The component of an atom that possesses relatively little mass, thus being negligible in calculating the atomic mass number, is the

The correct answer is B. Uracil is a nitrogenous base found in RNA, replacing thymine which is found in DNA. Adenine, guanine, and cytosine are common to both RNA and DNA.

The correct answer is A. Chromatin is a complex of DNA and proteins, including histones, found in the nucleus of eukaryotic cells. It carries the hereditary information in the form of genes. ATP, plasmids, and histones are involved in cellular processes but do not carry hereditary information.

The correct answer is C. The digestive system is responsible for breaking down complex food molecules, including proteins, into simpler components such as amino acids that can be absorbed and utilized by the body.

The correct answer is B. Emphysema is a disease that primarily affects the alveoli, which are tiny air sacs in the lungs responsible for gas exchange. The destruction of alveoli walls in emphysema reduces the surface area available for oxygen and carbon dioxide exchange.

The correct answer is B. Parathyroid hormone (PTH) regulates blood calcium levels by stimulating the release of calcium from bones, reabsorption of calcium in the kidneys, and absorption of calcium in the intestines. Norepinephrine, growth hormone, and melatonin do not play a primary role in calcium regulation.

The correct answer is D. The typical pathway of blood flow involves arteries branching into arterioles, which further branch into capillaries, facilitating the exchange of nutrients and gases with the organ's tissues.

The correct answer is C. Helper T-cells play a crucial role in the immune system by coordinating and stimulating other immune cells, including cytotoxic T-cells, to attack and destroy foreign agents.

The correct answer is B. Objects A and B have the same mass, but B falls faster because it has less air resistance. Objects C and D have different masses, but C falls faster because it has a higher mass-to-surface-area ratio, which reduces the effect of air resistance.

The correct answer is C. The renal vein is responsible for draining oxygen-depleted blood from the kidneys. After the kidneys filter waste and excess substances from the blood, the deoxygenated blood is carried away from the kidneys by the renal vein

The correct answer is choice B. This is the plate that represents the highest number of bacteria. The bacteria that grow on this plate are the most resistant to the antibiotic because they can survive in a high concentration of the substance. In the other plates, the antibiotic inhibits the growth of the bacteria to a greater or lesser extent, depending on their sensitivity.