Grade 10 general science – Microorganisms Quiz

1. Which of the following is NOT a type of microorganism?

Insects such as mosquitoes
Bacteria
Fungi
Viruses
Explanation:

Insects are multicellular animals visible to the naked eye and are not classified as microorganisms. Bacteria, viruses and fungi can be microscopic.

2. What is the main way most bacteria reproduce?

Budding like yeast
Spore formation
Sexual reproduction with gametes
Binary fission (splitting into two)
Explanation:

Most bacteria reproduce asexually by binary fission, where one cell divides into two genetically similar cells. Some microbes like fungi use spores and some yeasts bud, but binary fission is typical for bacteria.

3. Which statement correctly distinguishes viruses from bacteria?

Viruses can reproduce on their own outside a host cell, bacteria cannot
Bacteria always cause disease while viruses never do
Viruses are visible with a light microscope but bacteria are not
Bacteria are much larger than viruses and can live independently, viruses need host cells to replicate
Explanation:

Bacteria are generally larger and can grow and reproduce independently, whereas viruses are much smaller and require a host cell's machinery to replicate.

4. Which microorganism is the cause of malaria?

A virus (Influenza)
A bacterium (Vibrio)
A fungus (Aspergillus)
A protozoan (Plasmodium)
Explanation:

Malaria is caused by protozoan parasites of the genus Plasmodium, which are transmitted to humans by Anopheles mosquitoes.

5. Which of the following diseases is caused by a bacterium?

Measles
HIV/AIDS
Cholera
Common cold
Explanation:

Cholera is caused by the bacterium Vibrio cholerae. Measles and the common cold are viral, and HIV/AIDS is caused by the human immunodeficiency virus.

6. Which practice helps make drinking milk safer by killing many harmful microorganisms?

Pasteurization (heating milk briefly)
Filtering milk through cloth only
Letting milk sit at room temperature
Adding sugar to milk
Explanation:

Pasteurization involves heating milk to a specific temperature briefly to kill many harmful microbes while preserving nutritional quality; simply letting milk sit or filtering through cloth does not reliably eliminate pathogens.

7. Which microorganisms fix atmospheric nitrogen in root nodules of beans and other legumes?

Rhizobium bacteria
Influenza viruses
Green algae
Fungi like Penicillium
Explanation:

Rhizobium bacteria form symbiotic relationships with legume roots and convert atmospheric nitrogen into forms the plant can use, improving soil fertility.

8. Why are antibiotics not effective against viral infections?

Viruses are too large for antibiotics to enter
Antibiotics target bacterial structures/processes not found in viruses
Viruses live only in water and antibiotics dissolve there
Antibiotics always cause viruses to mutate faster
Explanation:

Antibiotics interfere with bacterial cell walls, protein synthesis or other bacterial-specific processes; viruses lack these structures and use host cells to replicate, so antibiotics do not work on them.

9. Which Kenyan food or product commonly involves beneficial microorganisms during preparation?

Boiled tea without fermentation
Raw, unprocessed meat left at room temperature
Uji (fermented porridge)
Fresh roasted maize that is not fermented
Explanation:

Uji is often prepared by fermentation using naturally occurring bacteria or yeasts, which improve flavor and sometimes digestibility. Fresh roasted maize or boiled tea don’t rely on microbial fermentation.

10. Which microorganism group includes yeasts used in bread making?

Viruses
Bacteria
Protozoa
Fungi
Explanation:

Yeasts are single-celled fungi (e.g., Saccharomyces cerevisiae) that ferment sugars to produce carbon dioxide and alcohol, causing bread to rise.

11. What is a safe household method to reduce microbes in drinking water?

Boiling the water for at least one minute
Adding sugar to the water
Storing water in any open container
Leaving water in sunlight for several hours without a cover
Explanation:

Boiling water kills most disease-causing microorganisms. Leaving water uncovered or adding sugar does not make it safe.

12. Which microorganism causes the disease tuberculosis (TB)?

A bacterium (Mycobacterium tuberculosis)
A virus (Rhinovirus)
A protozoan (Giardia)
A fungus (Candida)
Explanation:

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis and is transmitted mainly via droplets when an infected person coughs or sneezes.

13. In a classroom microscope practical, which stain is commonly used to see bacteria more clearly by increasing contrast?

Iodine for plant cell walls only
Carmine for animal tissues only
Crystal violet or simple staining
No stain, because bacteria are always colored
Explanation:

Simple stains like crystal violet color bacterial cells so they are easier to see under a light microscope. Without staining bacteria are often hard to see because they are nearly transparent.

