HESI A2 Elsevier (HESI): HESI Admission Assessment - Set 3 - Part 2

Correct Answer: Membrane-bound nucleus

A membrane-bound nucleus is the defining feature of eukaryotic cells. Prokaryotes such as bacteria have their DNA loose in a region called the nucleoid and lack any nucleus surrounded by a membrane in their cells. Option b is incorrect because Ribosomes are present in both prokaryotic and eukaryotic cells, although they differ slightly in size. They are the cellular structures responsible for protein synthesis in essentially every type of cell across all living organisms. Option c is incorrect because All cells, prokaryotic and eukaryotic, have a cell membrane separating their interior from the outside environment. Therefore, the cell membrane is not unique to eukaryotic cells and cannot serve as a distinguishing feature. Option d is incorrect because Cytoplasm fills the interior of every cell, prokaryotic or eukaryotic, providing the medium in which cellular reactions take place. Because both cell types have cytoplasm, it is not unique to eukaryotes in any way.

Correct Answer: To package and process materials for transport

The Golgi apparatus modifies, sorts, and packages proteins and lipids received from the endoplasmic reticulum. It then ships these molecules in vesicles to their final destinations inside or outside the cell as needed. Option a is incorrect because Digestion of macromolecules into their components is the function of lysosomes. They contain hydrolytic enzymes that break down worn organelles, food particles, and foreign material brought into the cell by various processes. Option b is incorrect because Detoxification of drugs and harmful products is performed mainly by the smooth endoplasmic reticulum, especially in liver cells. The Golgi apparatus does not specialize in detoxification within the cell and serves a different role. Option c is incorrect because Cellular respiration to make ATP takes place in the mitochondria, often called the powerhouse of the cell. The Golgi apparatus is involved in modifying and shipping molecules, not generating ATP energy for the cell.

Correct Answer: On rough ER and in cytoplasm

In a eukaryotic cell, ribosomes occur both attached to the rough endoplasmic reticulum and free within the cytoplasm. Free ribosomes typically make proteins used inside the cell, while bound ones make proteins for export. Option a is incorrect because Ribosomes are found in the cytoplasm, but they are not limited to that location. Many ribosomes are also attached to the rough endoplasmic reticulum, where they synthesize proteins for export or for use in membranes. Option c is incorrect because Although ribosomes are found on the rough endoplasmic reticulum, they are not limited to that location. Many ribosomes float freely in the cytoplasm, especially when making proteins that will be used inside the cell. Option d is incorrect because Lysosomes contain digestive enzymes, but they do not house ribosomes. Lysosomal enzymes themselves are made on rough endoplasmic reticulum ribosomes and then shipped through the Golgi apparatus to lysosomes for storage.

Correct Answer: Active transport

Active transport moves substances against their concentration gradient, from low to high concentration. This requires energy from ATP, often coupled with carrier proteins such as the sodium potassium pump found in cell membranes. Option a is incorrect because Diffusion is the movement of particles from high concentration to low concentration without any energy input from the cell. It relies only on the random motion of molecules and does not require ATP. Option b is incorrect because Osmosis is the diffusion of water across a selectively permeable membrane and does not require ATP. Water moves passively from a region of higher water concentration to one of lower water concentration through the membrane. Option d is incorrect because Facilitated diffusion uses membrane proteins to help substances cross the membrane down their concentration gradient. Because it moves with the gradient, no ATP is required for facilitated diffusion to occur within the cell.

Correct Answer: Swell and burst as water enters

Pure water has fewer dissolved solutes than the inside of a red blood cell, making the surroundings hypotonic. Water moves into the cell by osmosis, causing the cell to swell and eventually burst. Option b is incorrect because Cells shrivel when placed in a hypertonic solution, which has more solutes than the cell. Pure water has very few solutes, so the cell takes in water rather than losing it outward. Option c is incorrect because A cell stays the same size in an isotonic solution where solute concentrations are equal inside and outside the cell. Pure water is hypotonic to the cell, so the cell cannot stay constant. Option d is incorrect because Osmotic stress does not cause a red blood cell to undergo division. Mature red blood cells in humans cannot divide because they lack a nucleus and the machinery required to copy DNA during cell division.

