Defence Against Disease

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Pathogens and Disease

A pathogen is any microorganism that causes disease in another organism.
Pathogens include bacteria, fungi, protists, and viruses; all viruses are pathogenic, while not all bacteria, fungi, and protists are.
Pathogens cause communicable (infectious) diseases that transfer from a diseased host to a healthy organism.
Examples of communicable diseases: tuberculosis, athlete's foot, malaria, cholera.
Non-communicable diseases are non-infectious, e.g., cancer, cardiovascular disease, malnutrition.
Careful observation of symptoms, incubation times, and transmission mechanisms is crucial to control the spread of disease.

Barriers to Pathogens: Skin and Mucous Membranes

The skin and mucous membranes form the primary defence against pathogens.
The skin provides a tough physical barrier that prevents pathogen entry; cuts are sealed by blood clots.
Sebum from sebaceous glands maintains a low skin pH, inhibiting microorganism growth.
Mucous membranes line airways, reproductive areas, and the digestive system, and contain goblet cells that produce mucus.
Mucus traps microorganisms and particles, which are swept by cilia to be swallowed and destroyed by stomach acid.
Mucus also contains lysozyme enzymes with antibacterial properties.

A cross-section of human skin

Blood Clotting

When the skin is cut, platelets form a temporary plug to stem bleeding.
Platelets release clotting factors that trigger a chemical cascade.
Clotting factors stimulate release of the enzyme thrombin.
Thrombin catalyses conversion of soluble fibrinogen into insoluble fibrin.
Fibrin forms a mesh that traps more platelets and blood cells, sealing the wound.
Exposure to air hardens the mesh to form a scab.

Composition of human blood

The Immune System: Innate vs Adaptive

The innate immune system recognises any non-self item (e.g., bacteria, fungi, viruses, pollen) via non-self antigens.
Innate responses are non-specific and do not change during an individual's lifetime; phagocytes carry out this response.
The adaptive immune system responds to specific non-self antigens and involves antibody production and memory cells.
On first exposure, the adaptive response is slow; on second exposure, it is faster and produces more antibodies.
Immunological memory develops over a lifetime as exposure to different pathogens occurs.
Vaccination uses the adaptive immune system to speed up the response on later exposure.

Lymphocytes and antibodies

White Blood Cells

Phagocytes are white blood cells produced in bone marrow; they remove dead cells and pathogens non-specifically.
Phagocytes move by amoeboid movement, engulf pathogens by endocytosis, and digest them using lysosomal enzymes.
Lymphocytes are white blood cells involved in specific immune responses; two types: T cells and B cells.
T cells mature in the thymus and have T cell receptors specific to particular antigens.
T cells are activated when they bind to their specific antigen on an antigen-presenting cell (e.g., macrophage, infected cell).
Activated T cells divide by mitosis to form clones with identical receptors.
B cells mature in bone marrow and have antibody receptors on their surface; each B cell binds a different antigen.
When a B cell binds its specific antigen, it forms an antigen-antibody complex and is activated by T helper cell signalling.

Phagocytosis

Adaptive Immune Response

Antigens are molecules that trigger an immune response; they are found on cell surface membranes, cancer cells, bacterial cell walls, virus envelopes, and pollen grains.
The immune system distinguishes self from non-self based on antigens.
Red blood cells have antigens determining blood group: ABO and Rhesus (Rh) markers.
Blood type A has N-acetylgalactosamine modification; type B has galactose; type AB has both; type O has neither.
Incompatible blood transfusion triggers immune response, causing agglutination (clumping) of red blood cells, which can be fatal.
T-helper cells bind to antigens on antigen-presenting cells and become activated.
Activated T-helper cells bind to complementary B cells and release signalling proteins to activate them.
Activated B cells undergo clonal expansion, producing plasma cells (secrete antibodies) and memory cells (provide immunity).

