What is the protective protein coat that surrounds a virus's nucleic acid called?
Capsid
✓
Envelope
Cell wall
Plasma membrane
Correct Answer
Capsid
The capsid is a shell of protein subunits that encloses and protects the viral genome, and every virus has one. Envelope refers to the outer layer of phospholipid membrane and protein that only some viruses carry, taken from the host cell. Cell wall is a structure of bacteria, plants and fungi, not viruses. Plasma membrane is a feature of cells, and viruses are not cells.
Category: Virus Structure and Replication
Question 2
HIV copies its RNA genome into DNA before inserting it into the host genome. Which enzyme carries out this copying step?
DNA ligase
Reverse transcriptase
✓
Helicase
Restriction enzyme
Correct Answer
Reverse transcriptase
Reverse transcriptase builds DNA using an RNA template, which is the defining step of retroviruses such as HIV. DNA ligase joins existing DNA fragments but does not read RNA. Helicase unwinds double-stranded DNA during replication. Restriction enzyme cuts DNA at specific sequences and does not make new DNA.
Category: Virus Structure and Replication
Question 3
In the replication cycle of an animal virus, which step comes directly after penetration into the host cell?
Attachment
Assembly
Uncoating
✓
Release
Correct Answer
Uncoating
The usual order is attachment, penetration, uncoating, replication, assembly and release, so uncoating comes next: the capsid is broken down and the viral nucleic acid is freed inside the cell. Attachment is the first step, when viral proteins bind a receptor on the host cell. Assembly happens after the genome and proteins have been made. Release is the final step, when new virions leave the cell.
Category: Virus Structure and Replication
Question 4
Why must a new influenza vaccine be prepared every year, while the same measles vaccine is used year after year?
Influenza has a DNA genome that is unusually large
Influenza lacks a protein coat around its genome
Influenza infects only bacteria in the airway
Influenza has an RNA genome that mutates rapidly
✓
Correct Answer
Influenza has an RNA genome that mutates rapidly
Influenza is an RNA virus, and its RNA polymerase makes many copying errors, so its surface proteins change quickly and last year's vaccine may no longer match. Influenza has a DNA genome that is unusually large is wrong because its genome is RNA. Influenza lacks a protein coat around its genome is wrong because all viruses have a capsid. Influenza infects only bacteria in the airway is wrong because it infects human epithelial cells, not bacteria.
Category: Viral Disease Control
Question 5
Which type of vaccine usually gives the strongest and longest-lasting protection but carries a small risk of causing the disease?
Weakened live virus vaccine
✓
Killed virus vaccine
Subunit vaccine
Inactivated toxin vaccine
Correct Answer
Weakened live virus vaccine
A weakened live virus can still replicate a little in the body, which stimulates strong immunity, but in rare cases it can mutate back to a disease-causing form. Killed virus vaccine cannot cause disease but tends to give weaker or shorter protection. Subunit vaccine contains only pieces of the pathogen and also cannot cause the disease. Inactivated toxin vaccine contains a harmless form of a toxin and cannot replicate or cause infection.
Category: Viral Disease Control
Question 6
Which tough protein in the outer layer of skin helps prevent pathogens from entering the body?
Hemoglobin
Keratin
✓
Insulin
Actin
Correct Answer
Keratin
Keratin is a durable structural protein in the outer skin cells that makes the skin surface a physical barrier against pathogens. Hemoglobin is the oxygen-carrying protein of red blood cells. Insulin is a hormone that regulates blood glucose. Actin is a cytoskeleton and muscle protein, not a barrier protein of the skin surface.
Category: Innate Immunity
Question 7
Which white blood cells are the most abundant in the blood and are among the first to arrive at a site of inflammation, where they engulf pathogens?
Basophils
Eosinophils
Neutrophils
✓
Monocytes
Correct Answer
Neutrophils
Neutrophils make up the largest share of white blood cells and move quickly into inflamed tissue, where they phagocytize pathogens. Basophils are the least common white blood cells and release chemicals such as histamine rather than leading phagocytosis. Eosinophils are relatively few and are known for fighting parasites and intensifying allergic inflammation. Monocytes arrive later and mature into macrophages in the tissue.
