What is a cell

A cell is a functional and structural unit of all the organisms.A single cell can do all the functions that amulti-cellular organism can do.

Cell theory: Given bySchleiden and Schwann.

Later on modified by Rudolf Virchow(1855) i.e.


 * cell is the unit of all multi-cellular organisms.
 * pre-existing cells give rise to the new cells.

Cell can be divided into two categories:-


 * prokaryotic cells
 * eukaryotic cell

Difference between prokaryotic and eukaryotic cell:-


 * bacteria,blue green algae andmycoplasma represents the prokaryotic cell while eukaryotic cell is represented by plant, animal cell and by protists.
 * prokayotes have nucleoid instead of nucleus but a well defined nucleus is found in eukaryotes.
 * DNA is circular in prokaryotes.

Revision questions

1. Differentiate between the following terms:


 * Community and Population


 * Habitat and Ecosystem


 * Habitat and Territory


 * Society and Community


 * Society and Population


 * Environment and Society


 * Fauna and Flora


 * Environment and Ecosystem


 * Ectoparasite and Endoparasite


 * Biotic and Abiotic


 * Food chain and Food web


 * Cell membrane and Nuclear membrane


 * Aquatic and Terrestrial


 * Breathing and Respiration


 * Multicellular organism and Unicellular organism


 * Eukaryotic cell and Prokaryotic cell

2. Define the following terms:


 * Ecology


 * Zoology


 * Botany


 * Autotrophs


 * Heterotrophs


 * Herbivores


 * Carnivores


 * Omnivores


 * Parasites

3. There are seven life processes that all living organism should demonstrate. All the life processes depend on one another.

a) Explain how each of the life processes are dependent on one another.

b) Explain how and why all the life processes depend entirely on that of respiration.

c) Explain how a cell is able to carry out all the life processes. In your explanation indicate the part of the cell that is responsible for the life process.

d) Explain the "cell theory" and all its principles.

e) Give a detailed account of how cell specialisation occurs, giving examples of different specialised cells.