Prelim Biology: Unicellular to Multicellular – What is Cell Specialisation?

8 Mins Read | Written by Simon Tang

Key Points Summary

• All living organisms have the same few requirements to survive – food, water, etc.
• Cell specialisation is a process by which certain cells in an organism become very good at a certain task, which will help the whole organism survive.
• Unicellular organisms have no specialisation, and must complete all these survival tasks by themselves.
• Colonial organisms can have slight specialisation when they live together, some cells focus on vision, others for reproduction.
• Multicellular organisms have a lot of specialisation, to the point that cells cannot live separate from the organism.

Content

Syllabus

Students:

• Compare the differences between unicellular, colonial and multicellular organisms by:
  • investigating structures at the level of the cell and organelle
  • relating structure of cells and cell specialisation to function

Introduction

Living things on Earth have a great diversity. From large elephants to tiny bacteria, we all are so different. However, despite this great variety of life, we all still have similar needs – food, water, shelter, etc. How is it that an organism like the elephants can survive just as well as something much smaller?

It all comes down to the idea of cell specialisation. This is a process by which certain cells in an organism become very good at a certain function that will help the whole organism survive. This blog will cover this in depth by showcasing the difference between unicellular, colonial and multicellular organisms. 

Unicellular

Unicellular organisms, such as bacteria, archaea, protozoa and some fungi, have only one cell. Therefore, this cell must be capable of all functions required by the organism, like finding food and water, reproducing, etc. It must have mechanisms to allow digestion of nutrients, elimination of wastes, movement, response to stimuli and reproduction.

Therefore, unicellular organisms have cells that are structured to allow for all these functions. As a case study, let us consider the unicellular protozoan Paramecium. Paramecium is a genus of protozoa. Observe the structure below.

Deuterostome, CC BY-SA 4.0, via Wikimedia Commons

While the Paramecium is unicellular, it possesses quite a complex cell structure in order to accommodate for all the different functions that the organism needs to survive.

Colonial

It is believed that the evolution of unicellular organisms into multicellular organisms proceeded via colonial organisms, which are groups of genetically identical, interdependent individuals that exist together in physical space. However, they are still individual organisms that can, theoretically, survive outside of the colony.

Colonial organisms can be unicellular or multicellular. For our purposes, we will focus on a unicellular colonial organism – the green algae Volvox.

By Nimasha Liyanage (Shutterstock)

Volvox form spherical colonies of thousands of individual cells of two main cell types – reproductive cells and non-reproductive cells. Because these colonial organisms are still individual unicellular organisms, each cell still possesses the necessary structures for basic survival functions, such as the metabolism of nutrients. However, these cells are minimally specialised, with some cells in the colonies performing one special function in addition to their routine functions needed for individual cell survival.

• Reproductive cells do not move but they do produce gametes for reproduction. They are located at the centre of the colony.
• Non-reproductive cells have flagella for movement, and eyespots with photoreceptors to detect light.

Multicellular

Multicellular organisms possess large numbers of highly specialised cells. The cells cannot survive individually, and solely exist to provide a special function for the whole organism. This specialisation vastly increases the efficiency of function and allows for a high level of complexity in multicellular organisms. Think about how our blood cells are very different from our brain cells, which are then very different from our bone cells. Check them out, and more, below:

By brgfx (Shutterstock)

Due to this high degree of specialisation, the arrangement of cells within the organism is crucial for efficient function. The cells in a multicellular organism must be arranged strategically for efficient function. To achieve this, cells are arranged into tissues, which are arranged into organs, which are arranged into several organ systems within the body that each carry out a particular role. 

Conclusion

So there you have it, prelim bio cell specialisation in a nutshell! Want to learn more about the science of life? Come to Dymocks Tutoring for a FREE TRIAL HERE