What is the main difference between the clonal selection theory proposed by MacFarlane Burnet and the selection theory proposed by Paul Ehrlich?

Correct Answer: B

Rationale: The correct answer is B because Ehrlich proposed that each cell producing antibodies would express several receptors, each specific for different antigens, whereas Burnet proposed that each single antibody-producing cell expresses only one type of receptor. This is the main difference between the two theories. Ehrlich's concept of multiple receptors per cell allows for a broader range of specificity and diversity in the immune response. The other choices are incorrect because they do not directly address the main difference between the two theories as outlined above. Choice A is incorrect because both Ehrlich and Burnet emphasized the importance of specificity, but they differed in their views on receptor diversity per cell. Choice C is incorrect because it focuses on the identity of soluble antibodies and receptors, which is not the main differentiator between the two theories. Choice D is incorrect as it mentions the release of soluble antigen receptors, which is not the main point of differentiation between Ehrlich and Burnet's theories.

Correct Answer: B

Rationale: Step 1: Acute-phase proteins are a group of proteins produced by the liver in response to inflammation or infection. Step 2: Mannose binding lectin (MBL) is an acute-phase protein that plays a role in the innate immune response. Step 3: MBL binds to pathogens and activates the complement system to enhance immune responses. Step 4: Selectins are cell adhesion molecules, not acute-phase proteins. Step 5: Lysozyme is an enzyme that destroys bacterial cell walls, not typically classified as an acute-phase protein. Step 6: Defensins are antimicrobial peptides, not typically classified as acute-phase proteins. Summary: MBL is the correct choice as it is a well-known acute-phase protein involved in the immune response. Selectins, Lysozyme, and Defensins are not typically classified as acute-phase proteins and are involved in different functions.

Correct Answer: A

Rationale: The correct answer is A: IgM. During a primary immune response, IgM antibodies are the first class produced by plasma cells. IgM is the largest antibody and is effective at agglutinating pathogens. It is later followed by IgG production. IgE is involved in allergic reactions and parasitic infections, not typically produced in large amounts during a primary response. IgA is more abundant in mucosal tissues and secretions.

Correct Answer: D

Rationale: The correct answer is D because plant hormones are used in agriculture to control fruit production, ripening, dropping, and to produce seedless fruits. Choice A is correct as plant hormones regulate these processes. Choice B is also correct as certain plant hormones can induce seedless fruit formation. Choice C is incorrect as plant hormones are not typically used as weed killers in agriculture. Overall, the correct answer, D, encompasses all the agricultural uses of plant hormones listed in the other choices.

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.