Page 10 - Biology_F5

Cytology

was among the first scientists to accept cells and origin of life. The study of viruses
and extend the work of Robert Hooke. indicated that these living particles are non-
He showed that, the origins of cells was cellular. Schleiden and Schwann could not
the division of pre-existing cells, and he explain the structure and functioning of a
concluded that “new cells arise from pre- virus. They reported that the body function is
existing cells”. coordinated by the cell, which is not the case
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in virus because it only starts its functioning
1.2.1 The main ideas of the Cell theory
The principal ideas of the Cell theory are when hosted by bacterial, plant or animal
as follows: cell. Thus, as per the Cell theory, they are
(a) All living organisms are composed of non-living creatures (akaryotes). However,

one or more cells and cell products. when they are in host cells, they exhibit
(b) Cells are the basic or fundamental living characteristics. Regarding the cell
units of life, as all life processes are theory, there should be genetic material
controlled by cells. in every cell, but mature human red blood
(c) All new cells arise from pre-existing
cells. cells and sieve tube cells of angiosperm are
some of the cells that lack genetic materials.

However, in the modern version of the Furthermore, the cell theory revealed that
Cell theory, the following were added: new cells arise from the pre-existing cells by
(a) Cells contain genetic materials which cell division. However, it does not explain
carry hereditary information (DNA) about the origin of the first cell.
that is passed from one generation to
another. Exercise 1.1
(b) Energy flow occurs within cells in
which all metabolic processes of life 1. Explain the importance of studying
cytology.
occur.
(c) All cells have the same basic chemical 2. Analyse the main ideas and short-
composition, whereby structure and comings of the Cell theory.
functions of cells complement each 3. Explain why the Cell is regarded
other. The living organism’s activities as a basic unit of life.
depend upon the combined actions of
individual cells.
(d) All new cells arise from pre-existing 1.3 Types of cells
cells through cell division.
Task 1.2
1.2.2 Shortcomings of the Cell theory Search for information from the
Due to increased understanding on cell library and internet sources about
biology, the theory has been challenged based the cell structure and organisation of
prokaryotic and eukaryotic cells. Note
on the modern knowledge of virology, blood down their main differences.

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