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Cells: The Building Blocks of Life

Updated on August 17, 2013

Cells are the individual units of life. The human body is composed of trillions of cells and they are fundamental to the existence of life. Before we continue we must ask ourselves, what is a cell? Cells are microscopic structures that contain various organelles (think organs) that allows the cell to perform its designated function. Each cell has it's own function and are all extremely interesting and important to maintaining life on this planet

Picture of a cell and the organelles that compose it
Picture of a cell and the organelles that compose it | Source

What do Cells do?

This truly depends on the type of cell. Think of a community filled with many people. Everyone has a role to perform whether it be a doctor, a policeman, and a baker to name a few. That is the same with cells. Certain cells are made to combat illness; others are designated to become certain tissues but all have a purpose.

The Cell Theory

The cell theory is composed of three points.

1. All cells came from pre-existing cells

2. The cell is the basic unit of life

3. All life is either unicellular or multicellular

The founders of this theory are Theodor Schwann, Matthias Schleiden, and Rudolph Virchow.


Organelles are the various subunits found within a cell. They are parts of the cell specialized in doing something. There are multiple types of organelles found within a cell.

Chromosomes: Chromosomes are strands of DNA that contain genetic information. They are what makes you "you" essentially. They have codes on them they determine your hair colour, eye colour and all the features that you have today. There is a set number per species, humans having 23 pairs!

Chromatin: Chromatin are uncondensed versions of chromosomes essentially. They are found within the nucleus and only become chromosomes during cell replication.

Nucleus: The nucleus is essentially the brain of the cell. It controls eating, movement, and reproduction. Within it is found the chromatin and all genetic information.

Nuclear membrane: It is two layers of a membrane that surround the nucleus and determine what enters and what exits the cell.

Nucleous: It produces RNA that goes on to make proteins

Centrioles: Paired cylindrical organelles that are used during cellular division (mitosis)

Chloroplast: An organelle usually found in plant cells where photosynthesis takes place.

Endoplasmic Reticulum: A series of tubes that form a network which acts as the cell's transport system.

Lysosome: Organelle that helps in digesting waste and old cellular debris.

Golgi apparatus: Organelle that is a "packaging plant". It takes in simple molecules and adds to them to make them more complex!

Mitochondria: A large organelle that looks somewhat like a bean. It produces the energy of the cell and contains it's own unique DNA.

Ribosomes: Organelles that make various proteins

Vacuoles: Membrane-bound sacs for storage, digestion, and waste removal

Labelled organelles of an animal cell
Labelled organelles of an animal cell | Source
Labelled organelles of a plant cell
Labelled organelles of a plant cell | Source


How do cells replicate? There is a complex process known as mitosis which shows how almost all cells divide (except for sex cells). There are 6 stages of mitosis.

Interphase: This is the first stage of mitosis. It is also known as the grow stage, This is where the cell decides to take in additional resources so that it can split in two. The organelles are all duplicated and the genetic information is as well. There is still chromatin and they have not become chromosomes yet.

Prophase: The DNA molecules shorten and condense, turning chromatin into chromosomes. The nuclear membrane and nucleolus are no longer visible in this stage.

Metaphase: Thread like spindle fibres come out of the centrioles and attach to the centromere of the chromosome. The centromere is the middle joining two replicated chromatids. A chromatid is one half of the "x" shape that the chromosomes make during mitosis. The spindle fibres align the chromosomes in what is called the metaphase plate.

Anaphase: This is where the spindle fibres pull away and separate the joined chromatids.

Telophase: The chromosomes reach the poles of their respective spindles where they disintegrate. The nuclear membranes begin to reform and the chromosomes begin to uncoil and become chromatin.

Cytokinesis: This is where the cell divides into two, completing the process of mitosis.

Diagram of all the stages taking place during mitosis
Diagram of all the stages taking place during mitosis | Source

Knowing more about cells is vital to our understanding of life and how it works. Learn more about cells by visiting websites such as


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