What Is A Cell? Definition, Functions, Types, and Examples.

 Definition: A cell is the basic unit of all living organisms. Your body is made up of hundreds of billions of cells that provide it with; characteristic structure, ability to absorb and assimilate those nutrients into food and carry out specific functions. Cells are specialized and adapted according to the function they perform; white blood cells, gametes etc. In addition to this the cells in your body carry your genetic material which allows them to make copies of themselves and allow you to pass on your traits to your offspring.

Inside each cell are smaller structures referred to as cell organelles, these perform different kind of functions that allow the cell to survive at carryout its tasks. Various functions carried out by cell organelles include;

1.  Transportation
2.    Metabolism
3.    Secretion of chemicals

Some cells such as the red blood cells, Nerve cells, root hair cells etc. have special structures modified to help them carry out they specific functions, for example red blood cells lack a nucleus to allow them carry more oxygen by creating more room for the oxygen carrying molecule called haemoglobin.

Organelles in the cell are suspended in a gelatinous liquid called the cytoplasm. The cytoplasm is made of water, salts and various organic compounds.

Cells group together to form tissues, tissues group to form organs such as kidneys, the brain etc. organs group to form the complete organism.

Without further ado lets learn more about cells, we are going to ponder question such as;

1.        What are the functions of a cell?  
2.         What types of cells are there?
3.         How do cells reproduce?
4.        What is the structure of a cell?

FUNCTIONS OF A CELL

Cells perform six basic functions:

1)      Provide mechanical support to organisms

2)      Aid in growth of Organism through cell division (mitosis)

3)      Allow transportation of nutrients through passive and active transport

4)      Production of energy

5)      Facilitate metabolic reactions

6)      And allow for reproduction (especially formation of gametes)

  Provide Machenical (Structural) Support to Organisms

Cells account for the structure of all living organisms we see in our daily lives. Even though some cells where specially meant for physical support, virtually all cells provide the mechanical basis of all living organisms.

Examples:

-          The Sclerenchyma and collenchyma cells in plants and specifically meant for structural support.

-          Skin cells and muscle cells also provide structural support to the skin and muscles respectively.

Aid in Growth of Organisms through Mitosis

Mitosis is when a single cell divides to form two daughter cells identical to the parent cell. Through this process, we are able to witness living organisms grow bigger and bigger with time as a result of the increased number of cells. In addition to this mitosis also allows simpler organisms to produce offspring.

Allow transportation of nutrients through passive and active transport

Cells acquire nutrients that they need through small molecules like carbon dioxide, ethanol and oxygen that are taken up passively through simple diffusion. Diffusion is regulated by tcells through a concentration gradient across the cell membrane. On the other hand cells allow the body to acquire and utilize larger molecules against their concentration gradient through an active process called active transport. During this process cells use vesicles to absorb or excrete molecules.

Production of energy

Energy production in all living organism large and small, terrestrial or aquatic, plant or animal is done through cells. Cells through the processes of respiration and photosynthesis are able to produce the energy needed for daily life in organisms.

Cells Account For All Metabolic Reactions In The Body

Metabolism refers to all chemical reactions occurring inside an organism supporting life. There basically two types of metabolic reactions.

Catabolic

Catabolic reactions refer to those reactions that break down molecules.

 Anabolic

Anabolic reactions refer to those reaction that use energy to make complex compounds from simpler compounds such as photosynthesis.

Allow for Reproduction

Any specie you have ever come across increases in numbers as a result of reproduction, be that rabbit you are petting or dog you are petting they all depend on reproduction for continuity of species. There are two main types of reproduction; Asexual Reproduction and Sexual Reproduction. Asexual reproduction is when an organism reproduces through mitosis (i.e. through dividing to form new cells). Sexual reproduction is when gametes are produced (through meiosis) by the male and female organism which joins to form a genetically unique offspring from the parent.

STRUCTURE OF A CELL

The living contents of the cell such as the nucleus, mitochondria etc. make up what is known as the Protoplasm. Protoplasm in addition to these is primarily made up of biomolecules like proteins, lipids, carbohydrates and nucleic acids. Some inorganic molecules such as salts are found in it as well as water. Protoplasm of a cell is surrounded by the cell membrane.

The basic structure of a cell constitutes;

v  Cytoplasm

v  Nucleus

v  Cytoskeleton

v  Plasma membrane

v  Endoplasmic reticulum

v  Golgi apparatus

v  Mitochondria

v  Lysosomes and peroxisomes

v  Ribosomes

Cytoplasm

This is consists of a jelly-like liquid known as cytosol with a suspension of cell organelles or genetic material (prokaryotic cells).

Nucleus

This cell organelle is responsible for controlling all cell activities. The nucleus:

v  Signals Cell growth and maturity

v  Triggers Cell Division and death.

v  Contains the cells genetic material (DNA)

The nucleus is enclosed in a nuclear envelope, this is a membrane that protects cell DNA and separate the nucleus from the rest of the cell.

Cytoskeleton

This refers to the network of long fibers that form the cell’s mechanical framework. The cytoskeleton:

v  Makes up the structural framework of a cell.

v  Gives the cell its shape.

v  Allows cells to move

v  Takes part in cell division

Plasma Membrane (Cell Membrane)

This is the structure that separates the cell from its environment. The cell membrane is partially permeable. Smaller molecules diffuse across it while larger ones pass through using active transport.

Endoplasmic reticulum (ER)

This serves as the transport system of the cell. The endoplasmic reticulum moves molecules created by the cells to various destination within or outside cells. I addition to this, the ER helps in processing molecules that are produced by the cell.

Golgi apparatus

The main function of the golgi apparatus is to package molecules that are processed by the ER in order to be sent out side of the cell. Hence it complements the endoplasmic reticulum in function.

Lysosomes and Peroxisomes

These help the cell in two main ways:

1)      Defense from foreign material

2)      Excretion

They aid in defense by digesting foreign bacteria or molecules that invade the cell. In other words the help get rid of toxic substances that invade the cell.

They help in excretion in that they are responsible for recycling worn out cell organelles.

 Mitochondria

Also referred to as the power house of the cell, mitochondria refer to complex cell organelles that convert energy from the nutrients taken into a form that can be used by cells for their daily activities. They are the only cell organelles that have they own genetic material which is separate from cellular DNA; hence they are able to replicate on their own without the nucleus. Cool uh???

Ribosomes

These organelles are responsible for processing the genetic instructions contained in cellular DNA into proteins which can be used to create cellular structures. Ribosomes are found floating freely in cellular cytoplasm however some are attached to the endoplasmic reticulum in which case the ER is called a rough endoplasmic reticulum.

TYPES OF CELLS

There are two main types of cells; eukaryotic cells and prokaryotic cells

Eukaryotic cells

These are cells that contain membrane bound organelles such as nucleus, mitochondria, vacuole etc. eukaryotic cells are cells that make up animals, plants, fungi and protists. These cells are usually found in multicellular organisms and sometimes in complex unicellular organisms.

Prokaryotic Cells

These cells include cells that don’t have membrane bound organelles such as nucleus, mitochondria vacuole etc. in such cells, DNA is found floating freely within the cell cytoplasm. The DNA is found in circular chromosomes called plasmids or in a region we refer to as the nucleoid. Organisms made up of prokaryotic cells are always unicellular and these include bacteria and archaea.

CELL OVERVIEW