3. mammals lack the enzymes for the net conversion of acetyl-coa into oxaloacetate or any other citric acid cycle intermediate, but if oxaloacetate (or some other citric acid cycle intermediate) is drawn off for biosynthesis, it must be replenished. how is oxaloacetate replenished? under what cellular conditions would this enzymatic step be favored?

-Oxaloacetate is replenished by enzyme pyruvate carboxylase.

-This enzymatic reaction is favored when there is an increased demand of energy required by the cell.

Explanation:

Citric acid cycle is a major pathway for the ATP production. Oxaloacetate plays an important role in citric acid cycle as it starts with transfer of acetyl group of acetyl CoA to oxaloacetate with formation of citrate.

As mammals lack enzyme to convert acetyl-CoA into oxaloacetate, in mammals oxaloacetate is replenished by enzyme pyruvate carboxylase that performs carboxylation of pyruvate to form oxaloacetate.

Activity of this enzymatic reaction increases by high energy demand of cell,  and increased level of acetyl CoA as it shows increased demand of oxaloacetate to perform citric acid cycle for energy production.

1. a tropical dry forest carries out more rapid nutrient cycling

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."