which of the following is always true about molecules
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HESI A2

Biology HESI A2 Practice Test

1. Which of the following is always true about molecules?

Correct answer: C

Rationale: The statement that molecules move from high concentration to low concentration without using energy is always true due to the natural process of diffusion. This movement occurs to reach equilibrium and does not require any additional energy input directly from the molecule itself. Choice A is incorrect because not all molecules can travel through all cell membranes. Choice B is incorrect as molecules typically move from high concentration to low concentration in a process known as passive transport. Choice D is incorrect as molecules are in constant motion due to factors like temperature and kinetic energy.

2. In a strand of DNA, you would expect to see adenine paired with ___________.

Correct answer: C

Rationale: In a strand of DNA, adenine always pairs with thymine through two hydrogen bonds. This pairing is a fundamental aspect of DNA structure, where adenine and thymine complement each other in the double helix. Choice A (cytosine) is incorrect because adenine does not pair with cytosine in DNA. Choice B (uracil) is incorrect as uracil is found in RNA, not DNA. Choice D (guanine) is incorrect as guanine pairs with cytosine, not adenine, in DNA.

3. What is the function of platelets in the blood?

Correct answer: B

Rationale: Platelets, also known as thrombocytes, are responsible for clotting blood. When there is an injury, platelets help form blood clots to prevent excessive bleeding. This function is crucial in maintaining hemostasis and preventing hemorrhage. Choices A, C, and D are incorrect. Platelets do not transport oxygen, fight infection, or transport nutrients in the blood.

4. Which statement would not be inferred by the reader?

Correct answer: D

Rationale: The correct answer is D. While the passage extensively discusses the benefits and applications of phototherapy, it does not mention that ultraviolet rays can cause damage to eyes and skin. This statement goes beyond the information provided in the passage and cannot be inferred. A. The passage mentions that phototherapy has been around for more than a century, supporting the statement that some forms of phototherapy have been around for decades. B. The passage discusses how new applications of phototherapy, like the phototherapy blanket, are being developed, making this statement valid as it aligns with the information provided. C. Phototherapy being most often used to treat skin problems is supported by the passage, which mentions its applications in treating acne, psoriasis, and eczema. Therefore, this statement can be inferred from the passage.

5. Cytosine and thymine are known as:

Correct answer: B

Rationale: Cytosine and thymine are known as pyrimidines because they have a single carbon ring structure. Purines, on the other hand, have a double-ring structure. Choice A ('Purines') is incorrect because purines have a double-ring structure, unlike cytosine and thymine. Choice C ('Both') is incorrect as it implies they are both purines and pyrimidines, which is not true. Choice D ('None of the above') is incorrect because cytosine and thymine are indeed pyrimidines.

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