which of the following molecules is an important component of the plasma membrane

HESI A2

HESI A2 Practice Test Biology

1. Which of the following molecules is an important component of the plasma membrane?

A. Phospholipids
B. Steroids
C. Sugars
D. Amino acids

Correct answer: A

Rationale: Phospholipids are indeed a crucial component of the plasma membrane. They have a unique structure with hydrophilic heads and hydrophobic tails, which allows them to form the lipid bilayer of the membrane. Steroids, sugars, and amino acids are not primary components of the plasma membrane. Steroids are a different type of lipid, sugars are often found in glycoproteins on the membrane surface, and amino acids are the building blocks of proteins, some of which are membrane proteins, but not the membrane itself.

2. How many pairs of homologous chromosomes do humans have?

A. 13
B. 23
C. 26
D. 46

Correct answer: D

Rationale: The correct answer is D: 46. Humans have 23 pairs of chromosomes, which include 22 pairs of autosomes and 1 pair of sex chromosomes. Homologous chromosomes are pairs of chromosomes that contain the same genes, one from each parent. Therefore, humans have a total of 46 chromosomes, with 23 pairs of homologous chromosomes. Choices A, B, and C are incorrect as they do not represent the total number of chromosomes in humans or the number of pairs of homologous chromosomes.

3. Which organelle provides storage space for the cell?

A. Mitochondrion
B. Vacuole
C. Cell membrane
D. Ribosome

Correct answer: B

Rationale: The correct answer is B: Vacuole. The vacuole is the organelle responsible for providing storage space in the cell. It stores water, nutrients, waste products, and other essential materials required by the cell. Vacuoles are crucial for maintaining cell structure and regulating cellular processes. Mitochondrion (choice A) is known as the powerhouse of the cell, responsible for producing energy. The cell membrane (choice C) is a protective barrier around the cell, regulating what enters and exits the cell. Ribosomes (choice D) are involved in protein synthesis, not storage.

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 of the following is false?

A. Animal cells use lysosomes to break down old cells
B. Animal cells use chloroplasts to gain energy
C. Plant cells have a cell wall to maintain structure
D. All of the above are true

Correct answer: B

Rationale: The statement "B. Animal cells use chloroplasts to gain energy" is false. Chloroplasts are only present in plant cells and certain algae, where they are responsible for photosynthesis to generate energy from sunlight. Animal cells rely on other organelles, such as mitochondria, for energy production. Choice A is true because animal cells use lysosomes to break down old cells and cellular waste. Choice C is true as plant cells have a cell wall composed of cellulose that provides structural support and protection.