Do larger unicellular eukaryotic organisms have larger organelles?

Do larger unicellular eukaryotic organisms have larger organelles?

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It seems that many of the giant unicellular eukaryotic organisms (size 1mm and above) are multinucleate but there are some with a single nucleus as well (the genus of Acetabularia). My question is: do they have proportially larger organelles (mitochondria etc.)? If so, can they be seen by a person with sharp eyesight when removed from the cell?

The cell has the amount of organelles necessary to perform its function. If a cell requires a lot of protein, it must have multiple nuclei to produce this protein. If the cell performs many activities that require energy, it needs many mitochondria. So the size and quantity of the organelles will be proportional to their function, not their size. In relation to Acetabularia, it is a single-celled organism visible to the naked eye. The nucleus is visible, but other organelles are not.

Cells are called the building blocks of life because they often come together to form multicellular organisms, such as plants or animals. However, some organisms consist of only one cell. These are called unicellular organisms. Although much smaller, unicellular organisms can perform some of the same complex activities as multicellular organisms.

Many unicellular organisms live in extreme environments, such as hot springs, thermal ocean vents, polar ice, and frozen tundra. These unicellular organisms are called extremophiles. Extremophiles are resistant to extremes of temperature or pH, and are specially adapted to live in places where multicellular organisms cannot survive. This unique feature allows scientists to use unicellular organisms in ways previously only imagined. When Thermus aquaticus was discovered in the boiling water of a Yellowstone Park hot spring, scientists used its special enzyme TAQ polymerase to replicate DNA billions of times in the span of just a few hours. Without this discovery, forensic science and genetic testing as we know them wouldn’t exist. Other extremophiles have been used for treating arthritis and autoimmune diseases, making paper, treating waste, and radiation resistance.

However, not all unicellular organisms are extremophiles. Many types live under the same narrow range of living conditions as multicellular organisms, but still produce things necessary to all life forms on Earth. For example, phytoplankton is a type of unicellular organism that lives in the ocean. Not only are they the very foundation of the ocean’s food chain, but phytoplankton also provide most of the oxygen in Earth’s atmosphere. Without them, humans could not breathe, plants could not thrive, and life would cease to exist completely.

Advantage to Colony

Even though the individual single-celled organisms remained separate and could survive independently, there was some sort of advantage to living close to other prokaryotes. Whether this was a function of protection or a way to get more energy, colonialism has to be beneficial in some manner for all of the prokaryotes involved in the colony.

Once these single-celled living things were within close enough proximity to one another, they took their symbiotic relationship one step further. The larger unicellular organism engulfed other, smaller, single-celled organisms. At that point, they were no longer independent colonial organisms but instead were one large cell.

When the larger cell that had engulfed the smaller cells started to divide, copies of the smaller prokaryotes inside were made and passed down to the daughter cells.

Eventually, the smaller prokaryotes that had been engulfed adapted and evolved into some of the organelles we know of today in eukaryotic cells such as the mitochondria and chloroplasts.

Multicellular Vs. Unicellular Organisms

As the name suggests, the main difference between multicellular and unicellular organisms is the number of cells that are present in them. This leads to the development of all other characteristics and properties of these living organisms. Read about the distinction between these two types in this BiologyWise article.

As the name suggests, the main difference between multicellular and unicellular organisms is the number of cells that are present in them. This leads to the development of all other characteristics and properties of these living organisms. Read about the distinction between these two types in this BiologyWise article.

Cells are the building blocks of all life forms. Every living thing has cells within its body. The composition, distribution, and the number of cells that are present in an organism determine whether it is multicellular or unicellular. Cells in the human body play a vital role in the sustenance of life.

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In simple terms the difference between unicellular and multicellular organisms arises from the number of cells that are present in them. As the name suggests, unicellular organisms contain one single cell, while multicellular organisms contain more than one cell within them. All their physical characteristics and traits can be traced to the difference in the number of cells they comprise.

Unicellular Organisms

Due to the presence of only one cell in them, these organisms are much smaller in size and are very simple in structure. Most of these organisms fall under the category of ‘prokaryotes’, or ‘prokaryotic entities’, because their composition and structure is not complex. The structure known as the cell nucleus is completely absent in these prokaryotes, and this leads to their inability to handle their surface area to volume ratios. Owing to this reason, their sizes are very small.

