It was the British botanist Robert Hooke who, in 1664, while examining a slice of bottle cork under a microscope, found its structure resembling the box-like living quarters of the monks in a monastery, and coined the word “cells”
In the year 1838, Matthias Schleiden, a German botanist, first proposed the idea that all plants consist of cells
The Dutch scientist A.V.Leeuwenhoek, in 1674, discovered the minute forms of life such as bacteria and single celled animals in a drop of water
In 1839, Theodar Schwann, another German botanist, asserted that all plants and animals are made up of cells
In 1831, Robert Brown discovered the nucleus in the cell
J.E.Purkinje, in 1840, used the term protoplasm to describe the juicy, slimy gelatinous contents of the cell
In 1885, Rudolf Virchow expressed that all cells arise from pre-existing cells
In 1932, two German Scientists, Ruska and Knoll, invented the electron microscope
Endoplasmic Reticulum (ER) This is a complex network of tubes, the lumen of which is filled with fluid. Two types of endoplasmic reticula are seen.They are:
Organisms may be broadly classified into two kinds: Unicellular and Multicellular
The cytoplasm consists of the matrix and the organelles. The matrix is a transparent semi fluid substance.
When active, it is always in a state of movement. The organelles are found embedded in the cytoplasm. They have definite shape, structure and function. All the metabolic activities of the cell such as synthesis, secretion, digestion and energy generation, are performed by the different cell organelles. Cell organelles can be seen only with the help of an electron microscope.
The functions of the endoplasmic reticulum are to form the skeletal framework of the cell, to provide a pathway for the distribution of nuclear material from one cell to the other and to synthesize fats, steroids and cholesterol with the help of enzymes secreted by the cell.
Also known as Golgi Complex or Golgi Bodies, they consist of tiny, elongated, flattened sacs (cisternae), which are stacked parallel to one another along with some vacuoles and clusters of vesicles.
These are tiny, spherical, sac-like structures scattered all over the cytoplasm. Their main function is digestion. They contain powerful destructive enzymes capable of digesting all organic material, and hence called “digestive bags”.
present in white blood cells are capable of digesting bacteria and viruses. During starvation, lysosomes digest proteins, fats and glycogen in the cytoplasm, and supply energy to the cell. They are also capable of digesting worn out cell organelles, or even digesting the entire damaged cell containing them. Hence, “suicide bag” is a sobriquet that is often used for Lysosomes.
These organelles are found in the liver and kidney cells. They are small, membrane-bound sacs, and contain powerful oxidative enzymes.
These are spherical, granular particles which occur freely in the matrix or remain attached to the rough endoplasmic reticulum. Ribosomes contain RNA (ribonucleic acid) and proteins. Their function is to provide the surface for protein synthesis.
This is found in the cytoplasm near the outer surface of the nucleus and contains two cylinders called centrioles. The centrosome is found only in the animal cell. The centrosome and the centrioles play an important role by forming the poles of the spindle during cell division.
These may be cylindrical, rod-shaped or spherical and distributed in the cytoplasm. Each mitochondrion is bound by a double membrane. The inner membrane is folded into ridges called cristae, which increase the surface area of the membrane. It is in the mitochondria that the sugar is finally burnt during cellular respiration. The energy thus released is stored as high-energy chemicals called ATP (adenosine triphosphate). Hence, mitochondria are termed as the “power house” or the “power plant” of the cell. The body cells use the energy stored in ATP for synthesis of new chemical compounds, the transport of these compounds and for mechanical work.
Plastids are of three types: Chloroplasts Chromoplasts Leucoplasts
Chloroplasts They are green and found in leaves. The green colour is due to the presence of chlorophyll.
The nucleus is composed of the following structures:
Nuclear Membrane : Nucleoplasm Nucleolus Chromatin network
The structure of the cell that we have studied so far is that of a eukaryotic cell. How is a prokaryotic cell different from a eukaryotic cell? The main difference between these two cell types is that prokaryotic cells do not have a nuclear membrane. The nuclear material consists of a single chromosome and lies in the cytoplasm. The nuclear region in the cytoplasm is called nucleoid. Membrane-bound organelles are absent. Prokaryotic cells are found in bacteria and cynobacteria (blue-green algae).
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