14. Which role do decomposer microorganisms play in the environment?

Make soil sterile and remove all nutrients
Prevent plants from taking up water
Break down dead organic matter and return nutrients to the soil
Cause immediate extinction of other species
Explanation:

Decomposer bacteria and fungi break down dead plants and animals, releasing nutrients that plants can reuse, maintaining ecosystem nutrient cycles.

15. What is the main purpose of the Gram stain in microbiology?

Detect viruses in a sample
Sterilize the sample before viewing
Measure bacterial motility
Differentiate bacteria by cell wall structure into Gram-positive and Gram-negative
Explanation:

The Gram stain differentiates bacteria based on cell wall properties: Gram-positive retain crystal violet and appear purple, while Gram-negative do not and appear pink after counterstaining.

16. Which microorganism is responsible for athlete's foot and ringworm?

Bacteria
Protozoa
Fungi (dermatophytes)
Viruses
Explanation:

Athlete's foot and ringworm are caused by fungi called dermatophytes that infect skin, hair and nails.

17. Algae in freshwater lakes are important because they:

Stop sunlight from reaching beach sand
Consume large fish as their main food
Cause soil erosion on lake shores
Produce oxygen through photosynthesis and form the base of the food web
Explanation:

Photosynthetic algae produce oxygen and serve as primary producers that support aquatic food chains.

18. Why is handwashing with soap effective at reducing disease spread?

Soap causes immediate immunity to diseases
Soap makes the skin waterproof against bacteria
Soap feeds microbes so they stay on the hands
Soap removes and helps destroy microbes on the skin by breaking down oils and disrupting membranes
Explanation:

Soap emulsifies oils that trap microbes and can disrupt membranes of some microbes, allowing them to be rinsed away, reducing disease transmission.

19. Which of the following is a viral disease that has vaccines available in Kenya?

Cholera
Giardiasis
Measles
Ringworm
Explanation:

Measles is caused by a virus and effective vaccines are part of routine immunisation programs. Cholera is bacterial, ringworm is fungal, and giardiasis is protozoan.

20. What is the role of fermented foods in relation to microorganisms?

Fermentation removes all vitamins from food
Fermentation makes food heavier and toxic
Beneficial microbes transform food (flavour, preservation, nutrients)
Microbes always spoil fermented foods making them unsafe
Explanation:

During fermentation, yeasts and bacteria produce acids, alcohols and enzymes that preserve food, change flavour and sometimes increase nutritional value.

21. Which method is used in laboratories to grow and study bacteria safely?

Culture on sterile nutrient agar plates in controlled conditions
Mixing bacteria with household cleaning agents for fun
Growing bacteria only in drinking water at home
Leaving samples open on a bench to collect dust
Explanation:

Lab cultures on sterile agar allow scientists to grow, isolate and study bacteria safely under controlled conditions with proper aseptic technique.

22. A student observes small, moving single-celled organisms in pond water under a microscope. These are most likely:

Fungi
Protozoa
Large insects
Viruses
Explanation:

Protozoa are single-celled, often motile organisms commonly seen moving in pond water under a light microscope; viruses are too small to see with a basic light microscope.

23. Which practice contributes to antibiotic resistance in communities?

Using antibiotics unnecessarily or not finishing prescribed courses
Vaccinating children according to schedule
Washing hands regularly with soap
Boiling water before drinking
Explanation:

Misuse of antibiotics (overuse, underuse or incomplete courses) allows bacteria to survive and develop resistance; good hygiene and vaccination help prevent infections and reduce antibiotic use.

24. During a practical, how should a student dispose of used microbial culture plates to be safe?

Wash them in the sink with cold water only
Throw them into a classroom dustbin with food waste
Place them in a labelled biohazard container for autoclaving or appropriate disposal
Take them home to show friends
Explanation:

Used culture plates may contain live microbes and must be decontaminated (e.g., autoclaved) and discarded as biohazardous waste following safety protocols to prevent contamination and spread.

25. Which statement best describes the size ranking from smallest to largest among these microorganisms?

Bacteria, viruses, fungi, protozoa
Viruses, bacteria, protozoa, fungi
Fungi, protozoa, bacteria, viruses
Protozoa, viruses, bacteria, fungi
Explanation:

Viruses are the smallest, followed by bacteria, then protozoa (single-celled eukaryotes), and fungi which are often larger (including multicellular forms).