English scientist Robert Hooke used
a microscope, to investigate cork. He saw that cork resembled a
honeycomb. The cork was made of small boxes that
Hooke described as cellulae (a Latin word meaning
‘little storage rooms’)Hooke had discovered
cells. Cork cells are dead plant cells and
have nothing inside them; therefore
Hooke saw only cell walls
Ernst Ruska designed
and built the
scientists to see
things such as
are too small
to be seen
However, it was
1935 before these agents were made visible using
an electron microscope and viruses were seen for
the first time.
Since their invention, the magnification of electron
microscopes has improved and they are
now capable of magnifying an object
up to 1 000 000 times.
the Dutchman Antonie van
Leeuwenhoek used a microscope to look at pond
water and saw small things moving about. What he
was seeing were small, single-celled (unicellular) living
things. This made Leeuwenhoek the first person to
observe and describe microscopic living things.
Robert Brown discovered that plant cells were not
just empty boxes but that they had a nucleus inside
Matthias Schleiden, a German scientist,
analysed the known information about plant cells.
He proposed that cells are the basic building blocks
of all plants, and that new plants start off as a
A year later a friend of Schleiden’s, Theodor
Schwann, proposed that all animals are made
of cells and that the cell is the basic unit of life.
Swiss scientist Karl Nägeli observed
cells dividing to make new cells. This was the first
time that scientists understood that new cells came
from existing cells.
German scientist Rudolf Virchow linked
the observations of Nägeli and Brown. He proposed
that all cells develop from existing cells and don’t
just spring up from nowhere.
It had been
1898 that ‘invisible agents’ called viruses caused
diseases in plants and animals.