HIV and AIDS

HIV is a retrovirus with RNA and reverse transcriptase; it cannot survive outside the human body.
HIV is transmitted by direct exchange of body fluids: sexual intercourse, blood donation, sharing needles, mother to child (placenta, birth, breast milk).
HIV infects and attacks T-helper cells, which are key for antibody production.
Early infection: antibodies produced against HIV can be detected; individual is HIV positive.
Progression: reduced antibody production leads to opportunistic infections; when multiple diseases occur, it is AIDS.
Anti-retroviral drugs can slow progression, allowing many HIV-positive individuals to live full lives with normal life expectancies.
HIV is the virus; AIDS is the syndrome it causes.

How HIV infects a lymphocyte

Antibiotics and Antibiotic Resistance

Antibiotics inhibit growth of microorganisms, mostly bacteria, by targeting prokaryotic processes (transcription, translation, DNA replication, ribosome function, cell wall formation).
Penicillin is produced by fungi of the genus×Penicillium×and interferes with bacterial cell wall production.
Antibiotics are ineffective against viruses because viruses are non-living particles with no metabolism or cell structure.
Antibiotic resistance arises from random mutations; resistant bacteria survive treatment and reproduce, passing on resistance alleles.
This is evolution by natural selection; overuse of antibiotics exerts selective pressure.
MRSA (methicillin-resistant×Staphylococcus aureus×) is resistant to multiple antibiotics.
Measures to avoid resistance: avoid antibiotics for non-bacterial infections, maintain hygiene, minimise agricultural use, develop new antibiotics.

How penicillin works

Zoonoses

Zoonotic diseases cross the species barrier from animals to humans.
Species specificity may be due to lack of necessary receptors or body temperature differences.
Zoonoses are a growing global concern due to close human-animal relationships and potential for pandemics (e.g., COVID-19).
Some zoonotic diseases can emerge from animal populations and develop into human-only strains (e.g., HIV).

Vaccines and Immunity

A vaccine contains antigens or DNA/RNA coding for antigens, inducing immunity without causing disease.
Types: live attenuated (weakened pathogen) and inactivated (killed components or antigens alone).
Vaccines are administered by injection or orally; they trigger a primary immune response and produce memory cells.
On re-exposure, memory cells produce a faster, stronger secondary response with more antibodies.
Herd immunity occurs when a large percentage of the population is vaccinated, protecting unvaccinated individuals.
Herd immunity prevents epidemics and pandemics; vaccination programmes can eradicate diseases (e.g., smallpox eradicated in 1980).

How a vaccine produces immunity

Evaluating COVID-19 Data: Skills

Percentage difference compares two directly comparable values at the same time: (difference / average) × 100.
Percentage change compares values from the same data set at different times: (change / original value) × 100.
If original value is larger, change is a percentage decrease; if smaller, a percentage increase.
Example: Europe had 18,392 cases in mid-July 2023 vs 1,584 in South-East Asia; percentage difference = 168.3%.
Example: Europe had 38,950 cases in mid-June 2023 and 18,392 in mid-July 2023; percentage change = -52.8% (decrease).

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Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 56 câu hỏi. Đăng ký để xem tất cả.

1.Which component of blood has a role in preventing pathogens from entering the body?
Easy
- ARed blood cells
- BBlood plasma
- CPlatelets
- DWhite blood cells
2.What is the principal purpose of sebum secretions onto the surface of the skin?
Easy
- ATo prevent microorganisms from sticking to the skin.
- BTo lower skin pH, which slows down the growth rate of microorganisms.
- CTo provide a surface texture to the skin that aids the evaporation of sweat.
- DTo assist in the formation of blood clots as a way of sealing wounds after a cut or graze.
3.Which phrase best fits into the gap in the following sentence? The shape of antibody molecules gives each one a particular 3-D configuration. This allows each antibody to be ______________ each individual pathogen.
Easy
- A...well suited to...
- B...specific to...
- C...functional against...
- D...the same shape as...
4.Which of the following are considered primary defence against infectious disease?
Easy
- ASkin and mucous membranes.
- BHair and skin.
- CPhagocytes and fever.
- DLymphocyte production of antibodies.
5.Which of these statements correctly describes a lymphocyte?
Easy
- AThey have many mitochondria to produce ATP to allow endocytosis of pathogens.
- BThey have many lysosomes containing hydrolytic enzymes to digest pathogens.
- CThey provide specific defence against disease-causing organisms.
- DThey are white blood cells with a lobed nucleus.
6.What is adaptive immunity?
Easy
- ATreating a specific disease through use of antibiotics.
- BProduction of monoclonal antibodies.
- CProduction of antibodies by lymphocytes.
- DEndocytosis of pathogens by phagocytes.
7.Which of the following is not a contributing factor towards the development of antibiotic resistance in bacteria?
Easy
- AStopping a course of antibiotics once symptoms improve.
- BDevelopment of new antibiotics.
- CNatural selection which favours mutations in bacteria.
- DOveruse of antibiotics in agriculture.
8.When a B-lymphocyte is activated by an antigen, what action is taken?
Medium
- AIt engulfs the infected body cell which displays a complementary antigen.
- BIt secretes signalling proteins that stimulate T-lymphocytes to produce plasma cells.
- CIt divides repeatedly to form clones of genetically identical plasma cells.
- DIt attaches to the infected cell displaying the antigen and destroys it.

