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the main producers in aquatic environments are
a.
phytoplankton
b.
zooplankton
c.
kelp
d.
fish

The correct answer for the blank is- a)  Phytoplankton.

Phytoplanktons are the autotrophic, microscopic organisms ( such as dinoflagellates, diatoms, blue-green algae) that are present in the aquatic enviornments ( both salty and freshwater).

They possess green pigment that is chlorophyll like green plants on land.

They are the main producers in the aquatic environments as they synthesize their own food through the process called photosynthesis, which is then consumed by other organisms ( such as zooplanktons) in the aquatic food chain. By doing so, they form the base of aquatic food chain.

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.