Cell structure and Organisation

Cell Structure and Organisation

Animals as well as plant are made up cell. An average large organism will be made up of several millions of cells.

In 1667, a scientist named Hooke, during an experiment discovered that under a primitive microscope, a slice of a cork and other plant material consist of many small compartments, separated by a partition. What he believed in his experiment then was that cells were empty, and that cell wall was the most important part of a cell. But now, it has been realized that the most important part of a living cell is not just their cell wall but their contents.

Most plants and animal are multicellular, however, there are some which are one of one cell, and they are termed unicellular.

What is a Cell?

A cell is the basic unit of all living organisms. What does this mean? It means every living organisms is made up Of cell, whether plant or animal. The smallest cell ever known are the bacteria, while on the other hand , the largest cells are bird's egg.

In diameter, the size of most cells ranges between 0.25mm to 0.025mm

Types of Cell

In general, there are two major types of Cell

Prokaryotic cells
Eukaryotic cells

Prokaryotic cells: These are the type of cells that have no distinct nucleus, with no nucleus membrane, and they lack membrane bounded organelles (i.e chloroplast and mitochondria).

In this type of cell mitosis or meiosis (division of cell) does not take place.

Eukaryotic Cells: They're the type of cell with a distinct nucleus bounded by a membrane. Majority of organisms are made up Of eukaryotic cell. Most plants and animal are eukaryotic. Mitosis and meiosis do take place in this type of cell.

Eukaryotic cells are further divided into ;

Plant cell
Animal cell

Although eukaryotic cells are divided into plant and animal cells, but they both have their similarities and differences.

What are the similarities of Plant and Animal Cell?

They both contain nucleic acid, which made up the chromosomes
They both contain cytoplasm
They both contain ribosome, Golgi apparatus, and mitochondria
They both have cell membrane, which act as boundary between cell and it environment.

Plant and Animal Cell also have their differences.

What are the differences of Plant and Animal Cell ?

Plant cell has cellulose cell wall, while Animal Cell has no cellulose cell wall, only membrane.
Plant cell has large vacuole, while Animal cell has small numerous vacuole.
There are pits in the cell wall of plants, while Animal cell lacks cell wall, and no pit.
Plant cell has plasmodesmata, while Animal cell lack this.
Plant cell has varieties of plastids (such as leucoplast, chloroplast, etc), while this is absent in Animal cell.

Cell Organelles

Cell fractionation is usually used to separate the different parts of cell, for a detailed study of it. This process of separating these cell organelles is termed differential centrifugation.

Cell organelles

Nucleus: The nucleus controls all the organelles within the cell. It's bounded by a double unit membrane, and the nuclear envelope. It also controls the physiological activities of the cell , play an essential role in cell division, contains genetic materials of the cell , and it produces ribosome and RNA.

Cell membrane: All cell membrane are basically the same, they are known as unit membrane. They act as boundary between cell and it environs. The entering of different substance at different rate into the cell entirely is controlled by the cell membrane.

Golgi Apparatus: physically, when observed using a primitive microscope, they look like a stack of pilled up plates. It function in the cell is to;

Form lysosome
Produce glycoprotein
Transport and store lipids etc.

Mitochondria: Typically, it's 5 micrometer in length, and 0.2 micrometer in diameter. Mitochondria is often called the power house of the cell. A doubled membrane organelle which encloses the inner matrix, having a numerous fold called cristae (i.e muscle cell)

Endoplasmic Reticulum: it's a doubled membrane organelle which form a series of sheets which encloses flattened sacs known as cisternae. Smooth endoplasmic reticulum and rough endoplasmic reticulum are two known type of endoplasmic reticulum. The area of the endoplasmic reticulum lined with ribosome is the rough ER, while the one where where the ribosome is absent the smooth ER. Generally, the functions of endoplasmic reticulum are;

To help maintain the shape o the cell by forming a structural skeleton.
For protein synthesis
To collect and store the materials manufactured by the cell, etc.

Cellulose cell wall: They're non-living structure of the cell , lacking in most animal cells. When observed under a primitive microscope, they have distinct boundary layer, this layer is known as cellulose cell wall. It's term cellulose because it's made up of fibrils of cellulose, which isa polysaccharide. The main function of cellulose cell wall is to give support and protection. Also it allows the movement of water through and along it.

Chloroplast: Chloroplast is only found in plant cell . They vary in shape and size in different plants.

This chloroplast is responsible for photosynthesis in plants, as they contain chlorophyll.

Ribosomes: Ribosomes are cytoplasmic granules made up of small RNA molecules and protein. They are mostly present in plastids and mitochondria.

Vacuoles: They are fluid filled sac surrounded by a single membrane. Vacuole contains dissolved sugar, salt of organic acids, protein, mineral salts, pigment and oxygen.

Lysosomes: lysosomes are spherical organelle which contains around 50 enzymes. The functions of lysosome are;

Complete digestion of cell after it dies( also called autolysis)
The digestion of worn-out or unwanted cell organelles
The releasing of enzymes outside the cell, to digest materials that are outside the cell ( also known as exocytosis).

In conclusion

Cell is the basic unit of all living organisms, generally, there are two major types of Cell, which are prokaryotic cells and eukaryotic cells. Plant and Animal Cell are the type of eukaryotic cell.

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