HESI A2 Biology Practice Test

Try our free HESI A2 Biology practice test. This is an online exam with instant scoring and detailed explanations. While the actual test has only 25 questions, our website features 50 HESI Biology practice questions. These are challenging questions covering all of the key concepts. Read each question carefully and then choose the best answer. Click on the arrow in the lower right corner to move on to the next one.

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Question 1
Which of the following is a correct description of metaphase during mitosis?

A
Chromosomes condense and the nuclear envelope disappears.
B
Chromosomes gather on either side of the now dividing cell.
C
Chromosomes start to separate from each other.
D
Chromosomes align along the center of the cell.
Question 1 Explanation: 
During metaphase, the chromosomes align along the center of the cell. During prophase, chromosomes condense, and the nuclear envelope disappears during prometaphase. Anaphase is when the chromosomes start to separate from each other. Telophase is when the chromosomes gather on either side of the now dividing cell; it is followed by cytokinesis.
Question 2
Where can ribosomes be found inside of a eukaryotic cell?

A
On the rough endoplasmic reticulum and in the cytoplasm
B
Only in the cytoplasm
C
Only on the rough endoplasmic reticulum
D
On both the rough and smooth endoplasmic reticulum
Question 2 Explanation: 
Ribosomes can be found in two places in a eukaryotic cell: on the rough endoplasmic reticulum (rough ER) or free floating in the cytoplasm.
Question 3
What is the role of the Golgi apparatus in the eukaryotic cell?

A
To digest macromolecules into their components
B
To package and process materials for transport
C
To detoxify drugs and other harmful products
D
To perform cellular respiration to make ATP
Question 3 Explanation: 
The Golgi apparatus is responsible for the packaging and processing of materials for transport throughout the cell or for secretion. Lysosomes digest macromolecules into their components using hydrolytic enzymes. The smooth ER detoxifies drugs and other harmful products. Cellular respiration resulting in ATP production is the function of mitochondria.
Question 4
Which best describes the bonds between atoms within a water molecule?

A
Nonpolar ionic
B
Polar ionic
C
Nonpolar covalent
D
Polar covalent
Question 4 Explanation: 
The bonds between atoms within the water molecule are polar covalent bonds, resulting in the unequal sharing of electrons. Within a water molecule, the electrons in each covalent bond are held closer to the O atom compared to the H atoms. This makes the O-end of each water molecule have a partial negative charge, while the H ends have a partial positive charge. Therefore, a partial positive end of one water molecule is attracted to the partial negative charge of another water molecule, forming a hydrogen bond.
Question 5
Which of the following is the MOST inclusive category in the hierarchical organizational system for nomenclature?

A
Kingdom
B
Class
C
Genus
D
Species
Question 5 Explanation: 
The most inclusive category is Kingdom. The most restrictive would be Species. The mnemonic “King Philip Came Over For Great Spaghetti,” can be used to recall the order of the categories within this organizational system from most inclusive to most restrictive.
Question 6
During which phase of the eukaryotic cell cycle is DNA replicated?

A
G1
B
S
C
G2
D
M
Question 6 Explanation: 
The G1, S, and G2 phases are all phases within interphase. S phase is when DNA is replicated. The G1 and G2 phases are periods of cell growth (G1 = first growth phase, G2 = second growth phase and preparation for division). M phase includes mitosis and cytokinesis.
Question 7
Which of the following processes begins with a diploid cell and ends in the formation of diploid cells?

A
Meiosis only
B
Mitosis only
C
Both meiosis and mitosis
D
Neither meiosis nor mitosis
Question 7 Explanation: 
Mitosis makes two identical daughter cells from an original parent cell and does not reduce chromosome content. Meiosis is a process that begins with a diploid cell and results in the formation of haploid cells.
Question 8
Which of the following types of cell results from cell division by meiosis?

A
Kidney cell
B
Sperm cell
C
Brain cell
D
Skin cell
Question 8 Explanation: 
Meiosis results in the formation of gametes like sperm cells (in males) and egg cells (in females). All other body cells, called somatic cells, undergo mitosis, not meiosis, to produce more cells.
Question 9
What are the products of the Krebs cycle?

