Saprotrophs are organisms that feed on the organic matter of dead organisms or the secretions of living organisms. Examples are bacteria (Escherichia coli, Pseudomonas aeruginosa), some types of fungi (the same penicillin). Parasites are organisms that feed on the organic substances of living organisms, both nutrients (parasites in the digestive system) and living flesh. The parasite the main time of its life is in the body of the carrier. In addition to destroying the flesh or reducing the amount of nutrients, the parasite often poisons the host organism with the products of its vital activity. Examples: Malarial amoeba (unicellular), roundworm, bovine tapeworm, cat fluke (different groups of worms), ergot and late blight (mushrooms).
Symbionts are organisms that, when interacting with organisms of other species, give mutual or one-sided benefits (in other words, they are in symbiosis with another species). There are many examples of pair symbionts. Lichen – a symbiosis of fungus and algae. Ant and aphid, etc.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.