MCAT BIOLOGY PRACTICE EXAM 2025/2026 QUESTIONS
WITH SOLUTION GRADED A+
✔✔Obligate Anaerobes - ✔✔Cannot survive in an oxygen-containing environment.
✔✔Facultative Anaerobes - ✔✔Toggle between metabolic processes. Can do aerobic
and anaerobic respiration.
✔✔Aerotolerant Anaerobes - ✔✔Unable to use oxygen for metabolism but are not
harmed by its presence
✔✔Prokaryotic Cell Structure - ✔✔Major difference is that there is a lack of a nucleus
and membrane-bound organelles. They do have ribosomes. They are single celled.
✔✔Cell Wall - ✔✔Outer barrier of the cell. Provides structure and controls the
movement of solutes into and out of the bacterium. This maintains concentration
gradients relative to the environment. Two types: gram positive and gram negative.
✔✔Gram Positive Bacteria
What color is it?
Is there a thick or think cell wall (peptidoglycan)?
What does the cell membrane contain? - ✔✔purple
thick later of peptidoglycan (aa + sugar)
It aids a pathogen by providing protection from a host organism's immune system.
It also contains lipoteichoic acid
✔✔Cell Membrane - ✔✔Next layer of the prokaryotic cell. It is composed of
phospholipids.
✔✔Envelope - ✔✔The cell wall and cell membrane together.
✔✔Bacterial Flagella - ✔✔Used for propulsion. Triggered via chemotaxis which is the
movement to or from a chemical stimuli. Made of a filament, hollow structure of flagellin
anchored by a basal body, and a hook, which connects the filament and the basal body
to increase torque.
✔✔Plasmids - ✔✔Small circular structures of DNA acquired from external sources.
They carry DNA that is not necessary for survival of the prokaryote, but may confer an
advantage such as antibiotic resistance.
✔✔Prokaryotic vs Eukaryotic ribosome - ✔✔Prokaryotes have a 30 S and 50 S
ribosome
Euk have 40 and 60s ribosome
,✔✔Generation of ATP (in bacteria) - ✔✔Done via the cell membrane where ETC lies.
✔✔Gram Negative Bacteria
What color is it?
Is there a thick or think cell wall (peptidoglycan)?
What does the cell membrane contain? - ✔✔Appears pink
Thin cell wall
phospholipids and lipopolysaccharides (elicit a stronger immune response)
✔✔Binary Fission - ✔✔Simple form of asexual reproduction in prokaryotes.
Chromosome attaches to the cell wall and replicates while the cell continues to grow in
size.
✔✔Genetic Recombination - ✔✔Plasmids will carry genes that impart some benefit on
the bacteria or carry virulence factors that increase how pathogenic it is. .
✔✔Transformation - ✔✔Integration of foreign genetic material into the host genome.
✔✔Conjugation - ✔✔Bacterial sexual reproduction. Two bacteria form a conjugation
bridge, made from the sex pili and sex factors (plasmids containing necessary genes),
that allows for transfer of materials. Donor male (+) to the recipient female (-).
Unidirectional.
✔✔Sex Factor F - ✔✔Best studied sex factor is the Fertility factor. F+ cells with it, F-
without it. F+ cell replicates its F factor, donates it to the recipient, and makes it an F+
factor. Then they can copy and transfer genetic material via conjugation; great for
sharing antibiotic resistance or virulence factors.
✔✔Hfr - ✔✔High frequency of recombination. Incomplete transfer of genetic information
to the female recipient - sex pilus bridge breaks before the whole DNA sequence can be
transferred. Sex factor often incorporates itself into host genome so in conjugation, host
genome bits also are transferred.
✔✔Transduction - ✔✔Requires a vector, or a virus that carries genetic material from
one bacteria to the other. Bacteriophages can trap a segment of host DNA during
assembly, it can then release it in another infection later on.
✔✔Transposons - ✔✔Genetic element capable of inserting and removing themselves
from the genome.
✔✔Phases of Bacterial Growth - ✔✔Lag phase: Adaptation to the new local conditions
of the environment.
Log phase: Adaptation, growth increase, increase in bacterial colony.
Stationary phase: Reduction of resources slows reproduction. Characterized by flat top
of curve
,Death phase: Lack of ability to support the number of bacteria. Decline in number.