Thêm câu hỏi

9.Which type of molecule is most important to directly identify a cell as non-self?
Medium
- AProteins
- BPhospholipids
- CCarbohydrates
- DNucleic acids
10.A child is given a vaccine for a viral disease. A few months later she is in contact with the same virus. What is the expected response to the second contact with the virus?
Medium
- AIncreased number of T-lymphocytes.
- BLarge numbers of antibodies are released.
- CLarge numbers of antigens are released.
- DIncreased number of B-lymphocytes.
11.Which of the following are ways in which HIV can be transmitted? (select all that apply)
Medium
- ASexual intercourse
- BBlood donation
- CSharing of needles used by intravenous drug users
- DFrom mother to child across the placenta
- EAirborne droplets from coughing
12.The innate immune system is able to recognise and respond to any item that enters the body that is 'non-self'.
Easy
True or false?
13.Antibiotics are effective against viruses because they target viral enzymes.
Easy
True or false?
14.Match each white blood cell type with its correct description.
Medium
- Phagocyte
- T cell
- B cell
- Engulfs and digests pathogens by endocytosis
- Matures in the thymus and has T cell receptors
- Matures in the bone marrow and has antibody receptors
15.Place the events of phagocytosis in the correct order.
Medium
- Phagocyte membrane extends out
- Endocytosis
- Vacuole formation
- Enzymatic digestion
16.Scientists use theories to explain observed phenomena. Which combination of observed phenomenon and explanation shows how scientists developed the theory that explains antibiotic resistance in bacteria?
Medium
- AObserved: Resistance to an antibiotic appears soon after an antibiotic is first used. Explanation: Bacteria respond to a new antibiotic by developing resistance.
- BObserved: Resistance to an antibiotic appears soon after an antibiotic is first used. Explanation: Bacteria with alleles that provide resistance to the antibiotic survive treatment and pass on their alleles.
- CObserved: Bacteria with alleles that provide resistance to the antibiotic survive treatment and pass on their alleles. Explanation: The frequency of resistant alleles increases in a bacterial population.
- DObserved: Antibiotic resistance in bacteria is on the increase in hospitals. Explanation: Patients in hospitals are more susceptible to infection than the general population.
17.Which of the following statements correctly describes a zoonotic disease?
Medium
- AA disease that can cross the species barrier from animal to human.
- BA disease that only affects humans.
- CA disease caused by a virus that infects only birds.
- DA disease that is transmitted by a vector.
18.Which of the following correctly describes the primary immune response?
Medium
- AIt occurs immediately upon first exposure to an antigen and produces a large amount of antibodies.
- BIt occurs slowly upon first exposure to an antigen and leads to the production of memory cells.
- CIt occurs rapidly upon second exposure to an antigen and produces a large amount of antibodies.
- DIt is a non-specific response involving phagocytes.
19.Which of the following is the correct sequence of events in blood clot formation?
Medium
- AProthrombin → Thrombin → Fibrin → Fibrinogen
- BClotting factors → Thrombin → Fibrinogen → Fibrin
- CFibrin → Fibrinogen → Thrombin → Clotting factors
- DClotting factors → Thrombin → Fibrin → Fibrinogen
20.Which of the following is not a component of the innate immune system?
Easy
- APhagocytes
- BAntibody production by plasma cells
- CSkin
- DMucous membranes
21.Which of the following are measures that can help to avoid antibiotic resistance? (select all that apply)
Medium
- AAvoiding prescription of antibiotics for non-serious or non-bacterial infections
- BMaintaining high standards of hygiene in the hospital environment
- CMinimising use of antibiotics for routine treatment of animals in agriculture
- DDevelopment of new types of antibiotic
- EIncreasing the use of broad-spectrum antibiotics
