Starting with shredded spinach leaves, you follow a procedure that separates cellular organelles into different fractions. To identify the fraction that contains the mitochondria, you should test for the presence of:
A. insulin receptors
B. aquaporin
C. phospholipids present only in the mitochondrial outer membrane
D. electron transport proteins
E. mitochondrial wall polysaccharides

D. electron transport proteins

Explanation:

In order to identify which faction contains the mitochondria, we have to test for the presence of the substance that is common to mitochondria alone. Insulin receptors, aquaporin, phospholipids in the outer membrane, and polysaccharides are not unique substances common to mitochondria.  Electron transport proteins are unique to mitochondria, which are present in the inner membrane of mitochondria.

A mitochondrion has an outer and an inner membrane. The inner membrane is not easily permeable as the outer membrane, and as such, the inner membrane contains electron transport proteins that help in that regard. The presence of electron transport protein is the unique substance to be tested for, to determine the fraction that contains the mitochondria.

more words for this could be abiotic and biotic

abiotic: living organisms within an ecosystem

biotic: non-living organisms within an ecosystem