Definition:
Microorganisms are tiny living things that are too small to be seen with the naked eye.
Presence:
Microorganisms are found everywhere, such as:
- In the air
- In water
- In soil
- Inside our body
- On surfaces
- In food
Classification:
Most microorganisms are unicellular (made of a single cell).
Basic Needs:
Like all living things, microorganisms need:
- Food
- Air
- Water
- A suitable environment (right temperature and conditions)
Ways of Getting Food:
- Producers: Make their own food using sunlight.
- Consumers: Eat other organisms for food.
Impact on Life:
- Useful microorganisms: Help in making food (like yogurt, bread) and medicines (like antibiotics).
- Harmful microorganisms: Cause diseases and make us sick (called germs).
Viruses
Meaning:
Viruses are very small germs that can only be seen with a microscope.
Action:
Viruses make living things sick by changing how their cells work. They affect the body’s normal functions and can cause diseases.
Presence and Spread:
- Found everywhere
- Very dangerous
- Spread very fast from one person to another
Entry into the Body:
Viruses can enter through:
- Nose
- Mouth
- Skin cuts
Our body’s defense system fights them using white blood cells (WBCs) — the body’s army that protects us from infection.
Diseases Caused by Viruses:
- Flu (Influenza)
- Measles
- Polio
- Hepatitis
- Smallpox
- Dengue
- Chikungunya
- Covid-19
Dengue (Example of Viral Disease):
Cause: Spread by mosquito bite
Main Symptoms:
- Acute flu (high fever)
- Body pain
- Pain behind eyes
- Muscle and joint pain
- Nausea
- Vomiting
Bacteria
Meaning:
Bacteria are microscopic (very tiny), single-celled living organisms. They are present everywhere — in air, water, soil, food, and even inside our bodies.
Classification:
Bacteria belong to the group (kingdom) called Monera.
Role:
Bacteria are important decomposers. They help:
- Break down dead plants and animals.
- Return nutrients to the environment, making the soil rich for other living things.
Diseases Caused by Bacteria:
- Cholera
- Typhoid
- Food poisoning
- Tooth decay
Prevention:
- Keep surroundings clean
- Wash hands before eating
- Use clean drinking water
Fungi
Kingdom: Fungi belong to their own kingdom separate from plants and animals.
Structure:
Fungi do not have stems, leaves, roots, or flowers.
Nutrition:
Fungi cannot make their own food. They get food by living on other living or dead things. This is called parasitic nutrition.
Reproduction:
Fungi reproduce through spores (tiny cells that grow into new fungi).
Examples of Fungal Parasites:
Fungi live on their hosts (plants or animals) to get food and nutrition.
Protists
Meaning:
Protists are microscopic, single-celled living organisms. They are somewhat similar to bacteria but have more complex cell structures.
Main Groups of Protists:
- Protozoa
- Algae
Structure:
- Microscopic (very tiny)
- Mostly single-celled
- Some move using small arm-like parts called pseudopodia or cilia
Feeding:
- Most do not feed on other organisms directly.
- Some, like protozoa, can eat tiny organisms.
Importance:
- Some protists are food for fish and aquatic animals.
- A few cause diseases in humans and animals.
Example – Amoeba:
- Lives in water or on decaying (rotting) food.
- Uses arm-like structures called pseudopodia to move and grab food.
Algae
Meaning:
Algae are plant-like microorganisms. Some are single-celled, while others have many cells.
Features:
- Have plant-like cells
- Live in water
- Make their own food using sunlight (photosynthesis)
- Example: Seaweed
Microorganisms – All Good or All Bad?
Some are Helpful:
- Help in making food such as yogurt and cheese.
- Help in preventing diseases.
Role in Nature (Decomposers):
- Some bacteria and fungi cannot make their own food.
- They feed on dead plants and animals.
- They produce liquids that dissolve dead material, then absorb and break it down into simple chemicals.
- These nutrients are returned to the soil, helping new plants grow.
- Fungi help dead plants to rot, acting like natural recyclers.
- Microorganisms also break down waste in sewage plants, making waste disposal safe.
Microorganisms in Cooking and Food Preparation
Bacteria are used to make:
- Yogurt
- Cheese
- Sour cream
- Buttermilk
- Vinegar
Yeast (a type of fungus) is used to:
- Bake bread
- Make soy sauce
- Make salami
Microorganisms and Digestion
- Some bacteria help break down food into smaller parts so our body can easily absorb nutrients.
- Some microorganisms produce nutrients that our body needs.
How Microorganisms Harm
Harmful microorganisms include:
- Bacteria
- Viruses
- Protozoa
Diseases Caused:
- Malaria – by Protozoa
- Typhoid, Cholera, Diphtheria, Pneumonia – by Bacteria
- Cold, Covid-19 – by Viruses
Other Effects:
- Some bacteria damage clothes, shoes, and carpets.
- Fungi can grow on food and spoil it.
Food and Decay
How Food Decays:
- When food is kept outside at room temperature, bacteria and fungi grow on it.
- They produce poisonous substances (toxins) that can cause food poisoning when eaten.
