There are lots of different ways to categorize living organisms.
One of the most important ways is to sort them into eukaryotes and prokaryotes.
All living things can be put into one of these two categories based on their cell structure.
But what is the difference between eukaryotes and prokaryotes? What do they have in common and what sets them apart?
We have put together this useful guide to tell you everything you need to know about eukaryotes and prokaryotes.
Keep reading to find out more.
Eukaryotes VS Prokaryotes
All organisms share four common characteristics, which form the basic principles of cell theory.
They contain at least one cell, the life of the organism is contained within the cell or cells, all cells from pre-existing cells, all cells hold the genetic material required for the cell to function and this information is passed onto the new daughter cells that are created from the original parent cell.
The basic difference between eukaryotes and prokaryotes is the presence or absence of internal cell membranes.
Cells are surrounded by a cell membrane, but certain cells also have internal plasma membranes which hold the nucleus and other organelles.
Eukaryotes have internal cell membranes, whereas prokaryotes do not.
Eukaryotes include animals, plants and fungus. Prokaryotes include bacteria, mycoplasma and certain types of algae.
As the biggest difference between eukaryotic and prokaryotic cells is related to the cell membrane, it is important to understand cell membranes.
Each type of cell has a different function within an organism, or within an environment of single celled organisms.
These functions require different chemical processes, often complex ones.
In order to keep these chemical processes separate, all cells have an external membrane to separate them from other cells or from their surroundings.
Cell membranes are selectively permeable. This means that they allow certain chemicals into the cell but not others, and they also allow particular chemicals to leave the cell.
This maintains the right balance of chemicals within the cell to keep it functioning and healthy.
There are three different processes used to control the flow of chemicals in and out of the cell – diffusion, osmosis, and selective transport.
Diffusion is the movement of solute molecules from an area of high concentration to an area of low concentration.
Osmosis is the movement of solvent molecules through a membrane to balance the concentration of non-solvent material on either side.
Selective transport is when molecules are moved from one side of the cell membrane to the other using membrane pumps and channels.
Certain cells also have internal membranes.
These are similar to external membranes, except they surround structures within the cell to separate them from each other and from the cytoplasm within the cell.
This allows the different organelles to keep their own functions and processes separate and to keep the cytoplasm free from contamination, improving cell health.
The more complex the cell, the more internal membranes it is likely to have.
Features Of Eukaryotic Cells
Most Eukaryotic organisms are multicellular, though there are a few examples of single cell eukaryotes.
There is a range of structures surrounded by internal membranes within a single eukaryotic cell.
Here is what you can expect to find within a eukaryotic cell:
- Plasma Membrane – The plasma membrane is the external membrane around the outside of the cell that separates it from its surroundings and other cells
- Cell Wall or Cytoskeleton – This is another perimeter around the cell that provides protection and structure. It also assists with cell movement and is involved in the process of cell division. Cell walls are found most commonly in plant cells and are made from cellulose. Cytoskeletons are made from overlapped proteins.
- Cytosol – This substance within the cell has a gel like consistency and is where the organelles are found
- Nuclear Envelope – This is a double membrane that surrounds the nucleus and allows it to communicate with the cytoplasm via a series of pores. It is also connected to the endoplasmic reticulum via the pores.
- Cytoplasm – The cytoplasm sits between the plasma membrane and the nuclear envelope
- Nucleus – The nucleus is the area of the cell that holds all of DNA and genetic information in the form of chromatids. It is often referred to as the brain of the cell.
- Chromosomes – Chromosomes hold the genetic information in the form of chromatids. Chromatids are threads of DNA which are then compressed into coils to form chromosomes.
- Nucleolus – Ribosomal RNA is made in this area of the cell that is found within the nucleus
- Ribosomes – These organelles synthesize proteins
- Mitochondria – These organelles are responsible for the production of energy that supplies the whole cell. They use aerobic respiration to convert the food of the cell into adenosine triphosphate- energy. They are often called the powerhouse of the cell. They are smooth on the outside, with a large surface area on the inside made up of folds called cristae. The inside of the mitochondria is called the matrix, and it is filled with fluid.
- Vesicles and Vacuoles – Vesicles and vacuoles are sacs within the eukaryotic cells which have their own membrane. They store important molecules and move them to the areas of the cell that need them. Vacuoles can be used to store food to use later, or they can be used to store waste to keep the cytoplasm free from contaminants.
- Endoplasmic Reticulum – This organelle is used to mature and transport materials around the cell. It is often called the intracellular highway. There are two types of endoplasmic reticulum- rough and smooth. Rough endoplasmic reticulum is coated with ribosomes and is used to form and transport proteins. Smooth endoplasmic reticulum produces lipids and helps to detoxify the cell by getting rids of poisonous or harmful compounds.