A
NADH, ATP, and pyruvate
B
CO2, ATP, and NADH
C
H2O and ATP
D
O2 and glucose
Question 9 Explanation: 
The Krebs cycle breaks down pyruvate fully to CO2, producing energy in the form of ATPs and NADH (and FADH2). Glycolysis breaks down glucose to produce NADH, ATP, and pyruvate. The passage of electrons through the electron transport chain results in the formation of H2O and ATP. Photosynthesis results in the formation of O2 and glucose.
Question 10
The plasma membrane of a cell is composed of:

A
a single layer of phospholipids with proteins inserted.
B
a bilayer of phospholipids with proteins inserted.
C
a single layer of proteins with cholesterol inserted.
D
a bilayer of proteins with cholesterol inserted.
Question 10 Explanation: 
The plasma membrane is composed of a bilayer of phospholipids into which proteins and cholesterol are inserted.
Question 11
Which of the following activities does NOT lead to ATP production?

A
Glycolysis
B
Calvin cycle
C
Krebs cycle
D
Electron transport chain
Question 11 Explanation: 
The various steps in cellular respiration (glycolysis, Krebs cycle, electron transport chain) each produce ATP. The Calvin cycle takes place during photosynthesis and does not produce ATP but rather uses it to produce sugar.
Question 12
Which of the following is an example of a heterozygous genotype?

A
TT
B
Tt
C
tt
D
T
Question 12 Explanation: 
A heterozygote is diploid and has two different alleles for a given gene. Here, only Tt is a heterozygous genotype. Both TT and tt are homozygous, having two copies of the same allele for a given gene. The genotype T does not indicate a diploid cell.
Question 13
The alternate versions of a single gene are known as:

A
phenotypes
B
genotypes
C
chromosomes
D
alleles
Question 13 Explanation: 
Alleles are alternate versions of a single gene that codes for a certain trait. The genotype refers to what alleles for a given gene an individual possesses, while the phenotype refers to the physical characteristics that an individual displays related to a given gene. Chromosomes are the DNA structures that each contain many genes.
Question 14
For a trait that shows a simple dominance inheritance pattern, which genotypes will result in the individual having the dominant phenotype?

A
RR and Rr
B
RR and rr
C
Rr and rr
D
RR, Rr, and rr
Question 14 Explanation: 
For simple dominance, an individual requires only one copy of the dominant allele (R in this case) to have the dominant phenotype. Therefore, individuals having the RR and Rr genotypes will have the dominant phenotype. An individual with the rr genotype will have the recessive phenotype.
Question 15
The term that describes a phospholipid having both a hydrophilic end and a hydrophobic end:

A
Unsaturated.
B
Saturated.
C
Selectively permeable.
D
Amphipathic.
Question 15 Explanation: 
Amphipathic is the term that describes how phospholipids each have a hydrophilic end as well as a hydrophobic end. A fatty acid having one or more double bonds is unsaturated. A saturated fatty acid lacks double bonds. Cell membranes composed of phospholipids with embedded proteins are selectively permeable, meaning that they allow some substances to freely flow through while restricting the movement of other substances.
Question 16
Which type of large biological molecule is correctly matched with the type of small molecule that composes it?

A
Lipids: amino acids
B
Carbohydrates: sugars
C
Nucleic acids: fatty acids
D
Proteins: nucleotides
Question 16 Explanation: 
Carbohydrates are composed of sugars like glucose. Lipids including fats and phospholipids are composed of fatty acids. Nucleic acids are composed of nucleotides. Proteins are composed of amino acids.
Question 17
Which process synthesizes mRNA using DNA as the template?

A
Replication
B
Translation
C
Cytokinesis
D
Transcription
Question 17 Explanation: 
Transcription is the process that synthesizes mRNA using DNA as the template. Replication duplicates DNA using DNA as the template. Translation (protein synthesis) uses mRNA to make a protein. Cytokinesis is the process by which two newly made cells fully divider from each other.
Question 18
Which of the following is a typical base pair seen in double-stranded DNA?

