Which of the following types of cells stimulates other immune cells to attack and destroy foreign agents?

The correct answer is A. Endocrine glands secrete hormones directly into the bloodstream without ducts, while exocrine glands have ducts through which their secretions are transported to specific locations. This fundamental difference in the mode of secretion distinguishes endocrine from exocrine glands.

The correct answer is C. 9. The pH is determined by taking the negative logarithm (base 10) of the hydrogen ion concentration ([H+]). In this case, -log(10^(-9)) equals 9, so the pH of the solution is 9.

To find the pH of a solution with a hydrogen ion concentration ([H+]) of \(10^{-9}\) M using the equation \(pH = -\log[H^+]\):

\[ pH = -\log(10^{-9}) \]

Now, since \( \log(10^{-9}) = -9 \), the negative sign before the logarithm makes the value positive:

\[ pH = -(-9) = 9 \]

Therefore, the solution has a pH of 9

Phosphates are found in both DNA and cell membranes. In DNA, they form part of the backbone structure, linking the nucleotides together. In cell membranes, phosphates are a component of phospholipids, which are critical to the membrane's structure and function.

The pharynx is primarily composed of muscle tissue. It plays a role in swallowing and is part of both the respiratory and digestive systems, which requires coordinated muscular activity.

The correct answer is D. Cardiac muscles contain intercalated discs, whereas skeletal muscles do not. Intercalated discs are unique features of cardiac muscle cells, providing a structural and functional connection between adjacent cells. Skeletal muscles lack intercalated discs.

The correct answer is A. The endocardium is the innermost layer of tissue that lines the interior surfaces of the heart, providing a smooth surface for blood flow. The myocardium is the middle muscular layer, the pericardium is the outer protective sac, and the epicardium is the outermost layer covering the heart.

The correct answer is A. A gene is a segment of DNA that contains the instructions for building a specific protein or performing a specific function.

The correct answer is B. Facilitated diffusion is the passive movement of molecules, including water, across a membrane with the help of specific transport proteins. Water moves through specialized channels called aquaporins during facilitated diffusion.

The correct answer is C. Chlorine molecule (Cl2) has only one covalent bond between the two chlorine atoms, which share one pair of electrons. The other molecules have more covalent bonds: water has two, methane has four, and ammonia has three.

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.