HESI A2 Biology Practice Questions

Question 1

What must any solution injected into tissues be to prevent cells from shrinking or swelling?

Your Answer: Option(s)

Correct Answer: Option(s) D

Rationale

Any solution injected into tissues must be isotonic to prevent cells from shrinking or swelling.

Isotonic solutions have the same concentration of solutes as the cells in the body. When a solution with the same solute concentration is injected into the body, there is no net movement of water into or out of the cells. This equilibrium prevents the cells from shrinking (which happens when water moves out of the cell) or swelling (which happens when water moves into the cell).

A) Distilled
Distilled water is pure water with no solutes. If this were injected into tissues, it would be hypotonic relative to the cells. That is, it would have a lower concentration of solutes than the cells. This would cause water to move from the hypotonic solution (distilled water) into the cells, leading to cell swelling and possible rupture.

B) Hypertonic
A hypertonic solution has a higher concentration of solutes than the cells in the body. If a hypertonic solution were injected into tissues, water in the cells would move out to the hypertonic solution in an attempt to equilibrate the solute concentration. This would cause the cells to shrink, potentially leading to cell damage or death.

C) Hypotonic
A hypotonic solution has a lower concentration of solutes than the cells in the body. If a hypotonic solution were injected into tissues, water would move from the hypotonic solution into the cells in an attempt to equilibrate the solute concentrations. This would cause the cells to swell, potentially leading to cell damage or death.

D) Isotonic
An isotonic solution has the same concentration of solites as the cells in the body. Hence, there is no net movement of water in or out of the cells. This equilibrium maintains the cell's size and prevents cell damage.

Conclusion
To prevent cells from shrinking or swelling when a solution is injected into tissues, the solution must be isotonic, meaning it has the same concentration of solutes as the cells. Hypotonic solutions would cause cells to swell, and hypertonic solutions would cause cells to shrink, both potentially leading to cell damage or death. Distilled water, lacking any solutes, would act as a hypotonic solution and thus would be inappropriate for injection into tissues.

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Question 2

What structure in a plant cell is surrounded by a double membrane and contains most of the genetic information used to control the cell?

Your Answer: Option(s)

Correct Answer: Option(s) B

Rationale

The nucleus is the structure in a plant cell that is surrounded by a double membrane and contains most of the genetic information used to control the cell.

The nucleus is an organelle present in eukaryotic cells, including plant cells. It is surrounded by a double membrane called the nuclear envelope and contains the cell's DNA, which carries the genetic information needed for cellular control.

A) Mitochondrion
The mitochondrion is a double-membrane organelle that is primarily responsible for producing energy through the process of cellular respiration. Although it does contain a small amount of its own DNA, the vast majority of a cell's genetic information is not stored in the mitochondria but in the nucleus.

B) Nucleus
The nucleus is indeed surrounded by a double membrane and contains most of the genetic information used to control the cell. This organelle is the control center of the cell, regulating its activities and housing the DNA that carries genetic information.

C) Chromatin
Chromatin, which consists of DNA and protein, is found inside the nucleus and carries genetic information. However, it is not itself surrounded by a double membrane and is actually a component of the nucleus, not a separate structure.

D) Chromosome
Chromosomes, which are made of tightly coiled chromatin, carry genetic information and are found within the nucleus. Like chromatin, they are not surrounded by a double membrane and are a part of the nucleus rather than a separate organelle.

Conclusion
The nucleus is the organelle in a plant cell that is surrounded by a double membrane and contains most of the genetic information used to control the cell. While other options, such as the mitochondrion, chromatin, and chromosomes, are involved in genetic information storage or energy production, only the nucleus fulfills both criteria of being a separate organelle surrounded by a double membrane and housing most of the cell's genetic material.

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Question 3

Osmotic pressure is the tendency for a single solution to absorb what substance?

Your Answer: Option(s)

Correct Answer: Option(s) B

Rationale

Water is the substance that a single solution tends to absorb due to osmotic pressure.

Osmotic pressure refers to the force that drives solvent molecules, typically water, from an area of lower solute concentration to an area of higher solute concentration across a semipermeable membrane. This process aims to equalize solute concentrations on both sides of the membrane and is a fundamental concept in biology and chemistry.

A) Sodium
Sodium is a solute, not a solvent. While sodium may be present in a solution and could influence osmotic pressure due to its role as a solute, it is not the substance that a solution tends to absorb due to osmotic pressure. The process of osmosis primarily involves the movement of the solvent (usually water), not the solute.

B) Water
Water is the substance that tends to move across a semipermeable membrane due to osmotic pressure. In an attempt to balance the solute concentrations on either side of the membrane, water molecules will naturally move from an area of lower solute concentration to an area of higher solute concentration.

