IB Biology - The Unicellular and Multicellular Organisms
Chapter 1.1 Introduction to cells
Unicellular organisms = organisms with one cell
The cell theory indicates that a cell exerts all functions of life so even though is a single cell, it is a life!
Functions of life:
Unicellular Organisms Examples
multicellular organisms = body composed of >1 cells
Surface area to volume ratio
We human or your pet are multicellular organisms. But as an IB biology student, have you ever wondering why the multicellular organisms don't grow into a single big cell but require plenty of cells to constitute our body? It is due to the Surface area to Volume ratio
Surface area determines the rate of material exchange, greater surface area --> better contact with the outside --> better material exchange with the outside
In the graph, the volume of a single cube to a large cube constituted by 27 cubes increases by 27 times, while the surface area just increases by 9 times. The increase is not proportional. (Imaging you are blowing a balloon)
The Larger the Volume, The Lower the ratio of Surface Area : Volume
If we grew as large single cell, sure the cell volume increases, but the ratio of Surface Area : Volume decreases which is not favouring material exchange. The cell can't efficiently excrete the waste to the outside and obtain sufficient food from the outside.
Increase Surface Area : Volume Ratio enhance the material exchange
To maintain a desirable ratio, the cells have two adaptations: folding, microvilli (you will learn in digestion chapter) to increase the surface area which boosts up the material exchange.
But once the cell reaches a limit, it divides --> multicellular, thus, a cell cannot unlimitedly grow.
That is the end of today topics!~
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Written by Queenie l IBDP Biology Specialist @ TUTTEE
Photo References:1. Medical News. Retrieved URL from: news-medical.net
2. Diagram of Paramecium. Retrieved URL from: http://33.dv.zimmer-in-zwickau.de/diagram-of-paramecium.html
3. Chlorella: Therapeutic powers of the billion-year-old algae now within your reach. (24 June 2019). FactDr. Retrieved URL from: https://factdr.com/supplements/wellness/chlorella/
4. Paramecium. Wikipedia. Retrieved URL from: https://en.wikipedia.org/wiki/Paramecium
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