Temperature can cause an enzymes shape and function to alter due to the fact that once an enzyme reaches its optimum level, if it goes over it begins to denature. If the temperature is below optimum, then an enzyme will work at a slower rate. Also, the pH can affect an enzyme.
Yeast is a prokaryote that is not bacteria
Boron's atomic number is 5, so for its 5 protons, it should have 5 electrons if it's neutral.
To make it an ion, Boron's charge would have to be negative or positive. It could lose one electron to have a charge of +1, gain an electron to be -1 ion.
Ions aren't at specific number. So the answer depends on Boron's tendency to gain or lose electrons.