Biology · Unit 14

Microbes and Disease

Bacteria, viruses and immunity

Microbes are the majority of life on Earth by almost any measure, and the small fraction that cause disease has shaped human history more than most wars.

The unit covers the main groups - bacteria, viruses, fungi, protists - and what makes each one different to fight. Antibiotics work on bacteria and do nothing to viruses, and understanding why is the difference between knowing a fact and knowing some biology.

This unit breaks down into 14 short steps and 86 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 14
Questions: 86
Difficulty: 1-3

What this unit covers

Viruses
The Immune System and Vaccines
Types of Microbes
Bacteria and Antibiotics
Disease, Discovery, and the Microbiome

Where this fits

Sits alongside The Immune System. The microbiome material connects to Digestion and Nutrition.

Where people slip

Whether viruses are alive is a real open question, not a trick. They reproduce, but only by hijacking a host cell, and they do nothing else on the list from What Is Life?

How the unit is structured

Microbes and Disease runs as 14 short steps that unlock in order. 10 are practice rounds and 4 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 14 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 86 in the unit altogether.

Bacteria and Antibiotics

Choose all that applyLevel 2
1. Which of these are helpful things that bacteria can do? Select all that apply.
- Help digest food in the human gutcorrect
- Ferment milk into yogurt and cheesecorrect
- Break down dead matter as decomposerscorrect
- Cause every disease that humans get
Most bacteria are harmless or helpful, aiding digestion, fermenting foods, and recycling nutrients, while only some cause disease.
Fill the blankLevel 2
2. The time taken for a bacterial population to double in number is called the ____ time.
- generationcorrect
- stationary
- incubation
- lysogenic
Generation (or doubling) time is how long a population takes to double under set conditions.
Guess the numberLevel 2
3. Under ideal conditions, about how many minutes does it take the bacterium E. coli to divide once by binary fission?
Answer: 20 minutes
In ideal conditions E. coli can divide roughly every 20 minutes, so a population can grow extremely fast.
Fact or fibLevel 3
4. Freezing food usually only makes microbes dormant rather than killing them, so they can grow again once the food thaws.
Answer: True
Freezing halts microbial growth but most microbes survive and become active again when the food warms up.
Match the pairsLevel 3
5. Match each phase of the bacterial growth curve to what is happening to the cells.
Answer: Lag phase = Cells adapt and make enzymes, with little division; Log phase = Cells divide rapidly and numbers double repeatedly; Stationary phase = New cells form at the same rate as cells die; Death phase = Cells die faster than new ones are made
Each phase reflects the balance between how fast cells are being made and how fast they are dying.
Multiple choiceLevel 3
6. How does antibiotic resistance spread through a population of bacteria?
- Resistant bacteria survive treatment, reproduce, and can pass resistance genes to others
- The antibiotic teaches each bacterium to fight back
- The patient's own cells become resistant instead of the bacteria
- Bacteria choose to grow thicker walls when they are attacked
Antibiotics kill non-resistant bacteria, so resistant ones survive, multiply, and can share their resistance genes, increasing resistance over time.

Disease, Discovery, and the Microbiome

Build the sentenceLevel 2
7. Build a true sentence about how a pathogen can spread.
Answer: Pathogens can spread through contaminated water
Many pathogens spread through contaminated water, along with routes like air, food, and direct contact.
Fact or fibLevel 2
8. Diabetes and heart disease are infectious diseases that spread from person to person.
Answer: False
Diabetes and heart disease are non-infectious, so they are not caused by pathogens and cannot be caught from others.
Fill the blankLevel 2
9. The community of trillions of bacteria and other microbes living in and on the human body is called the human ____.
- microbiomecorrect
- nucleus
- capsid
- antigen
The human microbiome is the huge community of microbes that live with us, many of which are helpful.
Multiple choiceLevel 2
10. Whose experiments supported germ theory, the idea that microorganisms cause many diseases?
- Louis Pasteurcorrect
- Gregor Mendel
- Charles Darwin
- Isaac Newton
Louis Pasteur's work supported germ theory, showing that microbes cause disease and food spoilage.
Guess the numberLevel 3
11. In a school lab, agar plates of bacteria are usually incubated at a maximum of about what temperature (in degrees Celsius) to avoid growing human pathogens?
Answer: 25 C
Keeping plates at around 25 C avoids body temperature (37 C), reducing the chance of culturing microbes that thrive in humans.
Match the pairsLevel 3
12. Match each pathogen to the disease it causes.
Answer: Plasmodium = Malaria; Mycobacterium tuberculosis = Tuberculosis; Vibrio cholerae = Cholera; HIV = AIDS
Malaria is caused by the protist Plasmodium, TB and cholera by bacteria, and AIDS by the HIV virus.

