The shape of the lesson
By the end of the lesson, learners can
- Meet the pathogens: The lab opens on cholera.
- Four routes between hosts: Pick each disease and follow the moving dots along its route.
- Why the route matters: Knowing exactly how a pathogen gets from one host to the next tells you where the chain of transmission can be broken.
- Cholera: Vibrio cholerae, bacterium; faecal-oral in water and food.
- Malaria: four Plasmodium species, protoctist; female Anopheles mosquito vector.
- TB: Mycobacterium tuberculosis and M. bovis, bacteria; droplets, unpasteurised milk.
- HIV/AIDS: HIV, virus; sex, blood and needles, mother to baby.
One picture every idea returns to
An infectious disease is caused by a pathogen, an organism or virus that causes disease, and it is transmissible: it can be passed from one host to another. Cholera is caused by the bacterium Vibrio cholerae and spreads by the faecal-oral route in contaminated water and food. Malaria is caused by the protoctists Plasmodium falciparum, P. malariae, P. ovale and P. vivax and is carried by a vector, the female Anopheles mosquito. Tuberculosis (TB) is caused by the bacteria Mycobacterium tuberculosis and M. bovis and spreads in airborne droplets, with M. bovis also caught from infected cattle in unpasteurised milk or undercooked meat. HIV/AIDS is caused by the human immunodeficiency virus and is passed in body fluids: unprotected sex, shared needles and infected blood, and from mother to baby.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Four diseases, four routes between people.. An infectious disease is caused by a pathogen that can pass from one person to another. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Meet the pathogens | The lab opens on cholera. Project tab 1 of the lab (Infectious diseases lab, the pathogens) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Four routes between hosts | Pick each disease and follow the moving dots along its route. Project tab 2 of the lab (Infectious diseases lab, transmission) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Why the route matters | Knowing exactly how a pathogen gets from one host to the next tells you where the chain of transmission can be broken. | Jigsaw |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 20 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Why the route matters, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Malaria is not caused by a bacterium or by the mosquito. | The pathogen is the protoctist Plasmodium; the mosquito is only the vector that carries it. Name the pathogen with its genus (and species where asked), written in italics or underlined. |
| HIV does not survive long outside the body and is not spread by touching, coughing, sharing cups or by mosquitoes. | A mosquito transmits Plasmodium because the parasite completes part of its life cycle inside the insect; HIV does not. |
Pathogens and how they are transmitted: worksheet
6 questions, 20 marks. Written in the style of the papers; no past paper question is reproduced.
State what is meant by an infectious disease.
Complete the statement: malaria is caused by four species of a pathogen. Name the four species and state the type of organism they are.
Explain how malaria is transmitted from one person to another.
Explain why tuberculosis spreads most rapidly among people living in crowded, poorly ventilated housing.
Compare the transmission of cholera with the transmission of HIV.
In a village, cases of TB rose among farm workers who drank milk straight from their own cattle, even though none lived in crowded housing. Suggest which pathogen was most likely involved, how it was transmitted and one measure to prevent further cases.
Answer key and marking notes
- A disease caused by a pathogen (a microorganism or virus).
- That is transmissible: it can be passed from one person (host) to another.
- Plasmodium falciparum and Plasmodium malariae.
- Plasmodium ovale and Plasmodium vivax.
- They are protoctists.
- (single-celled eukaryotes; accept protoctists / protists, not bacteria)
- A female Anopheles mosquito acts as the vector.
- It takes a blood meal from an infected person and takes in Plasmodium gametes.
- The parasite develops inside the mosquito and moves to its salivary glands.
- When the mosquito bites another person it injects saliva containing the parasite into the blood. (also: blood transfusion, shared needles, across the placenta)
- TB bacteria are released in droplets when an infected person coughs or sneezes.
- In a crowded room people are close together, so more people breathe in the droplets.
- Poor ventilation means the droplets stay in the air for longer and are not diluted.
- Poverty linked to crowding may mean poor diet or HIV infection, so immune systems are weaker.
- Cholera is transmitted by the faecal-oral route, in water or food contaminated with faeces; HIV is transmitted in body fluids.
- Cholera bacteria enter by being swallowed; HIV enters the blood (through sex, needles, transfusion, or from mother to baby).
- Neither has a vector; cholera bacteria can survive in water outside the body, but HIV does not survive long outside the body.
- Mycobacterium bovis.
- It was transmitted from infected cattle in unpasteurised milk.
- Pasteurise (heat-treat) milk before drinking; or test cattle and remove infected animals.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which of these is not an infectious disease?
- Asickle cell anaemia
- Btuberculosis
- Cmalaria
- Dcholera
Which pair of organisms both cause tuberculosis (TB)?
