like chambers in cork. They were only the chambers of dead cells, and he named them “cell”. He published it in Micrographia.
1674, Leeuwenhoek. The first living cells, with their contents. This is what separates him from Hooke's empty chambers.
1838-1839, Schleiden and Schwann. Schleiden was a botanist, Schwann a zoologist. Together they gave the cell theory.
1855, Virchow. New cells arise from pre-existing cells. The last piece of the theory is his.
The first three statements of the cell theory: the cell is the structural, physiological and organisational unit of a living entity. The cell is the basic unit of life. The cell is the unit of heredity.
The fourth statement: every living thing is made of one or more cells, and new cells arise only from pre-existing cells. Now make sure the seven properties and the statements of the theory do not blur together.
sort themtap a chip, then pick a bin
Which goes where?
Pick up a chip, then drop it in a bin. Ask: is this a claim about all living things, or about what a single cell does?
Right. Next one.
Not yet. Is it about how all living things are built or arise, or about what the cell itself does?
All in place. Unit of heredity is the third statement, basic unit of life the second, all organisms made of cells the first half of the fourth, and new cells from old ones is Virchow's addition. Responding, growing and keeping steady are among the seven properties.
6. Check yourself
The first question is in the exam's style.
check yourselfpick one answer
Question 1
Cytology, a rich branch of biology, discusses:
i. Types of cells ii. Physical and chemical structure of organelles iii. Cell division, development and biological activities
i and ii are right, but iii is too: cytology also covers division, development and biological activities.
i and iii are right, but ii is too: the physical and chemical structure of organelles is also covered.
ii and iii are right, but i is too: cell types are also covered.
Right. Cytology deals with cell types, the physical and chemical structure of organelles, and cell division, development and biological activities.
In the second, watch the names and years.
check yourselfpick one answer
Question 2
The cell that Robert Hooke saw under the microscope was mainly:
Right. What Hooke saw in cork were the walls of dead cells.
The pit membrane was not what he saw.
Hooke’s microscope could not show mitochondria.
Nuclear pores are too fine for Hooke to see.
The third is the last bend.
check yourselfpick one answer
Question 3
Who first gave the idea of the cell?
Right. Robert Hooke first used the name ‘cell’ in 1665 while looking at cork.
Robertson gave the unit membrane theory, not the idea of the cell.
Flemming worked on chromosomes and cell division.
Hutchinson did not give the idea of the cell.
The whole topic on seven cards.
cut from the notetap to turn over
Seven cards
QuestionWhat did Hooke actually see: living or dead cells?
AnswerDead cells, only the empty chambers (cell walls). Leeuwenhoek saw living cells.
QuestionWho first observed living cells with their contents, and when?
AnswerThe Dutch scientist Antony van Leeuwenhoek, in 1674.
QuestionList the seven properties of a cell.
Answer(1) holds all structural and molecular components (2) takes in raw materials (3) harvests energy and synthesises molecules (4) controlled growth (5) responds to stimuli (6) keeps a homeostatic state (7) adapts over time.
QuestionWho is the father of cytology, and who of modern cytology?
AnswerRobert Hooke; Carl P. Swanson (1911-1996) for modern cytology.
QuestionWho proposed the cell theory and when?
AnswerThe botanist Schleiden and zoologist Theodor Schwann (1838-39); later Rudolf Virchow in 1855.
QuestionState the first three statements of the cell theory.
Answer(1) the cell is the structural, physiological and organisational unit of a living entity (2) the basic unit of life (3) the unit of heredity.
QuestionState the fourth statement of the cell theory.
AnswerEvery living thing is made of one or more cells, and new cells arise only from pre-existing cells.
Source: Biology 1st Paper (Botany), Classes 11-12 (NCTB), Chapter 1 “Cell and Its Structure”, the “The Cell, Cytology and Cell Theory” part.