Why bigger organisms need a specific structure for transport compare to small organism?
The larger the organism, the smaller the TSA/V ratio, so the slower the rate of diffusion.
In transporting all dissolved nutrients & getting rids of waste products in and out of the body, involving the process of diffusion (active & passive transport). If multicellular organisms depend on the simple diffusion alone, it takes a longer time for the molecules/nutrient substances to reach to the target cell.
The size of organism will affects affects the rate of diffusion of materials into and out of its body. The Paramecium has a TSA/V ratio of about 400 whereas man has a TSA/V ratio of about 0.3. The smaller the organism, the larger/wider surface for diffusion.
There are 2 problems that could be faced by multicellular organisms:
- The TSA/V becomes smaller because the size is large. Many layers of cells & tissues.
- The cells are situated far away from the external environment.
Simple diffusion cannot bring enough oxygen & nutrients to these cells. Neither can waste products be removed quickly enough.
How to overcome these problems?
By having a specific circulatory sytem to transport substances throughout the body as examples blood circulatory system in animals and vascular bundles (xylem & phloem tisssues) in plants.
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