- High temperature kills harmful microorganisms, which is why cooking and boiling food make it safe to eat.
Infection
How Infection Happens:
- Occurs when harmful microorganisms enter our body.
- Once inside, they multiply quickly and release toxins (poisonous materials).
- These toxins damage body cells and make us sick.
Body Defense:
- The body fights germs using white blood cells (WBCs) — they act like soldiers to destroy harmful microorganisms.
Preventing Diseases
Helpful Microorganisms:
Some microorganisms produce antibiotics, which help in fighting diseases.
Example:
- The mould Penicillium produces Penicillin, discovered by Alexander Fleming.
Antibiotics:
- Medicines that kill or stop bacteria from growing.
- Used to treat bacterial infections.
- Do not work against viruses.
Vaccines
How Vaccines Work:
- Antibiotics fight diseases after they start.
- Vaccines help prevent diseases before they start.
Made from:
- Weakened or dead microorganisms.
Function:
- Vaccines train the body to make antibodies, which protect us from future infections.
Summary:
- Food spoils due to bacteria and fungi that release toxins.
- Infections happen when harmful microbes enter and multiply inside the body.
- Antibiotics cure bacterial infections, while vaccines prevent many diseases in advance.
Conceptual Questions and Answers
Q: What are microorganisms?
A: Microorganisms are minute, tiny living organisms that can’t be seen with the naked eye.
Q: Where are microorganisms found?
A: They’re present almost everywhere: in the air, water, soil, in our bodies, and on the surface of every object, including the food we eat.
Q: What is a key characteristic of microorganisms?
A: They are all living organisms. They can be unicellular or single-celled. They require food, air, water, and an environment to live.
Q: What are “germs”?
A: All microorganisms that cause diseases are called germs.
Q: Who was Louis Pasteur?
A: Louis Pasteur was one of the most famous scientists in history, living in France in the 19th century.
Viruses
Q: What is a virus?
A: A virus is an extremely small germ that makes living things ill by causing their cells to work abnormally. They can only be seen with very powerful microscopes.
Q: How do viruses spread and what diseases do they cause?
A: They can enter through the nose, mouth, or cuts in the skin. They cause diseases like the common cold, influenza, measles, polio, hepatitis, smallpox, and Covid-19.
Q: How is the dengue virus transmitted?
A: The Dengue virus (DENV) is transmitted through mosquitos.
Bacteria
Q: What are bacteria?
A: Bacteria are microscopic life forms that live on and in other living things, belonging to the kingdom Monera. They are the simplest, single-celled forms of living things.
Q: What is the main role of bacteria in nature?
A: The main role of bacteria is to act as decomposers, breaking down the chemical elements inside other organisms.
Q: Name some diseases caused by bacteria.
A: Bacteria cause diseases such as cholera, typhoid, TB (Tuberculosis), food poisoning, and throat infection. Bacteria in the mouth can also cause tooth decay.
Fungi
Q: Why are fungi classified in their own kingdom, separate from plants?
A: Fungi were once classified as plants. The main differences are that fungi do not have stems, leaves, roots, or flowers like plants, and they cannot produce their own food.
Q: How do fungi obtain food?
A: Because they can’t make their own food, fungi attach themselves to other living things, such as plants and animals (including humans), to find nourishment.
Q: What are examples of fungi?
A: Mushrooms and toadstools are examples of fungi.
Protists
Q: What are the two main types of protists?
A: The two main types of protists are protozoa and algae.
Q: Describe protozoa.
A: Protozoa are microscopic, single-celled organisms, similar to bacteria, but they are free-living instead of living on other organisms. They have animal-like cells.
Q: What is an amoeba?
A: The amoeba is a type of protozoa that lives in water, among rotting food, and in humans. They have arm-like structures that help them move and grasp food particles.
Q: Describe algae.
A: Algae have a plant-like cell and live in water. They are producers, meaning they can make their own food from sunlight. Most are single-celled and microscopic, but some, like seaweed, are much larger.
Decomposition and Recycling
Q: How do microorganisms act as decomposers?
A: Some bacteria and fungi feed on dead plants and animals. They produce a liquid that dissolves the dead organism, absorb it back, and break down the large, complex chemicals into small, simple chemicals.
Q: Why are decomposers important?
A: Decomposers are natural recyclers. They return the basic chemicals from dead organisms to the environment for other living organisms to use, enabling new life to grow. They also break down waste at sewerage plants, making disposal safer.
Food Preparation and Digestion
Q: How are microorganisms used in food preparation?
A: Bacteria are used to make milk products like yoghurt, cheese, and sour cream, as well as vinegar. Yeast, a fungus, is used to bake bread and make products like soy sauce.
Q: What role do microorganisms play in human digestion?
A: Microorganisms inside the human body provide us with nutrients and break down big food particles into tiny, usable ones, making food easier to digest.
Q: What major diseases are caused by harmful bacteria and protozoa?
A: Bacteria cause diseases like tuberculosis, typhoid fever, cholera, and pneumonia. Protozoa cause diseases like malaria.
Q: Why does leftover food go bad?
