BIOLOGY : CELL I

Cell structure and functions of the cell components

Cell is the basic structural and functional unit of living organisms .It is referred to as the ‘units of life’ and the building blocks from which living organisms are made. It is regarded as the basic unit of all organisms because it can carry out all life activities such as feeding, movement, reproduction, respiration, growth e.t.c

Living organisms are classified based on the number of cells. This include;

-Unicellular or Acellular organisms
-Multi-cellular organisms

In unicellular organisms, a single cell carries out all the life activities while multi-cellular organisms are composed of groups of cells which works together to carry out the life activities.

                      THE CELL THEORY

The cell theory was postulated based on the observations of some scientists on cell viewed under microscope and certain discoveries in plants and animals .

These scientists include RROBERT HOOKE ,THEODOR SCHWANN , MATTHIAS SCHLEIDEN , FELIX DUJARDIN and RUDOLF VON VIRCHOW.

Robert Hooke is referred to as the ‘father of cells’ .He was the first scientist to discover the honey comb structure of cells in 1665. In 1839, Theodor Schwann and Matthias Schleiden stated that the bodies of all plants and animals are composed of cells.

 In 1835, Felix Dujardin discovered that  cell was made up of living substance .He named the living substance PROTOPLASM. Another biologist in 1855, Rudolf Von Virchow stated that all cells come from previously existing cells.

 All what we discussed above led to the postulation of the cell theory…

-The cell is the basic structural and functional unit of life.
-All living organisms are made up of cells
-There is no life apart from the life of cells
-All cells come from previously existing cells
-All living organisms are either single celled (Unicellular) or group of cells (Multi-cellular).



Cell components and their functions

 -Nucleus: This is enclosed by a double layered membrane, nuclear membrane, which has pores for the exchange of materials between the nucleus and the cytoplasm. It controls all the life activities of the cell and also stores hereditary information as it contains the DNA.
NOTE: The nucleus is easily stained by dyes...

-Cell Wall: The cell wall is only present in plant cell and is composed mainly of cellulose. It provides mechanical support and protection to the cell.

-plasma Membrane: This is a selectively permeable membrane which controls the inflow and outflow of materials in the cell. It is made up of mainly proteins and lipids. The lipids are of three types CHOLESTEROL, GLYCOLIPIDS, and PHOSPHOLIPIDS.

-Protoplasm: The most important colloid in cell of living organisms. It was first discovered by FELIX DUJARDIN and consists of the Nucleus and the Cytoplasm.

-Cytoplasm: The main component of the cytoplasm are the Cytosol , Organelles and Cytoplasmic Inclusions. The Cytosol is a gel-like substance of the cytoplasm, the organelles include the cell’s sub-structures and the cytoplasmic inclusions include the starch grains, the oil globules and excretory crystals. It is the cell components in which the cell organelles are suspended.

-Mitochondria: This is referred to as the 'power house’ of the cell. It has an inner membrane folded to form a partitions of Cristae. All energy obtained during the oxidation of food substances are stored here and supply to the cell when needed.

-Chloroplasts: This is only present in plants and contain chlorophyll which aids in photosynthesis in green plants.

-Nucleolus: A darkly stained structures within the nucleus. They produce the ribosomes for protein synthesis.

-Endoplasmic Reticulum: They are of two types; Rough and Smooth Endoplasmic Reticulum. They aid in transport of materials within the cytoplasm.

NOTE: The significant difference between the smooth and rough endoplasmic reticulum is that ribosomes are attached to the surface of the rough endoplasmic reticulum and can help to transport proteins made by ribosomes.

-Vacuole: A very large central vacuole is present In plant cell. It is lined with a membrane called TONOPLAST and filled with cell sap…It act as an omoregulator by removing excess water in  cells.

Compiled: Ismail Opaleye


     




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