Organisms can be of different types and complexity. An organism is made up of tiny compartments called cells. One cell can make up the whole organism, or many cells can assemble into complex organisms.
The more cells, the more complex the organism. Less the cells of organisms more the functions of the cells.
Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function. Their structure is related to their function, meaning each type of cell takes on a particular form in order to best serve its purpose.
In general, unicellular organisms fall under the umbrella of prokaryotes or prokaryotic entities. They are called prokaryotes because they are not as specialized as the more complex eukaryotes.
Unicellular organisms and the prokaryotes do not have the structure called cell nuclei. In addition, their bodies are very limited in size due to their inability to cope with certain surface-to-volume ratio issues. The result of this is that unicellular organisms are mostly microscopic. They are so tiny that they cannot be seen with the naked eye.
Aside from not having a cell nucleus, prokaryotes are ones that do not have internal organ bodies covered with organic coats called membranes. They are also the ones that often live in habitats that are too dangerous to support life, such as the highly acidic environments and irradiated areas.
On the other hand, multicellular organisms are those that harbor multiple numbers or many cell types. These organisms are usually larger, have more specialized functions, and are classified as eukaryotes.
These organisms are called eukaryotes because they have nuclei and their DNA is placed differently than the rest of the cell. Because of these facts, they can actually grow to larger sizes; They can carry out more complex activities or functions and their cells constantly interact harmoniously.
Although these organisms can grow exponentially to amazing sizes, some of them are also classified as microscopic (Myxozoa).
Unicellular organisms include bacteria, protists, and yeasts. A paramecium, for example, is a slipper-shaped, unicellular organism found in pond water. It takes food from the water and digests it in organelles known as food vacuoles.
Nutrients from food travel through the cytoplasm to the surrounding organelles and help keep the cell, and therefore the organism, functioning.
Multicellular organisms are made up of more than one cell, with groups of cells differentiating to perform specialized functions. In humans, cells differentiate early in development into nerve cells, skin cells, muscle cells, blood cells, and other cell types.
One can easily observe the differences in these cells under a microscope. Their structure is related to their function, meaning each cell type takes on a specific shape to best serve its purpose.
Nerve cells have appendages called dendrites and axons that connect to other nerve cells to move muscles, send signals to glands, or register sensory stimuli.
Outer skin cells form flattened stacks that protect the body from the environment. Muscle cells are slender fibers that bundle together for muscle contraction.
The life span of unicellular organisms is short as compared to multicellular organisms due to the high workload.
Unicellular organisms have low operational efficiency as compared to multicellular species.
Unicellular organisms generally do not go through any cell differentiation, except unicellular yeasts. While multicellular organisms go through categorized cell division to form differentiated cells, which can perform particular tasks.
The unicellular organisms are immortal, as they are capable of regeneration whereas multicellular organisms lose the regeneration ability for cell growth and differentiation of cells aging.
The lifespan of unicellular organisms is short compared to multicellular organisms due to the high workload.
Unicellular organisms have low operating efficiencies compared to multicellular species.
Unicellular organisms generally do not undergo cell differentiation, except for unicellular yeasts. While multicellular organisms undergo categorized cell division to form differentiated cells capable of performing specific tasks.
The unicellular organisms are immortal as they are capable of regeneration, while multicellular organisms lose the regenerative ability for cell growth and cell differentiation with age.