Activity 1.3 — a ten-year-old boy is very sick. The suspects are too small to see.
8 days · You will read his medical file, meet the three kinds of invaders, name
the one making him sick, and run a lab to choose his medicine.
Tap any glowing word for the meaning in English and Spanish.
Think of the last time you had a cold, the flu, or a stomach bug. How did it start? Who around you was sick first?
Two minutes. Tell your partner what the first day felt like, and where you think you caught it.
Colds, flu and stomach bugs are all caused by tiny invaders that get inside the body. By the end of this activity you will know what they are — and how doctors fight them.
She carries her ten-year-old son in her arms. His fever has left him too weak and tired to walk. The nurse takes his vital signs. The boy answers a few questions, but he leaves most of the details to his mother.
Everything they say goes into his medical file. That file is your evidence. Read it the way a detective reads a case.
Your job today: find the clues — in the vital signs, in the story, and in the physical exam.
Full file: Patient Medical Case File (PDF)
Previously healthy 10-year-old boy. Says he is hot and tired, and points to his chest when asked what hurts.
His mother says he came home from school five days ago with what she thought was a cold — but it has only gotten worse. He has had a constant fever for days and complains of being cold. He has a dry cough that gets worse at night, and at times he really struggles to breathe.
He is extremely weak and sleeps 12–14 hours a day. Store medicine has not helped the fever or the pain. He is drinking plenty of water and eating small meals.
No travel, no big crowds besides school and soccer. Nothing is going around school that his mom knows of — but two teammates were coughing at practice a week ago.
Tap every clue from the file that you think helps explain why he is sick. Then tap Show the detective's board and compare.
A clue that says NO is still a clue. "No rash" and "no runny nose" cross whole suspects off the list. Write your list on Worksheet 1 — The Mystery Infection.
A stuffy nose — extra mucus in the passages of the nose.
A damaged spot on the body, from an injury or a disease.
Lymph nodes in the neck — small bean-shaped organs that help the body fight germs.
Lymph nodes at the back of the throat.
A high whistling sound when breathing. Air is squeezing through narrowed tubes in the lungs.
On Worksheet 1 — The Mystery Infection, list the important symptoms you found — from the vital signs, from the story, and from the exam. Use the sentence starters.
Pay special attention to anything about his breathing and his chest.
Exit ticket: the ONE clue you think matters most, and why.
Tomorrow: meet the invaders.
Everybody gets sick sometimes. Colds, the flu, and stomach bugs are caused by invaders that take hold inside our bodies.
Three kinds cause most infectious disease in people: viruses, bacteria, and fungi. Together they are called microorganisms — "micro" because they are tiny. They differ in how they get in, how they multiply, and how they are treated.
Warm-up first: from memory, three clues from Patient 1's file.
About as wide as this circle. You can see it.
About 5 of these fit across one hair.
About 40 fit across one hair. A school microscope can show it.
About 20 fit across one bacterium — roughly 700 across a hair. Far too small for any school microscope.
Why it matters: a virus is so small it has to hide inside a cell to make copies. A bacterium is a whole living cell on its own. That one difference decides how doctors treat them.
A virus is not a full cell. It breaks into a host cell and forces that cell to build copies of the virus. The copies burst out and attack more cells. No host cell — no copies.
Tap every statement that is true. Then check.
Some bacteria split in two about every 20 minutes. Start with ONE. Predict first: how many after one hour? After eight hours?
Every press is one split. Watch the count: it doesn't add — it doubles.
That is why a few bacteria on a plate become a "lawn" that covers the whole plate in two days — and why an infection can go from "a cold" to "struggling to breathe" in five.
Tap every statement that is true. Then check.
Finish the guided notes on Worksheet 2 — Viruses & Bacteria. Use the word bank — every blank is a word from today's slides.
Exit ticket: one way viruses and bacteria are DIFFERENT, in your own
words. Sentence starter: "A virus needs ______, but a bacterium ______."
Tomorrow: the third suspect — and it might be in your shoes.
Warm-up first: virus or bacterium? "Needs a host." "Splits in two." "Too small for a school microscope."
