What is the effect of temperature and pH on the activity of an enzyme?

What is the role of a competitive inhibitor during enzyme action?

Under which conditions do metabolic reactions generally occur at a slower rate?

The curve given below shows enzymatic activity in relation to three conditions ($pH$,temperature and substrate concentration). What do the two axes ($x$ and $y$) represent?

Enzymes are destroyed at:

Enzymes are proteins. Proteins are long chains of amino acids linked to each other by peptide bonds. Amino acids have many functional groups in their structure. Many of these functional groups are ionisable. As they are weak acids and bases in chemical nature,this ionisation is influenced by the $pH$ of the solution. For many enzymes,activity is influenced by the surrounding $pH$. This is depicted in the curve below. Explain briefly.