which of the following is not one of the four nitrogenous bases that make up the dna structure

HESI RN

Biology Practice Test

1. Which of the following is not one of the four nitrogenous bases that make up the DNA structure?

A. Adenine
B. Guanine
C. Uracil
D. Thymine

Correct answer: C

Rationale: The correct answer is C: Uracil. Uracil is found in RNA, not DNA. The four nitrogenous bases in DNA are adenine, thymine, cytosine, and guanine. Choice A, Adenine, is a nitrogenous base in DNA. Choice B, Guanine, is another nitrogenous base in DNA. Choice D, Thymine, is also one of the four nitrogenous bases in DNA. Therefore, the correct answer is Uracil (Choice C).

2. What is the most important function of carbohydrates?

A. Store and provide energy for the body
B. Create amino acids
C. Maintain body temperature
D. Insulate body organs against shock

Correct answer: A

Rationale: The most important function of carbohydrates is to store and provide energy for the body through metabolic processes. Carbohydrates are broken down into glucose, which is used as the primary source of energy for various cellular functions. Choice B is incorrect because amino acids are the building blocks of proteins, not directly created by carbohydrates. Choice C is incorrect as the regulation of body temperature is primarily controlled by mechanisms such as sweating and shivering, not carbohydrates. Choice D is incorrect as insulation of body organs against shock is mainly provided by adipose tissue, not carbohydrates.

3. Binary fission is a type of asexual reproduction. Which of the following occurs during the binary fission process?

A. The chromosomes bind to the plasma membrane
B. The chromosomes attach to the spindle formed along the axis
C. The chromosomes gather in the center of the cell
D. The chromosomes begin to separate

Correct answer: A

Rationale: The correct answer is A. In binary fission, the chromosomes bind to the plasma membrane before the cell splits into two. This initial step ensures that each daughter cell receives a complete set of genetic material. Choice B is incorrect because the spindle apparatus is characteristic of eukaryotic cell division (mitosis), not prokaryotic binary fission. Choice C is incorrect as chromosomes do not necessarily gather in the center of the cell during binary fission. Choice D is incorrect because the chromosomes do not begin to separate in binary fission; they replicate and then move to opposite ends of the cell before division.

4. What percentage of the parents' offspring is predicted to have a cleft chin if one parent carries the recessive gene for a cleft chin (c) while the other parent does not?

A. 25%
B. 50%
C. 0%
D. 75%

Correct answer: C

Rationale: The correct answer is C (0%). If one parent carries the recessive gene for a cleft chin while the other parent does not carry it, none of their offspring is predicted to have a cleft chin. This is because the cleft chin trait is recessive, so for an offspring to express this trait, they would need to inherit the gene from both parents. In this scenario, none of the offspring will inherit the recessive gene from both parents, so the percentage of offspring predicted to have a cleft chin is 0%. Choices A, B, and D are incorrect because in this situation, the offspring will not express the cleft chin phenotype, although they could be carriers of the recessive gene.

5. Which of the following do prokaryotic cells lack?

A. A cell membrane
B. Genetic material
C. Cytoplasm
D. Membrane-bound organelles

Correct answer: D

Rationale: The correct answer is D: Prokaryotic cells lack membrane-bound organelles, such as mitochondria or a nucleus, distinguishing them from eukaryotic cells. Prokaryotic cells do have genetic material, a cell membrane, and cytoplasm. Choice A is incorrect because prokaryotic cells do have a cell membrane, which is essential for maintaining cell structure and regulating what enters and exits the cell. Choice B is incorrect because prokaryotic cells contain genetic material, typically in the form of a single circular chromosome. Choice C is incorrect because prokaryotic cells have cytoplasm, where various cellular activities take place.