Biology:- Cell the unit of life

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Cell : The Unit of Life

1. WHAT IS A CELL?
 You have learnt that biology is the study of living organisms. There is a huge range of living organisms - from the microscopic Amoeba to the blue whale. But all living organisms have a basic feature in common - they are made up of building blocks, called cells.
    The cell is the fundamental structural and functional unit of all living beings. It is the smallest part of the body of an organism which is capable of independent existence and of performing the essential functions of life.
Every organ in our body - the skin, the brain, the muscle or even the bone - is composed of hundreds of thousands of such cells. Similarly, every part of a plant - the leaf, the flower, the root and even the wood - is composed of an exceedingly large number of cells.
Every cell has its own life. Old and weak cells in the body continually die and are replaced by new cells. Red blood cells for instance die after about 120 days. All organisms including ourselves, start life as a single cell called the zygote.
Cells are so small that they cannot be seen with the naked eye. It was, therefore, natural that their existence could not be detected by man until he invented magnifying aids in the form of microscopes
2. THE INVENTION OF THE MICROSCOPE AND THE DISCOVERY OF CELL
The first microscope was constructed by Dutch scientist Antony van Leeuwenhoek (1632-1723).He was an ordinary public official who ground lenses and made microscopic observations as a hobby. He is said to have constructed 400 microscopes. Basically, all his microscopes consisted of a single biconvex lens and were called simple microscopes.
Robert Hooke (1635-1703), an English scientist, developed a microscope by using two lenses for achieving greater magnification. Such microscopes were later know as compound microscopes.
3. CELL THEORY
In 1838, Matthias Schleiden, a German Botanist, announced that every plant is made up of a large number of cells. He added that each of these cells performed various life processes. A year later, Theodor Schwann, a German zoologist, made similar discoveries in animals. He declared that all animals and plant are composed of cells which serve as the units of structure and function. This, in short , is called the Cell Theory, having been proposed by Schwann and Schleiden in the year 1839. Rudolf Virchow in 1858 made an addition to the cell theory by saying that all cells arise from pre-existing cells.
4. CELL SHAPE

  • The shape of the cell may be disc like , polygonal , rectangular , cuboid , thread-like, branched or even irregular.
  • The cell are of  different shape because they have to perform various function in the body fo living organism.
STRUCTURE OF CELL
Cell mainly consist of three parts:-

  1. Cell membrane
  2. Nucleus
  3. Cytoplasm
  • Cell membrane / Cell wall
Cell wall is present only a plant cell. It is made up cellulose. It is a non-living structure and the main function of cell is to provide definite shape and provide rigidity. Cell wall is freely permeable. Cell membrane is present just below cell wall. It is semi-permeable. It is made up of lipids and protiens. It is the living structure.
  • Cytoplasm
Cytoplasm is a semi-liquid substance. It is present in between nuclear membrane and cell membrane. It is living and is in continuous state of motions. Many Biochemical reactions take place in it.
NOTE:-  Protoplasm is everything inside a cell i.e. nucleus + cytoplasm

Cell organelles
Cells have many small structure present in the cytoplasm. These structures are known as cell organelles.
DIFFERENCE BETWEEN PLANT CELL AND ANIMAL CELL

         Plant cell

  • It has cell wall.
  • Centrosome is not present.
  • Vacuoles are present
  • Usually contain plastids.
  • Cytoplasm not so dense.
  • Only a thin lining of cytoplasm, mostly pushed to the periphery.      
    Animal cell

  • No cell wall.
  • Centrosome is present.
  • Vacuoles are absent and if present very few in number and small in size.
  • Do not contain plastids.
  • Cytoplasm denser and more granular.
  • Cytoplasm fills almost the entire cell.
Protoplasm :-
It is a living matter present inside the cell. It includes cytoplasm and nucleous.

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Biology:- Tissue plant & animal

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<html> <head> <script data-ad-client="ca-pub-8232053510703465" async src="https://pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script> A brief understanding of their location , basic structure and function. A brief understanding of their role in different physiological processes in plants and animals. Tissue:- Tissues are group of similar cells which perform specific function.   PLANT TISSUE:- Plant tissues are basically of two types- Meristematic tissue or Meristem The cells of meristamic tissue have the power of division. These tissue are found on the growing regions of plants. The cells of meristematic tissue are small, cuboidal and large nucleus. Vacuoles are absent and they cells are having no intercellular space between them. According to the position of the meristematic tissue, they are divided into three types- Apical or Terminal:-  Apical meristem is present at the tip of root and shoot of plant. Thi...
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