So let's start
1. Resolving Power: Ability to distinguish two close points as two separate points by
any optical system is called as its resolving power. The resolving power of human eye
is 100 micron. Mathematically, resolving power = l2 where l is the source of
illumination. Resolving power of compound microscope & electron microscope is 0.3
microns & 10 Å respectively.
2. Zacharis Janssens combined lenses in an effort to improve magnifying efficiency
and resolving power. He produced the first compound microscope which combines
two lenses for greater magnification.
3. About Cell Concept :
(a) Marcello Malpighi (1628-1694), an Italian microscopist, studied the structure
of plants. He believed that the plants are composed of separate structural units
which he called “utricles”.
(b) Robert Hooke (1635-1703), examined thin slices of cork (dead outer bark of an
oak) under his microscope. He saw hundreds of very small hexagonal ‘boxes’ or ‘chambers’ which are together appeared like a ‘honeycomb’. The term ‘cell’ was coined by Robert Hooke to denote these chambers. His observations, along with the figures, were published in 1665 in Micrographia.
(c) Anton von Leeuwenhoek, 1674, using good quality simple lenses (magnifying
upto 200 times) observed unicellular organisms and called them ‘wild
animalcules’. In this way, he was the first to observe “living and moving individual” cells as compared to the “fixed” cells seen by earlier workers.
(d) H.J.Dutrochet (1824), a French scientist, boiled some tissues and separated the cells from one another. He expressed the idea of individual cells i.e., cells were not just spaces between a network of fibres, but that these were separate and separable units.
4. Concept of Protoplasm :
Corti (1772) first of all observed that all cells contain a living substance. This was first observed by Corti (1772). Felix Dujardin (1836), observed it in living amoebae, and called it ‘Sarcode’. In 1839, J.E. Purkinje used the word ‘protoplasm’ to describe the living substance. Hugo von Mohl (1846), also suggested the same name protoplasm– for the similar substance found in plant cells.
5. Robert Brown, an English naturalist, described in 1828, characteristic dancing of
cell particles. It is now, therefore, known as Brownian movement.
6. Nucleus : In 1831, Robert Brown saw that small spherical body was present in every plant cell. He used the word ‘nucleus’ to identify them.
7. Cell Theory : Two German biologists, M.J. Schleiden (1838) and Theodor Schwann
(1839) proposed cell theory (or cell doctrine) – which unified the ideas prevailing at that time. He stated that –
(a) living things are composed of cells and cell products.
(b) cells are the fundamental structural units of living organisms.
In fact, Schwann coined the word “metabolism” for all chemical processes carried on in the cell. Actually, he called cells “the unit of life”.
8. Rudolf Virchow (1858), a German pathologist, developed the idea of generation to generation continuity of cell that Omnis cellula e cellula (i.e. cells arise from pre-existing cells). This occurs by the division of cell.
9. Nucleolus: In 1781, Fontana had seen dense spherical body inside nucleus.
Schleiden (1838) also described it. But, it was given the name “nucleolus” by Bowman (1840).
10. Nageli and Cramer (1855) gave the name “cell membrane” to the outer boundary of
the protoplasm. Overton (1899) proved its existence. J.Q. Plowe (1931), later on,
called it ‘plasmalemma’.
11. Protoplasm Theory : Max Schultze (1861) proposed the protoplasm theory.
According to it “cell is an accumulation of living substance (or protoplasm) which is
limited by an outer membrane, and possesses a nucleus”.
12. Plastids : N. Pringsheim and J. Sachs (1865-1892) described coloured bodies in the cytoplasm which were called plastid by Haeckel in 1866.
13. Schimper (1883) classified plastids into three types – Leucoplasts (colourless),
Chloroplasts (green) and Chromoplasts (colour other than green). The green
plastids were also identified by Meyer (1883) who called them autoplasts. However, Errera gave the name chloroplasts to them.
14. Mitochondria : Kollicker (1880) was the first to observe small thread-like structures
in the cytoplasm of the striated muscle cells of insect. These were called ‘fila’ by
Flemming (1882). Altmann (1890) described them as “bioplasts”. It was Benda (1897)
who coined the term mitochondria.
15. Centrosome : Boveri (1888) used the word “centrosome” for a body found at one
pole of the cell near the nucleus in animal cells. Most of the plant cells were found to
be lacking it.
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