Name two positive behaviors of a protist
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Protists serve as a food source, they benefit their ecosystem, and they are a part of symbiotic relationships.  

Explanation:

Food Source: Protists are a food source for many animals. Phytoplankton is one of the sole food sources for whales, some of the largest creatures on Earth. Zooplankton are fed on by various sea creatures including shrimp and larval crabs. Humans even harvest various protists for food. Seaweed is an algae, which is considered a plant-like protist. Many also eat spirulina and aphanizomenon flos-aquae in supplements for omega-3 fatty acids and other purported nutrients. Protists serve as the foundation of the food chain.

Benefit Their Ecosystem: Protists, such as aphanizomenon flos-aquae and spirulina, are types of blue-green algae that also produce oxygen as a by-product of their respiration cycle. If not for these little cyanobacteria, Earth would not be the oxygen rich planet it is today. Blue-green algae provides 80% of the Earth's oxygen. Algae, such as seaweed, also serve as mini-ecosystems for other marine life, especially the juvenile and larval forms that need to hide for safety.

Symbiotic Relationships: Other types of protists offer more direct benefits for animals in the form of symbiotic relationships. Trichonymphs live in the intestines of termites, feeding on the wood cellulose that termites eat and breaking it down into digestible components. These protists live in the digestive tracts of several cellulose eating organisms. Various protists and bacteria also live in the digestive tracts of ruminants, such as cows, and help them break down the food they eat for nutrients and energy.

Protists are single-celled lifeforms that display both plant or animal characteristics.

They can be beneficial in the way that they are helpful to the environment. Not only that but are good food source and have a relation with other organism. Some even produce oxygen, and are used to produce biofuel.

Explanation:

I did not want to copy the other person's answer so I kept it simple.