Simple multicellular organisms - SS2 Biology Lesson Note

Simple multicellular organisms, such as sponges, hydra, and some algae, employ different mechanisms for transportation within their bodies. While their transport systems are less complex compared to higher organisms, they still ensure the distribution of essential substances. Here are some mechanisms of transportation in simple multicellular organisms:

1.       Diffusion:

·         Simple multicellular organisms have a relatively small size and a high surface-to-volume ratio, allowing for efficient diffusion of gases, nutrients, and waste products across their cell membranes.

·         Diffusion occurs based on concentration gradients, where substances move from areas of higher concentration to areas of lower concentration.

·         Nutrients and gases can diffuse directly between cells or through the extracellular matrix.

2.       Circulation in Gastrovascular Cavity:

·         Some simple multicellular organisms, such as hydra and jellyfish, have a gastrovascular cavity.

·         The gastrovascular cavity acts as a central cavity for digestion, nutrient absorption, and distribution.

·         Nutrients and gases are transported within the gastrovascular cavity through diffusion and active transport across the cells lining the cavity.

3.       Cytoplasmic Streaming:

·         Cytoplasmic streaming, also known as cyclosis, is a mechanism of transportation in certain simple multicellular organisms like algae and plant cells.

·         Within these organisms, the cytoplasm moves in a circulating manner, aided by the action of cytoplasmic filaments and molecular motors.

·         This movement facilitates the distribution of organelles, nutrients, and other substances within the cells and helps maintain cellular homeostasis.

4.       Cell-to-Cell Transport:

·         Simple multicellular organisms may utilize direct cell-to-cell transport mechanisms, such as gap junctions or plasmodesmata.

·         These small channels or connections allow for the exchange of ions, small molecules, and signals between neighboring cells.

·         Through these connections, essential substances, such as nutrients and signaling molecules, can be transported between cells.

It's important to note that the mechanisms of transportation in simple multicellular organisms are relatively limited compared to more complex organisms. Their smaller size, simpler body structure, and reliance on diffusion and localized transport mechanisms accommodate their basic physiological needs for gas exchange, nutrient distribution, and waste removal.

Circulation in insects (Britannica.com)