1. The stomach acid or the gastric acid is composed of hydrochloric acid (HCl), potassium chloride (KCl), and sodium chloride (NaCl).The pH of this acid is between 1.5 and 3.5. The more acidic the acid is, the more hydrogen ions (H+) are in it. If the pH of stomach acid is 1:
pH = -log[H+]
1 = -log[H+]
-1 = log[H+]
Raising 10 to the exponent of each side
10^(-1) = 10^(log[H+])
10^(-1) = [H+]
[H+] = 10^(-1) M = 0.1 M = 0.1 moles/Liter
It is 0.1 mol/l * 6.022 x1023 mol-1 (Avogadro number) = 0.6022 x 1023 ions of hydrogen
2. Cells of the immune system are responsible for the phagocytosis of pathogens such as bacteria. Those cells are neutrophils, macrophages, dendritic cells, and B lymphocytes. Phagocytosis is specific process, meaning that the cell has to recognize the foreign cell via surface receptor (physical contact). After the contact the cell engulfs it.
Epithelial tissue is the first line of defense against microbes and the cells of this tissue use mechanisms of phagocytosis as a response against invading pathogens. Subtype of this tissue is stratified epithelia which builds a barrier to the environment (skin).
3. Na/K pump (or Na/K ATPase) moves Na+ out of cells, and K+ into them. This transport process uses ATP as an energy source (because it moves ion against the gradient), so it is an example of primary active transport. When this pump works, for three ions of Na that move out, only two ions of K move in, which results in a more negative cell interior. Because of this (and because of high concentration of K inside the cell) this pump is responsible for making membrane potential. One ATP molecule is necessary for the export of three sodium ions and import of two potassium ions.
4. The cells with Na/K pump are necessary for nervous system where they control neuron activity. Since the pump is involved in different kinds of transport it is also part of the digestive system and the process of absorption. In the renal system, transport with Na+-K+ also occurs, and the pump helps to maintain the right concentrations of ions (osmolarity of the cell).