22.All viruses are pathogenic.
Easy
True or false?
23.What is the role of memory cells in the immune system?
Medium
- AThey engulf and digest pathogens.
- BThey produce antibodies immediately upon first exposure to an antigen.
- CThey remain in the blood and allow a faster immune response to the same pathogen in the future.
- DThey present antigens to T-helper cells.
24.Which of the following statements about HIV/AIDS is correct?
Medium
- APeople infected with HIV will always show symptoms immediately.
- BPeople infected with HIV can be completely cured with antibiotics.
- CPeople infected with HIV may live for many years after infection.
- DHIV is transmitted by a vector.
25.Which of the following is the correct order of events in the adaptive immune response?
Medium
- AT-helper cell activation → B cell activation → clonal expansion → antibody production
- BB cell activation → T-helper cell activation → clonal expansion → antibody production
- CClonal expansion → T-helper cell activation → B cell activation → antibody production
- DAntibody production → B cell activation → T-helper cell activation → clonal expansion
26.What is herd immunity?
Medium
- AImmunity acquired through natural infection.
- BProtection of the entire population when a large enough percentage is vaccinated.
- CImmunity passed from mother to child.
- DImmunity produced by antibiotics.
27.Which of the following best explains why antibiotics are ineffective against viruses?
Hard
- AViruses are too small for antibiotics to target.
- BViruses have no metabolism or cell structure and use host cell mechanisms.
- CViruses have a protein coat that antibiotics cannot penetrate.
- DViruses are living cells that are resistant to antibiotics.
28.Which of the following is a non-communicable disease?
Easy
- ATuberculosis
- BAthlete's foot
- CMalaria
- DCancer
29.What is the role of T-helper cells in the immune response?
Medium
- AThey produce antibodies.
- BThey engulf pathogens.
- CThey activate B cells and stimulate them to divide.
- DThey directly kill infected cells.
30.Which of the following is a characteristic of the innate immune system?
Medium
- AIt is specific to a particular antigen.
- BIt responds the same way to any non-self antigen.
- CIt produces memory cells.
- DIt involves antibody production by plasma cells.
31.Which of the following statements about vaccines is correct?
Medium
- AVaccines contain live pathogens that cause disease.
- BVaccines induce immunity by introducing antigens without causing disease.
- CVaccines provide immediate immunity without memory cells.
- DVaccines are only effective against bacterial diseases.
32.Memory cells are produced during the primary immune response.
Easy
True or false?
33.What is the function of antibodies in the immune response?
Medium
- ATo engulf pathogens.
- BTo directly kill pathogens.
- CTo bind to specific antigens and neutralise or agglutinate pathogens.
- DTo produce memory cells.
34.Which of the following best describes the secondary immune response?
Hard
- AIt is slower and produces fewer antibodies than the primary response.
- BIt is faster and produces more antibodies than the primary response.
- CIt occurs only after vaccination.
- DIt is non-specific.
35.Which of the following is a zoonotic disease?
Medium
- AMalaria
- BCOVID-19
- CCholera
- DAthlete's foot
36.Match each barrier defence with the correct description.
Medium
- Sebum
- Mucus
- Lysozyme
- Cilia
- Antibacterial enzyme found in mucus
- Lowers skin pH to inhibit microorganism growth
- Traps microorganisms and particles in the airways
- Sweeps mucus upwards to be swallowed
37.Place the events of blood clotting in the correct order.
Medium
- Clotting factors stimulate the release of thrombin
- Thrombin catalyses the conversion of fibrinogen to fibrin
- Fibrin forms a mesh that traps platelets and blood cells
- Exposure to air hardens the mesh to form a scab
38.Which of the following are functions of antibodies? (select all that apply)
Medium
- ANeutralisation of toxins
- BAgglutination of bacteria
