What is the primary function of the respiratory system?

Correct Answer: B

Rationale: The primary function of the respiratory system is to take oxygen into the body through inhalation and remove carbon dioxide through exhalation. Oxygen is essential for cellular respiration and energy production, while carbon dioxide is a waste product that needs to be expelled from the body. This process is vital for the functioning of the body's cells and tissues. Choices A, C, and D are incorrect because sound and speech production, nutrient transport, and acting as a barrier against outside influences are not the primary functions of the respiratory system. While the respiratory system is involved in speech production to some extent, its primary role is in gas exchange for respiration.

Correct Answer: A

Rationale: The correct answer is the smooth endoplasmic reticulum. This organelle lacks ribosomes on its surface, unlike the rough endoplasmic reticulum, which is involved in protein synthesis. The enzymes present in the smooth endoplasmic reticulum are responsible for synthesizing lipids such as phospholipids and steroids. Choice B, ribosomes, are responsible for protein synthesis and not lipid synthesis. Choice C, rough endoplasmic reticulum, is involved in protein synthesis due to the presence of ribosomes. Choice D, Golgi apparatus, is responsible for modifying, sorting, and packaging proteins for secretion, not lipid synthesis.

Correct Answer: A

Rationale: A cell placed in a hypertonic solution has a higher solute concentration outside the cell compared to inside. This creates a concentration gradient that causes water to move out of the cell through osmosis to equalize the concentrations on both sides. As a result, the cell will shrink or undergo plasmolysis, as water is pulled out of the cell. Choice B is incorrect because a hypertonic solution causes water to move out of the cell, leading to shrinkage rather than swelling. Choice C is incorrect as a hypertonic solution results in a concentration gradient that leads to water leaving the cell, causing it to shrink. Choice D is incorrect because pH is not directly affected by being placed in a hypertonic solution; the change in solute concentration primarily impacts water movement.

Correct Answer: C

Rationale: When two mice that are heterozygous for white fur (Ww) and short fur (Ss) mate, they can produce offspring with different combinations of the two traits. The Punnett square for this cross shows that the most likely genotype for the offspring is WwSs. In this case, each offspring receives one allele for white fur (W) and one for short fur (S) from each parent, resulting in a heterozygous genotype for both traits. Choice A (wwss) is incorrect as it represents a homozygous recessive genotype for both traits. Choice B (WWSS) is also incorrect as it represents a homozygous dominant genotype for both traits. Choice D (WWSs) is incorrect as it represents a genotype where one trait is homozygous dominant (W) and the other is heterozygous (S), which is not the most likely outcome based on the given parental genotypes.

Correct Answer: D

Rationale: The neuromuscular junction is the specific area where nerve impulses trigger the release of neurotransmitters that cross the synaptic gap to bind to receptors on the muscle cell membrane. This binding initiates muscle contraction by stimulating the muscle cell. The sarcomere is the basic contractile unit in a muscle fiber, not the location where nerve impulses communicate with muscle cells. Tendons are connective tissues that attach muscles to bones and are not involved in transmitting nerve impulses. The myelin sheath is a protective covering around nerve fibers but is not directly involved in transmitting neurotransmitters to muscle cells for muscle contraction.

Correct Answer: B

Rationale: The correct answer is B: semilunar valves. Semilunar valves are primarily responsible for preventing blood flow from major blood vessels to the heart. These valves are located at the base of the aorta and the pulmonary artery, ensuring blood flows in one direction only by closing when the ventricles relax to prevent blood from flowing back into the heart. Choices A, C, and D are incorrect. Atrioventricular valves (choice A) include the tricuspid and bicuspid valves, which prevent backflow between the atria and ventricles, not major blood vessels. Tricuspid valves (choice C) and bicuspid valves (choice D) are specific types of atrioventricular valves located between the atria and ventricles, not at the base of major blood vessels.

Correct Answer: D

Rationale: The correct answer is D: There is no control group in this experiment. A control group is a group in an experiment that does not receive the treatment being studied in order to serve as a baseline for comparison. In this case, all three tanks (A, B, and C) are being treated with different amounts of fertilizer, and there is no group that is left untreated to serve as a control for comparison. Choices A, B, and C are incorrect because they all represent tanks that are part of the experimental groups receiving different amounts of fertilizer, thus none of them can be considered the control group.

Correct Answer: A

Rationale: Progesterone plays a key role in the regulation and preparation of the endometrial lining of the uterus for potential pregnancy. It also inhibits contractions of the uterus as the ovum is released and stimulates milk production in the breasts. However, the expression of secondary sexual characteristics, such as enlarged breasts, is primarily influenced by estrogen, not progesterone. Therefore, choice A is the correct answer as it is not a function directly attributed to progesterone in the female reproductive system.

Correct Answer: B

Rationale: In genetics, dominance refers to the relationship between two different alleles of a gene where one allele (dominant) masks the expression of another allele (recessive) in an individual's phenotype. The correct statement about dominance is that a dominant allele will always be expressed in the phenotype, even in the presence of a recessive allele. This means that if an individual has at least one dominant allele for a particular trait, that trait will be expressed. Choice A is incorrect because not all genes follow Mendel's law of dominance; exceptions do exist. Choice C is incorrect because when two dominant alleles are present, only one will be expressed due to complete dominance. Choice D is incorrect as there can be more than three alleles for a gene, and not all genes have three or more alleles.