Cell is defined as the structural and functional unit of a living organism. In another words the cells is the simplest smallest and basic unit of life. All living things (plants and animals) are made up of cells. The cell is regarded as the basic unit of all living things because it can carry out all life activities such as: Feeding, Reproduction, Creation, Growth, Adaptation, Respiration, Definite Life Span, Sensitivity and Movement.
CLASSIFICATION OF LIVING ORGANISM BASED ON THE NUMBER OF CELLS.
- a) Unicellular or Acellular organism: These are organism which consists of only one cell. Examples are: Amoeba, Chlamydomonas, Euglena, Paramecium e.t.c.
- b) Multicellular organism: these are organism which consists of two or more cells. Other words, this organism have many cells. Examples are: Volvox, Hydra, Spirogyra, Flowering Plants, Fish, Bird and Manet.
HISTORY OF CELLS
Many scientists contributed to the history of the cell. Among the scientists are:
1. Robert Hooke: An English Scientist that could be seen as the father of cell, he was the first human to discover the honey comb structure of the cell in 1665.
2. Felix Dujardin: A French Biologist in 1835 who discovered that the cell was made up of living substance. He however named the living substance. He however named the living substance Protoplasm.
3. Matthias Schleidan: A German Botanist in 1838 who revealed that the bodies of plants are made up of cells which were described as units of life.
4. Theodor Schwann: Another German Zoologist in 1839 who also discovered that the bodies of all animals are composed of cells. His discoveries of Schleidan and Schwann led to the postulation of the cell theory in 1839.
THE CELL THEORY
The cell theory stated that:
1. The cell is the structural and functional unit of life.
2. All living organism are made up of cells.
3. All cells come from previously existing cells.
4. There is no life apart from the life of cells.
5. All living thing are either single cells (Unicellular) or group cells (Multi-cellular).
THE FORM IN WHICH CELLS EXIST
There are four forms in which living exist. These are:
As independent or single and free-living organism: Independent and free living organisms are organisms which assess only one cell and are capable of living freely on their own.
Examples are: Amoeba, Euglena, Paramecium and Chlamydomonas e.t.c.
A. Amoeba has irregular shape and changes constantly.
B. The protoplasm is made of nucleus and cytoplasm.
C. Embedded in the cytoplasm are food vacuole and contractile vacuole.
D. Amoeba moves with the aid of Pseudopodia.
Paramecium is often described as having a slipper shape. The Cytoplasm is composed of Cytoplasm and Endoplasm. The nucleus consists of two Micro-nucleus and Mega-nucleus. The Cytoplasm also house the food Vacuole, Contractile Vacuole And Cytostome. Paramecium moves with the aid of Cilia.
Euglena viridis is a protest and a typical example of an organism having the characteristics of plant and animal. The organisms possess Flagellum, Gullet, Contractive Vacuole, Eye Spot, Pellicle, and Myonemer e.t.c. Which makes it an animal chloroplasts, Pyrenoids and Parasylum granules which also make the organism a plant.
Chlamydomanas is a simple microscopic plant. It is a unicellular plant having flagella for movement, eye spot, chloroplasts, food vacuole and contractile vacuole.
AS A COLONY
Some organisms are made up of many similar cells which are joined massed together but they cannot be differentiated from each other. In other words, these cells from a loosely arranged association two or more cells but the cells cannot be differentiated from each of them.
This aggregation of independent cells or protists is called a Colony.
Examples are: Volvox, Pandorina And Sponges.
AS A FILAMENT
Certain cells are organized into filaments in which identical cells joined end to form un-branched filament. Each cells function as an independent living cell. Such organisms are multi-cellular and therefore exist as a filament.
Popular examples of filament organisms are the: Spirogyra Zygnema, Oseillateria and Oedogonium.
CELLS AS PART OF A LIVING ORGANISM
In multi-cellular organism, a group of numerous, similar cells arranged together and performing a specific function is cells. Tissue group of similar tissues forming a layer in an organism which forms a specific function is called an Organ. A group of organs which work together to perform specific function is called a System. From an explanation above, it is deduced that cells lead to tissues, tissues lead to organs while organs lead to system.
PLANT CELL AND ANIMAL CELL
Animal cells have centrosomes (or a pair of centrioles), and lysosomes, whereas plant cells do not. Plant cells have a cell wall, chloroplasts, plasmodesmata, and plastids used for storage, and a large central vacuole, whereas animal cells do not.
|S/N||CELL COMPONENT/ORGANELLES||FUNCTIONS OF THE CELL COMPONENTS|
|1.||Nucleus||1. It control all life activities of the cell. |
2. It stores hereditary information as it contains DNA inside chromosome which take part in cell division.
|2.||Chromosomes||It contains DNA which stores genetic traits.|
|3.||Mitochondria||It is described as the power house of the cell, they are site of respiration or where energy is released from simple sugar.|
|4.||Vacuole||It contains cell sap which act as an osmoregulator by helping in removing excess water in cells.|
|5.||Nucleolus||It produces the ribosome for protein synthesis.|
|6.||Endoplasmic Reticulum||It aids the transport of materials within the Cytoplasm.|
|7.||Golgi Bodies||It functions in synthesis, packaging which aid photosynthesis.|
|8.||Chloroplasts||They contain chlorophyll which aid photosynthesis in Green plants.|
|9.||Lysosomes||They are site for respiratory enzymes.|
|10.||Ribosomes||They are responsible for protein synthesis.|
|11.||Cell wall||1. It provides protection, shape and mechanical support for cell.|
2. It is also allows free passage of nutrient in and out of the cell.
|12.||Cell Membrane||It provides protection, shape and serves a great role in selective absorption of materials.|
|13.||Centrioles||They are important in cell division. They may also serve as a basal body from which Flagella or Cilia arise.|
|14.||Starch Granules||They store starch for the cell.|