The answer is C. nitrogen.
Plants are main producers in ecosystems so, primary productivity of ecosystems depends on them. Carbon is necessary for plants, but it is widely present in plants. On the other hand, calcium and sodium are not as essential. However, nitrogen is important for plants because it is necessary to make proteins. Proteins take part in many different processes such as photosynthesis (this is actually primary productivity). But, nitrogen is not available to plants, they cannot absorb it simply from the air but rely on some symbiotic bacteria which are able to.
The brain is part of the central nervous system
Answer:
d. Nucleus
Explanation:
the nucleus stores the DNA which is the genetic code for the organism.
The Richter scale is a way of giving the intensity of all earthquakes a numerical value. this allows the strengths of different earthquakes to be compared. Because of this, i think the best answer is D
we aren't given options but in order from longest to shortest it is radiowaves, microwaves, infared,visible light, ultraviolet, x rays, gamma rays
