Positive in nature:
- provide food for animals
- provide oxygen
- break down the remains of other organisms into simple minerals
- are involved in cellulose digestion
- form layers of limestone
- purify water
- provide shelter for animals living in the water

Positive for humans:
- Provide food
- are used in the pharmaceutical and food processing industry
- used for dyes (coloring)
- provide oxygen
- indicate the purity of the water and clean water
- used as fertilizer

Negative in nature:
- cause disease in animals and plants
- cause rot
- parasites (both on plants and animals )
- some pollute the water (blue-green algae and green algae have an adverse impact on water tanks, the water turns green and the lack of air causes dying of life in reservoirs)

Negative for humans:
- cause diseases (fungal and other skin condition, also during pregnancy - fetal infections cause by protists can lead to cerebral palsy or even miscarriage)
- cause spoilage of food (which causes food poisoning and various kinds of allergies)
- causes decay and diseases of plants
- some of them produce poisonous toxins that are poisonous to humans and some species of fish

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