Cell Structure and Function: The Cell and Cell Theory and Basic Types of Cells (For CBSE, ICSE, IAS, NET, NRA 2022)

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Landmarks in Cell Study

In 1665, Robert Hooke observed cells in piece of cork under the microscope. In 1672, Leeuwenhoek observed bacteria, sperm and red blood corpuscles in cells. In 1831, Robert Brown (Englishman) observed nucleus which all cells had a centrally positioned body.

The Cell Theory

In 1838, Theodor Schwann and Matthias Schleiden formulated the cell theory. This theory states that; all living things are made of cells, Cells are the basic units of structure and function in living things, Living cells come only from other living cells and all cells at some stage in their life cycle, contain the genetic material for the entire organism.

The Cell

Each cell is made of a small mass of protoplasm containing a nucleus and a plasma membrane with or without a cell wall on its outer side. Protoplasm is the living substance containing cytoplasm and nucleus in a living cell. There are many cell organelles which are found in cytoplasm, Endoplasmic reticulum, Golgi apparatus, Ribosomes, Lysosomes, Mitochondria, Plastids, Vacuoles and Centrosome. The bacteria have neither organelles nor a well-formed nucleus. But every cell has three major components; plasma membrane, cytoplasm and DNA (naked in bacteria and covered by membrane in all other organisms) .

Two Basic Types of Cells

Organisms whose cells lack a nuclear membrane are called prokaryotes and organisms with cells having a nuclear membrane are called eukaryotes.

Differences between Eukaryotic and Prokaryotic Cells

Image Showing Difference between Eukaryotic Cell and Prokaryotic Cell
Eukaryotic cellProkaryotic cell
Nuclear is distinct with well-formed nuclear membrane.Nucleus not distinct, it is the form of nuclear zone nucleoid. Nuclear membrane absent.
Cellular organizations mostly are multicellular.

Double-membraned cell organelles (Chloroplasts, mitochondria, nucleus) and single membraned (Golgi apparatus, lysosomes, vacuole, endoplasm reticulum)

Cellular organizations mostly are unicellular. Single-membraned cell bodies like mesosomes present. Endoplasmic reticulum and Golgi body absent.
Ribosomes (80S) consists 2 subunits; 60S and 40S.Ribosomes (70S) consists 2 subunits; 50S and 30S.
Distinct compartments in the cell, i.e.. the cytoplasm and the nucleus.No compartments.
Image Showing Difference between Eukaryote and Prokaryote

The ribosomes are of two basic types, 70S and 80S ribosomes. Thus, S refers to Svedberg units. The ribosomes are usually isolated from the cell by the differential centrifugation method in which analytical centrifuge is employed. The sedimentation coefficient of the ribosomes is determined by the various optical and electronic techniques. The sedimentation coefficient is expressed m the Svedberg unit, e. g. , ‘S’ unit.

Difference between Plant Cell and Animal Cell

Image Showing Difference between Plant Cell and Animal Cell
Plant cellAnimal cell
Cell wall made up of cellulose is present.Cell wall is absent.
Vacuoles are well-developed.Vacuoles are either absent or if present are small in size and scattered.
The components of golgi bodies are diffused in the plant cells and are called dictyosomes.Golgi bodies are well-developed and present near nucleus.
Centrosome and centrioles are absent, instead polar caps are present.Centrosome and centrioles are present.
Plastids are present.Plastids are absent.
In plant cells, reserve food is stored in the form of starch or oil.In animal cells, reserve food is stored in the form of glycogen.
Image Showing Difference between Animal Cell and Plant Cell

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