Category: Innate Immunity
Question 8
Monocytes circulating in the blood leave the vessels and develop into which large phagocytic cells in infected tissue?
Plasma cells
Mast cells
Platelets
Macrophages
✓
Correct Answer
Macrophages
Monocytes mature into macrophages in tissue, where they engulf pathogens, finish phagocytosis after neutrophils and clear debris. Plasma cells develop from B cells and secrete antibodies. Mast cells live in connective and mucosal tissue and release inflammatory chemicals. Platelets are cell fragments involved in blood clotting.
Category: Innate Immunity
Question 9
Virus-infected cells release small proteins that signal neighboring uninfected cells to make compounds that block viral replication. What are these proteins called?
Interferons
✓
Antibodies
Albumins
Perforins
Correct Answer
Interferons
Interferons are early-acting signaling proteins released by infected cells that put nearby cells into an antiviral state and also activate macrophages. Antibodies are made by plasma cells of the adaptive response and bind specific antigens. Albumins are blood plasma proteins that help maintain osmotic pressure and carry substances. Perforins are pore-forming proteins released by killer lymphocytes onto target cells, not warning signals between neighbors.
Category: Innate Immunity
Question 10
Besides marking microbes for phagocytes, how do some activated complement proteins directly destroy a microbe?
They block its ribosomes
They form pores in its membrane
✓
They cut its DNA into pieces
They digest its protein coat
Correct Answer
They form pores in its membrane
Some complement proteins assemble into a structure that punches pores in the microbial membrane, so water and ions rush in and the cell lyses. They block its ribosomes describes how some antibiotics act, not complement. They cut its DNA into pieces describes restriction enzymes, not complement. They digest its protein coat is not how complement works, since complement kills by damaging membranes rather than by digesting proteins.
Category: Innate Immunity
Question 11
B and T lymphocytes are both produced in red bone marrow. In which organ do T cells complete their maturation?
Spleen
Liver
Thymus
✓
Lymph node
Correct Answer
Thymus
T cells leave the bone marrow and mature in the thymus, where cells that bind too strongly to self molecules are eliminated. Spleen is where mature lymphocytes wait for antigens carried in the blood, not where T cells mature. Liver produces many blood proteins, including complement, but is not the site of T cell maturation. Lymph node is a site where mature lymphocytes meet antigens carried in lymph.
Category: Cell-Mediated Immunity
Question 12
During the humoral immune response, activated B cells divide and some of their daughter cells secrete large amounts of antibody. What are these antibody-secreting cells called?
Memory B cells
Helper T cells
Natural killer cells
Plasma cells
✓
Correct Answer
Plasma cells
Plasma cells are the effector cells of the humoral response and release enormous numbers of antibody molecules. Memory B cells stay inactive until the same antigen returns, then produce new plasma cells. Helper T cells release cytokines that activate B cells but do not make antibodies. Natural killer cells are innate lymphocytes that kill infected and cancerous cells.
Category: Humoral Immunity and Memory
Question 13
Helper T cells recognize processed antigen fragments only when the fragments are displayed on which molecules of an antigen-presenting cell?
MHC class II molecules
✓
MHC class I molecules
B cell receptors
Toll-like receptors
Correct Answer
MHC class II molecules
Antigen-presenting cells load fragments of engulfed pathogens onto MHC class II molecules, and helper T cells respond only to antigen held in this complex. MHC class I molecules are found on nearly all body cells and are checked by cytotoxic T cells and natural killer cells, not helper T cells. B cell receptors bind whole antigens on B cells and do not present fragments to T cells. Toll-like receptors detect general microbial patterns in innate immunity rather than displaying antigen.
Category: Cell-Mediated Immunity
Question 14
Which antigen-presenting cells live in the linings of the skin, lungs and intestine, capture antigens there and then travel to lymph nodes or the spleen?
