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HESI A2 Biology study materials
HESI A2 Biology study resources

HESI A2 Biology practice questions

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Question 1Biology

Which organelle is the primary site of ATP production in a eukaryotic cell?

  1. Lysosome
  2. Ribosome
  3. Mitochondrion Correct answer.
  4. Golgi apparatus

Explanation

The mitochondrion carries out oxidative phosphorylation, using the electron transport chain and ATP synthase to generate most of the cell's ATP. Its folded inner membrane (cristae) increases the surface area available for these reactions. Other organelles perform different specialized roles.

Question 2Biology

A solution is prepared with a solute concentration higher than that inside a red blood cell. What happens to the cell when placed in this solution?

  1. It shrinks as water leaves Correct answer.
  2. It actively pumps solute inward
  3. It swells and may burst
  4. It stays the same size

Explanation

A hypertonic solution has a higher solute concentration than the cytosol, so water moves out of the cell by osmosis. The cell loses volume and shrinks, a process called crenation in red blood cells. Water always moves toward the side with the higher solute concentration.

Question 3Biology

Which molecule stores the genetic instructions that are transcribed into messenger RNA?

  1. ATP
  2. Glucose
  3. Phospholipid
  4. DNA Correct answer.

Explanation

DNA holds the base sequence that RNA polymerase reads during transcription to build mRNA. The mRNA then carries that information to ribosomes for translation. The other molecules serve energy, membrane, or metabolic roles rather than information storage.

Question 4Biology

During which phase of mitosis do sister chromatids separate and move toward opposite poles of the cell?

  1. Metaphase
  2. Prophase
  3. Anaphase Correct answer.
  4. Telophase

Explanation

Anaphase begins when cohesin is cleaved and sister chromatids are pulled apart by shortening spindle microtubules. Each chromatid becomes an independent chromosome moving toward a pole. This separation is the defining event of anaphase.

Question 5Biology

Which type of bond forms between the amino group of one amino acid and the carboxyl group of another during protein synthesis?

  1. Hydrogen bond
  2. Ionic bond
  3. Glycosidic bond
  4. Peptide bond Correct answer.

Explanation

A peptide bond is a covalent bond produced by a dehydration reaction between the carboxyl carbon of one amino acid and the amino nitrogen of the next. Repeated peptide bonds create the polypeptide backbone. Hydrogen and ionic interactions contribute to folding but do not link residues in the chain.

Question 6Biology

In a food chain, which trophic level contains organisms that capture sunlight and convert it into chemical energy?

  1. Producers Correct answer.
  2. Secondary consumers
  3. Primary consumers
  4. Decomposers

Explanation

Producers, such as plants and algae, occupy the first trophic level and perform photosynthesis to convert light energy into chemical energy stored in organic molecules. All other trophic levels ultimately depend on this captured energy. Consumers and decomposers obtain energy from organic matter rather than sunlight.

Question 7Biology

Which enzyme unwinds the DNA double helix ahead of the replication fork?

  1. DNA ligase
  2. Primase
  3. DNA polymerase
  4. Helicase Correct answer.

Explanation

Helicase breaks the hydrogen bonds between complementary bases, separating the strands so replication machinery can access each template. This unwinding creates the replication fork. The other enzymes act later in the process.

Question 8Biology

Which characteristic distinguishes prokaryotic cells from eukaryotic cells?

  1. Prokaryotic cells lack ribosomes
  2. Prokaryotic cells lack a plasma membrane
  3. Prokaryotic cells lack a membrane-bound nucleus Correct answer.
  4. Prokaryotic cells lack genetic material

Explanation

Prokaryotes keep their circular chromosome in a nucleoid region without a nuclear envelope, whereas eukaryotes enclose DNA in a true nucleus. Prokaryotes still possess ribosomes, a plasma membrane, and DNA. This absence of a membrane-bound nucleus is the key structural distinction.

Question 9Biology

A cross is made between two heterozygous pea plants for seed shape, where round (R) is dominant to wrinkled (r). What phenotypic ratio is expected among the offspring?

  1. 1 round : 3 wrinkled
  2. All wrinkled
  3. 1 round : 1 wrinkled
  4. 3 round : 1 wrinkled Correct answer.