Most unicellular organisms are so small and microscopic in nature, that they are almost invisible to the naked human eyes. They do not have internal organs as well, and this means that the membranes which are the organic coats around the organs are also absent. Due to their highly simplistic life form, these can exist in areas that are perceived to be hazardous to human life and are highly acidic or radioactive in nature.

It is believed by many scientists that the human race is the result of long term evolution of many unicellular organisms that existed millions of years ago. The two sets of organisms exist in harmony with each other on our planet. Besides this, all these organisms have their own specific roles to play in nature’s ecosystem.

Examples: All forms of bacteria, amoeba, yeast, and paramecium.

Multicellular Organisms

On the other hand, these organisms are those forms of life that have more than one cell present in them. In fact, they have millions of cells present in them.

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The larger number of cells means that these organisms are much bigger in size and are very complex and intricate in their composition as well as structure. Human beings are the best example of multicellular organisms, and the large number of cells leads to the birth of many different organs for carrying out different functions. Most ‘eukaryotes’ or ‘eukaryotic entities’ are multicellular. The cell nuclei present in eukaryotes and the DNA of the organisms are separately placed, unlike the case of unicellular organisms. All these cells work in tandem with each other to keep the life form alive, and this leads to a variety of complex functions occurring simultaneously.

The organisms in both the categories differ greatly in their appearance, and even though multicellular organisms grow to large sizes, some of them are still microscopic in nature. These are also known as ‘myxozoa’.

Examples: Human beings, animals, plants, myxozoa, and all kinds of fungi.

Scientists discovered all the differences between multicellular and unicellular organisms and this laid the foundation for the rest of biology to develop. The advanced study of the structure of all animals and plants would not be possible without proper knowledge about the cell structure of these organisms, since the cells are the primary life forces and no organism can be alive without the presence of cells in them.

The desire to know the differences between organisms is an important event in human history, and medical science would not be where it is today without this discovery.

Related Posts

Unicellular organisms refer to living entities that have only one cell, and the cell is responsible for performing all the functions. Some examples are amoeba, paramecium, bacteria, and cyanobacteria.

The following article presents before us monocot vs. dicot differences by considering their various features. Read on to known more about dicotyledon and monocotyledon classifications.

Exocytosis is the reverse of endocytosis. This article gives you a brief explanation of these processes and also compares the two.

The Cytoskeleton

If you were to remove all the organelles from a cell, would the plasma membrane and the cytoplasm be the only components left? No. Within the cytoplasm, there would still be ions and organic molecules, plus a network of protein fibers that helps to maintain the shape of the cell, secures certain organelles in specific positions, allows cytoplasm and vesicles to move within the cell, and enables unicellular organisms to move independently. Collectively, this network of protein fibers is known as the cytoskeleton. There are three types of fibers within the cytoskeleton: microfilaments, also known as actin filaments, intermediate filaments, and microtubules (Figure 3.10).

Figure 3.10 Microfilaments, intermediate filaments, and microtubules compose a cell’s cytoskeleton.

Microfilaments are the thinnest of the cytoskeletal fibers and function in moving cellular components, for example, during cell division. They also maintain the structure of microvilli, the extensive folding of the plasma membrane found in cells dedicated to absorption. These components are also common in muscle cells and are responsible for muscle cell contraction. Intermediate filaments are of intermediate diameter and have structural functions, such as maintaining the shape of the cell and anchoring organelles. Keratin, the compound that strengthens hair and nails, forms one type of intermediate filament. Microtubules are the thickest of the cytoskeletal fibers. These are hollow tubes that can dissolve and reform quickly. Microtubules guide organelle movement and are the structures that pull chromosomes to their poles during cell division. They are also the structural components of flagella and cilia. In cilia and flagella, the microtubules are organized as a circle of nine double microtubules on the outside and two microtubules in the center.

The centrosome is a region near the nucleus of animal cells that functions as a microtubule-organizing center. It contains a pair of centrioles, two structures that lie perpendicular to each other. Each centriole is a cylinder of nine triplets of microtubules.

The centrosome replicates itself before a cell divides, and the centrioles play a role in pulling the duplicated chromosomes to opposite ends of the dividing cell. However, the exact function of the centrioles in cell division is not clear, since cells that have the centrioles removed can still divide, and plant cells, which lack centrioles, are capable of cell division.

