Difference Between Multicellular and Unicellular

Multicellular vs Unicellular

All living things are made up of cells that are the building blocks of life. You would be surprised to know that there are organisms with billions of cells like animals and human beings while there are organisms that have only single cell. This has led to the bifurcation of organisms between unicellular and multicellular. There are great differences between multicellular and unicellular organisms that will be discussed in this article.

Unicellular Organisms

As the name implies, these are single cell organisms that are very small in size and also have a very simple structure. Unicellular organisms are classified as Prokaryotes as they do not have a complex structure. They are almost invisible to human eyes. They do not possess internal organs and also lack in cell membranes. As they are simplistic in nature, they are found in environments that are considered hazardous for multicellular organisms such as acidic and radioactive environments. It is believed that all other complex life forms are a result of a long and arduous evolution from this unicellular life form. Unicellular organisms have their own specific role to play in the unique ecosystem of nature. Some of the examples of unicellular organisms are bacteria, yeast, amoeba and paramecium.

Multicellular Organisms

These are organisms that have more than one cell (in fact have millions of cells). They are bigger in size and have a complex structure. Also known as eukaryotes, such organisms have internal organs. These have cell nuclei with DNA of cells separately placed. All cells work in close cooperation and their functioning is what keeps the organism alive. Multicellular organisms vary greatly in terms of size and shape and some of the examples are plants, animals and human beings.

Differences between Multicellular and Unicellular Organisms

• Cell size in unicellular organisms is 0.5-10 micrometer whereas in multicellular organisms, cell size is 10-100 micrometer.

• Unicellular organisms evolved earlier than multicellular organisms around 3.5 thousand million years ago while multicellular organisms are believed to have evolved from unicellular organisms 1.2 thousand million years ago.

• Cell division in unicellular organisms is mostly binary fission and has no spindle. On the other hand cell division in multicellular organisms takes place through mitosis, meiosis or both with spindle formed.

• DNA is circular and lies free in the cytoplasm in case of unicellular organisms whereas DNA is linear and contained in a nucleus in case of multicellular organisms

• In unicellular organisms, there is no protein synthesis whereas it takes place regularly in multicellular organisms.

• In unicellular organisms, photosynthesis does not take place because of absence of chloroplast where as this is a major function in multicellular organisms.

• Some unicellular organisms have the ability of nitrogen fixation while multicellular organisms do not have this ability

• Respiration is through mesosomes in bacteria while there is mitochondrion for aerobic respiration in multicellular organisms.

• Unicellular organisms have very few organelles whereas multicellular organisms have well developed organelles that are enveloped with membranes.