The Immune System and Vaccines

Fact or fibLevel 1
13. After you recover from an infection, memory cells stay in the body so you can respond faster if the same pathogen returns.
Answer: True
Memory cells remain after an infection and let the immune system react quickly to a repeat attack by the same pathogen.
Fill the blankLevel 1
14. White blood cells that surround and engulf pathogens are called ____.
- phagocytescorrect
- platelets
- neurons
- hormones
Phagocytes are white blood cells that engulf and digest invading pathogens.
Match the pairsLevel 2
15. Match each part of the immune response to what it does.
Answer: Phagocyte = Engulfs and digests pathogens; B lymphocyte = Produces antibodies; Memory cell = Gives a faster response if the pathogen returns; Antigen = Molecule that triggers the immune response
Phagocytes engulf pathogens, B lymphocytes make antibodies, memory cells speed up future responses, and antigens are the molecules that trigger a response.
Build the sentenceLevel 3
16. Build a true sentence about what activated B cells do.
Answer: Activated B cells produce antibodies
When a B cell meets its matching antigen it divides into plasma cells that pump out specific antibodies.
Choose all that applyLevel 3
17. Which statements about vaccines and herd immunity are correct? Select all that apply.
- A vaccine exposes the immune system to a harmless form of an antigencorrect
- Vaccination can create memory cells for a faster future responsecorrect
- When enough of a population is immune, herd immunity protects those who cannot be vaccinated
- Vaccines work by giving the body antibiotics to kill bacteria
Vaccines train the immune system with a safe antigen and build memory cells, and widespread immunity shields vulnerable people, but vaccines contain no antibiotics.
Guess the numberLevel 3
18. For a very contagious disease like measles, roughly what percentage of a population needs to be immune to reach herd immunity?
Answer: 95 %
Highly contagious diseases such as measles need around 95 percent immunity before herd immunity protects the unvaccinated.

Types of Microbes

Picture questionLevel 1
19. 🦠 Living things this tiny, which can only be seen with a microscope, are called what?
- Microbescorrect
- Minerals
- Molecules
- Magnets
Microbes, or microorganisms, are living things too small to see without a microscope.
Fill the blankLevel 2
20. A single-celled fungus that reproduces by budding and is used in baking and brewing is called ____.
- yeastcorrect
- mould
- algae
- amoeba
Yeast is a single-celled fungus that buds and is used to make bread rise and to ferment alcohol.
Odd one outLevel 2
21. Which one of these is NOT a microbe?
- Earthwormcorrect
- Bacterium
- Amoeba
- Yeast
An earthworm is a large, visible animal, while bacteria, amoebas, and yeasts are all microscopic microbes.
Sort into groupsLevel 2
22. Sort each microbe by whether its cells are prokaryotic or eukaryotic.
Answer: Bacterium = Prokaryote; Cyanobacterium = Prokaryote; Yeast = Eukaryote; Amoeba = Eukaryote
Bacteria and cyanobacteria are prokaryotes with no nucleus, while yeasts (fungi) and amoebas (protists) are eukaryotes with a true nucleus.
Multiple choiceLevel 3
23. How does a prion cause disease in the brain?
- It makes normal brain proteins fold into the wrong shape, damaging tissue
- It injects viral DNA into brain neurons
- It releases toxins that dissolve neurons
- It blocks the blood supply to the brain
A prion makes normal brain proteins fold into the wrong shape, damaging nervous tissue in a chain reaction.
Type the answerLevel 3
24. What is the name for an infectious agent made only of a misfolded protein, with no DNA or RNA (it causes diseases such as CJD)?
Answer: prion
A prion is an infectious misfolded protein that contains no genetic material yet can still cause disease.

Viruses

Fill the blankLevel 1
25. A virus that specifically infects and destroys bacteria is called a ____.
- bacteriophagecorrect
- bacillus
- antibody
- antibiotic
A bacteriophage is a virus that attacks bacteria, injecting its genetic material into the bacterial cell.
Multiple choiceLevel 1
26. Why can a virus only reproduce inside a living host?
- It must use the host cell's machinery to make copies of itselfcorrect
- It needs sunlight to make its own food
- It reproduces by binary fission like bacteria
- It slowly grows larger until it splits in two
Viruses lack their own cellular machinery, so they must hijack a living host cell to build new virus copies.
Build the sentenceLevel 3
27. Build a true sentence describing the start of the lysogenic cycle.
Answer: the virus inserts its DNA into the host chromosome
In the lysogenic cycle the virus inserts its DNA into the host chromosome instead of bursting the cell straight away.
Odd one outLevel 3
28. Which of these diseases is NOT caused by a virus?
- Tuberculosiscorrect
- Influenza
- Measles
- COVID-19
Tuberculosis is caused by bacteria, whereas influenza, measles, and COVID-19 are all viral diseases.
Put in orderLevel 3
29. Put the steps of a virus infecting a cell (the lytic cycle) in the correct order.
Answer: Virus attaches to the host cell -> Viral genetic material enters the cell -> The host cell's machinery copies viral parts -> New virus particles are assembled -> The host cell bursts and releases new viruses
A virus attaches, injects its genes, forces the host to build new virus parts, assembles them, then bursts the cell to release new viruses.
Sequence recallLevel 3
30. Memorise and repeat the order of stages in the lysogenic cycle.
Answer: Virus attaches and injects its DNA -> Viral DNA integrates into the host chromosome as a prophage -> The host cell divides, copying the prophage to daughter cells -> A trigger switches the prophage into the lytic cycle
The virus injects DNA, it integrates as a prophage, the host copies it as it divides, then a trigger switches it to the lytic cycle.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Microbes and Disease

86 questions across 14 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Microbes and Disease

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

More units in Biology

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