Communicable diseases

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What Are Communicable Diseases?

Communicable diseases are caused by microorganisms called pathogens and can spread between individuals, or between individuals and animals.
Examples include chickenpox, caused by the varicella-zoster virus, and Covid-19, caused by the SARS-CoV-2 virus.
Non-communicable diseases are not caused by pathogens and cannot be passed between individuals; examples are asthma, coronary heart disease (CHD) and most cancers.
Non-communicable diseases tend to have longer-lasting effects, and the risk of developing them can be increased by factors such as diet, stress and life situations.
If an individual suffers from one disease, they are likely to be more susceptible to others because the immune system may be compromised or diseases may interact.

Types of Pathogen

A pathogen is any microorganism that causes disease in another organism, such as in plants or animals.
The main groups of pathogens are bacteria, fungi, protists and viruses.
Not all species within these groups are pathogens — many bacteria, fungi and protists are harmless — but all viruses are pathogenic because they can only exist by living inside the living cells of other organisms.
Pathogenic bacteria are small, reproduce very quickly, and may remain within body cavities or spaces; the toxins they produce also damage cells.
Pathogenic fungi can be single-celled or multicellular (with threads of hyphae) and produce spores that allow them to infect other organisms; fungal diseases are much more common in plants than in animals.
Pathogenic protists are parasites that need a host to survive; only a small number are pathogenic, but the diseases they cause are often serious.

Pathogen groups

How Viruses Reproduce

Viruses are not usually classified as living organisms because they do not carry out the eight life processes for themselves.
Viruses are small particles (always smaller than bacteria), are parasitic, and can only reproduce inside living cells.
They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA.
In the lytic pathway, the virus injects its DNA into the host cell, uses the host's proteins and enzymes to produce new virus particles, and then the cell bursts, releasing the virus particles.
In the lysogenic pathway, the viral DNA becomes incorporated into the host DNA and replicates as the host cell replicates, but no new virus particles are made while the virus is dormant.
Changes in the environment (e.g. a chemical trigger) can cause the viral DNA to move to the lytic pathway to make new virus particles.

Lytic replication of a virus

Common Infections

Mycobacterium tuberculosis causes tuberculosis (TB) in humans; the bacteria infect the lungs, causing a chronic cough and bloody mucus, and the disease is often associated with poor hygiene and sanitation.
Vibrio cholerae causes cholera; the bacteria infect the intestines, causing diarrhoea, vomiting and leg cramps, and it can lead to death if not treated quickly.
Helicobacter pylori causes stomach ulcers; infection commonly occurs during childhood and often gives no symptoms, but can lead to abdominal pain, loss of appetite, bloating and nausea.
Chlamydia trachomatis causes chlamydia, a sexually transmitted infection that may cause no symptoms or pain when urinating, unusual discharge or bleeding after sex; it can cause infertility if left untreated.
Chalara ash dieback is a fungal infection that affects ash trees of all ages, causing dark patches on the leaves, early leaf loss and bark lesions; its spores travel large distances in the wind.
Plasmodium falciparum is a protist that causes severe forms of malaria in humans; it is spread by mosquitoes and causes damage to the blood and the liver.

Examples of communicable infection

Human Physical Barriers

The human body's first line of defence includes physical barriers — structures that make it difficult for pathogens to get past them and into the body.
Skin covers almost all parts of the body to prevent infection; if it is cut or grazed, it immediately begins to heal itself, often by forming a scab.
Hairs and mucus in the nose make it difficult for pathogens to get further up the nose so they are not inhaled into the lungs.
Mucus and cilia in the trachea and bronchi trap pathogens; cilia are microscopic hair-like structures that waft mucus up to the back of the throat so it can be removed from the body by coughing, blowing the nose or swallowing.

First-line defences against pathogens

Human Chemical Barriers

Chemical barriers are substances produced by body cells that trap or kill pathogens before they can get further into the body and cause disease.
Stomach acid contains hydrochloric acid which is strong enough to kill pathogens that have been swallowed in mucus, food or water.
Lysozymes are enzymes produced by the eyes and released in tears that break down and kill bacteria on or around the eye.
Natural bacterial flora in the gut and vagina protect against infection from pathogenic bacteria by outcompeting the pathogen.
Sebum on the surface of the skin kills bacterial and fungal pathogens.

