1. Small Size and High Surface Area to Volume Ratio: These organisms are very small, and their cells are close to the external environment. This means that the diffusion of nutrients and gases can occur efficiently directly across their cell membranes. The small size and high surface area to volume ratio allow for rapid exchange of substances without the need for complex circulatory systems.
2. Limited Metabolic Needs: Bacteria and simple multicellular organisms have relatively low metabolic demands compared to larger, more complex organisms. They require less energy and nutrients to sustain themselves. Diffusion is sufficient to meet these needs. In contrast, complex organisms like mammals have much higher metabolic requirements that necessitate efficient transport of oxygen, nutrients, and waste products throughout their bodies.
