About the cell , cell organells , Structure of the cell ,Function of the cell ,cell membrane and cell theory
What is cell ?
Cell is the smallest structural and functional unit of of all living organisms. Cells of different tissues perform different function.
• all organisms are composed of cells. Some are composed of single cell and are called unicellular organisms while others are are of many cells called multicellular organisms
• Who is invented the cell ----> ROBERT HOOK .
• Who is first saw and descreibed a live cell ------> Anton von Leeuwenhoek.
A cell is made up of the following structures
1. Cell wall
It is the external boundary of the living cell. It is three layered structure mede up of lipids and proteins. It measures approximately 70 angstrom in thickness. Cell wall allows the diffusion of substances into to and out of the cell.
• cell wall not only gives shape to the cell and protects the cell from mechanical damage and infection , it also helps in Cell to cell interaction and provides barrier to to undesirable macromolecules .
• Algae have cell wall made up of cellulose , galactans and Minerals like calcium carbonate while in other plants it consists of cellulose , hemicellulose ,pectins and proteins .
2.Nucleus
It is the largest structure present in the centre of of course sale. It is more or less sherical in shape .It is bounded by nuclear membrane. The nucleus contains nucleolus and chromatin
3. Cytoplasm
It is the region lying between the cell membrane and nucleus the cytoplasm contains cell organelles like endoplasmic reticulum Golgi apparatus mitochondria lysosomes and centrosome.
Cell organelles of cytoplasm
Following are the important cell organelles present in the cytoplasm
1. Endoplasmic reticulum
It is the most extensive cell organelle present in cytoplasm. It consists of two membranes which are separated by space.
• Rough endoplasmic reticulum is frequently observed in the cells actively involved in protein synthesis and secretion they are extensive and continuous with the outer membrane of the nucleus.
• The smooth endoplasmic reticulum is the major site for synthesis of lipid. In animal cells liquid like steroidal hormone are synthesized in in SER.
2. Golgi apparatus
It is a Cup shaped structure and contains vesicles. It is situated between the nucleus and the apex of the cell. It is it is concerned with concentration of proteins Prior to their secretion
3.Mitochondria
They occur in cytoplasm at variable numbers that is few hundreds to few thousands. The mitochondria is composed of two layers of membranes they are an outer layer which is smooth and inner layer folded into sheets of tubules called cristae. Both these layers enclose Central cavity called matrix .
• Mitochondria are the the sites of aerobic respiration they produce cellular energy in the form of of ATP hence they are called powerhouse of the cell.
4. Lysosomes
They are small or oval bodies surrounded by a single membrane they are vary in number and contain a variety of hydrolytic enzymes like lipases proteases and carbohydrate sources optimally active at the acidic PH.
The lysosomes breakdown bacteria and cell debris engulfed by the cell the damaged intracellular organelles are also broken down and digested by lysosomes.
4.Centrosome
It is a small rod shaped body found near the nucleus it plays an important role during cell division the centrosome is surrounded by radiating thread like structure it contains two centrioles
structure of a animal cell
Functions of the cell
Metabolism
This involves two processes
• Anabolism in which the ingested and assimilated food material is used for growth and repair.
• Catabolism in which food material is broken down to release energy for various functions of the cell.
Respiration
It involves transport of oxygen from lungs Through Blood to the tissues and removal of waste products like carbon dioxide .This is essential for the survival and function of cell
Excretion
The cell eliminates waste products resulting from catabolism into the The interstitial fluid. These products are carried by blood for elimination through lungs and Kidneys .
Type of the cells
There are two types
1. Prokaryotic cell
The prokaryotic cells are represented by bacteria blue green algae mycoplasma and pleuro pneumonia like organisms
They are generally smaller and multiply more rapidly than the Eukaryotic cells. They may vary greatly in shape and size .
Four basic shapes of bacteria are bacillus (Rod like ) , coccus (spherical), vibrio (comma shaped) , and spirillum (spiral)
2. Eukaryotic cell
The eukaryotes include all the protests plants animals and fungi in eukaryotes cells there is an extensive compartmentalization of cytoplasm through the presence of membrane bound organelles .
All Eukaryotic cells are not identical plant and animal cells are different as the farmer possess cell wall plastids and a large central vacuole which are absent in animal cells while animal cells have centrioles which are absent in almost all plant cells .
Cell Membrane
The cell membrane is mainly composed of lipids and proteins the major lipids are phospholipids that are arranged in a bilayer. Also the lipids are are arranged within the membrane with the polar head towards the outer sides and hydrophobic Tails towards the part
In human beings the cell membrane of eukaryotes has approximately 52% protein and 40% lipids .
Depending on the the ease of extraction membrane proteins can be classified as integral and peripheral. Peripheral proteins lie on the the surface of membrane while the integral proteins are partially o r totally buried in the membrane
Structure of cell membrane
CELL THEORY
In 1838 Matthias Schleiden a German botanist examined large number of plant and observed that all plants are composed of different kinds of cells which form the tissue of the plant
In 1839 Theodore Schwann a british the largest studied different types of of animal cells and reported that cells had a thin outer layer which is today known as the plasma membrane
Schleiden and Schwann together formulated the cell theory but did not explain as to how how new cells were formed
Rudolf Virchow 1855 first explained that cells divided and new cells are formed from pre-existing cells (Omnis Cellula-e- cellula)
The cell theory as understood today is
• all living organism are composed of cells and products of cells
• all cells arise from pre-existing cells
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