Lactic acid is a byproduct of short-term cellular respiration do to exercise, but if you mean lactose, then it's just the enzymes, that your stomach produces
I'm not 100% sure, but I'd say the availability of vaccines and medicine.
Mutations are not a mechanism for evolution.
Answer;
-Pellicle
Explanation;
-Protist cells may contain a single nucleus or many nuclei; they range in size from microscopic to thousands of meters in area. Protists may have animal-like cell membranes, plant-like cell walls, or may be covered by a pellicle.
-On a paramecium's exterior is found the pellicle. The pellicle is stiff to maintain the paramecium's shape and provide stability but it is also flexible to allow movement. It also acts as an attachment site for external organelles such as cilia.
