Uni cellular are the single celled organisms,they live on simpler form of food(organic food)they just engulf the food in its food vacuole and after cyclosis it excretes it out,it gives the organism enough energy to live,uni cellular organisms have their body made of water or can say it is a jelly like structure(like in amoeba).so they don't need the food to make blood and run through the vessels,that is why they donot have circulatory system as well as other systems like in multi celluler organism.
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