Explanation

A monohybrid cross Rr x Rr produces genotypes in a 1 RR : 2 Rr : 1 rr ratio. Because R is dominant, both RR and Rr show the round phenotype, giving three round to one wrinkled. Only the rr homozygote appears wrinkled.

Question 10Biology

A student measures enzyme activity at several temperatures. Activity rises to a peak near 37 degrees Celsius and then falls sharply at higher temperatures. What best explains the decline?

  1. The enzyme denatures and loses its active-site shape Correct answer.
  2. Substrate concentration decreases
  3. The enzyme is diluted by the added heat
  4. The pH of the solution rises with temperature

Explanation

Above an enzyme's optimal temperature, hydrogen bonds and other weak interactions holding the tertiary structure break, so the active site loses its complementary shape. Substrate can no longer bind efficiently and activity drops. Denaturation is generally irreversible for many enzymes.

Question 11Biology

In humans, how many chromosomes are present in a normal somatic cell and in a gamete, respectively?

  1. 23 and 46
  2. 23 and 23
  3. 46 and 23 Correct answer.
  4. 46 and 46

Explanation

Human somatic cells are diploid with 46 chromosomes, arranged as 23 homologous pairs. Meiosis halves the chromosome number so each gamete carries 23 chromosomes, restoring the diploid number at fertilization.

Question 12Biology

Which statement correctly describes the role of mRNA in gene expression?

  1. It forms the structural core of the ribosome
  2. It carries the coding sequence from DNA to the ribosome Correct answer.
  3. It carries amino acids to the ribosome
  4. It catalyzes peptide bond formation

Explanation

Messenger RNA is transcribed from a gene and transports that coding sequence to the ribosome, where codons are matched to amino acids. It acts as an intermediary between DNA and protein. Transfer RNA and ribosomal RNA carry out the other listed functions.

Question 13Biology

A cell is placed in a solution and begins to swell. Which conclusion about the solution is best supported?

  1. It is hypotonic to the cytoplasm Correct answer.
  2. It contains no water
  3. It is isotonic to the cytoplasm
  4. It is hypertonic to the cytoplasm

Explanation

Water enters a cell when the surrounding solution has a lower solute concentration than the cytoplasm, meaning the solution is hypotonic. The influx increases cell volume and produces swelling. Hypertonic and isotonic solutions would cause shrinking or no net change.

Question 14Biology

Which process produces the greatest number of ATP molecules per glucose molecule under aerobic conditions?

  1. The Krebs cycle alone
  2. Glycolysis alone
  3. Lactic acid fermentation
  4. Oxidative phosphorylation Correct answer.

Explanation

Oxidative phosphorylation, driven by the electron transport chain and chemiosmosis, yields the majority of ATP from glucose, roughly 26 to 28 molecules in current estimates. Glycolysis and the Krebs cycle generate only small direct ATP amounts; most of their energy is captured in NADH and FADH2.

Question 15Biology

Two organisms live closely together, and both benefit from the association. This relationship is best described as which of the following?

  1. Parasitism
  2. Commensalism
  3. Competition
  4. Mutualism Correct answer.

Explanation

Mutualism is a symbiotic relationship in which both participating species gain a fitness benefit, such as pollinators receiving nectar while plants receive pollination. The other categories involve harm to one partner or no benefit to one side.

Question 16Biology

In a pedigree, a trait appears in every generation and affects roughly equal numbers of males and females, with affected individuals always having an affected parent. Which inheritance pattern fits best?

  1. Autosomal recessive
  2. Y-linked
  3. X-linked recessive
  4. Autosomal dominant Correct answer.

Explanation

Appearance in every generation with an affected parent for each affected child indicates vertical transmission typical of a dominant allele. Equal sex distribution supports an autosomal rather than X-linked or Y-linked location. Autosomal recessive traits more often skip generations when carriers are unaffected.

Question 17Biology

Which structural feature of the plasma membrane is best described by the fluid mosaic model?

  1. A single layer of protein with no lipid component
  2. A rigid layer of cellulose surrounding the cell
  3. A phospholipid bilayer with embedded proteins that move laterally Correct answer.
  4. A solid protein shell that prevents all movement

Explanation

The fluid mosaic model describes the membrane as a phospholipid bilayer in which proteins are embedded and can drift laterally, giving it a mosaic appearance and fluid character. Cholesterol and carbohydrates further modulate the membrane. This arrangement allows selective transport and signaling.