C) Positive ions
Positive ions, similar to sodium, act as solutes in a solution. Although they can influence osmotic pressure through their contribution to the solute concentration, they are not the substance that gets absorbed by the solution due to osmotic pressure. Again, it is the solvent that moves in the process of osmosis, not the solute.

D) Negative ions
Negative ions also serve as solutes in a solution. While they may influence osmotic pressure, they are not the substance absorbed due to osmotic pressure. As with positive ions and sodium, osmotic pressure primarily drives the movement of the solvent, not the solute.

Conclusion
Osmotic pressure drives the movement of a solvent, typically water, from an area of lower solute concentration to an area of higher solute concentration across a semipermeable membrane. Sodium, positive ions, and negative ions can influence the osmotic pressure as solutes, but they are not the substances absorbed due to osmotic pressure. Understanding the concept of osmosis and osmotic pressure is critical in various scientific fields, including biology, chemistry, and medicine.

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Question 4

Skin cells undergo what type of cellular division?

Your Answer: Option(s)

Correct Answer: Option(s) D

Rationale

Skin cells undergo mitosis.

Mitosis is a type of cellular division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. This is important for growth, development, and repairing damaged tissues in multicellular organisms like humans. Skin cells, being part of such organisms, undergo this process for the same reasons.

A) Melosis
Melosis is not a recognized term in biology or cellular division. It appears to be a misspelling of "meiosis," which is a different type of cell division involved in sexual reproduction. Meiosis generates four daughter cells each with half the number of chromosomes as the parent cell. This process is not applicable to skin cells.

B) Binary fission
Binary fission is a method of asexual reproduction that involves the division of a single entity into two or more parts and the regeneration of those parts into separate entities. This process is primarily seen in prokaryotic organisms such as bacteria. Skin cells, being eukaryotic, do not undergo binary fission.

C) Sexual reproduction
Sexual reproduction involves the fusion of two specialized cells (gametes), one from each parent, to form a zygote that develops into a new organism. It does not involve the division of cells, but rather their union. Skin cells do not participate in sexual reproduction.

D) Mitosis
Mitosis is the process by which a cell duplicates its chromosomes and divides into two identical daughter cells, each with a full set of chromosomes. This is the primary process through which multicellular organisms like humans grow and repair tissues, including skin cells.

Conclusion
Skin cells, like other somatic cells in multicellular organisms, undergo mitosis for growth, development, and repair. This process results in two identical daughter cells, each with the same number and type of chromosomes as the parent cell. Other options like "melosis", binary fission, and sexual reproduction either do not exist, apply to different types of organisms, or involve different biological processes, making them incorrect choices for the type of cellular division undergone by skin cells.

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Question 5

A plant cell is placed in a solution and it shrinks from water loss. In what type of environment was the cell placed?

Your Answer: Option(s)

Correct Answer: Option(s) B

Rationale

The plant cell was placed in a hypertonic solution.

When a cell is placed in a hypertonic solution, the water concentration is lower outside the cell than inside. This causes water to flow out of the cell, through the process of osmosis, leading to the cell shrinking or shriveling due to water loss.

A) Plasmolytic
Plasmolysis is a cellular state that occurs when a plant cell is placed in a hypertonic solution and water leaves the cell, causing the cell to shrink. However, plasmolytic is not a type of solution, but rather describes the condition of the cell after it has lost water.

B) Hypertonic
A hypertonic solution has a higher solute concentration compared to the inside of the cell, which causes water to flow out of the cell in an attempt to balance the concentration. This is the correct answer as the cell shrinks due to water loss when placed in a hypertonic solution.

C) Hypotonic
In a hypotonic solution, the solute concentration is lower outside the cell than inside. As a result, water flows into the cell, causing it to swell and potentially burst. This is contrary to the given scenario where the cell shrinks due to water loss.

D) Isosmotic
An isosmotic solution has the same solute concentration as the cell. Therefore, there is no net movement of water in or out of the cell. The cell would neither swell nor shrink in an isosmotic solution, which contradicts the given scenario.

Conclusion
A hypertonic solution leads to water flow out of the cell due to its higher solute concentration compared to the inside of the cell. This results in the cell shrinking or shriveling, a process known as plasmolysis. Other solution types like hypotonic and isosmotic would not result in the cell shrinking as observed in the scenario. Thus, the plant cell in question was undoubtedly placed in a hypertonic solution.

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Any solution injected into tissues must be isotonic to prevent cells from shrinking or swelling.

The nucleus is the structure in a plant cell that is surrounded by a double membrane and contains most of the genetic information used to control the cell.

Water is the substance that a single solution tends to absorb due to osmotic pressure.

Skin cells undergo mitosis.

The plant cell was placed in a hypertonic solution.

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