Free HESI A2 Biology practice for HESI A2 Biology Version 5 (HESI A2). Answer 25 nursing exam-style questions with rationales, exam mode, and progress tracking
How is the plasma membrane arranged?
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Explanation:
The plasma membrane is arranged in a double layer of phospholipids, known as a lipid bilayer. This structure consists of two layers of phospholipid molecules with their hydrophilic (water-attracting) heads facing outwards and their hydrophobic (water-repelling) tails facing inward. This lipid bilayer provides a barrier that separates the interior of the cell from the external environment, regulating the passage of substances in and out of the cell.
In a phospholipid, the head:
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Explanation:
The head of a phospholipid is hydrophilic, meaning it is water-loving, and faces the outer side of the lipid bilayer. This arrangement allows the hydrophilic head to interact with water while the hydrophobic tails are shielded from it. Therefore, option D, 'Both A and C,' is the correct answer as the head is hydrophilic and faces the outer side of the layer.
Why does cytokinesis occur?
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Explanation:
Cytokinesis is the process of cell division following mitosis, where the cytoplasm of a cell is split into two daughter cells. The main purpose of cytokinesis is to physically separate the newly formed nuclei and organelles into individual cells, ensuring that each daughter cell receives a complete set of cellular components to function independently. Therefore, the correct answer is D, as the primary outcome of cytokinesis is the division of daughter cells.
How do animal cells divide during cytokinesis?
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Explanation:
Animal cells divide using a contractile ring during cytokinesis. The contractile ring is composed of actin and myosin filaments and contracts to pinch the cell into two daughter cells. In contrast, cell plate formation is a mechanism observed in plant cells, not animal cells. Therefore, the correct answer is the contractile ring.
Why can animal cells use a contractile ring but plant cells cannot?
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Explanation:
The correct answer is D because plant cells have a cell wall surrounding them, which provides structural support but makes it challenging for them to form a contractile ring during cell division. The cell wall restricts the flexibility needed for the contractile ring to constrict and separate the cells. In contrast, animal cells do not have a cell wall, allowing them to form a contractile ring composed of actin filaments that constrict during cytokinesis, facilitating cell division.
Which of the following nucleotides is not a component of DNA?
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Explanation:
The four nucleotides that make up DNA are Adenine, Thymine, Cytosine, and Guanine. Uracil is a nucleotide base that is present in RNA but not in DNA. Therefore, Uracil is the correct answer as it is not a component of DNA.
Which of the following is not an RNA base?
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Explanation:
In RNA, the bases are Adenine, Uracil, and Cytosine. Thymine is uniquely found in DNA and not RNA. Adenine pairs with Uracil, while Cytosine pairs with Guanine in RNA. Thus, Thymine is not an RNA base, making it the correct answer.
Select the two bases that are purines:
Select the best answer.
Explanation:
Purines are adenine (A) and guanine (G), which are the larger nitrogenous bases found in DNA and RNA. Adenine (A) is one of the purine bases, whereas cytosine (C) and thymine (T) are pyrimidines. Therefore, the correct answer is A. Option D, 'N,' is not a purine base.
Which base has two carbon rings?
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Explanation:
The correct answer is G. In organic chemistry, the base Guanine (G) contains two carbon rings in its structure. Guanine is one of the four main nucleobases found in DNA and RNA. The other options, N, C, and T, do not have two carbon rings in their structures. Therefore, Guanine is the only option that fits the description of a base with two carbon rings.
Cytosine (C) and Thymine (T) are known as:
Select the best answer.
Explanation:
Cytosine (C) and Thymine (T) are both pyrimidines. Purines, on the other hand, refer to adenine and guanine. Pyrimidines are characterized by a single-ring structure, while purines have a double-ring structure. Therefore, the correct answer is B: Pyrimidines. Remember, pyrimidines consist of cytosine and thymine, while purines include adenine and guanine.
Which of the following options best represents complementary base pairing in DNA?
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Explanation:
In DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). This is known as complementary base pairing. The correct answer is 'A and T' because they form a complementary base pair in DNA. Adenine always pairs with thymine via two hydrogen bonds, while guanine pairs with cytosine via three hydrogen bonds. This base pairing specificity is crucial for DNA replication and genetic information transfer.
Which of the following DNA strands would complement the segment: ACTTGCA?
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Explanation:
In DNA, adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G). To find the complementary strand, you need to match each base with its complementary base. The segment ACTTGCA consists of bases A, C, T, T, G, C, A, which would pair with T, G, A, A, C, G, T, respectively. Therefore, the complementary strand would be TGAACGT. Thus, option A (TGAACGT) is the correct choice as it follows the base-pairing rules in DNA.
Enzymes can ................. reactions.
