PLEASE HELP is this right?? its timed and i put biosphere last time and got it wrong

answer; polycythemia is the correct answer;

the sphincter muscles at the end of the digestive tract is the anus.

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