- CIncreased susceptibility to phagocytosis
- DDirect destruction of viruses by enzymes
- EProduction of memory cells
39.Which of the following is the correct sequence of events in the adaptive immune response?
Medium
- AAntigen presentation → T-helper activation → B-cell activation → clonal expansion → antibody production
- BB-cell activation → T-helper activation → antigen presentation → clonal expansion → antibody production
- CClonal expansion → antigen presentation → T-helper activation → B-cell activation → antibody production
- DAntigen presentation → B-cell activation → T-helper activation → clonal expansion → antibody production
40.Which of the following are modes of HIV transmission? (select all that apply)
Medium
- ASexual intercourse
- BSharing needles for intravenous drug use
- CFrom mother to child across the placenta
- DCasual contact such as hugging
- EBlood donation
41.What name is given to any microorganism that causes disease in another organism?
Easy
42.In mid-July 2023, Europe had 18 392 confirmed cases of COVID-19, while South-East Asia had 1 584 confirmed cases. Calculate the percentage difference between the number of confirmed cases in Europe and South-East Asia. Give your answer to one decimal place.
Medium
43.Complete the sentence about blood clotting.
Easy
Thrombin catalyses the conversion of the soluble protein ____ into ____, which is insoluble.
44.Complete the sentence about HIV.
Medium
HIV is a ____ virus, meaning it uses the enzyme reverse transcriptase to produce DNA from its RNA genome.
45.What is the name of the process by which a phagocyte engulfs a pathogen?
Easy
46.In mid-June 2023, Europe had 38 950 confirmed cases of COVID-19, while in mid-July 2023, it had 18 392 cases. Calculate the percentage change in COVID-19 cases in Europe between June and July 2023. Give your answer to one decimal place.
Hard
47.Complete the sentence about mucous membranes.
Medium
Mucus contains ____ enzymes which have antibacterial properties.
48.Complete the sentence about zoonotic diseases.
Easy
Zoonotic diseases are those which can cross the species barrier from ____ to ____.
49.In mid-July 2023, Europe had 18,392 confirmed COVID-19 cases, while South-East Asia had 1,584 confirmed cases. Calculate the percentage difference between the number of confirmed cases in Europe and South-East Asia. Give your answer to one decimal place.
Medium
50.In mid-June 2023, Europe had 38,950 confirmed COVID-19 cases, while in mid-July 2023, it had 18,392 cases. Calculate the percentage change in COVID-19 cases in Europe between June and July 2023. Give your answer to one decimal place.
Medium
51.Explain how the skin and mucous membranes act as barriers to pathogens.
Medium
52.Explain how antibiotic resistance develops in a population of bacteria.
Hard
53.In mid-July 2023, Europe had 18 392 confirmed cases of COVID-19, while South-East Asia had 1 584 confirmed cases. Calculate the percentage difference between the number of confirmed cases in Europe and South-East Asia. Give your answer to one decimal place.
Medium
- A168.3 %
- B201.9 %
- C185.1 %
- D151.5 %
54.In mid-June 2023, Europe had 38 950 confirmed cases of COVID-19, while in mid-July 2023, it had 18 392 cases. Calculate the percentage change in COVID-19 cases in Europe between June and July 2023. Give your answer to one decimal place.
Hard
- A-47.5 %
- B-52.8 %
- C-58.1 %
- D-42.2 %
55.In mid-July 2023, Europe had 18,392 confirmed COVID-19 cases, while South-East Asia had 1,584 confirmed cases. Calculate the percentage difference between the number of confirmed cases in Europe and South-East Asia. Give your answer to one decimal place.
Medium
- A151.5 %
- B201.9 %
- C168.3 %
- D185.1 %
56.In mid-June 2023, Europe had 38,950 confirmed COVID-19 cases, while in mid-July 2023, it had 18,392 cases. Calculate the percentage change in COVID-19 cases in Europe between June and July 2023. Give your answer to one decimal place.
Medium
- A47.5 %
- B58.1 %
- C63.4 %
- D52.8 %

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