mechanism of transportation in unicellular organismsIn unicellular organisms, the continuous streaming movements of the cytoplasm circulate materials within one-cell body. In Amoeba for example, which changes its shape as it moves, the cytoplasm streams from the rear to the front of the organism along the direction of its movement.
In paramecium, another unicellular organism which do not change its shape, the continuous circular movement of the cytoplasm brings about the distribution of materials such as food, oxygen, and carbon dioxide within its body.

mechanism of transportation in simple multicellular organisms

HYDRA: hydra is a two layered body organism enclosed in a huge gut cavity. Movements of the gut wall draw water into the gut and cause digested food and oxygen within it to circulate.

This enables the cell lining the gut to absorb the materials. Some cells in the gut have flagellae. The whipping movement of the flagellae also help to circulate the materials in the gut.
FLATWORMS: flatworms, e.g. tapeworm, has a thin and flat body so that the surface area to volume ratio is large. In addition, the gut branches extend throughout the body. These features enable sufficient food and oxygen to diffuse into all the body cells. A branched excretory system is present to collect and get rid of waste products from the body. As in hydra, movements of the body wall aid the transportation of waste product out of its body.

INSECTS AND MOLLUSCS: insects and Molluscs have open circulatory system which helps to transport materials within the body. In the system, the heart pumps blood out into a blood vessel which branches and opens into spaces in the body cavity called heamocoels. The organs and tissues are bathed in blood, and exchange of materials occur between the body cells and the blood. Blood in the spaces eventually flows into vessels leading to the heart. Valves in the heart and blood vessels only allow the blood to flow in one direction. In this system, the distribution of blood to the various body parts is poorly controlled.

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