Explain how the ineractions between organisms in aan ecosystem can be halpful and harmful to these organisms?

Depends on what relationship the organisms have. Mutual relationships happen when both organisms benefit from the relationship(Fish and anemone). Commensalism is when one organism benefits while the other does not gain or lose anything(oxpeckers on elephants) . Parasitism is non-mutual where one organism (the parasite) benefits from the outdo of another (tick on a dog)

Nucleus is the organelle that contains chromosomes

The salt in the sea water dehydrated the sailor because her body could not take in the amount to salt in the sea water