QCAA Biology Alternative Sequence Infectious disease and epidemiology
14 sample questions with marking guides and sample answers
Non-infectious diseases can be
bacterial.
inherited.
pathogenic.
vector-borne.
Reveal Answer
bacterial.
Incorrect. Bacterial diseases are caused by bacteria, which are living pathogens, making them infectious rather than non-infectious.
inherited.
Correct. Non-infectious diseases are not caused by pathogens and can be inherited through genetics, such as cystic fibrosis or sickle cell anemia.
pathogenic.
Incorrect. Pathogenic diseases are caused by pathogens (like viruses or bacteria) that invade the body, which is the exact definition of an infectious disease.
vector-borne.
Incorrect. Vector-borne diseases are transmitted by organisms like mosquitoes or ticks that carry infectious pathogens, meaning they are infectious diseases.
Identify a pathogen with adherence factors.
Reveal Answer
Bacteria
| Descriptor | Marks |
|---|---|
identifies a pathogen | 1 |
Describe adherence factors and how they aid in pathogenesis.
Reveal Answer
Adherence factors (adhesins) are proteins that are produced on the surface of a pathogen. These attach to receptors on the cell membrane of a host. This provides an access point into host cells and allows the pathogen to start invading the host cell/tissue and for disease to begin.
| Descriptor | Marks |
|---|---|
describes adherence factors | 1 |
describes the role of adherence factors in pathogenesis | 1 |
A pathogen enters its host through a break in the skin. Describe a subsequent physical change that occurs in the host and how it stimulates the non-specific immune response.
Reveal Answer
If a pathogen enters through a break in skin, like a cut, the blood vessels dilate, causing swelling. Phagocytes move into the area to enter damaged tissues and engulf pathogens.
| Descriptor | Marks |
|---|---|
Describes a physical change in the host | 1 |
Describes how the non-specific immune response is stimulated by this change | 1 |
Explain why neutrophils and macrophages are referred to as phagocytes, but B cells and T cells are not.
Reveal Answer
Phagocytes are cells that engulf and digest solid material by endocytosis. Neutrophils and macrophages engulf invading cells and digest them to control infections. Because they engulf pathogens by phagocytosis, they are a type of phagocyte.
B cells and T cells aren't phagocytes because they don't remove pathogens by phagocytosis; they secrete proteins and antibodies.
| Descriptor | Marks |
|---|---|
Identifies a characteristic of phagocytes | 1 |
Identifies a feature of neutrophils and macrophages that categorises them as phagocytes | 1 |
Explains how B and T cells do not fit the characteristics of a phagocyte | 1 |
Describe the adaptive immune response once a pathogen has bypassed the innate immune response.
Reveal Answer
Cells that belong in the body carry specific markers that identify them as self and tell the immune system not to attack them. Specific immune responses are triggered by antigens. Antigens are usually found on the surface of pathogens and are unique to that particular pathogen.
The immune system responds to antigens by producing cells that directly attack the pathogen, or by producing special proteins called antibodies.
| Descriptor | Marks |
|---|---|
Describes one aspect of the adaptive immune response in correct context | 1 |
Describes a second aspect of the adaptive immune response in correct context | 1 |
Describes a third aspect of the adaptive immune response in correct context | 1 |
Describes a fourth aspect of the adaptive immune response in correct context | 1 |
Describes a fifth aspect of the adaptive immune response in correct context | 1 |
Identify an example of each type of immunity.
Naturally acquired active immunity:
Naturally acquired passive immunity:
Artificially acquired active immunity:
Artificially acquired passive immunity:
Reveal Answer
Naturally acquired active immunity: Natural exposure to pathogen
Naturally acquired passive immunity: Antibodies through breastfeeding
Artificially acquired active immunity: Vaccination
Artificially acquired passive immunity: Serum injection
| Descriptor | Marks |
|---|---|
Identifies an example of naturally acquired active immunity | 1 |
Identifies an example of naturally acquired passive immunity | 1 |
Identifies an example of artificially acquired active immunity | 1 |
Identifies an example of artificially acquired passive immunity | 1 |
Plant immune responses
are non-specific in their reaction to plant diseases.
employ T cells, B cells and other antigen-presenting cells.
rely exclusively on physical barriers to prevent entry to pathogens.
are adaptive and can discriminate between fungi, bacteria and viruses.
Reveal Answer
are non-specific in their reaction to plant diseases.
Plant immune responses are primarily innate and non-specific, relying on the recognition of broad, conserved pathogen-associated molecular patterns (PAMPs) rather than highly specific antigens.
employ T cells, B cells and other antigen-presenting cells.
Plants do not possess specialized immune cells such as T cells, B cells, or antigen-presenting cells, which are unique to the adaptive immune system of vertebrates.
rely exclusively on physical barriers to prevent entry to pathogens.
While physical barriers like bark and waxy cuticles are a first line of defense, plants also rely heavily on active chemical defenses, antimicrobial compounds, and cellular responses like the hypersensitive response.
are adaptive and can discriminate between fungi, bacteria and viruses.
