The Cell; Structure And Functions Of Cell Components

The cell is the basic functional and structural unit of life. Human beings are multi-cellular animals. What this means is that we humans are made of many cells of cells as opposed to unicellular organisms which are composed of only one cell. The cells in a lot of multi-cellular animals and plants are specialized.

This means that each of them carries out a specific function and when all the cells combine together with their functions, they can share out the processes of life. Each cell is dependent on the other and all of them function collaboratively to support the diverse processes in an organism.

The cell

  • All the living bodies are made up of protoplasm.
  • The fabric of life (protoplasm) is seldom found in large masses but is found in the form of discrete structures.
  • These minute morphological bodies are known as the
  • The term cell was first used by Robert Hook (1665).


  • Cell theory was formulated by Schleiden and Theodore Schwann (1938-39).
    • All living organisms are made up of one or more cells.
    • Cells are the basic unit of life.
    • All cells arise from pre-existing cells.(omni cellulae e cellula)
    • The cell is the unit of structure, physiology, and organization in living                 things.
    • The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.
    • Thus the cell is considered as the fundamental structural and functional unit of living organisms


1. Prokaryotes are primitive organisms (Pro = primitive; Karyon = nucleus)1. Eukaryotes are higher organisms (Eu = good or true; Karyon = nucleus)
2. They are generally uni-cellular2. They are generally multi-cellular
3. The average diameter of prokaryotic cell ranges from 5 – 10μm3. The average diameter of eukaryotic cell ranges from 10–100 μm
4. Possesss only one envelope system4. Possesss two envelope system
5. Don’t possess well defined cytoplasmic organelles5. Possess well defined cytoplasmic organelles like endosplasmic reticulum., golgi bodies, chloroplast, mitochondria
6. They lack nucleus and chromosomes6. Possess well developed nucleus and chromosomes
7. DNA is circular and lies free in the cytoplasm7. DNA is linear and lies within the nucleus
8. Cell division is by amitosis (binary fission)8. Cell division is by mitosis and meiosis
9. Possess ribosomes of 70 S type9. Possess ribosomes of 80 S type
10. Nucleolus is absent10. Nucleolus is present
11. Spindle fibres are absent11. Spindle fibres are present
12. Cell wall is made up of polysaccharides Eg: Muramic acid12. Cell wall is made up of cellulose, hemicellulose and pectins
13. Histone proteins are absent13. Histone proteins are present
14. Pigments are distributed throughout the cytoplasm14. Pigments are present in plastids
15. Nuclear membrane is absent15. Nuclear membrane is present
16. Mesosomes support respiration16. Mitochondria support respiration
17. Eg: Bacteria, blue green algae, E. coli, PPLOs (Pleuropheumonia like organisms)17. Eg: Plant and animal cells

Shape of the Cell

  • In general, the cell shape varies greatly from tissue to tissue.
  • It may be fixed or changeable; spherical or oval; flat or elongate; spindle shaped or globose; cylindrical or polyhedral and so forth.
  • These different shapes of the cells are related to
    • the particular functions they perform,
    • partly on the surface tension and viscosity of the protoplasm,
    • mechanical action exerted by the adjoining cell and
    • rigidity of the cell membrane,
    • cytoplasmic microtubules.

Size of the Cell

  • Mostly the eukaryotic cells are microscopic in size, but definitely they are larger in size than the bacterial cells.
  • The size of cells varies from 1μ to 175 mm.
  • The ostrich egg cell is usually considered as largest cell (with 175 mm diameter).
  • But certain longest nerve cells have been found to have a length of 3 to 3.5 feet.

You do not teach the path of the forest to an old gorilla. congo

  • The volume of the cell is fairly constant for a particular cell type and is independent of the organism.

Cell Number

  • The body of unicellular or acellular organisms (Protozoa and Protophyta) consists of single cell.
  • Most of the animals and plants are multicellular and may have many cells.
  • The number of cells in the multicellular organisms usually remains correlated with the size of the organisms.
  • Small-sized organisms have less number of cells in comparison to large-sized organisms.
The tables below show examples of some specialized animal and plant cells, together with their functions and special features.
Table illustrating the different types of animal and plant cells with their specific features and functions

Types of animal cell Function Special features

1. Red blood cells To transport oxygen round the body It has large surface area, for oxygen to pass through. The red blood cell contains haemoglobin, which reacts with oxygen to form oxyhaemaglobin.
2. Nerve cells Nerve cells transports nervous impulses to various parts of the body It has a long connections at each end and has the capacity to carry electrical signals.
3. Female reproductive cell also known as the egg cell. The egg cell’s function is to combine with the male cell, and subsequently to make food available for the new cell that was formed The egg cell is large and contains a lot of cytoplasm
Male reproductive cell which is also known as the sperm cell. The sperm cell function is to travel up and meet with egg cell for a fusion to form a zygote. The sperm cell has an elongated tail for swimming as well as a head which enables it to get attached with the female egg cell for a fusion.