✔✔Viral Structure - ✔✔Composed of genetic material, protein coat, and envelope
containing lipids. Genetic info is either circular or linear, single or double stranded, and
either made of DNA or RNA. The protein coat is the capsid. Envelope will surround the
capsid and is made of phospholipids that are sensitive to heat, detergents, and
desiccation.
✔✔Viral Host Cell - ✔✔Where the virus must express and replicate genetic information,
because they do not have their own ribosomes. It helps to produce the viral product,
virions (viral progeny).
✔✔Bacteriophages - ✔✔Viruses that specifically target bacteria. They only inject
genetic material via a tail sheath. The tail fibers help with connection to the host cell.
✔✔Viral Genome - ✔✔ssDNA, dsDNA, dsRNA, or ssRNA. ssRNA is either positive
sense or negative sense.
✔✔Retroviruses - ✔✔Enveloped, ssRNA viruses that carry reverse transcriptase in
order to synthesize dsDNA from single-stranded RNA (two rounds of reverse
transcription). The DNA then integrates into the host cell genome and acts as if it were
the host cell's own DNA. An example is HIV.
✔✔Viral Life Cycle - ✔✔1. Infection: Bind to receptors, fusion, entry of virion.
Bacteriophage only inserts genetic material.
2. Translation and Progeny Assembly: Translation must occur in order for a virus to
reproduce. DNA viruses go to the nucleus, +RNA viruses stay in the cytoplasm, -RNA
needs synthesis of the +RNA via RNA replicase for translations. Proteins are created
and packaging then occurs.
3. Progeny Release: Released via initiation of cell death or lysing due to a large number
of virions. It can also be released via extrusion, or fusing with its plasma membrane and
budding essentially. Can also leave by extrusion, where the virus fuses with the plasma
membrane and forms a vesicle.
✔✔Lytic Cycle - ✔✔Bacteriophage makes maximal use of the cell's machinery with little
regard for the survival of the host cell. the bacteria are termed virulent.
✔✔Lysogenic Cycle - ✔✔Integration into the genome as a provirus or prophage.
Environmental factors will revert the provirus back to a lytic cycle.
✔✔Superinfection - ✔✔Simultaneous infection, usually prevented by lysogenic cycles.
Infection with one strain of phage generally makes it harder for the bacterium to be
infected with other phages.
, ✔✔Prions - ✔✔Infectious proteins that are nonliving things. Cause disease via
misfolding other proteins, usually causing the change from an alpha helical structure to
a beta helical structure. Protein aggregates form and cell function is reduced. Mad cow
disease!!
✔✔Viroids - ✔✔Small plant pathogens that consist of a very short, circular, single-
stranded RNA. They silence genes in the PLANT genome. HDV (hepatitis D virus) is an
example of a human viroid. Although alone HDV is harmless, when coinfected with
hepatitis B, HDV is able to exert its silencing function on human hepatocytes (liver cell).
✔✔Episomes - ✔✔Episomes are a subset of plasmids that are capable of integrating
into the genome of the bacterium
✔✔Positive Sense Viruses - ✔✔Implies that the genome may be directly translated to
functional proteins by the ribosomes of the host cell, just like mRNA.
✔✔Negative Sense Viruses - ✔✔These viruses require synthesis of an RNA strand that
is complementary to the negative sense RNA strand, which can then be used as a
template for protein synthesis. These viruses must carry an RNA replicase in the virion
to ensure that this synthesis occurs.
✔✔Apoptosis - ✔✔Release of ETC enzymes
✔✔Autolysis - ✔✔Release of lysosome enzymes
✔✔Endosomes - ✔✔transport, package and sort materials to and from membrane. Can
send vesicles to:
1. Cell membrane for recycling
2. Lysosome for degradation
3. Golgi for transport or modification
✔✔Smooth Endoplasmic reticulum - ✔✔Smooth ER lacks ribosomes and is used for
lipid synthesis and detoxification of drugs and poisons. It also transports proteins from
the RER to the Golgi Apparatus.
✔✔HIV life cycle - ✔✔1. Proteins on the envelope bind to CD4 and CR5 on cell surface
2. Virus fuses with cell and empties content into cytoplasm
3. Reverse transcriptase converts RNA to DNA, making errors to generate diversity
4. Integrase inserts virus's DNA into host DNA
5. RNA polymerase converts DNA into RNA, ribosomes make proteins
6. Budding virus particle
7. Mature virus
WITH SOLUTION GRADED A+
✔✔Obligate Anaerobes - ✔✔Cannot survive in an oxygen-containing environment.