Non-Specific Immune Response

White blood cells are part of the body's immune system and defend against pathogenic microorganisms.
There are two main types of white blood cell: phagocytes, which carry out phagocytosis, and lymphocytes, which produce antibodies and antitoxins.
Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells; once they encounter a pathogen, they engulf it and release digestive enzymes to digest it.
This is a non-specific immune response because the response is the same for any pathogenic cell.
Phagocytes can be recognised under the microscope by their multi-lobed nucleus and granular cytoplasm.

Phagocytosis

Specific Immune Response

B-lymphocytes can be recognised under the microscope by their large round nucleus, which takes up nearly the whole cell, and their clear, non-granular cytoplasm.
B-lymphocytes produce antibodies, which are Y-shaped proteins with a shape that is specific (complementary) to the antigens on the surface of a pathogen.
This is a specific immune response because the antibodies produced will only fit one type of antigen on a pathogen.
Antibodies attach to antigens and cause agglutination (clumping together), meaning the pathogenic cells cannot move very easily.
At the same time, chemicals are released that signal to phagocytes that there are cells present that need to be destroyed.
Lymphocytes also produce antitoxins to neutralise toxins released by pathogens; these are specific to specific pathogens.

Specific immune response

Response to Infection and Memory Cells

The pathogen enters the bloodstream and multiplies; a release of toxins (in the case of bacteria) and infection of body cells causes symptoms in the patient.
Phagocytes that encounter the pathogen recognise it as invading and engulf and digest it (non-specific response).
Eventually, the pathogen encounters a B-lymphocyte which recognises its antigens; the lymphocyte starts to produce specific antibodies and clones itself to produce lots of lymphocytes all producing the specific antibody required.
Antibodies cause agglutination of pathogens, and phagocytes engulf and digest the agglutinated pathogens.
After the patient has recovered, they retain antibodies specific to the disease as well as memory cells (lymphocytes that recognise the pathogen).
If the patient encounters the same pathogen again, it triggers a secondary immune response: memory cells can produce much larger quantities of the required antibody in a much shorter time to fight off the pathogen before symptoms occur.

Vaccination

Vaccines are used to induce immunity to infectious diseases and contain harmless versions of a pathogen.
Harmless pathogens can be produced by killing the pathogen, making the pathogen unable to grow or divide (attenuated vaccine), or using fragments of pathogens that include the necessary antigens.
A vaccine may be administered orally, nasally or via an injection.
Once in the bloodstream, the antigens in the vaccine trigger an immune response: lymphocytes recognise the antigens, produce antibodies specific to the antigen encountered, and memory cells and antibodies remain circulating in the bloodstream.
Future infection by the same pathogen triggers a response that is much faster and much larger compared to the initial response, so the pathogen is unable to cause disease and the individual is said to be immune.
Vaccines protect the vaccinated individual and reduce the likelihood that an infected individual will spread the pathogen to others; if a large proportion of the population is vaccinated, it is unlikely that an unvaccinated individual will become infected — this is herd immunity.
Vaccines have reduced cases of certain diseases drastically or even eradicated many diseases worldwide, including smallpox, measles, mumps and tetanus.
Disadvantages of vaccination include mutations in the pathogen's DNA/RNA changing the antigen so lymphocytes no longer recognise the pathogen, vaccination not always giving immunity, and side-effects reducing uptake in the population.

Vaccination and long-term immunity

Plant Defence Responses

Plants have a range of defence mechanisms against infections and infestations, split into chemical and physical defences.
Chemical defences prevent herbivores from eating plants and include antiseptics or antimicrobial enzymes, chemical poisons to deter pests, and mechanisms to attract other insects as a biological control.
These same chemicals can sometimes be used to treat human diseases; for example, chemicals with antimicrobial properties can be extracted for human use such as in antibiotics.
Herbal face creams can use plant extracts such as tea tree oil, mint and witch hazel to have an antibacterial effect, and the pain relief drug aspirin originated from the bark of willow trees.
Physical defences include the cellulose cell wall, which provides support and protection from microorganisms, and the waxy cuticle of leaves and stems, which acts as a barrier to microbes; the only place microbes can enter a leaf is through the stomata.
Bark provides a tough layer around the stem to prevent pathogens from entering, and as deciduous trees lose leaves in winter the infection can be taken with them.
Thorns or hairy stems make it more difficult for pests to access plant tissue to feed.