A
A with T
B
A with U
C
A with C
D
A with G
Question 18 Explanation: 
A base-pairs with T in double-stranded DNA. There is no U in DNA, so A should not be seen base-pairing with U in double-stranded DNA. A does not typically base-pair with either C or G in double-stranded DNA.
Question 19
If an individual who is homozygous dominant for a given trait is crossed with an individual who is homozygous recessive for the same trait, what percentage of offspring should show the recessive phenotype? Assume a simple dominance inheritance pattern.

A
0%
B
25%
C
50%
D
100%
Question 19 Explanation: 
Because the homozygous dominant individual can only provide the dominant allele to its offspring, all of the offspring will have the dominant allele and express the dominant phenotype. Thus, none of the offspring would show the recessive phenotype.
Question 20
Which term refers to when one gene influences multiple seemingly unrelated phenotypic traits?

A
Simple dominance
B
Epistasis
C
Pleiotropy
D
Polygenic inheritance
Question 20 Explanation: 
Pleiotropy refers to when one gene influences multiple seemingly unrelated phenotypic traits. Simple dominance refers to when being either homozygous dominant or heterozygous results in the individual having the same dominant phenotype. Epistasis refers to an situation where two or more genes interact whereby the genotype at one gene influences the expression of the genotype at another allele. Polygenic inheritance refers to when one phenotypic trait is influenced by multiple genes.
Question 21
Which parts of two complementary nucleotides interact with each other in a double-stranded DNA molecule?

A
Phosphate groups
B
Sugar molecules
C
Nitrogenous bases
D
A sugar molecule with a phosphate group
Question 21 Explanation: 
The nitrogenous bases of complementary nucleotides hydrogen bond with each other in a double-stranded DNA molecule. Within a single DNA strand, a sugar molecule of one nucleotide covalently bonds to the phosphate group of the next nucleotide to form the sugar-phosphate backbone.
Question 22
Glycolysis is the conversion of _______ to ______ .

A
Glucose, pyruvate
B
Pyruvate, glucose
C
Glucose, CO2
D
CO2, glucose
Question 22 Explanation: 
Glycolysis is the conversion of glucose to pyruvate, and it is the first step in the process of cellular respiration. Cellular respiration is the group of processes that fully oxidizes glucose to CO2 to make ATP; it includes glycolysis, the Krebs cycle, and the electron transport chain. Glucose is made from CO2 during the Calvin cycle of photosynthesis, not during glycolysis.
Question 23
During which step of cellular respiration is NADH oxidized to produce ATP and water?

A
Calvin cycle
B
Krebs cycle
C
Electron transport chain
D
Glycolysis
Question 23 Explanation: 
The electron transport chain is the step of cellular respiration that oxidizes NADH molecules to produce ATP and water. The Calvin cycle is not a step within cellular respiration, but rather, is part of photosynthesis to make glucose. The Krebs cycle is the step within cellular respiration that oxidizes pyruvate to CO2, producing ATP, NADH, and FADH2 as a result. Glycolysis is the step within cellular respiration that breaks down glucose into two pyruvates, producing NADH and ATP as a result.
Question 24
For every glucose molecule that undergoes cellular respiration, approximately how many ATP molecules can be produced?

A
14 to 18
B
18 to 25
C
32 to 36
D
68 to 70
Question 24 Explanation: 
Cellular respiration can generate between 32 to 36 molecules of ATP for every glucose molecule broken down. The number of ATP is described as a range because the reaction is not perfectly efficient and will sometimes yield more or less ATP.
Question 25
Which cellular structure is the location of protein synthesis in a eukaryotic cell?

A
Mitochondrion
B
Ribosome
C
Lysosome
D
Golgi apparatus
Question 25 Explanation: 
The ribosome is the location of protein synthesis in a eukaryotic cell. Free ribosomes are located in the cytosol while other ribosomes are attached to the rough endoplasmic reticulum. The mitochondrion is the location of ATP synthesis during cellular respiration. The lysosome is responsible for the digestion of large biological molecules into smaller components. The Golgi apparatus is responsible for modifying and packaging materials for transport within the cell or for secretion from the cell.
Question 26
A statement or explanation of certain events is called a(n):

A
Hypothesis.
B
Experiment.
C
Observation.
D
Conclusion.
Question 26 Explanation: 
A hypothesis is a statement or explanation of certain events. A hypothesis is typically made after observation to explain the observation. Then, an experiment is designed to test the hypothesis. After collecting data generated from the experiment, a conclusion can be drawn to either refute or support the hypothesis.
Question 27
Which of the following correctly compares the molecular orientation of molecules in liquid versus solid water (ice)?