A: Bacteria and fungi land on the food from the air. They produce chemicals in the food that can cause food poisoning.
Q: What happens when harmful microorganisms cause an infection?
A: Harmful microorganisms reproduce rapidly in the body, feed on body cells, and produce poisonous waste substances called toxins. As their numbers increase, more cells are damaged and more toxins are produced, causing the person to feel ill.
Q: What are two key defense mechanisms our bodies use against infection?
A: Our body fights germs with the help of white blood cells. Sometimes, we also need to take medicines like antibiotics to kill the germs.
Q: What are the three main ways to prevent illness from microorganisms?
A: The three main ways are:
- Good Hygiene: Washing hands, properly cooking food, and protecting surroundings.
- Antibiotics: Medicines made from microorganisms that destroy, slow down, or prevent the growth of bacteria to cure bacterial infections. Penicillin was the first antibiotic, discovered from a fungus. Note: Antibiotics are useless against viruses.
- Vaccines: These are made from microorganisms that cause infectious diseases. They give the body a small amount of the disease so the body can produce antibodies to fight the virus/bacteria in the future, thus preventing the disease from becoming infectious.
Q: List one important food safety tip involving heat.
A: Cook food until it is really hot because high temperatures can kill microorganisms.
MCQ
I. General Concepts
- What is the defining characteristic of microorganisms?
A. They are always producers.
B. They cause all diseases.
C. They cannot be seen with the naked eye.
D. They are only found in soil and water. - What is the origin of the word “microorganism”?
A. Micro means small; organism means complex.
B. Micro means very small; organism means living.
C. Micro means single; organism means cell.
D. Micro means multiple; organism means life form. - What term is used for all microorganisms that cause diseases?
A. Decomposers
B. Producers
C. Germs
D. Protists - Which historical scientist, who lived in the 19th century in France?
A. Alexander Fleming
B. Louis Pasteur
C. Robert Koch
D. Jonas Salk
II. Types of Microorganisms
- Which type of microorganism is known to be the simplest form of living things, having only one cell, and belongs to the kingdom Monera?
A. Fungi
B. Bacteria
C. Viruses
D. Protozoa - Which statement is true about viruses?
A. They are cured by antibiotics.
B. They are easily seen with an ordinary microscope.
C. They make living cells work abnormally.
D. They can only enter the body through cuts in the skin. - What are the two main types of protists?
A. Bacteria and Fungi
B. Protozoa and Algae
C. Viruses and Germs
D. Mushrooms and Seaweed - Which microorganism is a type of protozoa advanced enough to have arm-like structures for movement and grasping food?
A. Virus
B. Bacteria
C. Amoeba
D. Yeast - What is the main difference between plants and fungi regarding nutrition?
A. Plants have spores for reproduction, but fungi do not.
B. Plants are able to produce their own food, but fungi are not
C. Fungi have stems, leaves, and roots, but plants do not.
D. Fungi are always microscopic, but plants are not.
III. Roles and Impact
- What is the primary role of bacteria in nature?
A. Causing influenza
B. Acting as decomposers
C. Producing their own food from sunlight
D. Making bread - What process do decomposers like bacteria and fungi carry out to return basic chemicals to the environment?
A. Digestion
B. Reproduction
C. Recycling
D. Photosynthesis - Which of the following foods is made using yeast, a type of fungus?
A. Vinegar
B. Cheese
C. Yoghurt
D. Bread - Which of these human health issues is caused by a protozoan?
A. Tuberculosis
B. Typhoid fever
C. Malaria
D. Common cold - Why does food, like leftovers, go bad if left out at room temperature?
A. Food loses its nutrients in the air.
B. High temperatures kill the organisms.
C. Bacteria and fungi land on it and produce chemicals.
D. The white blood cells in the food decay.
IV. Disease Prevention
- What are antibiotics designed to fight?
A. Only infections caused by viruses.
B. Infections caused by bacteria.
C. All diseases, including cold and flu.
D. Diseases caused by protozoa only. - How do vaccines primarily work?
A. By producing poisonous toxins to kill all germs.
B. By giving the body a small amount of the disease to produce antibodies.
C. By destroying existing bacteria that have already started to infect the body.
D. By breaking down food particles into tiny usable ones. - Who discovered Penicillin, the first antibiotic, and from what was it derived?
A. Louis Pasteur, from bacteria.
B. Alexander Fleming, from a fungi (penicillin mould).
C. Robert Koch, from a virus.
D. Jonas Salk, from yeast. - What is a key step to prevent food poisoning related to cooking temperature?
A. Stirring food only once.
B. Heating food just once.
C. Cooking food until it is really hot.
D. Thawing frozen foods after heating them.
Answer Key
| Question | Answer |
| 1 | C |
| 2 | B |
| 3 | C |
| 4 | B |
| 5 | B |
| 6 | C |
| 7 | B |
| 8 | C |
| 9 | B |
| 10 | B |
| 11 | C |
| 12 | D |
| 13 | C |
| 14 | C |
| 15 | B |
| 16 | B |
| 17 | B |
| 18 | C |