Vitamin D mostly helps the body absorb calcium (which we need for strong bones) and helps keep immune systems strong. Vitamin D deficiency leads to more flu and colds, fragile bones, weak muscles, high blood pressure and depression. Deficiency can lead to hundreds of diseases.
Hope this helps! :)
Viruses are not cells; they are a strand of genetic material within a protective protein coat called a capsid. They infect a wide variety of organisms, including both eukaryotes and prokaryotes. Once inside the cell, they use the cell's ATP, ribosomes, enzymes, and other cellular parts to replicate.
Increasing substrate concentration also increases the rate of reaction to a certain point. Once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.