Correct Answer: Mitochondrion

Mitochondria are often called the powerhouse of the cell because they carry out most of cellular respiration. The Krebs cycle and the electron transport chain occur inside mitochondria, producing the bulk of ATP. Option a is incorrect because The nucleus stores DNA and controls gene expression, but it is not the site of cellular respiration. Energy production for the cell occurs in a different organelle dedicated to the synthesis of ATP from glucose. Option b is incorrect because Chloroplasts perform photosynthesis in plant and algal cells, capturing light energy to make glucose. They are not the location of cellular respiration, which uses glucose to make ATP for the rest of the cell. Option c is incorrect because Ribosomes are responsible for protein synthesis, not cellular respiration. They translate messenger RNA into polypeptide chains and have no direct role in extracting energy from glucose to produce ATP for the cell.

Correct Answer: Cytoplasm

Glycolysis occurs in the cytoplasm of the cell, where glucose is split into two molecules of pyruvate. This first stage of cellular respiration produces a small net gain of ATP without using oxygen. Option a is incorrect because The mitochondrial matrix is the site of the Krebs cycle, which comes after glycolysis in respiration. Glycolysis itself takes place outside the mitochondria entirely, before pyruvate enters for further breakdown to release energy. Option c is incorrect because The inner mitochondrial membrane is the site of the electron transport chain and oxidative phosphorylation. These steps come after glycolysis and the Krebs cycle, not before, in the breakdown of glucose to release ATP. Option d is incorrect because The nucleus stores DNA and is the site of transcription, but no steps of cellular respiration occur inside the nucleus. Glycolysis takes place in the cytoplasm and is unrelated to nuclear activity in any way.

Correct Answer: Oxygen

Oxygen accepts electrons at the end of the electron transport chain, combining with hydrogen ions to form water. Without oxygen, the chain stops and aerobic ATP production cannot continue inside the mitochondria of human cells. Option a is incorrect because Carbon dioxide is a waste product of the Krebs cycle and is exhaled from the body. It is not used to accept electrons at the end of the electron transport chain during respiration. Option b is incorrect because Glucose is the starting fuel for cellular respiration, not the final electron acceptor at any stage. Electrons from glucose pass along the chain until they reach a different molecule at the end. Option d is incorrect because Water is produced when oxygen accepts electrons and combines with hydrogen ions, but it is the product, not the acceptor. The molecule that actually receives the electrons at the chain end is oxygen.

Correct Answer: Lactic acid fermentation

Lactic acid fermentation occurs in human muscle cells during intense exercise when oxygen is limited. Pyruvate from glycolysis is converted into lactic acid, which regenerates NAD plus so glycolysis can continue producing some ATP. Option b is incorrect because Alcoholic fermentation produces ethanol and carbon dioxide and occurs in yeast and some bacteria. Human muscle cells do not produce ethanol during low oxygen conditions, so this is not the correct pathway in this case. Option c is incorrect because Photosynthesis is the process by which plants make glucose using light energy, carbon dioxide, and water. It does not occur in human muscle cells and has no role in handling pyruvate during exercise. Option d is incorrect because The Krebs cycle is part of aerobic respiration that occurs only when oxygen is available. When oxygen is limited, the Krebs cycle slows or stops, and cells switch to fermentation to make ATP.

Correct Answer: Carbon dioxide plus water yields glucose

Photosynthesis uses carbon dioxide and water along with light energy captured by chlorophyll to produce glucose and release oxygen. This summarizes the overall conversion of light energy into chemical energy stored in plants. Option a is incorrect because This summary describes cellular respiration, in which glucose and oxygen are consumed and carbon dioxide, water, and energy are released. It is the reverse of the photosynthesis reaction shown in the correct option. Option b is incorrect because Photosynthesis does not use oxygen as a starting material. The reactants of photosynthesis are carbon dioxide, water, and light energy, while oxygen is one of the products released into the atmosphere by green plants. Option c is incorrect because This summary is missing light energy as an input and reverses several reactants and products. Photosynthesis builds glucose using carbon dioxide and water with light energy, producing oxygen as a byproduct of the reaction.