A
The water molecules are less polar in liquid water than they are in ice.
B
The water molecules form lattice structures in both liquid water and ice.
C
The water molecules are more spread out in liquid water than they are in ice.
D
The water molecules are more spread out in ice than they are in liquid water.
Question 27 Explanation: 
Water molecules form a lattice structure in ice, which causes the water molecules in ice to be more spread out than they are in liquid water. This is the reason that ice appears to “expand” in comparison to liquid water and can float on the surface of liquid water. The water molecules in both liquid water and ice are equally polar.
Question 28
What is the difference between saturated and unsaturated fatty acids?

A
Saturated fatty acids contain one or more double bonds, unlike unsaturated fatty acids.
B
Saturated fatty acids contain no double bonds, unlike unsaturated fatty acids.
C
Saturated fatty acids contain at least two double bonds, unlike unsaturated fatty acids.
D
Saturated fatty acids contain a phosphate group, unlike unsaturated fatty acids.
Question 28 Explanation: 
Saturated fatty acids contain no double bonds, while unsaturated fatty acids do contain one or more double bonds. Neither saturated or unsaturated fatty acids contain phosphate groups. However, in a phospholipid, a phosphate group is attached to the glycerol molecule to which fatty acids are also attached.
Question 29
What component of animal fats cause them to solidify at room temperature?

A
Phosphate groups
B
Steroids
C
Saturated fatty acids
D
Unsaturated fatty acids
Question 29 Explanation: 
Saturated fatty acids are the component of animal fats that cause them to solidify at room temperature. Oils have high amounts of unsaturated fatty acids which allow them to remain liquid at room temperature. Phosphate groups are found in phospholipids, but not typical fats. Steroids are a type of lipid, but are not the component of animal fats that make them solidify at room temperature.
Question 30
How do large bodies of water moderate climate?

A
Water stabilizes climate due to its low specific heat.
B
Water destabilizes climate due to its low specific heat.
C
Water stabilizes climate due to its high specific heat.
D
Water destabilizes climate due to its high specific heat.
Question 30 Explanation: 
Water stabilizes climate due to its high specific heat, meaning that it requires a relatively high amount of heat to raise the temperature by 1°C . Climate near large bodies of water tends to be pretty stable as a result.
Question 31
Which of the following descriptions relates to water’s property of cohesion?

A
Water beading together on top of a freshly waxed car
B
An ocean stabilizing the temperature of a region
C
Water dissolving salt to become salt water
D
A bottle of water cracking when left in the freezer
Question 31 Explanation: 
Cohesion describes the tendency of molecules of the same substance to bond together, as is demonstrated in water beading. An ocean stabilizing local temperature refers to water’s high specific heat. Water dissolving salt to become saltwater refers to dissolve many substances. A bottle of water that cracking after being left in the freezer is an example of the expansion of water during freezing due to its lattice structure and decreased density.
Question 32
In double-stranded DNA, the amount of cytosine is always equal to the amount of which other nucleotide base?

A
Adenine
B
Thymine
C
Guanine
D
Uracil
Question 32 Explanation: 
Due to complementary base-pairing, cytosine base-pairs with guanine. Therefore, in double-stranded DNA, the amount of cytosine is always equal to the amount of guanine. Similarly, the amount of adenine is always equal to the amount of thymine. Uracil is specific to RNA and is not found in DNA.
Question 33
A pea plant has alleles for the dominant tall gene (T) and the recessive short gene (t). Therefore, its genotype is Tt. Which of the following correctly describe its phenotype if there is complete dominance? Incomplete dominance? (complete, incomplete)

A
Tall, Tall
B
Average, Tall
C
Tall, Average
D
Tall, Short
Question 33 Explanation: 
For complete dominance, when at least one dominant allele is present, the pea plant will be tall. However, for incomplete dominance, being heterozygous will result in a height intermediate between tall and short: average.
Question 34
What is the function of tRNA during translation?

