This type of membrane transport moves substances against the concentration gradient from an area of low concentration to an area of high concentration using membrane protiens as carriers and requires the input of atp

Its called active transport. We call it active since it requires energy for the transport of molecules against the concentration gradient. ATP must break down to release energy for the process.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.

the tricuspid valve is present between right atrium and right ventricle