c and t are known as

HESI A2

Biology HESI A2 Practice Test

1. Cytosine and thymine are known as:

A. Purines
B. Pyrimidines
C. Both
D. None of the above

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.

2. The renal system consists of all the organs involved in the formation and release of urine and includes the kidneys, ureters, bladder, and urethra.

A. The digestive system
B. The reproductive system
C. The renal system
D. The kidney system

Correct answer: C

Rationale: The correct term for the system involving the organs responsible for the formation and release of urine is the renal system, not the digestive or reproductive system. The kidneys, ureters, bladder, and urethra are specifically part of the renal system, which is responsible for filtering the blood to remove waste and excess fluids, producing urine, and eliminating it from the body. The other choices, the digestive system and the reproductive system, are not responsible for the formation and release of urine, making them incorrect answers.

3. Which of the following is true of the Krebs cycle?

A. It is a redox reaction involving proteins produced during glycolysis
B. It is a redox reaction involving sugars produced during glycolysis
C. Protons are passed along a gradient to produce ATP
D. It is also known as the glycolic acid cycle

Correct answer: B

Rationale: The Krebs cycle, also known as the citric acid cycle, involves a series of redox reactions that occur in the mitochondria. The cycle begins with the oxidation of acetyl CoA, which is derived from the breakdown of sugars produced during glycolysis. These sugars are broken down further in the Krebs cycle to produce ATP and reduce electron carriers such as NADH and FADH2. The cycle does not involve proteins produced during glycolysis. Protons are not passed along a gradient to produce ATP directly in the Krebs cycle; rather, they are used in the electron transport chain to generate ATP. The Krebs cycle is not known as the glycolic acid cycle; glycolysis is the metabolic pathway that produces pyruvate from glucose.

4. Which cells in the human body lack nuclei?

A. Nerve cells
B. Red blood cells
C. Liver cells
D. Connective tissue cells

Correct answer: B

Rationale: Red blood cells, also known as erythrocytes, lack nuclei in humans. This absence of a nucleus allows more space for hemoglobin, the protein responsible for carrying oxygen, making red blood cells efficient at their function of oxygen transport in the body. Nerve cells (Choice A), liver cells (Choice C), and connective tissue cells (Choice D) all possess nuclei as they require genetic material for their functions, such as cell signaling, protein synthesis, and structural support.

5. Which organism reproduces via binary fission?

A. Mushroom
B. Blue whale
C. Rainbow trout
D. Salmonella

Correct answer: D

Rationale: The correct answer is D, Salmonella. Salmonella bacterium reproduces via binary fission, a form of asexual reproduction where the cell divides into two daughter cells with identical genetic material. This process is common among bacteria and single-celled organisms. Mushrooms reproduce through spores, blue whales and rainbow trout reproduce sexually, involving the fusion of male and female gametes. Therefore, choices A, B, and C are incorrect as they do not reproduce through binary fission.