Detecting and Identifying Plant Diseases

Plants can be infected with a range of bacterial and viral pathogens, such as tobacco mosaic virus (TMV) and rose black spot fungus, and can also be infested with insects such as aphids.
Aphids pierce the surface of the stem and feed off the sap in the phloem, causing physical damage and weakening the plant.
The symptoms of plant diseases can apply to more than one disease, which makes identifying them difficult.
In the field, studies of plant species in their natural environment might highlight the presence of certain diseases; observations by plant pathologists identify diseases based on symptoms.
It is important to determine whether a symptom is due to a proposed disease or an environmental issue such as mineral ion deficiency.
Assessing the distribution of plant populations may indicate what type of pathogen is involved and/or how it is being transmitted; patches of diseased plants may suggest infection through the soil, while random distributions may suggest airborne transmission such as the spores that cause Chalara ash dieback.
In the laboratory, ecologists may take cuttings of plants for chemical analysis, and culturing the pathogen from the sample may lead to accurate identification of the disease.
Monoclonal antibodies are antibodies specific to the antigens on the pathogen; if the antigen is present in the infected plant sample, the antibodies bind to them and allow accurate diagnosis, and DNA analysis can identify the specific pathogen causing the problem.

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1.Which organelle controls the activities of a white blood cell?
Easy
- AMitochondrion
- BRibosome
- CChromosome
- DNucleus
2.Which type of white blood cell produces antibodies?
Easy
- APhagocyte
- BLymphocyte
- CRed blood cell
- DPlatelet
3.Which of the following is a chemical barrier in the human body?
Easy
- ASkin
- BMucus in the nose
- CStomach acid
- DCilia in the trachea
4.Which of the following is a physical defence that helps protect a plant from pathogens?
Medium
- AProduction of poisons
- BWaxy cuticle on the leaf
- CRelease of antimicrobial enzymes
- DAttracting predatory insects
5.Which of the following is a reason why identifying plant diseases based solely on symptoms can be challenging?
Medium
- ASymptoms are always unique to a specific disease
- BMultiple diseases can exhibit similar symptoms
- CPlants do not show symptoms of diseases
- DIdentifying diseases based on symptoms is an easy process
6.Which type of pathogen causes Chalara ash dieback?
Medium
- ABacterium
- BVirus
- CFungus
- DProtist
7.Which of the following are physical barriers that help defend the human body against pathogens? (select all that apply)
Medium
- ASkin
- BHairs and mucus in the nose
- CLysozymes in tears
- DMucus and cilia in the trachea and bronchi
- EStomach acid
8.Antibodies are Y-shaped proteins that are specific to the antigens on the surface of a pathogen.
Easy
True or false?