There are other types of organelles that can be found in eukaryotic cells.
They are not found in all eukaryotic cells, and it depends on what type of cell it is and what function it has.
These include lysosomes, chloroplasts (found in plant cells), and golgi apparatus.
Chloroplasts are the equivalent of mitochondria in plant cells.
They contain their own DNA and they also contain chlorophyll, the enzyme that is needed for the process of photosynthesis – converting light into chemical energy.
Golgi Apparatus produces proteins, modifies proteins, and also packages important molecules like proteins or molecules so they can be transported to another area of the cell where they are needed.
Lysosomes digest bacteria in order to protect the cell from harmful compounds.
They also break down the cell food into smaller blocks of amino acids and glucose which can be used to produce energy or sent to certain areas of the cell to assist with cell function.
Cells in certain areas of an organism will contain more or less of the various organelles depending on the function of that area of the body.
For example, the liver is responsible for detoxification so it will contain a higher number of lysosomes.
The cells in the leaves of the plant will contain more chloroplasts because the leaves are responsible for absorbing sunlight and converting it into chemical energy.
In multicellular eukaryotic organisms, the different cells can communicate with each other to carry out complex biochemical and biological processes.
The health of an organism depends on all of the organelles functioning as they should.
If the organism comes into contact with parasites, viruses, diseases or free radicals then this can severely hinder the function of the cells and how they interact with each other.
This can also be caused by a lack of food or nutrition or high levels of stress.
If you want to get a good look at the organelles of a cell under a microscope, the best time to do this is around the process of cell division.
Just before, during, or just after the process of cell division is when the organelles will be most visible.
When you examine eukaryotic cells under a microscope you will see how similar they look even if they are taken from different organisms.
This is because the cell structure of eukaryotic cells is very similar and they contain the same kinds of organelles – the differences between the organisms is found in the strands of DNA which make up the chromosomes.
Features Of Prokaryotic Cells
Even though prokaryotic cells do not have an internal plasma membrane to hold the organelles, they do have different regions. The DNA in the cell will congregate in the nucleoid region.
Here is what you can expect to find within a prokaryotic cell:
- Cell Membrane – This external membrane separates the cell from its surroundings such as other cells or matter
- Cell Wall – The cell wall sits inside the cell membrane and provides the cell with protection from its surroundings. The cell wall is usually made up of carbohydrates and proteins.
- Capsule – Certain prokaryotes, such as some bacteria, have a capsule in between the cell wall and the external membrane. This enables the bacteria to cling to surfaces.
- Nucleoid – The nucleoid is the central region of the cell where the DNA collects
- Ribosomes – Ribosomes are a type of organelle that synthesizes proteins
- Flagella – Flagella are thin structures within a cell that help with movement
- Fimbriae – Are also thin structures, but thinner than flagella. They help the cell to attach to things
- Pili – These structures are rod shaped and they assist with a lot of functions in the cell including the attachment and transfer of DNA.
- Plasmids – These are the prokaryotic equivalent of chromosomes as they hold the DNA
What Are The Main Similarities And Differences Between Eukaryotic Cells And Prokaryotic Cells?
As you can see from the features of the two types of cells, there are some differences and similarities.
There are a lot of structural differences between the two, but they have some chemical similarities.
Both eukaryotic and prokaryotic cells contain or use the following- proteins, lipids, carbohydrates, and nucleic acids.
They also use chemical reactions in order to create and use energy and to produce proteins.
All types of cells need energy (usually in the form of adenosine triphosphate or glucose) and proteins (amino acids).
These substances are vital for the function of the cell and for cell reproduction, division and multiplication.
The biggest differences between eukaryotes and prokaryotes is arguably their structure.
Almost all prokaryotic organisms are single celled, and most eukaryotic organisms are multicellular.
Prokaryotic cells have an external membrane, but they don’t contain any organelles enclosed by a membrane.
Prokaryotes don’t contain endoplasmic reticulum like eukaryotes do.
Eukaryotes store their DNA in Chromosomes made up of chromatid threads compressed into coils.
Prokaryotes store their DNA in plasmids. Prokaryotes don’t have histones in their DNA, whereas eukaryotes do.
Histones are the proteins that eukaryotic cells wrap their DNA around.
An additional structural difference applies to prokaryotic bacteria. They can be identified by the different types of rods, spheres and spiral shaped structures that are within the cell.
Another big difference between eukaryotic cells and prokaryotic cells is the process they use for cell division.
Prokaryotic cells use a process called binary fission, whereas eukaryotic cells use a process called mitosis followed by cytokinesis.
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