A unicellular organism is an organism that is made of up of a single cell and the life processes such as reproduction, feeding, digestion, and excretion occur in one single cell. There are some examples of unicellular organisms like Amoeba, bacteria, and plankton. These unicellular organisms are typical microscopic which cannot be seen with the naked eyes. Unicellular organisms are of different types including bacteria, protozoa, and unicellular fungi. Asexual reproduction is famous among unicellular organisms. To make you more understanding, below are the details of types of bacteria.

This organism is unique because it can be both unicellular and multicellular. To fit this category, a cell must have membrane-bound organelles. These cells have a nucleus that consists of DNA, mitochondria for energy and other organelles to carry out the cell functions.

On the other hand, prokaryote consists of a single cell with no membrane-bound organelles. This organism has to adopt other ways of carrying out reproduction, feeding and waste excretion.

The structure of bacteria is too tiny and every bacterial cell id different from an animal and plant cell. The size of bacterial cell is about micrometers across. Even bacteria are of a single cell but it consists of different parts like Chromosomal DNA, Plasmid DNA, Cell Wall, Cell Membrane, and Flagellum.

It is a type of unicellular organism that lives in water or in damp places. Protozoa have adaption that it behaves like an animal a bit. It produces pseudopodia that let it move to surround food and let it take inside the cell. Once the process of taking food inside is done, contractile vacuoles appear inside the cell then combine with the surface to remove waste.

Yeast is another type of unicellular fungi. It may be possible you are familiar from seeing mushrooms and toadstools. Yeast has cell walls like plant cells and no chloroplasts that mean sugar is the main nutrition for them as they are not able to make their own food by photosynthesis.

The cyanobacterium is also known as Blue-Green Algae (BGA). It is the process of characteristics of both bacteria and algae. It resembles algae as photosynthesis for food production whereas the prokaryotic nature of BGA forms it similar to bacteria. Other than this, diatoms, euglena, chlorella, and Chlamydomonas includes in the example of cyanobacteria.

There are many unicellular organisms that live in extreme environments like hot springs, thermal ocean vents, polar ice, and frozen tundra. These unicellular organisms are called extremophiles. This unicellular organism is specially adapted to live in places where multicellular organisms cannot survive because they are resistant to extremes of temperature or pH. Although, not every unicellular organism are extremophiles because many live under the same range of living condition as multicellular organisms, but still necessary things to all life forms on earth. For instance, phytoplankton is a type of unicellular that lives in the ocean.

A multicellular organism, tissue or organ is organisms that are made up of many cells. Animals, plants, and fungi are multicellular organisms. Multicellular organisms are much bigger in size and are very complex and intricate in their composition along with structure. Human beings, animals, plants insects are the example of a multicellular organism.

What are cells?

Cells are the morphological and functional unit that make up every living being. All living organisms are composed of at least one. Most animal cells have sizes from 10 to 100 micrometers and have several key elements.

The most complex organisms, such as mammals, are composed of an enormous set of these vital units that work coordinately. They have different specialized parts to develop and carry out particular functions.

The human body is composed of more than 200 types of cells, each specialized in a specific function such as memory, sight, movement, or digestion, among many others. The diversity within the different cell types is really extensive.

Cell biology is a branch of biology that studies the different types of cells. The knowledge and basic information that has been discovered about this type of organism have also been extrapolated to other different ones over time.

The origin of the first cell

According to researchers, the first life emerged about 3,8 billion years ago, or 750 million years after the Earth formed. It is speculated that the first cell arose from the RNA envelope of self-replication in a membrane composed of phospholipids.

The self-replicating RNA envelope and the molecules associated with a lipid membrane have therefore been maintained as a unit capable of reproducing itself and evolving over time. The synthesis of proteins from RNA may already have evolved.

Examples of single-celled organisms

Some examples of single-celled organisms are:

  • Amoebas. Protozoa of irregular shape, that move moving their cytoplasm as if they were “fingers” (pseudopods), and through themselves, they feed, hunt, and engulf other microscopic organisms.

