If 10,000 kilocalories (kcal) of energy were contained in the primary producers (trophic level 1), on average how many kcal of energy would you expect to be transferred to second-order consumers (trophic level 3)?

Explanation:

Energy transfers from autotrophs ( producers) to heterotrophs (consumers).

In this way approx 90% of the total energy is consumed by each trophic level, means only 10% energy is transferred  from each tropic level.

So as given here, in primary trophic level ( producers), total energy is 10,000 kcal.

Now the 90% (9000 kcal) of this energy is consumed( like in the form of heat and respiration) in trophic level 1 and 10% (1000kcal )is transferred to the trophic level 2( first-order consumers).

And from this energy 90%(900kcal) is consumed in trophic level 2( first-order consumers) , so only 10% (100 kcal) is transferred to the trophic level 3 (second-order consumers).

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products