Phytoplankton are essential because they produce which of the following?

a. oxygen

b. nitrogen

c. sulfur

d. phosphorus

it's anything that aren't producers and consumers.

explanation:

you've got to be clear on what "this" is

answer: angiosperms

dicots

angiosperms are highly evolved plants, they produce seeds which are enclosed within in a carple. these are the largest group of plants on earth. they include trees, shrubs, herbs and small flowering plants. angiosperms exhibit a flowering stage in their life cycle. the flower serves the function of reproduction and fruit formation in majority of angiosperms. dicot is the term used to describe flowering plants that have two seed leaves. dicots are plants which develop seeds which split into two parts called cotyledons. each cotyledon contains one embryo.

here, a small purple flower development indicates that the plant belongs to angiosperms and having two embryonic leaves indicates it belongs to dicots.  

only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.