Mehr Fragen

9.Memory cells are a type of lymphocyte that remain in the body after an infection and can respond quickly to a future infection by the same pathogen.
Easy
True or false?
10.Match each plant defence to the correct description.
Medium
- Cellulose cell wall
- Waxy cuticle
- Bark
- Tough layer of dead cells around the stem
- Barrier around the outside of the leaf
- Provides support and protection from microorganisms
11.Place the stages of the specific immune response in the correct order.
Medium
- Pathogen enters the bloodstream and multiplies
- Phagocytes engulf and digest the pathogen
- A B-lymphocyte recognises the pathogen's antigens
- Lymphocytes produce antibodies specific to the pathogen
- Antibodies cause agglutination of pathogens
12.Which of the following are chemical barriers that help defend the human body against pathogens? (select all that apply)
Medium
- AStomach acid
- BLysozymes in tears
- CSebum on the skin
- DHairs in the nose
- EMucus in the trachea
13.Which of the following are ways of identifying plant diseases in the laboratory? (select all that apply)
Medium
- ADNA analysis
- BMonoclonal antibodies
- CObservations by plant pathologists
- DAssessing plant population distribution
- ETaking cuttings for chemical analysis
14.Match each disease with the correct type of pathogen that causes it.
Medium
- Chalara ash dieback
- Malaria
- Tobacco mosaic virus
- Virus
- Fungus
- Protist
15.A gardener notices that the leaves of one of his rose plants are falling off and those remaining are covered in black and purple spots with some areas of decay. Which pathogen causes these symptoms?
Medium
- ARose black spot fungus
- BTobacco mosaic virus
- CChalara ash dieback fungus
- DAphid infestation
16.Plants infested with aphids often show signs of magnesium deficiency. Which symptom would you expect to see?
Medium
- AYellowing of leaves (chlorosis)
- BDark patches on leaves
- CBark lesions on the stem
- DExcessive leaf growth
17.Aphids feed on plant sugars and carry pathogens. Which part of the plant do aphids pierce to feed?
Medium
- AThe phloem
- BThe xylem
- CThe stomata
- DThe waxy cuticle
18.Which of the following are ways of identifying plant diseases in the laboratory? (Select all that apply.)
Medium
- ADNA analysis
- BUsing monoclonal antibodies
- CObserving symptoms in the field
- DTaking cuttings for chemical analysis
- EAssessing plant population distribution
19.Monoclonal antibodies used to identify plant diseases are specific to the antigens on the pathogen.
Easy
True or false?
20.A student views a white blood cell using a light microscope. The cell appears 30 mm wide on the image, and the actual width of the cell is 15 μm. What is the magnification of the image?
Medium
- A2000
- B2
- C500
- D0.5
21.An ecologist takes cuttings from a diseased plant and returns them to the laboratory. Which technique would allow accurate identification of the specific pathogen by detecting its antigens?
Medium
- AUsing monoclonal antibodies that are specific to the pathogen's antigens
- BObserving the plant's symptoms with the naked eye
- CMeasuring the plant's rate of photosynthesis
- DAssessing the distribution of diseased plants in the field
22.Which of the following statements about the specific immune response are correct? (select all that apply)
Hard
- AAntibodies cause agglutination of pathogens so they cannot move easily
- BLymphocytes clone themselves to produce many cells making the same specific antibody
- CPhagocytes produce antibodies that are specific to one antigen
- DAntitoxins are proteins that neutralise toxins released by pathogens
- EMemory cells are formed before the first exposure to a pathogen
23.The waxy cuticle on a leaf acts as a physical barrier to microbes; the only place pathogens can enter the leaf is through the stomata.
Easy
True or false?
24.Match each human defence with its correct description.
Medium
- Lysozymes in tears
- Stomach acid
- Sebum on skin
- Natural bacterial flora in the gut
- Enzymes that break down and kill bacteria on or around the eye
- Hydrochloric acid that kills pathogens swallowed in food or water
- Kills bacterial and fungal pathogens on the skin surface
- Outcompetes pathogenic bacteria in the gut
25.Compare the antibody response after the first injection with the antibody response after the second injection.
Medium
- AThe second response is faster and produces a greater concentration of antibodies.
- BThe second response is slower and produces fewer antibodies.
- CBoth responses are identical in speed and concentration.
- DThe first response produces more antibodies than the second.
26.A gardener notices that the leaves of a rose plant are falling off and those remaining are covered in black and purple spots with some areas of decay. Which pathogen is most likely to cause these symptoms?
Hard
- AA fungus
- BA virus
- CA bacterium
- DAn aphid
27.Aphids feed on plant sugars and carry pathogens. Which of the following is a likely consequence of aphid infestation?
Hard
- AReduced growth due to physical damage and nutrient loss
- BIncreased photosynthesis due to sugar removal
- CEnhanced immunity to fungal diseases
- DImproved water uptake through the roots
28.Which of the following is the correct definition of a pathogen?
Easy
- AA microorganism that causes disease in another organism
- BA chemical produced by the body to kill bacteria
- CA type of white blood cell that engulfs pathogens
- DA protein that neutralises toxins produced by bacteria
29.Which of the following pathogens are always pathogenic?
Easy
- ABacteria
- BFungi
- CProtists
- DViruses
30.All bacteria are pathogens.
Easy
True or false?
31.Which of the following is a physical barrier in the human body?
Medium
- AStomach acid
- BSebum on the skin
- CCilia in the trachea
- DNatural bacterial flora in the gut
32.Which of the following statements about phagocytes is correct?
Medium
- AThey produce antibodies specific to antigens.
- BThey engulf and digest pathogens by phagocytosis.
- CThey produce antitoxins to neutralise toxins.
- DThey remain in the body as memory cells after an infection.
33.Which of the following describes the role of antibodies?
Medium
- AThey engulf and digest pathogens.
- BThey neutralise toxins produced by bacteria.
- CThey cause agglutination of pathogens, clumping them together.