Question 18Biology

A mutation changes a single DNA base but the resulting polypeptide has the same amino acid sequence. What type of mutation is this?

  1. Frameshift mutation
  2. Nonsense mutation
  3. Missense mutation
  4. Silent mutation Correct answer.

Explanation

A silent mutation alters a base but, because the genetic code is degenerate, the new codon still specifies the same amino acid. The protein sequence is unchanged, so function is typically unaffected. Missense and nonsense mutations change the amino acid or create a stop codon.

Question 19Biology

Which statement accurately compares photosynthesis and cellular respiration?

  1. Photosynthesis releases carbon dioxide, while respiration consumes it
  2. Both processes occur only in the dark
  3. Both processes produce oxygen as a product
  4. Photosynthesis stores energy in glucose, while respiration releases energy from glucose Correct answer.

Explanation

Photosynthesis uses light energy to build glucose from carbon dioxide and water, storing energy in chemical bonds. Cellular respiration oxidizes glucose to release that energy as ATP. The two processes are complementary in their inputs and outputs.

Question 20Biology

Which level of protein structure is defined by the folding of a single polypeptide into a three-dimensional shape stabilized by interactions among side chains?

  1. Secondary structure
  2. Primary structure
  3. Quaternary structure
  4. Tertiary structure Correct answer.

Explanation

Tertiary structure is the overall three-dimensional fold of one polypeptide chain, held together by hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges among side chains. Secondary structure refers to local alpha helices and beta sheets, while quaternary structure involves multiple chains.

Question 21Biology

In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is 0.2. What is the expected frequency of homozygous recessive individuals?

  1. 0.16
  2. 0.32
  3. 0.04 Correct answer.
  4. 0.80

Explanation

If q equals 0.2, the homozygous recessive frequency is q squared, or 0.04. The heterozygous frequency would be 2pq, equal to 0.32, and the dominant homozygote p squared equals 0.64. Hardy-Weinberg predicts these proportions when no evolutionary forces act.

Question 22Biology

A cell with a diploid number of 8 undergoes meiosis. How many chromosomes are present in each resulting daughter cell, and how many daughter cells are produced?

  1. 4 chromosomes in 2 cells
  2. 8 chromosomes in 2 cells
  3. 8 chromosomes in 4 cells
  4. 4 chromosomes in 4 cells Correct answer.

Explanation

Meiosis halves the chromosome number and produces four haploid cells. With a diploid number of 8, each of the four gametes receives 4 chromosomes, one from each homologous pair. This reduction is what restores the diploid number upon fertilization.

Question 23Biology

A mutation inserts two nucleotides into the coding region of a gene. What is the most likely consequence for the protein?

  1. The reading frame shifts, altering all downstream amino acids Correct answer.
  2. No effect occurs because insertions are always silent
  3. The protein is always longer by exactly two amino acids
  4. Only one amino acid is replaced with no other change

Explanation

Inserting two nucleotides is not a multiple of three, so the triplet reading frame is displaced from the mutation point onward. Every codon after the insertion is read differently, usually producing a nonfunctional protein and often a premature stop. Frameshift mutations are typically more disruptive than substitutions.

Question 24Biology

An enzyme is added to a reaction already at a high substrate concentration, and the reaction rate increases only slightly. Which explanation is most consistent with this result?

  1. The enzyme has denatured at room temperature
  2. All enzyme active sites are saturated with substrate Correct answer.
  3. The substrate has been completely consumed
  4. The reaction is inhibited by its product

Explanation

When substrate concentration is high enough that nearly every active site is occupied, the enzyme is saturated and works at its maximum rate Vmax. Adding more enzyme increases the total number of active sites, but the observed rate per enzyme molecule cannot rise further. Saturation explains why further substrate additions have little effect.

Question 25Biology

A woman who is a carrier for an X-linked recessive disorder has children with an unaffected man. What proportion of their sons is expected to be affected?

  1. Half of the sons Correct answer.
  2. All of the sons
  3. One quarter of the sons
  4. None of the sons

Explanation

Sons inherit their X chromosome from the mother and a Y from the father. A carrier mother has one normal and one affected X allele, so each son has a 50 percent chance of receiving the affected allele and expressing the disorder. Daughters are unaffected because they receive a normal X from the father.