Correct Answer: Chromosomes align along the cell center

During metaphase, the chromosomes line up along the equator, or center, of the dividing cell. This central alignment ensures that each new daughter cell will receive an identical set of chromosomes after separation in anaphase. Option a is incorrect because Chromosomes condensing and the nuclear envelope disappearing describes prophase, the first stage of mitosis. Metaphase comes after prophase and is defined by a different arrangement of the chromosomes within the dividing cell. Option b is incorrect because Chromosomes gathering at the cell poles describes telophase, when separated chromosomes reach the two poles of the dividing cell. By that point metaphase has long since ended, so this does not describe metaphase at all. Option d is incorrect because Chromosomes starting to separate from each other describes anaphase, when sister chromatids are pulled apart by the spindle. Metaphase is defined by alignment, not by separation, so this does not match the metaphase stage.

Correct Answer: Sperm cell

Meiosis produces gametes, which are the sex cells used in sexual reproduction. In males the gametes are sperm cells, and in females they are egg cells, each with half the parent chromosome number for fertilization. Option b is incorrect because Skin cells are somatic cells produced by mitosis, not meiosis at all. Mitosis maintains the same chromosome number across generations of body cells, supporting growth, repair, and replacement of damaged tissue throughout the body. Option c is incorrect because Brain cells, like other body cells, are produced by mitosis during development of the embryo. Most mature neurons do not divide further, but they originate from mitotic divisions of neural stem cells. Option d is incorrect because Kidney cells are body cells produced by mitosis, which keeps the chromosome number constant. Meiosis is reserved for producing gametes in the reproductive organs, not for forming organs such as the kidneys in the body.

Correct Answer: Two cells, each identical to the parent

Mitosis creates two daughter cells, each genetically identical to the parent and with the same chromosome number. This type of division supports growth, tissue repair, and asexual reproduction in single celled organisms across many groups. Option a is incorrect because Producing four cells with half the chromosomes describes meiosis, not mitosis. Meiosis is the type of cell division that creates haploid gametes from a diploid parent cell during sexual reproduction in many organisms. Option b is incorrect because Two cells with half the chromosome number do not result from mitosis. Mitosis preserves the parent chromosome number in each daughter cell, so the new cells are diploid like the parent cell that produced them. Option c is incorrect because Mitosis produces only two daughter cells, not four daughter cells. Although the cells are genetically identical to the parent, the number of cells produced is incorrect for mitosis as it occurs in living tissue.

Correct Answer: Crossing over during prophase I

Crossing over occurs during prophase I of meiosis, when homologous chromosomes exchange segments of DNA. This recombination shuffles alleles between maternal and paternal chromosomes, creating new combinations of genes in each gamete. Option a is incorrect because DNA replication during S phase produces identical copies of each chromosome and does not create variation by itself. It must occur before meiosis but is not the source of genetic differences among gametes. Option c is incorrect because Cytokinesis is the physical splitting of the cytoplasm to produce two daughter cells. It distributes the already separated chromosomes, but it does not change the genetic content of the cells being produced during meiosis. Option d is incorrect because Spindle fiber formation provides the machinery to move chromosomes during division steps. While it is essential to the process, it does not by itself rearrange genetic material to create variation among offspring during sexual reproduction.

Correct Answer: Two chromosomes with same genes from parents

Homologous chromosomes are pairs that carry the same genes in the same order, one inherited from the mother and one from the father. They may carry different alleles for the same gene position. Option a is incorrect because Two identical chromatids joined at a centromere describes sister chromatids, which form after DNA replication during S phase. Homologous chromosomes are not identical at every position and are not physically joined to each other. Option b is incorrect because Sex chromosomes are only one specific homologous pair, and a homologous pair is not limited to one parent or one sex. Homologous chromosomes refer broadly to matching pairs found across all autosomes and sex chromosomes. Option d is incorrect because A mutation refers to a change in a DNA sequence, not to the relationship between two chromosomes within a cell. Homologous chromosomes can be normal in sequence and still form a matched pair.