A
tRNA links together amino acids and then releases them to create a protein.
B
tRNA contains codons that each encode a specific amino acid to be added.
C
tRNA is a significant structural component of the ribosome.
D
tRNA brings the correct amino acids to the site of synthesis in the ribosome.
Question 34 Explanation: 
Transfer RNA (tRNA) brings the correct amino acids to the site of protein synthesis in the ribosome. Ribosomes link together amino acids and then release them to create a protein. tRNA contains anticodons, not codons. Codons that each encode a specific amino acid to be added to the growing protein are found within the messenger RNA (mRNA), not the tRNA. Ribosomal RNA (rRNA), not tRNA, is a significant structural component of the ribosome.
Question 35
The liver is an organ responsible for detoxifying the body of many harmful substances. Therefore, you might expect liver cells to each contain a high amount of:

A
Rough endoplasmic reticulum
B
Lysosomes
C
Mitochondria
D
Smooth endoplasmic reticulum
Question 35 Explanation: 
One of the functions of the smooth endoplasmic reticulum is to detoxify harmful substances. Therefore, since the liver is the organ specialized to perform this function, one would expect liver cells to each have a high amount of smooth endoplasmic reticulum. The rough endoplasmic reticulum contains ribosomes for protein synthesis. Lysosomes are specialized for the digestion of large biological molecules into smaller components. Mitochondria are specialized to make ATP from cellular respiration.
Question 36
A scientist conducts an experiment to discover the effect of music on the growth of pea plants. The scientist hypothesizes that the music will help pea plants grow at a faster rate than pea plants without music. By the end of the experiment, pea plants grown with music playing grew to an average height of 5.6 inches, while pea plants grown without music playing grew to an average height of 2.3 inches.

Which of the following is the correct conclusion from this experiment?

A
All plants grow better with music.
B
Pea plants grow better with music than without music.
C
Pea plants grow without music than with music.
D
Pea plant growth is unaffected by music.
Question 36 Explanation: 
The correct conclusion from this experiment is that pea plants grow better with music than without music. Because only one type of plant was tested (not “all plants”), one cannot conclude that all plants grow better with or without music. From this experiment, one can conclude that music affected pea plant growth positively.
Question 37
What type of biological molecules are enzymes?

A
Nucleic acids
B
Lipids
C
Carbohydrates
D
Proteins
Question 37 Explanation: 
Enzymes are a type of protein. Enzymes catalyze chemical reactions.
Question 38
Which cellular structure is found in both prokaryotes and eukaryotes?

A
Nucleus
B
Ribosome
C
Mitochondrion
D
Endoplasmic reticulum
Question 38 Explanation: 
Prokaryotes lack membrane-bound organelles while eukaryotes have membrane-bound organelles. Thus, while both prokaryotes and eukaryotes have ribosomes (which are not membrane-bound organelles), eukaryotes additionally each have a nucleus, an endoplasmic reticulum, and mitochondria.
Question 39
What is the largest type of biological molecule?

A
Lipids
B
Proteins
C
Carbohydrates
D
Nucleic acids
Question 39 Explanation: 
Proteins are the largest type of biological molecules. The other types of biological molecules are smaller.
Question 40
Which part of cellular respiration takes place in the cytosol of the eukaryotic cell?

A
Krebs cycle
B
Glycolysis
C
Electron transport chain
D
Calvin cycle
Question 40 Explanation: 
Glycolysis is the part of cellular respiration that takes place in the cytosol of the eukaryotic cell. The Krebs cycle takes place in the mitochondrial matrix, and the electron transport chain is found embedded in the inner mitochondrial membrane. The Calvin cycle is not a part of cellular respiration; rather, it is part of photosynthesis and takes place in the stroma of chloroplasts.
Question 41
Which best describes the light reactions of photosynthesis?

A
The light reactions convert solar energy to chemical energy through making ATP.
B
The light reactions convert chemical energy to solar energy breaking down ATP.
C
The light reactions convert solar energy to chemical energy through making glucose.
D
The light reactions make glucose using ATP, O2, NADPH, and light energy.
Question 41 Explanation: 
The light reaction converts solar energy to chemical energy, using the solar energy to make ATP. The light reactions do not convert chemical energy to solar energy, breaking down ATP. The light reactions also do not make glucose; glucose production happens during the Calvin cycle, which uses the ATP and NADPH made during the light reactions to drive this process.
Question 42
During which phase of mitosis do sister chromatids separate?