Question 26Biology

A solution with a pH of 3 is best described as which of the following?

  1. Neutral
  2. Strongly acidic Correct answer.
  3. Weakly basic
  4. Strongly basic

Explanation

pH is the negative logarithm of hydrogen ion concentration, so a pH of 3 means a relatively high hydrogen ion concentration. Values well below 7 indicate strong acidity, while values above 7 indicate basicity.

Question 27Biology

Which molecule serves as the primary energy currency that cells spend to drive endergonic reactions?

  1. NADH
  2. ATP Correct answer.
  3. Glucose
  4. Cholesterol

Explanation

ATP couples exergonic and endergonic reactions by transferring a phosphate group, releasing usable free energy. Glucose and NADH store energy but must be processed to regenerate ATP before most cellular work proceeds.

Question 28Biology

Which type of bond holds the two strands of a DNA double helix together?

  1. Ionic bonds
  2. Disulfide bonds
  3. Peptide bonds
  4. Hydrogen bonds Correct answer.

Explanation

Complementary nitrogenous bases pair through hydrogen bonds: adenine with thymine forms two, and guanine with cytosine forms three. These bonds are individually weak, which allows the strands to separate during replication and transcription.

Question 29Biology

Which blood component is primarily responsible for transporting oxygen from the lungs to body tissues?

  1. Erythrocytes Correct answer.
  2. Platelets
  3. Leukocytes
  4. Plasma proteins

Explanation

Erythrocytes contain hemoglobin, an iron-containing protein that binds oxygen in the lungs and releases it in tissues. The other blood components serve clotting, immunity, or transport of solutes rather than bulk oxygen carriage.

Question 30Biology

Which process allows water to move across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration?

  1. Facilitated diffusion of ions
  2. Phagocytosis
  3. Active transport
  4. Osmosis Correct answer.

Explanation

Osmosis is the passive diffusion of water through a selectively permeable membrane down its concentration gradient. It requires no energy input and specifically concerns water movement rather than solute transport.

Question 31Biology

Which of the following is the correct sequence of events in mitosis?

  1. Metaphase, prophase, telophase, anaphase
  2. Anaphase, telophase, prophase, metaphase
  3. Prophase, metaphase, anaphase, telophase Correct answer.
  4. Prophase, anaphase, metaphase, telophase

Explanation

Mitosis proceeds through prophase, metaphase, anaphase, and telophase, often remembered by the order of chromosome condensation, alignment, separation, and nuclear reformation. The sequence reflects the orderly progression required for accurate chromosome segregation.

Question 32Biology

Which group of organisms is capable of fixing atmospheric nitrogen into forms usable by plants?

  1. Protozoa
  2. Viruses
  3. Nitrogen-fixing bacteria Correct answer.
  4. Fungi

Explanation

Certain bacteria, including Rhizobium species in root nodules and free-living cyanobacteria, carry the nitrogenase enzyme that converts atmospheric nitrogen gas into ammonia. This fixed nitrogen then enters food webs and becomes available to plants.

Question 33Biology

A student observes that a plant wilts when its roots are placed in a concentrated salt solution. Which explanation best accounts for this observation?

  1. Water leaves root cells by osmosis because the external solution is hypertonic Correct answer.
  2. Salt actively pumps water into root cells
  3. Root cells burst from excessive water entry
  4. Salt crystals physically block water uptake channels

Explanation

A concentrated salt solution is hypertonic relative to root cell contents, so water moves out of the cells by osmosis and turgor pressure falls, causing wilting. The direction of water movement follows the gradient toward the higher solute concentration.

Question 34Biology

In a dihybrid cross between two organisms heterozygous for both traits (AaBb x AaBb), assuming independent assortment, what fraction of offspring is expected to show both recessive phenotypes?

  1. 1/16 Correct answer.
  2. 1/4
  3. 9/16
  4. 3/16

Explanation

Each trait separately shows a 3:1 phenotypic ratio, so the probability of the recessive phenotype for one trait is 1/4. Multiplying independent probabilities gives 1/4 x 1/4 = 1/16 for both recessive traits together.

Question 35Biology

A segment of DNA has the template strand sequence 3'-TAC GGA-5'. What mRNA sequence is transcribed from this template?