- AMycobacterium tuberculosis and Mycobacterium bovis
- BMycobacterium tuberculosis and Vibrio cholerae
- CMycobacterium bovis and Plasmodium vivax
- DMycobacterium bovis and the human immunodeficiency virus
A woman who has never been to a country where malaria occurs develops malaria. Which is the most likely way she was infected?
- Aa transfusion of blood from a donor carrying Plasmodium
- Bdrinking water contaminated with the faeces of an infected person
- Cbreathing in droplets coughed out by a person with malaria
- Deating meat from cattle infected with Plasmodium
Which activity carries a risk of HIV being transmitted?
- Ainjecting drugs with a needle already used by another person
- Bdrinking from a cup used by a person who is HIV positive
- Cbeing bitten by a mosquito that has fed on an infected person
- Dshaking hands with a person who is HIV positive
Which row correctly describes the pathogen that causes cholera?
- AVibrio cholerae; a prokaryote that infects the small intestine
- BVibrio cholerae; a protoctist that infects red blood cells
- CPlasmodium ovale; a prokaryote that infects the small intestine
- DMycobacterium bovis; a prokaryote that infects the lungs
The table shows the number of cholera cases per 1000 people in four districts during an outbreak. Which conclusion is best supported by the data?
- Acases were highest where drinking water was most likely to be contaminated with faeces
- Briver water always causes cholera, whatever the position of the town
- Cchlorine in water kills Vibrio cholerae in the small intestine
- Dpeople in districts B and C had weaker immune systems than people in A
Leishmaniasis is caused by a single-celled eukaryote, Leishmania, which is passed between people by the bite of a female sandfly. Which disease in the syllabus is it most similar to, in pathogen type and transmission?
- Amalaria, since both are caused by protoctists carried by an insect vector
- Bcholera, since both are caused by bacteria carried in contaminated water
- CTB, since both are caused by bacteria carried in droplets in the air
- DHIV/AIDS, since both are caused by viruses carried in body fluids
A city with a population of 2.5 million recorded 3750 new cases of TB in one year. What was the incidence of TB, in new cases per 100 000 people per year?
- A150
- B15
- C1.5
- D1500
Quiz key
Sickle cell anaemia is an inherited disease caused by a mutation in the gene for the beta-globin polypeptide; there is no pathogen and it cannot be caught from another person. Tuberculosis is caused by the bacteria Mycobacterium tuberculosis and M. bovis, malaria by species of the protoctist Plasmodium and cholera by the bacterium Vibrio cholerae; all three are transmissible, so all are infectious.
TB is caused by two bacteria of the genus Mycobacterium: M. tuberculosis and M. bovis (the cattle form). Vibrio cholerae causes cholera, not TB. Plasmodium vivax is one of the protoctists that cause malaria. HIV makes people far more likely to develop TB, but it is a virus that causes HIV/AIDS, not a cause of TB.
Plasmodium lives in red blood cells, so it can pass in a transfusion of infected blood (or on shared needles, or across the placenta) without any mosquito. Contaminated water is how cholera spreads. Droplets in the air spread TB; the malaria parasite is not in the airways. Cattle are a source of Mycobacterium bovis (TB), not of Plasmodium.
A used needle can carry infected blood straight into another person's bloodstream, so sharing needles transmits HIV. HIV does not survive well outside the body and is not passed in saliva on a cup. A mosquito does not transmit HIV: the virus does not reproduce in the insect and is not injected in its saliva (unlike Plasmodium). Casual contact such as shaking hands does not transfer body fluids into the blood.
Cholera is caused by the bacterium Vibrio cholerae, a prokaryote, which multiplies in the small intestine and releases a toxin, causing severe diarrhoea. Vibrio is not a protoctist and does not invade red blood cells; that describes Plasmodium. Plasmodium ovale is one of the malaria parasites, a eukaryote. Mycobacterium bovis infects the lungs, but it causes TB, not cholera.
Cases were high in B (wells beside pit latrines) and C (river below the town, which receives its sewage) and low in A (chlorinated piped water) and D (river above the town). The pattern fits the faecal-oral route. River water does not always cause cholera: district D uses the river and has few cases. Chlorine acts on bacteria in the water supply, not inside the intestine, and the table cannot show where it acts. The data give no information about immune systems, so that conclusion is not supported.
A single-celled eukaryote is a protoctist, and an insect that carries a pathogen from host to host is a vector, exactly as for Plasmodium and the Anopheles mosquito in malaria. Cholera and TB are caused by bacteria, which are prokaryotes, and neither has a vector. HIV is a virus, not a cell, and is passed directly in body fluids, without a vector.
Incidence = 3750 ÷ 2 500 000 × 100 000 = 150 new cases per 100 000 people per year. 15 comes from dividing by ten times too many people (25 million). 1.5 is the number per 1000 people, not per 100 000. 1500 comes from using 250 000 as the population.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.