A
Prophase
B
Metaphase
C
Anaphase
D
Telophase
Question 42 Explanation: 
Anaphase is the phase of mitosis during which sister chromatids (a pair of which composes a chromosome) separate. Each individual sister chromatid is now a chromosome. Prophase is when chromosomes condense. During prometaphase, the nuclear envelope begins to break down, and chromosomes attach to the developing spindle. During metaphase, the chromosomes line up along the center of the cell. During telophase, each group of chromosomes aggregates at each pole of the cell, and a new nuclear envelope begins to develop around each.
Question 43
Which of the following is a way to visualize a family’s history, indicating which individuals had a particular genetic trait?

A
Punnett square
B
DNA sequence
C
Pedigree
D
Hypothesis
Question 43 Explanation: 
A pedigree is a way to visualize a family’s history, indicating which individuals had a particular trait. A Punnett square is a device used in genetics to predict the genotypes and phenotypes of offspring when you know the genotypes of both parents. A DNA sequence is the order of nucleotides in a piece of DNA. A hypothesis is a statement or explanation of certain events.
Question 44
How many different amino acids are found in biological proteins?

A
3
B
4
C
20
D
64
Question 44 Explanation: 
There are 20 different amino acids found in biological proteins. There are 3 nucleotides in each codon as well as in each anticodon. There are 4 nucleotides found in DNA. There are 64 possible codons in mRNA.
Question 45
Which molecule contains the stop codon?

A
tRNA
B
DNA
C
ribosome
D
mRNA
Question 45 Explanation: 
The stop codon is 3-nucleotide sequence found within messenger RNA (mRNA) that does not code for an amino acid and therefore signals the termination of translation.
Question 46
Which of the following is a reactant of photosynthesis?

A
glucose
B
O2
C
CO2
D
ATP
Question 46 Explanation: 
CO2 is a reactant of photosynthesis; it is fixed to form glucose. O2 is a product of photosynthesis. ATP is made during the light reactions but consumed during the Calvin cycle to fix CO2.
Question 47
What is the product of meiosis?

A
2 genetically identical diploid cells
B
2 genetically different diploid cells
C
4 genetically identical haploid cells
D
4 genetically different haploid cells
Question 47 Explanation: 
Meiosis creates 4 genetically different haploid cells from 2 subsequent divisions (Meiosis I and Meiosis II) of a single diploid cell. Mitosis of a diploid cell results in 2 genetically identical diploid cells.
Question 48
When does exchange of genetic information between non-sister chromatids within a duplicated homologous chromosome pair occur?

A
prophase of mitosis
B
prophase I of meiosis
C
prophase II of meiosis
D
prometaphase of mitosis
Question 48 Explanation: 
The exchange of genetic information between non-sister chromatids within a duplicated homologous chromosome pair only occurs during prophase I of meiosis. Such exchange does not happen during prophase II of meiosis nor does it happen during mitosis.
Question 49
If a parent is heterozygous, what percent of its offspring will receive the recessive allele from this parent?

A
0%
B
25%
C
50%
D
100%
Question 49 Explanation: 
If a parent is heterozygous (Aa), half (50%) of its offspring will receive the dominant allele A and the other half (50%) of its offspring will receive the recessive allele a from this parent.
Question 50
An individual has the dominant phenotype for a given trait that shows a simple dominance inheritance pattern. This individual is crossed with a homozygous recessive individual. Half of their offspring have the dominant phenotype, while the other half of their offspring have the recessive phenotype for the trait.

What is the genotype of the parent having the dominant phenotype?

A
Homozygous dominant
B
Heterozygous
C
Homozygous recessive
D
Unable to determine
Question 50 Explanation: 
Since the homozygous recessive parent could only contribute the recessive allele to its offspring, any offspring that have the recessive trait have the homozygous recessive genotype and must have received a second recessive allele from the parent with the dominant phenotype. Therefore, the parent having the dominant phenotype must have both the dominant allele (making it phenotypically dominant) and the recessive allele and therefore must be heterozygous.
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