- DThey remain in the body to provide long-term immunity.
34.Which of the following statements about antitoxins is correct?
Medium
- AThey are produced by phagocytes.
- BThey are specific to particular pathogens.
- CThey cause agglutination of pathogens.
- DThey are found on the surface of pathogens.
35.Which of the following is a correct difference between antigens and antibodies?
Medium
- AAntigens are proteins made by lymphocytes; antibodies are molecules on the surface of pathogens.
- BAntigens are molecules on the surface of cells; antibodies are proteins made by lymphocytes.
- CAntigens cause agglutination; antibodies neutralise toxins.
- DAntigens are produced by phagocytes; antibodies are produced by pathogens.
36.Which of the following is the correct sequence of events in the specific immune response?
Medium
- APathogen enters → phagocytes engulf pathogen → B-lymphocyte recognises antigens → antibodies produced → agglutination → phagocytes digest agglutinated pathogens
- BPathogen enters → B-lymphocyte recognises antigens → phagocytes engulf pathogen → antibodies produced → agglutination → phagocytes digest agglutinated pathogens
- CPathogen enters → antibodies produced → B-lymphocyte recognises antigens → phagocytes engulf pathogen → agglutination → phagocytes digest agglutinated pathogens
- DPathogen enters → phagocytes engulf pathogen → antibodies produced → B-lymphocyte recognises antigens → agglutination → phagocytes digest agglutinated pathogens
37.Which of the following statements about memory cells is correct?
Medium
- AThey are a type of phagocyte that remains in the body after an infection.
- BThey are lymphocytes that recognise a pathogen and can produce a faster, larger secondary immune response.
- CThey produce antitoxins that neutralise toxins produced by bacteria.
- DThey are found on the surface of pathogens and trigger an immune response.
38.Memory cells are a type of phagocyte.
Easy
True or false?
39.Which of the following is a correct description of herd immunity?
Medium
- AWhen a large proportion of the population is vaccinated, it is unlikely that an unvaccinated individual will become infected.
- BWhen an individual is vaccinated, they are immediately protected against all diseases.
- CWhen a pathogen mutates, the vaccine becomes more effective.
- DWhen a person recovers from an infection, they cannot pass the pathogen to others.
40.Which of the following is a disadvantage of vaccination?
Medium
- AVaccines contain live pathogens that always cause disease.
- BMutations in the pathogen's DNA or RNA can change the antigen so lymphocytes no longer recognise it.
- CVaccines are only effective if given after the disease has developed.
- DVaccines provide immediate immunity without triggering an immune response.
41.Complete the sentences about plant defence mechanisms.
Medium
Plant cells have a cell wall made of ____ that acts as a physical barrier. The ____ on the outside of the leaf is a waxy physical barrier. The tough protective layer of dead cells around the stems of trees is called ____.
42.Complete the sentence about the human immune response.
Easy
White blood cells called ____ engulf and digest pathogens in a process called phagocytosis.
43.Name the type of white blood cell that engulfs and digests pathogens by phagocytosis.
Medium
44.In a population, 120 people are vaccinated against a disease. If 80% of the population is vaccinated, how many people are in the total population?
Medium
45.Complete the sentence about plant defence.
Easy
The waxy ____ of the leaf acts as a barrier to microbes entering the plant.
46.A population has 250 people. If 70% are vaccinated against a disease, how many people are vaccinated?
Medium
47.In a population of 2000 people, 85% are vaccinated against a disease. Calculate the number of people who are vaccinated.
Medium
48.A population has 5000 people. If 92% are vaccinated against measles, how many people are unvaccinated?
Medium
49.A plant cell measures 50 μm in width on a microscope image. If the actual width of the cell is 25 μm, what is the magnification? Give your answer as a number (no unit).
Medium
50.In a field trial, 15 out of 60 plants show symptoms of a disease. Calculate the percentage of plants affected.
Hard
51.Complete the sentences about plant physical defences.
Easy
The waxy ____ on the surface of leaves acts as a barrier to pathogens. The tough outer layer of dead cells on the stems of trees is called ____.
52.Complete the sentences about human chemical defences.
Medium
The stomach produces ____ acid, which kills pathogens swallowed in food. Tears contain ____ , which are enzymes that break down bacteria.
53.Describe how the physical barriers and chemical defences of the human body provide protection from diseases.
Medium
54.Explain why using an electron microscope shows the structures in the white blood cells more clearly than a light microscope.
Hard
55.Describe the events that occur after an antibody binds to an antigen on a pathogen.
Hard
56.Explain how memory cells provide long-term immunity after an infection or vaccination.
Hard
57.Explain how the ciliated cells and goblet cells in the airways help to protect an individual from harmful pathogens.
Hard
58.In a population, 120 people are vaccinated against a disease. If 80% of the population is vaccinated, how many people are in the total population?
Medium
- A135 people
- B180 people
- C165 people
- D150 people
59.A population has 250 people. If 70% are vaccinated against a disease, how many people are vaccinated?
Medium
- A175 people
- B211 people
- C193 people
- D157 people
60.In a population of 2000 people, 85% are vaccinated against a disease. Calculate the number of people who are vaccinated.
Medium
- A2040 people
- B1700 people
- C1870 people
- D1530 people
61.A population has 5000 people. If 92% are vaccinated against measles, how many people are unvaccinated?
Medium
- A400 people
- B480 people
- C360 people
- D440 people
62.A plant cell measures 50 μm in width on a microscope image. If the actual width of the cell is 25 μm, what is the magnification? Give your answer as a number (no unit).
Medium
- A3
- B1
- C4
- D2
63.In a field trial, 15 out of 60 plants show symptoms of a disease. Calculate the percentage of plants affected.
Hard
- A25 %
- B28 %
- C22 %
- D31 %