  1. 5'-ATG CCT-3'
  2. 5'-UAC GGA-3'
  3. 5'-AUG CCU-3' Correct answer.
  4. 5'-TAC GGA-3'

Explanation

Transcription builds mRNA complementary to the DNA template, substituting uracil for thymine. T pairs with A, A pairs with U, C pairs with G, and G pairs with C, yielding 5'-AUG CCU-3' antiparallel to the template.

Question 36Biology

Aerobic respiration and fermentation both begin with glycolysis, but they differ in which key respect?

  1. Glycolysis yields more ATP under anaerobic conditions
  2. Fermentation does not use the electron transport chain, whereas aerobic respiration does Correct answer.
  3. Only fermentation produces pyruvate
  4. Only aerobic respiration regenerates NAD+

Explanation

When oxygen is available, pyruvate enters the mitochondria and electrons flow through the electron transport chain to oxygen. Fermentation instead regenerates NAD+ by transferring electrons to organic molecules, producing far fewer ATP per glucose.

Question 37Biology

A leaf appears green to human observers. Which statement best explains this observation?

  1. Chlorophyll absorbs green wavelengths most strongly
  2. Green light carries no energy and cannot be absorbed
  3. Accessory pigments emit green light after absorbing red light
  4. Chlorophyll reflects green wavelengths that are not absorbed for photosynthesis Correct answer.

Explanation

Chlorophyll absorbs mainly blue and red wavelengths and reflects or transmits much of the green portion of the spectrum. The reflected green light reaching the eye is what makes leaves appear green.

Question 38Biology

In a certain species, a gene has two alleles. Homozygous dominant individuals are black, heterozygotes are gray, and homozygous recessive individuals are white. This pattern is an example of which phenomenon?

  1. Complete dominance
  2. Codominance
  3. Incomplete dominance Correct answer.
  4. Sex-linked inheritance

Explanation

In incomplete dominance the heterozygote shows an intermediate phenotype between the two homozygotes, as with black, gray, and white here. Codominance would instead show both parental phenotypes expressed distinctly at once.

Question 39Biology

Which statement best explains why enzymes are described as lowering the activation energy of a reaction?

  1. They stabilize the transition state and provide an alternate reaction pathway Correct answer.
  2. They permanently change the equilibrium constant of the reaction
  3. They increase the free energy released by the reaction
  4. They raise the temperature of the surrounding solution

Explanation

Enzymes bind substrates and stabilize the transition state, offering a lower-energy route to products. They do not alter the overall free energy change or the equilibrium position, only the rate at which equilibrium is approached.

Question 40Biology

A human cell in G1 phase contains 46 chromosomes. After S phase is complete but before mitosis begins, which description is accurate?

  1. 23 chromosomes, each with two sister chromatids
  2. 46 chromosomes, each with two sister chromatids Correct answer.
  3. 92 chromosomes, each with one chromatid
  4. 46 chromosomes, each with one chromatid

Explanation

DNA replication during S phase duplicates each chromosome into two sister chromatids joined at the centromere, but the chromosome count stays at 46 because chromatids remain attached. Segregation into separate chromosomes occurs later, during mitosis.

Question 41Biology

A freshwater fish placed in saltwater begins to lose water from its body. Which term best describes the saltwater relative to the fish's body fluids?

  1. Hypertonic Correct answer.
  2. Hypotonic
  3. Isotonic
  4. Hydrostatic

Explanation

Saltwater with a higher solute concentration than the fish's body fluids is hypertonic, so water moves out of the fish by osmosis. This causes dehydration and is why freshwater fish cannot survive in marine environments.

Question 42Biology

In a population of insects, individuals with a mutation that confers resistance to a pesticide survive and reproduce, while susceptible individuals die. Over several generations, resistance becomes common. This is best described as which process?

  1. Artificial selection
  2. Gene flow
  3. Genetic drift
  4. Natural selection Correct answer.

Explanation

Natural selection occurs when heritable variation affects survival and reproduction, shifting allele frequencies toward advantageous traits. The pesticide acts as a selective pressure, increasing the frequency of resistance alleles over generations.

Question 43Biology

A cell that lacks functional mitochondria would be expected to rely most heavily on which process for ATP production?

  1. Glycolysis Correct answer.
  2. Electron transport chain activity
  3. Oxidative phosphorylation
  4. The Krebs cycle

Explanation

Glycolysis occurs in the cytoplasm and does not require mitochondria, so it remains the main ATP source when oxidative metabolism is unavailable. It yields only a small amount of ATP per glucose, which is why mitochondrial function is essential for high energy demands.

