Which blood component is chiefly responsible for clotting?

Correct Answer: A

Rationale: The correct answer is A: Platelets. Platelets are small cell fragments in the blood that play a crucial role in clotting. When there is an injury, platelets adhere to the site and release chemicals that help form a clot to prevent excessive bleeding. Red blood cells transport oxygen, antigens are substances that trigger an immune response, and plasma cells are a type of white blood cell involved in producing antibodies, none of which are primarily responsible for clotting.

Correct Answer: A

Rationale: The correct answer is A. The initial event in a primary immune response is the phagocytosis of pathogens by macrophages and the subsequent presentation of their antigens, which is crucial for initiating the adaptive immune response. Neutrophils (Choice B) are also involved in the innate immune response, but they typically respond after macrophages. B lymphocytes (Choice C) produce antibodies later in the adaptive immune response, and Helper T cells (Choice D) help in coordinating the immune response but are not the first cells to act in a primary immune response.

Correct Answer: B

Rationale: The correct answer is B. In this experiment, the independent variable is the amount of poison because it is what is being manipulated by the researcher. The dependent variable is how quickly the rat dies, as it is the outcome that is being measured based on the different amounts of poison administered. Choice A is incorrect because the independent variable should be what is being manipulated or changed, which is the amount of poison in this case. Choice C is incorrect because whether the rat eats the poison is not being varied or controlled by the researcher. Choice D is incorrect because the cage the rat is kept in is not relevant to the relationship being studied between the amount of poison and the rat's survival time.

Correct Answer: C

Rationale: Visual processing begins in the retina, not the cornea, optic nerve, or eyelid. The retina is a layer of tissue at the back of the eye that contains photoreceptor cells responsible for converting light into neural signals that are then sent to the brain for processing. The cornea is the transparent outer layer of the eye that helps focus light, but it does not process visual information. The optic nerve transmits visual information from the retina to the brain, it does not initiate visual processing. The eyelid is a protective covering for the eye and is not involved in visual processing.

Correct Answer: D

Rationale: The correct answer is D. Gametes are the reproductive cells produced by meiosis. Meiosis is the cell division process that results in the formation of gametes, which are sperm cells in males and egg cells in females. Genes (A), alleles (B), and chromatids (C) are not the reproductive cells produced by meiosis. Genes are units of heredity, alleles are different forms of a gene, and chromatids are duplicated chromosomes involved in cell division.

Correct Answer: A

Rationale: A DNA mutation is the correct term used to describe an alteration in the normal gene sequence. It refers to changes in the DNA sequence that can result in different traits or characteristics. Gene migration involves the movement of genes between populations, polygenic inheritance refers to the inheritance of traits controlled by multiple genes, and incomplete dominance is a pattern of inheritance where neither allele is dominant.

Correct Answer: C

Rationale: The somatic nervous system is responsible for controlling voluntary movements of skeletal muscles. This system communicates sensory information and controls voluntary movements, such as walking or reaching for objects. Breathing is primarily regulated by the autonomic nervous system, which functions involuntarily. Thought processes involve complex interactions between various regions of the brain and are not directly controlled by the somatic nervous system. Fear is an emotional response that involves the limbic system of the brain and the autonomic nervous system, not the somatic nervous system.

Correct Answer: C

Rationale: A sensory pathway generally consists of three neurons: a first-order neuron, a second-order neuron, and a third-order neuron. The first-order neuron carries sensory information from the periphery to the spinal cord or brainstem. The second-order neuron then transmits this information to the thalamus or cerebellum. Finally, the third-order neuron projects the sensory input to the cerebral cortex for processing and perception. Therefore, the correct answer is 3 (C). Choices A, B, and D are incorrect as they do not align with the typical structure of a sensory pathway involving three neurons.

Correct Answer: D

Rationale: The correct answer is 'D: Catabolism.' Catabolism specifically involves breaking down large molecules into smaller ones to release energy. It is the opposite of anabolism, which is the process of building larger molecules from smaller ones. 'Metabolism' (choice A) is a broader term that encompasses all chemical processes in an organism, including anabolism and catabolism. 'Bioenergetics' (choice B) refers to the flow and transformation of energy in a biological system, not specifically the breakdown of molecules for energy.