Table of contents | |
Cytology | |
Cell | |
Discovery of Cell | |
Basic Criteria for Defining the Cell | |
Cell Theory | |
Prokaryotes and Eukaryotes | |
Types of Organisms on Basis of Number of Cells |
The cell and its structures are studied under a branch of biology called cytology.
1. Robert Hooke (1665): An English man and first curator of Royal Society of London.
2. Antony Van Leeuwenhoek (1674): was the first to observe living cells like Bacteria (from tartar of teeth), Erythrocytes (fish), Sperms, and Protozoans (Vorticella).
3. N. Grew (1682): Proposed cell concept which states that a cell is the unit of structure of organisms.
4. Rudolf Virchow (1858): Proposed that new cells formed from the pre-existing cells.
5. Knoll & Ruska (1931): Designed the electron microscope which was employed to study the ultrastructure of a cell and various cell organelles.
Microscope designed by Knoll and Ruska
(i) Presence of genetic material.
(ii) Presence of limiting plasma membrane.
(iii) Presence of metabolic machinery.
(i) All living organisms are composed of one or more cells.
(ii) All the cells have a similar basic structure.
(iii) Similar cell organelles of different cells perform similar functions.
Normal size in humans 20 µm to 30 µm in diameter.
The shape of a cell mainly depends upon the specific function it performs.
Characteristics | Prokaryotes | Eukaryotes |
Type of Cell | Always unicellular | Unicellular and multi-cellular |
Cell size | Ranges in size from 0.2 μm – 2.0 μm in diameter | Size ranges from 10 μm – 100 μm in diameter |
Cell wall | Usually present; chemically complex | When present, chemically simple |
Nucleus | Absent. Instead, they have a nucleoid region in the cell | Present |
Ribosomes | Present. Smaller in size and spherical in shape | Present. Comparatively larger in size and linear in shape |
DNA arrangement | Circular | Linear |
Mitochondria | Absent | Present |
Cytoplasm | Present, but cell organelles absent | Present, cell organelles present |
Endoplasmic reticulum | Absent | Present |
Plasmids | Present | Very rarely found in eukaryotes |
Ribosome | Small ribosomes | Large ribosomes |
Lysosome | Lysosomes and centrosomes are absent | Lysosomes and centrosomes are present |
Cell division | Through binary fission | Through mitosis |
Flagella | The flagella are smaller in size | The flagella are larger |
Reproduction | Asexual | Both asexual and sexual |
Example | Bacteria and Archaea | Plant and Animal cell |
Based on the number of cells the organisms can be categorised as:
(i) Unicellular: Single-celled
Example: Amoeba, Paramecium, Euglena, Plasmodium- Malarial parasite, Chlamydomonas.
(ii) Multicellular: Numerous cells
Example: Higher Plants & Animals.
Diversity of Cells
146 videos|358 docs|249 tests
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1. What is cytology? |
2. What are the basic criteria for defining a cell? |
3. What is the cell theory? |
4. What is the difference between prokaryotic and eukaryotic cells? |
5. How are organisms classified based on the number of cells they have? |
146 videos|358 docs|249 tests
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