enzymes are typically

HESI A2

HESI A2 Biology Practice Test

1. Enzymes are typically _ _.

A. Fats
B. Proteins
C. Sugars
D. Neurons

Correct answer: B

Rationale: Enzymes are typically proteins that act as biological catalysts, speeding up chemical reactions in living organisms. While most enzymes are made of proteins, a few exceptions, known as ribozymes, are made of RNA. Proteins are composed of amino acids arranged in specific sequences that give enzymes their unique shape and functionality. Choice A, 'Fats,' is incorrect as enzymes are not typically composed of fats. Choice C, 'Sugars,' is incorrect as enzymes are not typically composed of sugars. Choice D, 'Neurons,' is incorrect as neurons are a type of cell in the nervous system, not typically associated with enzymes.

2. Why can animal cells use a contractile ring but plant cells cannot?

A. Plant cells can use both methods to divide
B. Animal cells divide faster, requiring them to pinch apart
C. Plant cells are too rigid to use a contractile ring
D. N/A

Correct answer: C

Rationale: Plant cells have a rigid cell wall surrounding them, which prevents them from using a contractile ring for cell division. The rigid cell wall requires plant cells to form a cell plate during cell division instead of pinching apart like animal cells with a contractile ring. Choice A is incorrect because plant cells cannot use a contractile ring due to their rigid cell wall. Choice B is incorrect as the speed of cell division is not the primary reason for the difference in cell division mechanisms between plant and animal cells. Choice D is not applicable as plant cells indeed have a specific limitation in using a contractile ring for cell division.

3. What event occurs during telophase?

A. The nuclear envelope disappears.
B. Organelles double in number.
C. Chromosomes separate.
D. Two nuclei are formed.

Correct answer: D

Rationale: During telophase, the final stage of mitosis, the separated chromosomes reach opposite poles of the cell. At this stage, a new nuclear envelope forms around each set of chromosomes, creating two distinct nuclei. This marks the completion of cell division. Choices A, B, and C are incorrect because the disappearance of the nuclear envelope typically occurs during prophase, organelles do not double in number during telophase, and chromosomes separate during anaphase, not telophase.

4. How many pairs of chromosomes do all humans have?

A. 24 pairs
B. 23 pairs
C. 22 pairs
D. 20 pairs

Correct answer: B

Rationale: All humans have 23 pairs of chromosomes, totaling 46 chromosomes. Choice A is incorrect because humans do not have 24 pairs. Choice C is incorrect as humans have 23 pairs, not 22 pairs. Choice D is incorrect as humans have 23 pairs of chromosomes, not 20 pairs.

5. Two organisms live in a relationship from which both benefit. What is this called?

A. Mutualism
B. Parasitism
C. Commensalism
D. Competition

Correct answer: A

Rationale: Mutualism is a type of symbiotic relationship between two organisms in which both parties benefit from the association. It is a mutually beneficial interaction where both organisms gain something valuable, such as food, protection, or some other resource. This contrasts with parasitism, where one organism benefits at the expense of the other, commensalism, where one organism benefits while the other is unaffected, and competition, where both organisms are negatively affected by their interaction.