Types of plant cell Function Special features

1. Root hair cell The root hair cell absorbs water and minerals from the soil. It has a large surface area.
2. Leaf cell The leaf cell absorbs sunlight for the process of photosynthesis It has large surface area and lots of chloroplasts
Plant and animal cells have quite a few differences and similarities. For instance, animal cells do not have a cell wall or chloroplasts but plant cells have them. Animal cells are round and irregular in shape whereas plant cells have fixed rectangular shapes.


Our primary discussion here is on eukaryotic organelles, their functions inside the cell and the way they differ between plant and animal cells.
1. The Nucleus:
The nucleus is a home for the majority of genetic material of a cell. The nucleus is the “brain” of the cell and controls all activity that takes place inside the cell with the help of DNA as a outline to direct the production of proteins in the cell.
2. The Ribosomes:
The ribosomes function is to synthesize protein for the entire nucleus. They transport together all the raw ingredients like the RNA which are the replicas of the original DNA and amino acids to manufacture proteins. The proteins manufactured are very vital to cell and the optimum function of the organism.
Think of proteins as machinery for cell functions much like electricity and plumbing are essential in a real city. For example, enzymes are a type of protein without which life could not exist. The big and small subunits of ribosomal RNA translate an mRNA strand into a polypeptide chain.
3. The Endoplasmic Reticulum:
There are two types of endoplasmic reticulum (ER). The first on is the smooth endoplasmic reticulum and the second rough endoplasmic reticulum. This broad network of endoplasmic reticulum comprises about one half of all membranous tissue of the cell.
It is the site for membrane and protein synthesis. The Endoplasmic Reticulum system is very much like a road system that leads to an industry. Goods are produced in the factory and are transported to where it is needed through the same transport system
The Rough Endoplasmic Reticulum is thus named because of the presence of ribosomes along its membrane which is the source of proteins. Smooth Endoplasmic Reticulum does not have ribosomes and is in charge of lipid synthesis and processes a multiplicity of metabolic processes like the detoxification of drug.
4. Cell Membrane and Cell Wall
The cell membranes are present in animal cells while cell walls are present in plant cells. Cell walls and cell membranes have related functions. Just akin to a city outer limit, cell membranes enclose the cell and have the capability to control what enters in and out of the cell and by so doing, it regulates internal balance.
These membranes as well protect the inner cell from exterior forces. Cell walls, just like our city analogy, are much stronger than cell membranes and their function is to protect the cells from exploding in exceptionally hypotonic or diluted solutions.
5. Cytoskeleton:
The cytoskeleton is composed of an internal framework, which makes available to each one of the cell its distinctive shape and high level of organization that it contains. It is very significant for the movement of the and also for mitotic cell division or mitosis.
6. Cytoplasm:
Cytoplasm is a semi-fluid or gelatinous substance located inside the cell. The cytoplasm covers moderates and protects the inner organelles.
It is the cell background or surface area and is available anywhere in the cell where there are no organelles present. It is therefore very similar to the lawns and parks of our city which are normally cited where there are no residential or commercial houses.
7. Golgi Apparatus:
Golgi apparatus functions as a post office which is used for the transportation of the manufactured food by the endoplasmic reticulum and ribosomes to the rest of cell.
8. Chloroplasts:
Chloroplasts are organelles that are visible in the plant cells alone. They contain pigment known as chlorophyll which traps the energy of the sun to manufacture food for the plant during the process of photosynthesis.
Just similar to solar energy plant they make use of sunlight to manufacture energy for the plant. Chloroplasts are the place where photosynthesis- occurs in plants.
Photosynthesis is the process in which the plant makes use of carbon dioxide, water and sunlight to manufacture energy in the form of glucose for the plant cell as well as heterotrophs-animals that depends on plant for their food production.
9. Mitochondria:
Mitochondrion is present in both plant and animal cells and is the site where cellular respiration occurs. Through cellular respiration which would be covered in detail when explaining the process of photosynthesis and Respiration, a substance known as ATP is formed this is used for energy by the cell.
10. Lysosomes:
The lysosomes are digestive sacs that possess the tendency to be broken down into macromolecules in the cell through the process of hydrolysis. The digestion is carried out through the lysosomal enzymes located in the lysosome.
Lysosome is responsible with the disposal of excessive or bulky macromolecules in the same way the waste disposal in a city does. Lysosomes help to keep unnecessary or bulky macromolecules from mounting up in the cell.
11. The Cell Vacuoles and Vesicles:
These are similar in nature and function as membrane sacs that perform a lot of functions as control units for whatever thing that is in surplus in a city. They can contain a lot of substances starting from complex organic molecules to simple surplus water.
Plant cells possess a central vacuole that is very essential in keeping up and sustaining the turgidity of plants.

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