What are single-celled organisms? Unicellular organisms

Content: Unicellular vs Multicellular Organisms

Comparison Chart

PropertiesUnicellular OrganismsMulticellular Organisms
Cell numberSingle cellMultiple cells
Cell sizeSmallComparatively large
Cell shapeIrregularDefinite
Cell organizationSimpleComplex
Cell typeThey include organisms of both prokaryotic and eukaryotic cell typeThey include organisms of only eukaryotic cell type
Cell differentiationGenerally absent, but unicellular yeasts may undergo differentiationSpecialized cell differentiation occurs
Life spanShortLonger
Division of labourLimited to the organelle levelSpecified to cellular, tissue and organ system level
Operational efficiencyLowHigh
Regeneration abilityGreater tendency to regenerateLow regeneration ability
Reproduction methodsBudding and binary fissionGamete fusion
Transport mechanismThe transport mechanism for food and water occurs through simple diffusionThe transport mechanism for food and water occurs by the diffusion, active and passive transport methods
ExamplesBacteria, Protozoans, unicellular amoeba etc.Humans, animals, plants etc.

Definition of Unicellular Organisms

They refer to the living organisms, which possess a single cell only to perform different life processes or cellular activities in the cytoplasm. It includes prokaryotic organisms like bacteria and archaea and eukaryotic organisms like protozoa, unicellular algae and yeasts.

One of the most common features of unicellular organisms is their microscopic nature, i.e. unobservable through the naked eye. They commonly reproduce via asexual methods like budding, fragmentation and binary fission.

But a few reproduce sexually via conjugation (like bacteria and protists). Because of single-cell composition, the cell arrangement is quite simple. They can thrive in extreme heat, acidity, salinity, and other environmental stresses.

Definition of Multicellular Organisms

They refer to living organisms, which possess multiple cells with distinct cell organelles that perform separate cellular activities or different life processes within a body. It only includes eukaryotic organisms like insects, animals, birds, human etc.

One of the most common features of a multicellular organism is its macroscopic nature, i.e. easily noticeable through the open eye. They commonly reproduce via sexual methods (by the formation of a zygote).

But, few members can grow via asexual means like budding and spore formation. Because of multiple cell composition, it has a composite cell arrangement. Organism’s size increases as the cell number increases.

Components of Eukaryotic Cells

In nature, the relationship between form and function is apparent at all levels, including the level of the cell, and this will become clear as we explore eukaryotic cells. The principle “form follows function” is found in many contexts. For example, birds and fish have streamlined bodies that allow them to move quickly through the medium in which they live, be it air or water. It means that, in general, one can deduce the function of a structure by looking at its form, because the two are matched.

A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles, which have specialized functions. The rest of this chapter will discuss functions of the various organelles. The word eukaryotic means “true kernel” or “true nucleus,” alluding to the presence of the membrane-bound nucleus in these cells. The word “organelle” means “little organ,” and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.

Figure 2 A generalized eukaryotic cell showing some of the organelles. (Photo credit: Mediran, Wikimedia. 14 Aug 2002)

Both animals and plants are eukaryotes. Despite their fundamental similarities, there are some striking differences between animal and plant cells. Animal cells have centrioles, centrosomes (discussed under the cytoskeleton), and lysosomes, whereas plant cells do not. Plant cells have a cell wall, chloroplasts, plasmodesmata, and plastids used for storage, and a large central vacuole, whereas animal cells do not.


Because of the size difference, a unicellular organism is operating at a heavy workload as everything in its cell needs to perform to maintain the cell’s lifespan. A multicellular organism, however, have cells with less workload because it is working with other cells to perform certain functions. This affects the way unicellular organisms have a much shorter lifespan than multicellular organisms.

The differences between a unicellular organism from a multicellular organism has more to do than just numbers. However, it is these numbers that affect their differences. A unicellular organism must depend on everything it has inside of it to survive, and because it is exposed to harsh environments with no form of protection, it has a shorter lifespan and can easily die from the slightest form of trauma.

On the other hand, because multicellular organisms have over millions of cells to perform various functions, they’re more likely to survive the same form of trauma that can easily eliminate its unicellular counterpart. And out of these cells, not all of them provide the same function to the organism as each plays a specific role to ensure the organism’s survival for as long as possible.

However, that’s not to say that a unicellular organism is weaker than a multicellular organism. While bacteria have a short lifespan, they can still grow rapidly in numbers – enough to infect multicellular organisms like humans. This is why it’s important to study both unicellular and multicellular organisms to understand the implications of their characteristics and how they affect other organisms.

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