Neutrophils
Dendritic cells
✓
Red blood cells
Mast cells
Correct Answer
Dendritic cells
Dendritic cells sit in tissues that contact the outside world, take up antigens and migrate to lymphoid organs to present them to T cells. Neutrophils engulf pathogens but are short-lived and do not carry antigens to lymph nodes for presentation. Red blood cells carry oxygen and have no role in antigen presentation. Mast cells remain in connective and mucosal tissues and release histamine rather than migrating to present antigens.
Category: Cell-Mediated Immunity
Question 15
In cell-mediated immunity, which cells are the main effectors that attack and destroy body cells infected with a virus?
Helper T cells
Regulatory T cells
Cytotoxic T cells
✓
Memory B cells
Correct Answer
Cytotoxic T cells
Cytotoxic T cells recognize infected cells and kill them, which matters for viruses because they replicate inside cells where antibodies cannot reach. Helper T cells coordinate the response by releasing cytokines but do not kill infected cells themselves. Regulatory T cells suppress immune responses to limit damage to the body. Memory B cells are humoral cells waiting for reexposure to an antigen.
Category: Cell-Mediated Immunity
Question 16
When antibodies coat a virus and block the surface sites it uses to infect host cells, what is this antibody function called?
Agglutination
Opsonization
Extravasation
Neutralization
✓
Correct Answer
Neutralization
Neutralization means antibodies cover the parts of a pathogen it needs for entry, so it can no longer infect cells. Agglutination is antibodies linking many antigen particles into clumps. Opsonization is tagging a pathogen so phagocytes engulf it more readily. Extravasation is the movement of white blood cells out of blood vessels, not an antibody function.
Category: Humoral Immunity and Memory
Question 17
Which situation gives a person passive immunity?
A fetus receives maternal antibodies across the placenta
✓
A child forms antibodies after a measles shot
An adult recovers from chickenpox
A booster shot raises a person's memory cell count
Correct Answer
A fetus receives maternal antibodies across the placenta
Passive immunity comes from antibodies made by another person or animal, such as maternal antibodies crossing the placenta, so protection is immediate but temporary. A child forms antibodies after a measles shot is active immunity because the child's own plasma cells make the antibodies. An adult recovers from chickenpox is also active immunity, produced by natural infection. A booster shot raises a person's memory cell count describes active immunity strengthened by repeated exposure.
Category: Humoral Immunity and Memory
Question 18
Compared with the primary immune response, how does the secondary response to the same antigen differ?
It starts slower and makes less antibody
It starts faster and makes far more antibody
✓
It starts faster but makes less antibody
It starts slower but makes more antibody
Correct Answer
It starts faster and makes far more antibody
Memory cells left over from the first exposure quickly become effector cells, so the secondary response begins sooner and produces much more antibody. It starts slower and makes less antibody describes neither response accurately. It starts faster but makes less antibody misses that antibody output rises sharply. It starts slower but makes more antibody misses that memory cells speed the response up.
Category: Humoral Immunity and Memory
Question 19
In myasthenia gravis, autoantibodies attack which target, causing muscle weakness?
Insulin-producing pancreatic cells
The body's own DNA
Acetylcholine receptors on muscle cells
✓
Heart muscle proteins
Correct Answer
Acetylcholine receptors on muscle cells
In myasthenia gravis, antibodies bind the muscle receptors that respond to acetylcholine, so nerve signals no longer trigger strong contraction. Insulin-producing pancreatic cells are destroyed in type 1 diabetes. The body's own DNA is a major target in systemic lupus erythematosus. Heart muscle proteins are damaged in rheumatic fever after a strep infection.
Category: Immune Disorders
Question 20
Antibodies made against Streptococcus pyogenes during strep throat can later damage heart muscle that has a similar structure. Which proposed cause of autoimmunity does this illustrate?
Immune tolerance
Passive immunity
Immunodeficiency
Molecular mimicry
✓
Correct Answer
Molecular mimicry
Molecular mimicry occurs when a self molecule resembles a pathogen molecule closely enough that immune responses against the pathogen also attack the body, as in rheumatic fever. Immune tolerance is the opposite outcome, the prevention of harmful responses to self. Passive immunity is protection from antibodies made by another individual. Immunodeficiency is a failed or weakened immune response, not a misdirected one.
Category: Immune Disorders