Karteikarten

What is a communicable disease?

A disease caused by microorganisms called pathogens, which can spread between individuals or between individuals and animals.

What is a pathogen?

Any microorganism that causes disease in another organism, such as bacteria, fungi, protists or viruses.

Name the four main types of pathogen.

Bacteria, fungi, protists (protoctists) and viruses.

Why are all viruses considered pathogenic?

Because they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses).

How do pathogenic bacteria cause damage?

They can remain within body cavities or spaces, and the toxins they produce damage cells.

Give an example of a disease caused by a fungus in plants.

Chalara ash dieback, which affects ash trees, or Black Sigatoka in bananas.

Which protist causes severe forms of malaria in humans?

Plasmodium falciparum.

How is malaria spread?

By mosquitoes, which transmit the Plasmodium parasite.

What is the difference between a communicable and a non-communicable disease?

Communicable diseases are caused by pathogens and can spread between individuals; non-communicable diseases are not caused by pathogens, cannot be passed on, and tend to have longer-lasting effects.

State two physical barriers in plants that defend against pathogens.

The cellulose cell wall and the waxy cuticle on leaves and stems.

How does bark protect a plant?

It provides a tough layer around the stem of the plant to prevent pathogens from entering.

Give two chemical defences that plants use against herbivores.

Production of chemical poisons to deter pests, and antiseptics or antimicrobial enzymes.

How can chemicals produced by plants be useful to humans?