✔✔Facultative Anaerobes - ✔✔Toggle between metabolic processes. Can do aerobic
and anaerobic respiration.
✔✔Aerotolerant Anaerobes - ✔✔Unable to use oxygen for metabolism but are not
harmed by its presence
✔✔Prokaryotic Cell Structure - ✔✔Major difference is that there is a lack of a nucleus
and membrane-bound organelles. They do have ribosomes. They are single celled.
✔✔Cell Wall - ✔✔Outer barrier of the cell. Provides structure and controls the
movement of solutes into and out of the bacterium. This maintains concentration
gradients relative to the environment. Two types: gram positive and gram negative.
✔✔Gram Positive Bacteria
What color is it?
Is there a thick or think cell wall (peptidoglycan)?
What does the cell membrane contain? - ✔✔purple
thick later of peptidoglycan (aa + sugar)
It aids a pathogen by providing protection from a host organism's immune system.
It also contains lipoteichoic acid
✔✔Cell Membrane - ✔✔Next layer of the prokaryotic cell. It is composed of
phospholipids.
✔✔Envelope - ✔✔The cell wall and cell membrane together.
✔✔Bacterial Flagella - ✔✔Used for propulsion. Triggered via chemotaxis which is the
movement to or from a chemical stimuli. Made of a filament, hollow structure of flagellin
anchored by a basal body, and a hook, which connects the filament and the basal body
to increase torque.
✔✔Plasmids - ✔✔Small circular structures of DNA acquired from external sources.
They carry DNA that is not necessary for survival of the prokaryote, but may confer an
advantage such as antibiotic resistance.
✔✔Prokaryotic vs Eukaryotic ribosome - ✔✔Prokaryotes have a 30 S and 50 S
ribosome
Euk have 40 and 60s ribosome
,✔✔Generation of ATP (in bacteria) - ✔✔Done via the cell membrane where ETC lies.
✔✔Gram Negative Bacteria
What color is it?
Is there a thick or think cell wall (peptidoglycan)?
What does the cell membrane contain? - ✔✔Appears pink
Thin cell wall
phospholipids and lipopolysaccharides (elicit a stronger immune response)
✔✔Binary Fission - ✔✔Simple form of asexual reproduction in prokaryotes.
Chromosome attaches to the cell wall and replicates while the cell continues to grow in
size.
✔✔Genetic Recombination - ✔✔Plasmids will carry genes that impart some benefit on
the bacteria or carry virulence factors that increase how pathogenic it is. .
✔✔Transformation - ✔✔Integration of foreign genetic material into the host genome.
✔✔Conjugation - ✔✔Bacterial sexual reproduction. Two bacteria form a conjugation
bridge, made from the sex pili and sex factors (plasmids containing necessary genes),
that allows for transfer of materials. Donor male (+) to the recipient female (-).
Unidirectional.
✔✔Sex Factor F - ✔✔Best studied sex factor is the Fertility factor. F+ cells with it, F-
without it. F+ cell replicates its F factor, donates it to the recipient, and makes it an F+
factor. Then they can copy and transfer genetic material via conjugation; great for
sharing antibiotic resistance or virulence factors.
✔✔Hfr - ✔✔High frequency of recombination. Incomplete transfer of genetic information
to the female recipient - sex pilus bridge breaks before the whole DNA sequence can be
transferred. Sex factor often incorporates itself into host genome so in conjugation, host
genome bits also are transferred.
✔✔Transduction - ✔✔Requires a vector, or a virus that carries genetic material from
one bacteria to the other. Bacteriophages can trap a segment of host DNA during
assembly, it can then release it in another infection later on.
✔✔Transposons - ✔✔Genetic element capable of inserting and removing themselves
from the genome.
✔✔Phases of Bacterial Growth - ✔✔Lag phase: Adaptation to the new local conditions
of the environment.
Log phase: Adaptation, growth increase, increase in bacterial colony.
Stationary phase: Reduction of resources slows reproduction. Characterized by flat top
of curve
,Death phase: Lack of ability to support the number of bacteria. Decline in number.