Tap every statement that is true. Then check.
| Virus | Bacteria | Fungus | |
|---|---|---|---|
| Needs a host cell to multiply? | YES — only inside a living cell | No — a living cell on its own | No — some live alone, some live with plants or animals |
| How it multiplies | Takes over a cell and makes it build copies | Splits in two, again and again | Grows and spreads quickly in moist, humid places |
| School microscope? | No — far too small | Yes | Yes — a mold you can even see with your eyes |
| Example illnesses | Flu, common cold, measles | Strep throat, E. coli infection, pneumonia | Athlete's foot, ringworm |
| Treated with… | ? — Day 7 | ? — Day 7 | ? — Day 7 |
Copy the table onto Worksheet 3 — Fungi & Compare. Leave the last row blank — you will earn that answer on Day 7.
Best defense, every time: wash your hands, cover your cough, don't share drinks.
Finish Worksheet 3 — Fungi & Compare. Exit ticket: how do you think Patient 1 caught his illness? "I think he caught it from ______ because ______."
A doctor reads the vital signs and symptoms, then names the illness. That name is the diagnosis. But how do they get from "fever and cough" to an invader they cannot see?
Over many years, scientists cataloged what each agent does. Our Disease Dictionary lists, for each illness: the type of agent, its name, the incubation period, how long it lasts, the symptoms, how it spreads, and the treatment.
Warm-up: virus, bacteria, or fungus — athlete's foot? the flu? strep throat? Then open Worksheet 4 — Diagnose Patient 1.
The incubation period is the time between contact with the agent and the first symptoms. Every agent has its own.
Patient 1's contact was a week ago; his symptoms started five days ago. So his incubation was about two days. Any suspect whose incubation is weeks long is off the list before we even look at symptoms.
Every clue fits one suspect: pneumococcal pneumonia, caused by the bacterium Streptococcus pneumoniae. Fever and chills, cough, rapid and difficult breathing, chest pain, weakness — and it is one of the bacteria that also causes ear infections.
Bacteria are treated with antibiotics — medicines that kill bacteria or stop them from growing. But there are many antibiotics, and some work on some bacteria and not on others.
The next question is the real one: WHICH antibiotic? Doctors don't guess. They test — and so will you. Finish Worksheet 4 — Diagnose Patient 1: your claim, your evidence, your reasoning.
A microbiologist studies tiny organisms — bacteria, viruses, fungi — and the part they play in human health and the environment. Designing and running experiments is their everyday work, so they train hard in safe handling of samples.
Warm-up: what is Patient 1's diagnosis, and what kind of agent causes it? Today YOU take on the microbiologist's job: find the best antibiotic for him.
Aseptic technique means working so carefully that no stray germs get INTO your sample and no sample gets OUT onto your bench or hands.
Personal protective equipment: goggles, gloves, and a lab apron — on before you touch anything, off the safe way after.
Open a plate or tube only for the seconds you need. Never set a lid face-down on the table.
Dip the forceps in alcohol before every disc. Alcohol kills whatever hitched a ride.
Only the swab and the discs. Not your glove, not the pen, not the table.
Tape the plate shut and store it upside down. Once it is taped, it stays taped.
Soap, 20 seconds, after gloves come off — every time.
Good news: the bacteria in this kit cannot make you sick. You practice the technique anyway — a real lab does not give second chances.
The thing WE change: which antibiotic is on the disc.
The thing we MEASURE: the size of the clear ring, in millimeters.
A plain paper disc with no medicine. If a ring appears around IT, something else is stopping the bacteria — not the antibiotic.
One variable at a time: same plate, same bacteria, same day, same 48 hours — only the disc changes. Fill in Worksheet 5 — Design the Test.
PLTW wrote the eight steps for spreading the bacteria. You write the steps for placing the four discs. A stranger must be able to follow them exactly.
