Cell
What is the smallest part of ‘you’ that can actually be called ‘you’? I’m not asking this question to paint a cannibalistic picture. Don’t imagine yourself being cut into a million tiny pieces until you are indivisible. (ewww)
The cell is the basic structural and functional unit of any living organism. What this simply means is that the cell is the smallest part of you that can exist structurally. It is also the smallest part of you that can perform a function. Now you see why I nearly took you down the cannibalistic road? It totally works! Well almost.
For the chemistry buffs, think of the likeliest brother to an atom. The atom is the smallest part of a matter that has the same chemical properties of a chemical element. Yes, this works better than the cannibalistic approach. So the atom is to a chemical element what the cell is to your body.
What can something so tiny accomplish? You would be surprised. The cell has the same characteristics of living things. Surprised? Why should you be? Remember the cell is the smallest part of ‘you’, that can be ‘you’. So a cell has the following characteristics.
M- move
Source: Bulbeck
R- respire
N- nutrition
I- irritability
G-grow
E- excrete
R- reproduce
D- die
Where can you find cell?
They can be found in living organisms. (including you)
Cells are classified based where they can be found and type.
Based on ‘where they can be found’-
Unicellular organisms
The unicellular cell is a one-celled cell.(Now that sounds awkward. Let’s try again) a unicellular cell is a one-celled organism. (Woohoo, this is better)
One-celled or unicellular organisms are the simplest type of organisms ever! They contain only one cell. Examples are protozoa (A clue- proto means first), bacteria, unicellular algae and unicellular fungi. (You might wonder why I had to put unicellular before the last two-- because they have multicellular types)
Multicellular organisms
These are more complex organisms made of more than one cell. (A clue-- multi is gotten from multiple or ‘two or more’) Most plants and animals are multicellular organisms. They are more specialized than the simpler unicellular organisms.
What can you find inside a cell?
For the cell to perform the functions listed above (MR NIGER D) it contains the following organelles which help them perform those functions. Organelles are special substances inside a cell that has a specific role. Examples are-
Nucleus
Mitochondria
Ribosome
Lysosome
Golgi body
Endoplasmic reticulum (rough and smooth)
Peroxisomes
Vacuole
Chloroplast
cell wall
Centriole
Cilia and flagellae
Remember the cell is microscopic? We learnt that in the last blog post. Picture a family. You have the father, mother and children. Everyone has their role to play. No one is useless. The same with the cell. Everyone of this organelle within the cell organism, either unicellular or multicellular, prokaryotic or eukaryotic, has a function, a special role to play to help the cell carry out ‘MR NIGER D’
Let’s take a quick look at each organelle. (Clue- organelles means small organisms.) Why are they called small organisms? You will find out shortly.
| MR NIGER D | ORGANELLE | FUNCTION | |
|---|---|---|---|
| Movement | cilia and flagellae | These structures enable cell movement. | |
| Respiration | Mitochondria | They are the powerhouse of the cell, producing the energy required to do everything. In plant cells, peroxisomes have a major role in respiration. | |
| Nutrition | Lysosome | They help digest complex substances. | |
| Irritability | Cilia, flagellae and Mitochondria | Irritability is the ability to respond to outside stimuli in the environment. For the unicellular organism, the cilia and flagellae do this. For multicellular organisms, the nervous system is responsible. | |
| Growth | Golgi body | Mitochondria, Endoplasmic reticulum | |
| Excretion | |||
| Reproduction | Nucleus | ||
| Death | Mitochondria, and lysosome |
*For most of these functions, almost every organelle contributes to ensure 'smooth running' of every operation within the cell. What is listed here is the major orgelle involved. and where no organelle play a major role, I've left it blank.
For cell death, almost all the parts of a cell are responsible for this but the mitochondria and lysosomes majorly.
(Death here refers to cell death, cell suicide or programmed cell death. More on this later)
They are several differences between the plant cell and animals cells. Most of these are structural, with some structures found in one and not the other.
Smooth Endoplasmic reticulum- Lipid synthesis.
Rough Endoplasmic reticulum- Protein synthesis
Peroxisomes- Detoxification
Centrioles- These are special structures found only in animals cells that helps to give it a definite shape.
Cell wall- This is a rigid outer structure found only in plant cells but not animal cells.
Chloroplast- These are special structures found in plant cells but not animals cells that enable them to produce their own food through photosynthesis.
Vacuoles are special structures found only in plant cells. They are like ‘bags’. They carry food, waste, and other special substances to where they should be in the cell.
According to the evolutionary theory, one comes before the other. (Can you guess which?)
Prokaryotic cell
Source: Ali Zifan
Eukaryotic cell
To better understand these two- the prokaryotes and the eukaryotes, I love using the ‘house with rooms and the house with no rooms’ theory. (Sounds fishy doesn’t it? I’m weird that way, forgive me)
‘House with rooms and the house with no rooms’
A prokaryotic organism or cell is usually unicellular. It has no membrane-bound organelle. Let’s look at my ‘house with rooms and the house with no rooms’ model. It is simple really. The house with no rooms can almost be called a hall. That’s how the prokaryotic cell is. The organelles (chloroplast, vacuoles, mitochondria etc) are not enclosed by membranes, they are just scattered inside the cytosol. (A liquid medium inside a cell where the organelles kind of float about)
They are also able to manufacture their food from inorganic substances like ammonia and cellulose and nitrite. A process called chemosynthesis. (differs from photosynthesis. Clue- Photo means light)
They don’t have a nucleus (remember a nucleus is a membrane-bound organelle) instead they have a nucleoid which is a place where their nuclear material (for reproduction) can be found.
Examples are protozoa and bacteria.
The Eukaryotic organisms are mostly multicellular. They are different from the prokaryotic because of the presence of membrane-bound organelles.
Picture a house with rooms. Each room has its own walls and doors for privacy. A eukaryotic cell is far more specialized than the simpler prokaryotes. They can be found in plants and animals. Their organelles have their own membranes and perform their functions inside them.
Source : Mediran
According to evolutionists, this is a step up from the simpler life forms that are prokaryotes.
(Can you now guess which of them evolutionist says comes first?)
But why do the eukaryotes have membrane-bound organelles with ‘privacy’ to do their ‘business’ while the prokaryotes don’t?
Find out in the next blog post on this topic.
Why are organelles called small organisms?
References
Wikipedia contributors, "Chemosynthesis," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Chemosynthesis (accessed March 21, 2018).
Wikipedia contributors, "Prokaryote," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Prokaryote (accessed March 21, 2018).
Wikipedia contributors, "Cell Biology," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Cell_biology (accessed March 21, 2018).
Wikipedia contributors, "Unicellular Organism," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Unicellular_organism#cite_note-2 (accessed March 21, 2018).
Wikipedia contributors, "Unicellular Organism," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/wiki/Cell_physiology (accessed March 21, 2018).