Read the text and answer the questions.

Symbiosis (from Greek "together" and "living") is close and often long-term interaction between two different biological species. In 1877 Albert Bernhard Frank used the word symbiosis (which previously had been used to depict people living together in community) to describe the mutualistic relationship in lichens. In 1879, the German mycologist Heinrich Anton de Bary defined it as "the living together of unlike organisms."

The definition of symbiosis has varied among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any type of persistent biological interaction (in other words mutualistic, commensalistic, or parasitic). After 130 years of debate, current biology and ecology textbooks now use the latter "de Bary" definition or an even broader definition (where symbiosis means all species interactions), with the restrictive definition no longer used (in other words, symbiosis means mutualism).

Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival. For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own. Others are facultative (optional): they can, but do not have to live with the other organism.

1. What has varied among scientists?
2. What do some believe?
3. What about others?
4. How else could you describe it?
5. How many years was it debated?
6. What is used now?
7. By what?
8. What word is being defined?
9. What language did it originate from?
10. How was it used in 1877?
11. How was it used previously?
12. What about in 1879?
13. By whom?
14. What was his occupation?
15. Nationality?
16. What is obligate?
17. What does that mean?
18. What about others?
19. Meaning?
20. What does symbiosis mean in other words?
21. Are they biological?
1. The definition of symbiosis.
2. That it should only refer to persistent mutualisms.
3. They believe it should apply to any persistent biological interaction.
4. Mutualistic, commensalistic, or parasitic.
5. 130 years.
6. De Bary definition.
7. A broader definition.
8. Symbiosis.
9. Greek.
10. To describe the mutualistic relationship in lichens.
11. To depict people living together in community
12. The living together of unlike organisms.
13. Heinrich Anton de Bary.
14. Mycologist
15. German.
16. Some symbiotic relationships.
17. It means both symbionts entirely depend on each other for survival.
18. They are falculative.
19. Optional
20. It's the close and sometimes long-term interaction between two species.
21. Yes.