• which disc (E, AM, TE, or the plain control)
• where it goes — its own quarter of the plate
• how: forceps, set it down gently, press lightly so it sticks
• sterilize the forceps in alcohol BEFORE the next disc
• mark the lid so you know which disc is which
PPE · 1 tryptic soy agar plate · discs: erythromycin, ampicillin, tetracycline · plain paper discs · sterile cotton swab · bacterial culture · forceps · dish of alcohol · ruler · permanent marker · tape
Sentence starter for each step: "Dip the forceps in alcohol. Pick up the ______ disc and place it in the ______ quarter. Press gently. Mark ______ on the lid." Write them on Worksheet 5 — Design the Test, Part D.
Teacher note: if the kit has not arrived, run today as a dry run with an empty plate and paper discs, and use the practice plate on Day 8 for data. The science is identical.
Bacteria need about two days to grow a lawn. Start the clock when the plates go in, and this deck will tell you when they are ready to read.
Before you leave: your prediction on Worksheet 6 — Lab Day. "I predict ______ will have the biggest clear ring because ______." And draw your plate map — which disc is in which quarter.
Look again at the Disease Dictionary on Worksheet 7 — Treatments. One column is blank: Treatment. Today your group becomes the expert on one illness and fills that box in for the whole class.
Then we look for a pattern: does the treatment depend on the type of agent?
Warm-up: what is the control in our experiment, and why does it need to be on the same plate?
Find how your illness is treated and write it in the Treatment box on Worksheet 7 — Treatments. Good sources: cdc.gov, kidshealth.org, mayoclinic.org. Sentence starter for the share-out: "______ is caused by a ______. It is treated with ______."
As each group shares, fill in the other rows. Then answer: what do the treatments have in common inside each agent group? Tap to reveal after you have decided.
Cold · Covid-19 · Flu · Measles · Rotavirus · Zika
Treat the symptoms — rest and fluids while the body fights it. For a few (flu, Covid-19) an antiviral can shorten it if taken early.
Antibiotics do nothing to a virus.
Campylobacter · Cholera · E. coli · Listeriosis · Lyme · Pneumonia · Salmonella · Strep · TB
Antibiotics — every one of them. For the stomach ones, fluids and salt come first and antibiotics are added when the case is severe.
Ringworm / athlete's foot
Antifungal medicine — a cream or a pill made for fungi. Antibiotics do not work on it either.
Now go back to Day 3's table on Worksheet 3 — Fungi & Compare and fill in the last row.
Antibiotics attack things only bacteria have — like a cell wall. A virus has no cell wall, so an antibiotic has nothing to hit. Taking one for a cold does not help you.
Worse: every time bacteria meet an antibiotic and a few survive, those survivors multiply. Over time the medicine stops working when someone really needs it. Doctors call this antibiotic resistance.
Finish Worksheet 7 — Treatments. Exit ticket: "A doctor would NOT give antibiotics for the flu because ______."
Use this plate to practice — or as your data if your real plate did not grow. Tap a disc: a ruler appears with its 0 at the left edge of the ring. Read the number at the right edge and type it in.
| Disc | Antibiotic | Zone (mm) | |
|---|---|---|---|
| E | Erythromycin | ||
| AM | Ampicillin | ||
| TE | Tetracycline | ||
| C | Plain disc (control) |
Every group calls out its four numbers. Average each column on the board (add them, divide by the number of groups), then type the averages here.
The tallest bar is the antibiotic that stopped these bacteria best. The control bar should stay near 6 — if it doesn't, talk about why.
Use the class results to prescribe Patient 1 the antibiotic with the biggest clear ring. Fill in the prescription on Worksheet 8 — Results & Prescription: the medicine, and your reason in one sentence.
Sentence starter: "I prescribe ______ because its zone of inhibition averaged ______ mm, the largest of the three."
Detective's honesty check: is the control's ring close to 6 mm? If the plain disc made a ring too, the antibiotic may not deserve all the credit.
Claim — one sentence. Evidence — something from this activity: a clear ring, an agent type, the dictionary. Reasoning — connect the evidence to the claim.
Both answers go on Worksheet 8 — Results & Prescription.
You read a medical file, met the three invaders, matched the evidence to one suspect, and tested the medicines instead of guessing. That is exactly what a medical detective does.
Next up: Activity 1.4 — Disease Diagnosis.
Every academic word in Medical Detectives so far. Tap one for the full card.
Click any slide to jump there.