The answer is d. A large asteroid or comet impacted the Eartg
Regulation of amino acids
When amino acids are absorbed by liver cells a series of chemical reactions begins. ... The amine group is reduced to ammonia by the addition of a hydrogen atom. This process is called deamination. The non-nitrogenous portion of the molecule is converted to carbohydrates or fats.
In order for plants to make their own food, they must go through a process called photosynthesis. This process occurs in the chloroplasts of a cell. To begin this process, all items needed must go to the cells of a plant. Water and nutrient are absorbed from the soil through the roots. A tube called the xylem carries only water up the stem to the rest of the plant. Gas exchange in the plants occur in the tiny pores of a leaf called the stomata. This is opened and closed by the guard cells. The food produced by this process is called ATP and it is a macromolecule known as a nucleic acid.
Smooth muscles depolarize as a result of a transmembrane current of Calcium ions. When an action potential depolarizes the muscle cell membrane, it also travels into the body of the cell via the t-tubules. Unlike skeletal muscle, smooth muscle is dependent in two sources of calcium in order to intiate contraction. These two sources are calcium sequestered in the S.R. of the smooth muscle cell.
