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Biology for Advanced Level Secondary Schools

(d) Gives knowledge about the process and
significance of cellular differentiation,
that is, a process in which cells are
specialised for their functions, such
Chambers of
the cork cell as reproductive cells, absorptive cells,
and nerve cells.
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(e) Enables us to understand how similar
cells are organised into tissues.
Figure 1.1: First view of the cork cells by Robert (f) Helps to show how organisms are
Hooke evolutionarily related. For example,
Source: http://ucmp.berkeley.edu in the biochemical evolution theory
of origin of life on the earth, various
He was later followed by Anton von chemical compounds were combined
Leeuwenhoek, who in 1674 discovered free and mobilised into prokaryotes, which

living cells in pond water. Leeuwenhoek gave rise to eukaryotes in the course of
made a microscope consisting of a single evolution.
high-quality lens which could magnify an (g) Helps to understand the basis of
object 270 times. This instrument was at that genetics; the location, structure,
time referred to as a compound microscope. chemistry, and role of nucleic acids,
With this microscope, Leeuwenhoek was Deoxyribonucleic acid (DNA) and
Riboxyribonucleic acid (RNA).
able to make a number of important (h) Cytopathology, a study of cellular
scientific discoveries, including single- abnormalities, helps to diagnose
celled animals, plants, bacteria, and diseases through observation of
spermatozoa. cellular changes.

The importance of studying cytology 1.2 The Cell theory
The study of cytology helps us to
understand the role of cells as the The origin of the concept of “Cell theory”
building blocks of all living organisms, can be traced to as far back as 1830s
including their anatomy and physiology. when two scientists, Matthias Schleiden
Additionally, the significance of studying a Belgian botanist (1838) and Theodor
cytology include the following: Schwann, a German zoologist (1839)
(a) Helps to realise the role of cells provided the first definition of the cell.
in metabolic processes such as They stated that, all living organisms,
respiration, protein synthesis, excretion, both simple and complex, are made up of
and growth. one or more cells. They described a cell as
(b) Aids in understanding the detailed the structural and functional unit of life.
structure and functions of different
cells and organelles. This led to formulation of the Cell theory.
(c) Enhances an understanding on the The Cell theory states that “All living
structural (anatomical and chemical) organisms are made up of cells”. In 1855,
composition of cells. Rudolf Virchow, a German physiologist,

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