ati teas 7 science

Correct Answer: D

Rationale: The correct answer is D because all the options are valid obstacles to achieving controlled nuclear fusion on Earth. Lack of suitable materials (A) is crucial due to extreme conditions, limited fusion fuels (B) can hinder sustained reactions, and containing plasma (C) is challenging to prevent energy loss. Therefore, all factors must be addressed for successful fusion energy production.

Correct Answer: D

Rationale: The correct answer is D: tRNA. Transfer RNA (tRNA) carries amino acids to ribosomes during protein synthesis. tRNA has an anticodon that pairs with the mRNA codon, ensuring the correct amino acid is added to the growing polypeptide chain. A: DNA carries genetic information but does not directly participate in protein synthesis. B: mRNA carries the genetic information from DNA to the ribosomes but does not carry amino acids. C: rRNA is a structural component of ribosomes and helps in protein synthesis but does not carry amino acids to the ribosomes.

Correct Answer: A

Rationale: The correct answer is A: Calcitonin. Calcitonin is produced by the thyroid gland and functions to lower blood calcium levels by promoting calcium deposition in bones and inhibiting calcium reabsorption in the kidneys. This hormone opposes the action of parathyroid hormone (PTH), which increases blood calcium levels by promoting calcium release from bones and increasing calcium reabsorption in the kidneys. Thyroxine is a thyroid hormone that regulates metabolism and growth, not calcium levels. Insulin is a hormone produced by the pancreas that regulates blood sugar levels, not calcium levels. Thus, A is the correct answer as it directly regulates calcium levels in the blood through its actions on bones and kidneys.

Correct Answer: B

Rationale: When a sound wave travels from air to water, its speed decreases because sound travels faster in denser mediums. Water is denser than air, so the speed of sound decreases. This decrease occurs due to the change in the medium's properties affecting the wave propagation speed. The other choices are incorrect because the speed of sound is not dependent on frequency (choice D) and it doesn't remain the same (choice C) when transitioning between different mediums. Choice A is incorrect as an increase in density leads to a decrease in speed, not an increase.

Correct Answer: A

Rationale: The P wave on an ECG represents atrial depolarization. During the cardiac cycle, the electrical impulse originates in the sinoatrial (SA) node, causing the atria to contract. This depolarization of the atria is reflected as the P wave on the ECG. This occurs before the ventricles depolarize (choice B), repolarize (choice D), or before the atria repolarize (choice C). Therefore, the correct answer is A because the P wave specifically represents atrial depolarization in the cardiac cycle.