The human retina contains rods and cone which are able to

Correct Answer: C

Rationale: The correct answer is C because rods and cones in the human retina convert light energy into electrical signals through phototransduction, which are then sent as action potentials to the brain via the optic nerve. This process allows for visual information to be transmitted and processed by the brain. Choice A is incorrect as it refers to the conversion of light energy to chemical energy, which is not the primary function of rods and cones. Choice B is incorrect as rods and cones do not specifically absorb ultraviolet light. Choice D is incorrect as rods and cones do not absorb infrared light.

Correct Answer: A

Rationale: The correct answer is A: Ilya Metchnikoff. He discovered phagocytes through his research on immune responses in starfish larvae. Metchnikoff observed cells engulfing foreign particles, leading to the discovery of phagocytosis. Louis Pasteur is famous for his work in microbiology and vaccination. Emil von Behring discovered antitoxins. Robert Koch is known for his work in bacteriology and identifying the causative agents of diseases. Therefore, the correct answer is A as Metchnikoff specifically discovered phagocytes.

Correct Answer: D

Rationale: The correct answer is D because CD14 is a glycosylphosphatidylinositol (GPI)-anchored protein expressed on the cell membrane that binds to LPS and facilitates its delivery to the TLR-4/MD-2 complex for recognition. CD14 does not transport TLR-4 (Choice A), bind LPS internally (Choice B), or act as an adaptor in the signaling pathway (Choice C). The key role of CD14 is to shuttle LPS to TLR-4/MD-2, initiating the immune response.

Correct Answer: C

Rationale: The lectin and classical pathways both lead to the formation of the same C3 convertase (C4b2a). This is because in the lectin pathway, mannose-binding lectin (MBL) binds to specific sugar residues on pathogens, activating MBL-associated serine proteases (MASPs) that cleave C4 and C2 to form the C3 convertase. Similarly, in the classical pathway, C1 complex binds to antigen-antibody complexes, activating C1s to cleave C4 and C2 to form the C3 convertase. This convergent step in both pathways results in the cleavage of C3 into C3a and C3b, leading to downstream complement activation. The other choices are incorrect because they do not accurately reflect the key similarity between the lectin and classical pathways in terms of the formation of the C3 convertase.

Correct Answer: D

Rationale: The correct answer is D because the secondary immune response is faster and stronger compared to the primary response. This is due to the presence of memory B and T cells from the primary response that can quickly recognize and respond to the antigen upon re-exposure. These memory cells allow for a more rapid and robust immune response, leading to quicker elimination of the pathogen. Choices A and B are incorrect because both primary and secondary responses involve the adaptive immune system and are antigen-specific. Choice C is incorrect as the secondary response is faster and more potent than the primary response.