They can be extracted for human use, such as antibiotics, herbal face creams (e.g. tea tree oil) and the pain relief drug aspirin from willow bark.

Why is it difficult to identify plant diseases from symptoms alone?

Because the symptoms of plant diseases can apply to more than one disease, and environmental issues such as mineral ion deficiency can cause similar symptoms.

How can monoclonal antibodies be used to identify plant diseases?

They are specific to the antigens on a pathogen; if the antigen is present in the infected plant sample, the antibodies bind to them and allow accurate diagnosis.

Name two laboratory methods used to identify plant pathogens.

DNA analysis and culturing the pathogen from a sample taken from the plant.

How does the skin act as a physical barrier against pathogens?

It covers almost all parts of the body, preventing infection; if it is cut or grazed, it immediately begins to heal itself, often by forming a scab.

How do hairs and mucus in the nose defend against pathogens?

They make it difficult for pathogens to get past them further up the nose, so they are not inhaled into the lungs.

How do cilia in the trachea and bronchi help protect against pathogens?

Pathogens get trapped in mucus, and cilia waft the mucus up to the back of the throat so it can be removed from the body by coughing, blowing the nose or swallowing.

How does stomach acid defend the body?

It contains hydrochloric acid which is strong enough to kill pathogens that have been swallowed in mucus, food or water.

What are lysozymes and where are they found?

Enzymes produced by the eyes and released in tears that break down and kill bacteria on or around the eye.

How does the natural bacterial flora in the gut and vagina protect against infection?

It protects against infection from pathogenic bacteria by outcompeting the pathogen.

What is sebum and what does it do?

A substance on the surface of the skin that kills bacterial and fungal pathogens.

What are the two main types of white blood cell and what do they do?

Phagocytes carry out phagocytosis; lymphocytes produce antibodies and antitoxins.

Describe phagocytosis.

Phagocytes engulf and digest pathogens by releasing digestive enzymes; this is a non-specific immune response as it is the same for any pathogenic cell.

What is an antigen?

A molecule found on the surface of a cell.

What is an antibody?

A protein made by lymphocytes that is complementary to an antigen; when attached, it clumps pathogens together and signals the cells they are on for destruction.

What is an antitoxin?

A protein that neutralises the toxins produced by bacteria.

How do antibodies cause agglutination and why is this helpful?

Antibodies attach to antigens and cause pathogens to clump together, so they cannot move very easily and phagocytes can engulf and digest them.

What are memory cells and what is their role?

Lymphocytes that recognise a pathogen from a previous infection; they can produce much larger quantities of the required antibody in a much shorter time to fight off the pathogen before symptoms occur.

What is the secondary immune response?

When the same pathogen is encountered again, memory cells trigger a response that is much faster and much larger than the initial response.

What does a vaccine contain?

Harmless versions of a pathogen, such as killed pathogens, attenuated pathogens unable to grow or divide, or fragments of pathogens that include the necessary antigens.

How can a vaccine be administered?

Orally, nasally or via an injection.

How does vaccination lead to immunity?

Antigens in the vaccine trigger lymphocytes to produce specific antibodies; memory cells and antibodies remain in the blood, so a future infection triggers a faster, larger response that prevents disease.

What is herd immunity?

If a large proportion of the population is vaccinated, it is unlikely that an unvaccinated individual will become infected with the pathogen, which can prevent the spread of the disease.

Give two advantages of vaccination.

Vaccines protect the vaccinated individual and reduce the likelihood that an infected individual will spread the pathogen to others; they have also reduced or eradicated many diseases worldwide.

Give two disadvantages of vaccination.

Mutations in the pathogen's DNA/RNA can change its antigens so lymphocytes no longer recognise it; vaccination doesn't always give immunity; side-effects can reduce uptake in the population.

How does HIV affect the immune system?

It reduces the number of lymphocytes circulating in the body, which reduces the ability of the immune system to fight opportunistic infections like pneumonia.

How can a virus trigger cancer? Give an example.

Viruses living in cells can be the trigger for cancers; for example, the HPV virus can infect cells of the cervix, resulting in cervical cancer in some cases.

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