Write about the changes in the evolution of transport system in animals.
A. 1) In Amoeba due to Brownian movements nutrients and oxygen are distributed throughout the protoplasm equally.
2) The parazones like sponges, use sea water for transportation. Sponges create their own currents by beating of flagella that are present in their body.
3) Cnidarians developed blind sac like gastrovascular cavity, which has taken up the function of digestion and transportation of nutrients, e.g.: Hydra and jelly fish.
4) In platyhelmenthes, the digestive system supplies digested food to all the cells directly, excretory system collects wastes from each cell individually.
5) In animals belonging to Nematyhelmenthes the pseudocoelom has taken up the function of collection and distribution of materials.
6) In Annelids, animals have developed a pulsative vessel to move the fluid and the transporting medium is blood.
7) In Arthropods have developed a pulsative organ to pump the blood. The blood iloods the tissues, directly supplying the nutrients to the tissues.
8) Transportation system which supplies nutrients to the tissues directly is called open type of circulatory system. e.g.: Arthropods, many molluscs and lower chordates. The other type of transportation system where the blood takes the responsibility of delivering the materials, which flow in the blood vessels is called closed type of circulatory system.
9) Such type of closed circulatory system is present in annelids, echinoderms, cephalopod molluscs and all the higher animals.