# Symbiosis

A close, long-term relationship between two species. Mutualism helps both. Parasitism helps one and harms the other. Commensalism helps one and does not affect the other.

Biology (university) · Part 10: Ecology and the environment · Card 3 of 9 · Last updated 2026-10-19

## Analogy

Flatmates: some help each other, some freeload, some cause harm.

## In practice

Gut bacteria help digest food (mutualism). Tapeworms take nutrients from a host (parasitism).

## Practice

### Flashcards

- **Define mutualism and parasitism.** Mutualism benefits both species. Parasitism benefits one and harms the other.

## Questions people ask

### What is an example of mutualism between plants and fungi?

Mycorrhizae are partnerships between fungi and plant roots. The fungus spreads through the soil and brings the plant water and minerals such as phosphate. The plant provides sugars from photosynthesis. Most land plants depend on this partnership to grow well in poor soil.

### What is the difference between a parasite and a predator?

A predator kills and eats its prey quickly. A parasite lives on or in a host for a long time, taking resources while usually keeping the host alive. Some parasites eventually weaken or kill the host, but it is not in their interest to kill it quickly.

## Related concepts

- [Ecological niche](https://studyvisually.com/learn/science/biology-university/biology-university-part-10/biology-university-part-10-concept-2)
- [Ecological succession](https://studyvisually.com/learn/science/biology-university/biology-university-part-10/biology-university-part-10-concept-8)

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