The answer is "amino acids<span>".
Carbohydrates are easy to breakdown to make energy. But, if there is a carbohydrate deficiency, then the body will start to breakdown amino acids to make energy. The main energy sources are carbohydrates, fats and proteins. In order to keep the body alive, body will breakdown nucleic acids (RNA, DNA) when there is not enough food to make energy.</span>
Leaves are colored by molecules called pigments. The pigment that causes leaves to be green is chlorophyll. Chlorophyll is important for plants to make food using sunlight. During spring and summer when there is plenty of sunlight, plants make a lot of chlorophyll.
In autumn when it starts to get cold, some plants stop making chlorophyll. Instead, those plants break down chlorophyll into smaller molecules. As chlorophyll goes away, other pigments start to show their colors. This is why leaves turn yellow or red in fall.
pole star is a visible star, preferably a prominent one, that is approximately aligned with the Earth's axis of rotation; that is, a star whose apparent position is close to one of the celestial poles, and which lies approximately directly overhead when viewed from the Earth's North Pole or South Pole.
The dead plants and animals are the form of organic nitrogen. Microorganisms utilize these materials and break them down and convert into nitrates, which is a utilizable form and is used by plants and animals. The process is called as nitrogen fixation.