✔✔Viral Structure - ✔✔Composed of genetic material, protein coat, and envelope
containing lipids. Genetic info is either circular or linear, single or double stranded, and
either made of DNA or RNA. The protein coat is the capsid. Envelope will surround the
capsid and is made of phospholipids that are sensitive to heat, detergents, and
desiccation.
✔✔Viral Host Cell - ✔✔Where the virus must express and replicate genetic information,
because they do not have their own ribosomes. It helps to produce the viral product,
virions (viral progeny).
✔✔Bacteriophages - ✔✔Viruses that specifically target bacteria. They only inject
genetic material via a tail sheath. The tail fibers help with connection to the host cell.
✔✔Viral Genome - ✔✔ssDNA, dsDNA, dsRNA, or ssRNA. ssRNA is either positive
sense or negative sense.
✔✔Retroviruses - ✔✔Enveloped, ssRNA viruses that carry reverse transcriptase in
order to synthesize dsDNA from single-stranded RNA (two rounds of reverse
transcription). The DNA then integrates into the host cell genome and acts as if it were
the host cell's own DNA. An example is HIV.
✔✔Viral Life Cycle - ✔✔1. Infection: Bind to receptors, fusion, entry of virion.
Bacteriophage only inserts genetic material.
2. Translation and Progeny Assembly: Translation must occur in order for a virus to
reproduce. DNA viruses go to the nucleus, +RNA viruses stay in the cytoplasm, -RNA
needs synthesis of the +RNA via RNA replicase for translations. Proteins are created
and packaging then occurs.
3. Progeny Release: Released via initiation of cell death or lysing due to a large number
of virions. It can also be released via extrusion, or fusing with its plasma membrane and
budding essentially. Can also leave by extrusion, where the virus fuses with the plasma
membrane and forms a vesicle.
✔✔Lytic Cycle - ✔✔Bacteriophage makes maximal use of the cell's machinery with little
regard for the survival of the host cell. the bacteria are termed virulent.
✔✔Lysogenic Cycle - ✔✔Integration into the genome as a provirus or prophage.
Environmental factors will revert the provirus back to a lytic cycle.
✔✔Superinfection - ✔✔Simultaneous infection, usually prevented by lysogenic cycles.
Infection with one strain of phage generally makes it harder for the bacterium to be
infected with other phages.
, ✔✔Prions - ✔✔Infectious proteins that are nonliving things. Cause disease via
misfolding other proteins, usually causing the change from an alpha helical structure to
a beta helical structure. Protein aggregates form and cell function is reduced. Mad cow
disease!!
✔✔Viroids - ✔✔Small plant pathogens that consist of a very short, circular, single-
stranded RNA. They silence genes in the PLANT genome. HDV (hepatitis D virus) is an
example of a human viroid. Although alone HDV is harmless, when coinfected with
hepatitis B, HDV is able to exert its silencing function on human hepatocytes (liver cell).
✔✔Episomes - ✔✔Episomes are a subset of plasmids that are capable of integrating
into the genome of the bacterium
✔✔Positive Sense Viruses - ✔✔Implies that the genome may be directly translated to
functional proteins by the ribosomes of the host cell, just like mRNA.
✔✔Negative Sense Viruses - ✔✔These viruses require synthesis of an RNA strand that
is complementary to the negative sense RNA strand, which can then be used as a
template for protein synthesis. These viruses must carry an RNA replicase in the virion
to ensure that this synthesis occurs.
✔✔Apoptosis - ✔✔Release of ETC enzymes
✔✔Autolysis - ✔✔Release of lysosome enzymes
✔✔Endosomes - ✔✔transport, package and sort materials to and from membrane. Can
send vesicles to:
1. Cell membrane for recycling
2. Lysosome for degradation
3. Golgi for transport or modification
✔✔Smooth Endoplasmic reticulum - ✔✔Smooth ER lacks ribosomes and is used for
lipid synthesis and detoxification of drugs and poisons. It also transports proteins from
the RER to the Golgi Apparatus.
✔✔HIV life cycle - ✔✔1. Proteins on the envelope bind to CD4 and CR5 on cell surface
2. Virus fuses with cell and empties content into cytoplasm
3. Reverse transcriptase converts RNA to DNA, making errors to generate diversity
4. Integrase inserts virus's DNA into host DNA
5. RNA polymerase converts DNA into RNA, ribosomes make proteins
6. Budding virus particle
7. Mature virus
