Valleys are one of the most common landforms on the surface of the planet. They are carved by flowing water or flowing ice through the process of erosion, which is the gradual wearing away of Earth surfaces through the action of wind and water.
The cellular respiration processes of all living cells make use of the coenzyme Nicotinamide adenine dinucleotide (NAD). It plays a key role in energy metabolism by accepting and donating electrons.
Coenzymes, some of which are vitamins and some of which are synthesized directly from vitamins, activate enzymes by helping the enzyme to bind to its substrate. Coenzymes activate enzymes primarily by assisting in the transfer of specific particles or compounds involved in the chemical reaction.