Two trophic levels
Typically there are three or four trophic levels in a community because after this point, it becomes very hard to sustain organisms. The amount of energy lost at each trophic level makes it harder and harder to sustain life.
Answer: In the field of molecular biology the correct sequence of events are as follows:
1. Gregor Mendel proves the Laws of Inheritance in 1865.
2. Friedrich Miescher conducted experiments to identify nuclein as the building blocks of life in 1869.
3. James Watson and Francis Crick presented a model of DNA in 1953.
4. Frederick Sanger developed a method for sequencing DNA in 1977.
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