Plants lack an adaptive immune system; they do not undergo somatic recombination or produce memory cells to generate highly specific, long-lasting immunity to individual pathogen strains.
Describe how vectors transmit disease, using an example.
Reveal Answer
A vector such as a mosquito picks up the plasmodium that causes malaria from an infected host, then transfers it to a new host through biting them to feed.
| Descriptor | Marks |
|---|---|
identifies a specific example of a vector and disease | 1 |
identifies how the specific vector acquires the pathogen | 1 |
identifies how the specific vector transmits the pathogen | 1 |
Salmonella is a common bacterial infection that affects the intestinal tract. Salmonella bacteria typically live in animal and human intestines and are shed through faeces.
A cluster of human salmonella infections was identified in a regional centre. Many patients reported that they had contact with live poultry, primarily chickens. Since the poultry were from the same hatchery, it was determined that infections in the cluster were linked.
Identify and justify two practices to reduce the spread of salmonella infection and prevent further outbreaks.
Reveal Answer
Handwashing regularly to prevent the transfer of bacteria after touching the chickens, their bedding or coops.
Regular sanitation of cooking surfaces and implements, if poultry or related products (eggs) are being consumed, to remove bacterial contamination.
| Descriptor | Marks |
|---|---|
identifies a practice | 1 |
justifies this practice | 1 |
identifies a second practice | 1 |
justifies this practice | 1 |
What is a component of the innate immune response?
memory B cells
macrophages
antibodies
T cells
Reveal Answer
memory B cells
Incorrect. Memory B cells are part of the adaptive immune system, providing long-term immunity by remembering specific pathogens.
macrophages
Correct. Macrophages are phagocytic white blood cells that provide an immediate, non-specific defense, making them a key component of the innate immune system.
antibodies
Incorrect. Antibodies are highly specific proteins produced by B cells, which are part of the adaptive immune response.
T cells
Incorrect. T cells are lymphocytes that drive the cell-mediated adaptive immune response, rather than the non-specific innate response.
Explain the role of B lymphocytes in producing a humoral response to an antigen.
Reveal Answer
Antigens bind to receptors on the B lymphocyte. This stimulates the cell to clone itself. These clones can become plasma B cells, which can produce large numbers of antibodies to attack antigens. Cloned B cells can also become memory B cells, which are stored and ready to fight future infections by that antigen.
| Descriptor | Marks |
|---|---|
explains that antigens bind with receptors/antibodies on the B lymphocyte | 1 |
explains that antigen recognition by B lymphocyte triggers cloning of B lymphocyte | 1 |
explains that cloned B cells can become plasma B cells to release antibodies to attack antigens | 1 |
explains that cloned B cells can also become memory B cells, which are stored to respond to future infections | 1 |
Identify a similarity and a difference between passive and active immunity.
Reveal Answer
Passive immunity is the immunity gained from having antibodies transferred directly from an external source, whereas active immunity is the result of someone making their own antibodies. In both cases, the immunity result is the same — antibodies exist that offer a similar level of protection from an antigen.
| Descriptor | Marks |
|---|---|
Identifies a similarity | 1 |
Identifies a difference | 1 |
Identify a chemical defence strategy used by plants.
sharp thorns formed from modified branches
a small stomata size that prevents larger pathogens entering
a waxy cuticle on leaves to create an inhospitable environment for fungi
accumulated defensins in plant structures that inhibit fungal spore growth
Reveal Answer
sharp thorns formed from modified branches
Thorns are a physical or mechanical defense mechanism used to deter herbivores, not a chemical defense.
a small stomata size that prevents larger pathogens entering
Small stomata size acts as a structural or physical barrier to prevent pathogen entry, rather than a chemical defense.
a waxy cuticle on leaves to create an inhospitable environment for fungi
While made of chemical compounds, the waxy cuticle primarily serves as a physical surface barrier to block pathogen entry and prevent water loss.
accumulated defensins in plant structures that inhibit fungal spore growth
Defensins are antimicrobial peptides, which are active chemical compounds produced by the plant to inhibit the growth and spread of pathogens like fungi.
The complement system works in conjunction with
lymphocytes to produce antibodies.
prostaglandins to reduce inflammation.
the immune system to recognise self cells.
phagocytic cells to clear pathogens from an organism.
Reveal Answer
lymphocytes to produce antibodies.
The complement system does not produce antibodies; antibodies are produced by B lymphocytes (plasma cells) as part of the adaptive immune response.
prostaglandins to reduce inflammation.
The complement system actually promotes inflammation rather than reducing it, and prostaglandins are also typically pro-inflammatory mediators.
the immune system to recognise self cells.
While the complement system has regulatory proteins to prevent it from attacking self-cells, its primary function is to target and destroy foreign pathogens, not to recognize self-cells.
phagocytic cells to clear pathogens from an organism.
The complement system enhances the immune response by opsonizing pathogens, marking them for destruction and making it easier for phagocytic cells to engulf and clear them from the body.