Why did the enzymes stop working under high heat conditions? In theory the enzymes should
work in colder conditions but at a slower rate, why? How was the
active site of the enzyme affected by the pH changes and the high heat conditions? Why must the
body maintain a blood pH balance as well as normal body temperature?

Why did the enzymes stop working under high heat conditions?

Enzymes are made up of proteins which has a particular structure (3-dimensional) to perform the biological reaction, e.g. tertiary structure. Under high heat (temperature) conditions, the structure of protein is disturbed/changed. Typically,  increasing temperatures would increase the kinetic energy of the molecules and thus it will disturb the structure particularly the active. Once the structure of protein and/or active site is changed, it cannot perform a particular reaction.

In theory the enzymes should work in colder conditions but at a slower rate, why?

Because lower temperature would not affect the structure of the protein (enzyme), rather the biological activity would be slow down. Again, this is because of the decreased momvement of atoms/molecules (kinetic energy). If the temperature drops more than the working range of enzyme, the biological activity would completely stop unless it is raised again. It should be noted that maximum efficiency of enzyme is seen at optimum temperatures. The optimum temperature for many enzymes in humans is 37 degree Celsius.

How was the active site of the enzyme affected by the pH changes and the high heat conditions?

The enzyme activity can be affected by the change in pH as well as by heat as mentioned above. In both cases, the structure of active site is disturbed. We know that enzymes are made up of amino acids which carry specific charges on its atoms. The change in pH would change the intermolecular forces of enzymes because these atoms are attracted by the availability of hydrogen or hydroxyl ions. In the end, the structure of active sites is disturbed. Just like temperature, each enzyme works best at its optimum pH.

In case of temperature, the kinetic energy of the molecule is increased and if the temeprature is increased byond the limit, this will denature the protin structure.

Why must the body maintain a blood pH balance as well as normal body temperature?

To answer this question, we first need to understand "Acid–base homeostasis". Acid–base homeostasis is the maintenance of pH of the body's extracellular fluid. This is important for the normal functioning (physiology) and cellular metabolism of the cells. A balance of acid-base homeostasis is thus crucial for the blood as well because it carrys nutrients and energy molecules, and helps in transportation of gases (diffusion of oxygen and getting rid of CO2). If the blood pH changes, these processes would not occur optimally and results in the poor health. Similarly, the temperature of body should also be maintained, e.g. 37 degree Celsius for humans. This is called temperature homeostasis. In case of change in body temperature, many proteins (enzymes) would not be able to perform their function within the organism's body as stated above. Therefore, regulation of both parameters is crucual to keep body in appropriate functioning state.

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the speed decreases from x to y due to decrease in gravity

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