Because they don't need them. Cell walls, which are found in plant cells, maintain cell shape, almost as if each cell has its own exoskeleton. This rigidity allows plants to stand upright without the need for bones .
The protease enzyme pepsin is found in the stomach and has a highly acidic PH of just 2, so the line would be at PH 2, so lower down than amylase which has a PH 7 :)
What are the four steps that explain how traits in a population change over time?
There are four principles at work in evolution—variation, inheritance, selection and time. These are considered the components of the evolutionary mechanism of natural selection.