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Explanation:
Enzymes function to catalyze reactions, which means they accelerate the rate of chemical reactions without being consumed in the process. Enzymes do not inhibit or stop reactions; instead, they facilitate and enable reactions to occur more efficiently. Therefore, the correct answer is 'Catalyze.'
Enzymes are typically...
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Explanation:
Enzymes are typically proteins, not fats, sugars, or neurons. Proteins are large molecules made up of amino acids and are the most common type of enzymes. Enzymes play a crucial role in catalyzing biochemical reactions in living organisms by speeding up these reactions without being consumed in the process.
Which of the following statements is not true about enzymes?
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Explanation:
Enzymes function by lowering the activation energy required for a reaction to occur, not by raising it. This catalytic property allows enzymes to accelerate reactions without being consumed in the process. Enzymes are biological catalysts that are typically proteins and have specific active sites where substrates bind and reactions take place. The statement that enzymes raise the activation energy needed is incorrect as their role is to lower this energy barrier. Therefore, the correct answer is B.
Epithelial cells are:
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Explanation:
Epithelial cells are polarized, meaning they have distinct structural and functional differences between their apical and basolateral surfaces. This polarity allows them to perform specialized functions efficiently. The statement that epithelial cells are larger than other cells is incorrect as cell size can vary across different cell types, and being larger is not a defining characteristic of epithelial cells.
Where is the apical side of an epithelial cell located?
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Explanation:
The apical side of an epithelial cell refers to the top surface of the cell that is exposed to the external environment, such as fluid or air. This surface is specialized to perform specific functions like absorption, secretion, or protection. The apical side faces the lumen or external environment and is crucial for the cell's interactions with its surroundings. Therefore, the correct answer is that the apical side of an epithelial cell is on the top side of the cell.
Which of the following organisms would not have eukaryotic cells?
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Explanation:
The correct answer is A, Bacteria. Bacteria are prokaryotic organisms, meaning they lack a true nucleus and membrane-bound organelles, unlike eukaryotic cells found in dogs, humans, and onions. Dogs, humans, and onions are examples of organisms with eukaryotic cells that contain a true nucleus and various membrane-bound organelles.
Why do cells need to use exocytosis?
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Explanation:
Cells use exocytosis to eliminate waste from the cell. Exocytosis is the process by which cells expel waste materials or products outside the cell. This process helps maintain cellular cleanliness and proper functioning by preventing the accumulation of harmful substances inside the cell, ensuring the cell's health and survival.
When a child is sick and has a body temperature exceeding 37Å—C, the body begins to sweat in order to lower the temperature. What is this an example of?
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Explanation:
This scenario illustrates a negative feedback loop. In negative feedback, the body's response opposes the initial change, helping to restore equilibrium. In this case, the body's sweating is a response to reduce the elevated temperature, aiming to return the body to its normal state. This process helps regulate and maintain homeostasis, ensuring the body functions within a narrow range of optimal conditions.
Why is homeostasis necessary?
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Explanation:
Homeostasis is essential for the body to maintain internal balance and ensure optimal functioning. It is responsible for regulating temperature to prevent overheating or cooling, controlling pH levels to support biochemical reactions, and managing glucose levels for energy production. Therefore, all the options - maintaining temperature, pH, and glucose levels - are crucial functions of homeostasis.
A pencil measures 8 cm long. What is this length in mm?
Select the best answer.
Explanation:
To convert centimeters to millimeters, you multiply by 10 since there are 10 millimeters in 1 centimeter. Therefore, 8 cm x 10 = 80 mm. The correct answer is 80 mm.
A scientist needs 12 mL of a solution. They have a bottle with 0.12L in it. Do they have enough?
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Explanation:
To accurately compare the quantities, it is important to convert both to the same unit. As 1L is equal to 1000 mL, the bottle contains 120 mL (0.12L x 1000 mL/L). Since the scientist only needs 12 mL, it is evident that they have more than enough solution in the bottle, making choice B the correct answer.
What is the purpose of the mitochondria?
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Explanation:
The mitochondria's main function is to generate energy for the cell through the process of cellular respiration. This organelle is often referred to as the powerhouse of the cell due to its role in producing adenosine triphosphate (ATP), the cell's main energy currency. While other organelles are responsible for activities like controlling the cell (nucleus) or synthesizing proteins (ribosomes), the mitochondria's primary role is energy production.
Which organelle is responsible for protein synthesis?
Select the best answer.
Explanation:
The correct answer is A, Ribosome. Ribosomes are the organelles responsible for protein synthesis in a cell. They are the site where amino acids are assembled into proteins based on the genetic information carried by mRNA. Chloroplasts are responsible for photosynthesis in plant cells, Lysosomes contain enzymes for digestion and waste removal, and Mitochondria are known as the powerhouse of the cell, responsible for generating energy.
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