Most enzymes' optimum pH is neutral or close to neutral, like amylase found in saliva, which has an optimal pH = 6.8. Some enzymes prefer a more drastic pH, like pepsin, which can have an optimum pH of 1.7 to 2. Sometimes enzyme pH optima depends on where the enzyme is found.
DNA, nucleus, and cytoplasm are the answers. Cell membranes and chloroplast are only for animals. Cell walls are in plants only.<span />
To support the axial load on the column as it is delivered by body mass and gravity
The slowing down of the ray of light also causes the light to change direction
