The pancreas secretes digestive enzymes into the small intestine. What enzyme breaks down proteins into amino acids?

Correct Answer: D

Rationale: Trypsin is the correct enzyme that breaks down proteins into amino acids. It is produced by the pancreas and released into the small intestine to facilitate protein digestion. Pepsin is an enzyme from the stomach that also breaks down proteins, amylase targets carbohydrates, and lipase works on fats. In this context, since the question specifies the pancreas and small intestine, the correct answer is Trypsin as it is the pancreatic enzyme responsible for protein breakdown in the small intestine.

Correct Answer: C

Rationale: The correct answer is the uterus. The uterus is a muscular organ in the female body where a developing fetus is nourished and protected during pregnancy. It is the site where a fertilized egg implants and grows into a fetus. The ovaries produce eggs, the fallopian tubes transport the egg to the uterus for potential fertilization, and the vagina serves as the birth canal and the passage for menstrual blood to exit the body. Therefore, the uterus plays a crucial role in pregnancy by providing a nurturing environment for the developing fetus.

Correct Answer: C

Rationale: B cells are primarily responsible for antibody production in the adaptive immune system. When activated, B cells differentiate into plasma cells, which are specialized to produce antibodies. Helper T cells play a crucial role in activating B cells, but they do not directly produce antibodies. Cytotoxic T cells are involved in cell-mediated immunity by killing infected cells, while natural killer cells are part of the innate immune system and target virus-infected and cancerous cells. Therefore, the correct answer is C (B cells) as they are directly involved in the production of antibodies, essential for humoral immunity.

Correct Answer: A

Rationale: Antigen-antibody binding is the principle behind vaccination. When a vaccine containing antigens (weakened or killed pathogens) is introduced into the body, the immune system produces antibodies that bind to these antigens. This binding triggers an immune response, leading to the production of memory cells that provide immunity against future infections by the same pathogen. Vaccination helps the body develop immunity without causing the disease itself, thereby protecting individuals from infectious diseases. Disinfection and sterilization involve different processes to eliminate or reduce pathogens on surfaces or objects. Antibiotic resistance is a phenomenon where bacteria evolve to resist the effects of antibiotics and is not directly related to antigen-antibody binding.

Correct Answer: B

Rationale: Antigenic variation is a strategy used by some viruses to evade the host's immune response. By constantly changing their surface antigens, viruses can avoid recognition and destruction by the immune system. This allows the virus to persist in the host and continue replicating, leading to prolonged infection and potential transmission to other hosts. Antigenic variation does not directly involve the production of toxins, survival outside a host, or rapid replication, making options A, C, and D incorrect in this context.