Correct Answer: A

Rationale: Substances that stimulate adaptive immunity are called peptides. Peptides are short chains of amino acids that play a crucial role in activating the immune response by interacting with immune cells such as T cells and B cells. Peptides are important in antigen presentation and recognition, leading to the development of specific immune responses against pathogens. Choice B, phagocytes, are cells that engulf and digest pathogens but are not substances that stimulate adaptive immunity. Choice C, prions, are infectious agents made of misfolded proteins and are not related to stimulating adaptive immunity. Choice D, platelets, are cell fragments involved in blood clotting and have no direct role in stimulating adaptive immunity.

Correct Answer: B

Rationale: The statement provided in Option B is FALSE. Organs are actually made up of different types of tissues that work together to perform specific functions, rather than being composed of similar tissues. Organs consist of various tissues, each with their own specialized functions that collectively contribute to the overall function of the organ. Options A, C, and D are true statements. Option A correctly defines an organelle as a specialized structure in a cell, like a ribosome. Option C accurately describes organ systems as multiple organs working together to perform related functions. Option D correctly explains that a tissue is composed of different cells working together to carry out a specific function.

Correct Answer: A

Rationale: The most effective procedure in testing whether the drug is responsible for the recovery is to ensure that neither the subjects nor the investigators know which subjects are given the drug and which are given the placebo. This method is known as a double-blind study, which helps eliminate biases and ensures that the results are reliable and not influenced by expectations or beliefs. By keeping both the subjects and investigators unaware of who is receiving the drug or placebo, the study can accurately determine the true impact of the drug on recovery. Choice B is incorrect as it only prevents the subjects from knowing which treatment they are receiving, allowing for potential bias from the investigators. Choice C is also incorrect as it allows for potential bias from the subjects. Choice D is incorrect as full knowledge of treatment allocation can introduce bias and affect the study's validity.

Correct Answer: D

Rationale: Mildly elevated levels of thyroxine will increase the heart rate. Thyroxine, a hormone produced by the thyroid gland, regulates metabolism. Elevated thyroxine levels can lead to increased metabolism, resulting in an elevated heart rate. Choice A is incorrect as mildly elevated thyroxine levels do not stop the heart rate. Choice B is incorrect because elevated thyroxine levels do have an effect on heart rate. Choice C is incorrect as elevated thyroxine levels typically lead to an increase rather than a decrease in heart rate.

Correct Answer: C

Rationale: For an experiment to be considered successful, it is essential that the data collected and results obtained can be reproduced or replicated by others. This reproducibility ensures the reliability and validity of the experiment's findings. It allows for independent verification of the results and contributes to the overall scientific rigor of the study. While having a reasonable hypothesis, a well-written lab report, and computer-aided statistical analysis are important aspects of an experiment, the ability to reproduce the data is crucial for establishing the experiment's credibility and success. Without reproducibility, the findings may not be reliable, and the experiment's outcomes cannot be verified independently, leading to doubts about its validity.