AssalamOAllaikum all!

I hope everybody is having the time of their life!

I'm studying the EDS in textual manner (not objective one) and creating the best possible number of MCQs from the topic under study myself. While studying vitamins and enzymes today it tickled the curiosity in me to know more about the same and that's what makes me seek your help here. I need the answers to the following few questions to end my curiosity.

Q1: Why certain enzymes require co-factors or co-enzymes to carry out their biological activity whereas protease, lipase or carbohydrase can take part in metabolic activities without any assistance?

Q2: Which organic compounds are most abundantly present in red blood cells of mammals?

Q3: Which co-factor or co-enzyme assists hemoglobin in oxygen-transport within the blood?

Q4: What amount of oxygen present in a sample of arterial blood of a healthy human is chemically combined with hemoglobin?

Q5: What is the main reason of vitamin loss?

Details of the above asked questions would prove more handy if you can kindly provide...
Thanks