Correct Answer: Expressed when only one copy is present

A dominant allele is expressed in the phenotype whenever at least one copy is present in the cell. This means heterozygous individuals with one dominant and one recessive allele still show the dominant trait. Option b is incorrect because An allele that requires two copies to be expressed describes a recessive allele, not a dominant one. Recessive alleles are masked when paired with a dominant allele in a heterozygous individual carrying both forms. Option c is incorrect because Alleles can be located on any chromosome, autosomal or sex chromosome. Being dominant has nothing to do with chromosome location, so dominance is not specific to the X chromosome in human or other genetic systems. Option d is incorrect because An allele with no observable effect would not be classified as dominant by definition. Dominant alleles by definition produce a visible trait when present in either one or two copies in a given individual organism.

Correct Answer: Twenty five percent

A cross between two heterozygous parents gives a one to two to one genotype ratio. That means twenty five percent homozygous dominant, fifty percent heterozygous, and twenty five percent homozygous recessive offspring on average overall. Option a is incorrect because Heterozygous parents both carry one recessive allele each, so passing two recessive alleles to a child is possible. The probability is therefore not zero, and homozygous recessive offspring can clearly occur. Option b is incorrect because Fifty percent represents the probability of a heterozygous offspring, not a homozygous recessive one. Among offspring from a heterozygous cross, half are heterozygous, while only a quarter are homozygous recessive in any cross. Option c is incorrect because Seventy five percent represents the probability of having the dominant phenotype, which combines homozygous dominant and heterozygous offspring. This is the chance of dominant appearance, not specifically homozygous recessive offspring

Correct Answer: Genotype is the genetic makeup

Genotype refers to the actual combination of alleles an organism inherits for a particular gene, while phenotype is the observable trait that results, such as eye color or blood type seen in the individual. Option a is incorrect because This option reverses the definitions of the two terms. The observable physical trait is the phenotype, and the underlying allele combination is the genotype, not the other way around as stated in this answer choice. Option c is incorrect because Genotype and phenotype refer to two different concepts that should not be used interchangeably. The genotype is the genetic code, while the phenotype is the trait that is expressed and observable in the organism overall. Option d is incorrect because Both genotype and phenotype can involve dominant and recessive alleles within a given individual. Genotype includes any combination of alleles, and phenotype reflects the trait that results, regardless of which alleles are dominant or recessive.

Correct Answer: X linked recessive

X linked recessive traits appear more often in males because males have only one X chromosome in their cells. A single recessive allele on that X is enough to produce the trait. Option a is incorrect because Autosomal dominant traits are carried on autosomes, not on the X chromosome at all. They affect males and females about equally, so they do not match the pattern of male predominance described. Option b is incorrect because Autosomal recessive traits are carried on autosomes and require two copies for the trait to appear. They affect males and females equally and do not show the male predominance described in the question. Option d is incorrect because Y linked traits are passed only from father to son and affect only males overall, but most classic genetic diseases of this pattern are not Y linked. The example matches X linked recessive.

Correct Answer: Type A or type B only

The father with type AB blood has one A allele and one B allele, while the mother with type O blood has two O alleles. Each child gets one allele from each parent overall. Option b is incorrect because Type AB requires both an A and a B allele in one child, but the mother can only contribute an O allele. Type O requires two O alleles, which the father simply cannot provide. Option c is incorrect because All four blood types are not possible from this cross. Type AB requires two different alleles from the father plus one from the mother, and type O requires two O alleles only. Option d is incorrect because Type O requires both parents to contribute an O allele to the child during fertilization. The father with type AB has no O allele to pass on, so type O is impossible here.