Question 44Biology

Which statement accurately describes the relationship between the sequence of codons in mRNA and the resulting polypeptide?

  1. Each codon always specifies multiple amino acids
  2. Ribosomes translate mRNA in a 3' to 5' direction
  3. Stop codons code for the amino acid methionine
  4. The reading frame determines how nucleotides are grouped into codons Correct answer.

Explanation

Codons are read in non-overlapping triplets, and the starting point establishes the reading frame that determines which amino acids are specified. A shift in reading frame changes every downstream codon and typically alters the protein.

Question 45Biology

Two populations of the same species become separated by a river for thousands of years and diverge so that they can no longer interbreed successfully. This outcome is best described as which of the following?

  1. Coevolution
  2. Allopatric speciation Correct answer.
  3. Sympatric speciation
  4. Convergent evolution

Explanation

Geographic separation restricts gene flow, allowing mutations and drift to accumulate independently until reproductive isolation evolves, which defines allopatric speciation. Sympatric speciation would occur without geographic separation.

Question 46Biology

A gene regulatory protein binds to an enhancer region and increases transcription of a gene located thousands of base pairs away. Which mechanism best explains this effect?

  1. The protein changes the gene's codon sequence
  2. The protein removes introns from the pre-mRNA
  3. The protein directly phosphorylates RNA polymerase
  4. DNA looping brings the enhancer-bound protein into contact with the promoter region Correct answer.

Explanation

Enhancers act at a distance because the intervening DNA bends, placing bound activator proteins near the promoter and its associated transcription factors. This contact stabilizes the transcription initiation complex and increases RNA polymerase activity.

Question 47Biology

A couple in which both partners are heterozygous for an autosomal recessive disorder has an affected child. What is the probability that their next child will be a carrier, given that the child is unaffected?

  1. 2/3 Correct answer.
  2. 3/4
  3. 1/2
  4. 1/4

Explanation

Among unaffected offspring of two heterozygotes, the possible genotypes are AA and Aa in a 1:2 ratio, so two of the three unaffected outcomes are carriers. The probability is therefore 2/3 once the affected genotype is excluded.

Question 48Biology

A metabolic pathway is regulated by feedback inhibition. Which description best characterizes this control?

  1. An intermediate product increases the rate of all downstream enzymes
  2. A hormone irreversibly degrades the first enzyme in the pathway
  3. The final product binds an early enzyme and reduces its activity Correct answer.
  4. The substrate of the first step activates the final enzyme

Explanation

In feedback inhibition, accumulation of the end product signals that the pathway is overproducing and allosterically inhibits an upstream enzyme. This reversible regulation conserves resources and maintains product concentration within a useful range.

Question 49Biology

A population has genotype frequencies of 0.36 AA, 0.48 Aa, and 0.16 aa. Which conclusion about this population is best supported?

  1. The population is not in Hardy-Weinberg equilibrium because heterozygotes are too frequent
  2. The population has an allele frequency of 0.5 for both alleles
  3. The population is in Hardy-Weinberg equilibrium, with allele frequencies of 0.6 for A and 0.4 for a Correct answer.
  4. The population is evolving because the recessive genotype is present

Explanation

The allele frequencies are p = 0.36 + 0.24 = 0.6 and q = 0.16 + 0.24 = 0.4. Expected genotype frequencies under Hardy-Weinberg are p squared = 0.36, 2pq = 0.48, and q squared = 0.16, matching the observed values exactly.

Question 50Biology

A protein is synthesized on ribosomes bound to the rough endoplasmic reticulum. Which pathway best describes its subsequent route to the cell exterior?

  1. Rough ER to lysosome to nucleus to plasma membrane
  2. Rough ER to Golgi apparatus to secretory vesicles to plasma membrane Correct answer.
  3. Cytosol to smooth ER to mitochondrion to plasma membrane
  4. Golgi apparatus to rough ER to secretory vesicles to plasma membrane

Explanation

Proteins destined for secretion are translocated into the rough ER, packaged into transport vesicles, and modified and sorted in the Golgi apparatus. Secretory vesicles then fuse with the plasma membrane to release their contents outside the cell.