ati teas 7 science

Correct Answer: B

Rationale: The correct answer is B: Myosin. Myosin is the protein complex responsible for the thick filament in the sarcomere. It forms cross-bridges with actin during muscle contraction. Actin (choice A) is the thin filament in the sarcomere. Tropomyosin (choice C) is a regulatory protein that covers the myosin-binding sites on actin when the muscle is at rest. Troponin (choice D) is another regulatory protein that helps regulate muscle contraction by binding calcium ions.

Correct Answer: B

Rationale: The correct answer is B: Humoral immunity. B-cells produce antibodies that circulate in bodily fluids to combat pathogens. This is a key aspect of humoral immunity. A: Cell-mediated immunity involves T-cells directly attacking infected cells, not antibody secretion by B-cells. C: Innate immunity is non-specific and does not involve B-cells producing antibodies. D: Phagocytic immunity involves phagocytes engulfing and destroying pathogens, not antibody secretion by B-cells.

Correct Answer: C

Rationale: The correct answer is C: Luteinizing hormone (LH). LH surge triggers ovulation by causing the mature ovarian follicle to release the egg. Estrogen and progesterone play important roles in regulating the menstrual cycle but are not the primary triggers for ovulation. FSH stimulates the growth of ovarian follicles but does not directly trigger ovulation.

Correct Answer: B

Rationale: The correct answer is B: It runs 3' to 5'. The antisense strand of DNA runs in the opposite direction to the sense strand. This is essential for complementary base pairing during transcription. The 3' to 5' direction allows RNA polymerase to synthesize RNA in the 5' to 3' direction, following the template of the antisense strand. Therefore, choice B is correct. Choices A and C are incorrect because the directionality of the antisense strand is opposite to 5' to 3' and it is used in transcription, not replication. Choice D is incorrect as DNA is stored in the cell nucleus in a double helix structure, not in a specific direction.

Correct Answer: A

Rationale: The correct answer is A because the atomic number represents the number of protons in the nucleus of an atom, which determines the element's identity. The mass number is the total number of protons and neutrons in the nucleus, indicating the atom's mass. The number of electrons is not directly related to either the atomic or mass number, eliminating choices B and D. Choice C is incorrect because the atomic number specifically refers to the number of protons, not neutrons. Thus, choice A is the only accurate explanation of the difference between the atomic number and the mass number.