Unicellular vs Multicellular | Cells | Biology | FuseSchool
Did you know that some organisms exist of just one cell? These simple organisms, like amoeba, are unicellular. They depend on simple diffusion for life
They are usually too small to be visible to the naked eye, like bacteria, and so we need a microscope to see them. But there are some unicellular algae’s that are about 15 to 20 cm in size.
All other organisms are multicellular; they consist of multiple cells and are more complex.
The vast majority of plants and animals are multicellular. Being multicellular allows the organism to be larger and to have cell differentiation – so different types of cells to carry out different tasks.
Groups of cells then function in the same way to form tissues or organs. These specialised organs carry out our life processes, working together in systems.
Unicellular organisms can carry out all life processes in just the one cell, using internal structures called organelles. This decreased ability to share out the life processes means unicellular organisms have a low level of efficiency. Whereas multicellular organisms are highly efficient, with division of labour at the cellular, tissue, organ or organ system level.
Unicellular organisms cannot grow large because they are limited by a surface area to volume ratio.
Whereas multicellular organisms can increase the number of small cells to give it a large size overall.
Multicellular organisms can have long lifespans because individual cells have a relatively small workload. Whereas the hard-working single cell of a unicellular organisms has such a heavy workload that it can only maintain a very short lifespan.
I don’t need to tell you how we get our nutrition… but how does a single cell manage it?
Usually by phagocytosis, where the food is engulfed and then stored in food vacuoles inside the organism.
All prokaryotes are unicellular. Eukaryotes can be uni or multi-cellular organisms. We look at the differences between pro- and eu-karyotes in this video and will discover why the statement that “all prokaryotes are unicellular” is contended by some scientists. As well as prokaryotes, most protists and some fungi like yeast are also unicellular.
So, there we have unicellular and multicellular organisms. The final thought to leave with you, is that any injury to the cell of a unicellular organism can cause death; that one cell is everything to them. Whereas injury or death of some cells in a multicellular organism should not cause a problem; those cells can simply be replaced.
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