Not all the adhesive cell lines can become suspension cells. But however, cell lines such as Hek 293 cells and Hela cells can be used to make a suspension cell line. The main reason for that would be to generate more surface for application such as transfection for plasmids hard to enter the cells or escape lysosomal degradation. 

For two main reasons:

1. Serum is the source of inconsistency and variability. Each batch of serum is essentially different than another batch.
2. Serums are the source of early stages of some pathogens such as micrococcus. The small structure of these elements causes them passing through 0.22 µm. They adhere to flask and dishes and after about one week, they turn into mycoplasma.

1. The color of the media has NOT changed, and the media won’t be turbid. Whereas, with bacterial, mold, fungus contamination, you could clearly see the contamination.
2. The deteriorating impact is gradual and the change in functionality usually is overlooked.
3. the most important damage of mycoplasma to your laboratory is compromising reproducibility and reproductivity. So, if another lab performs the exact study and is free of mycoplasma, the result will be significantly different.

Endotoxins or lipopolysaccharides are the toxins released into the environment around the gram-negative bacteria caused by compromising or death of these organelles. Gram negative endotoxins are the most significant pyrogen which causes fever in humans and causes severe contamination in cell culture. 

It thoroughly depends on the cell lines. The heat inactivation of FBS is unnecessary for most of the cell lines. In has been proven to us that the differentiated cell line do much better in heat inactivated serum.

37°C is the temperature of the tissue which the cells coming from in normal conditions. So, we try to imitate the temperature where the cells have come from. 5% CO2 is to maintain the pH of the media and correlates with the amount of NaHCO3 in your media.