Class 8 | Science | Solutions and Q&As | Based on Ncert | Science Scholars.

Chapter 1: Exploring The Investigative World of Science.

A. Recalling Ideas

1. In the ice cube melting experiment, the cube melted fastest on the metal plate because:
(a) Metal is an insulator
(b) Metal is a good conductor of heat ✅
(c) Metal reflects heat
(d) Metal absorbs water

---

2. Which of the following is not a type of microbe?
(a) Bacteria
(b) Virus
(c) Yeast
(d) Pebbles ✅

---

3. Which state of matter has particles that are tightly packed and only vibrate in place?
(a) Gas
(b) Liquid
(c) Solid ✅
(d) Plasma

---

4. An ecosystem is made up of:
(a) Only plants and animals
(b) Only water and air
(c) Living things and their environment ✅
(d) Rocks and soil only

---

5. The first step in developing a scientific temperament is:
(a) Accepting information without doubt
(b) Asking questions and being curious ✅
(c) Memorising facts
(d) Avoiding experiments

---

6. Which of these is not a quality of scientific thinking?
(a) Observation
(b) Experimentation
(c) Superstition ✅
(d) Verification

---

7. Recording results during experiments is important because:
(a) It looks neat in notebooks
(b) It allows you to track and analyse findings ✅
(c) It proves you worked in class
(d) It avoids repeating experiments

---

8. A student notices bread turning green over time and decides to study why. This shows:
(a) Memory skills
(b) Curiosity leading to investigation ✅
(c) Time management
(d) Artistic talent

---

II. Assertion and Reasoning Questions

Codes: (a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true

---

1.
Assertion (A): Scientific temperament encourages people to question and test ideas before accepting them.
Reason (R): Evidence and experiments help confirm whether an idea is correct or not.
Answer: (a) Both are true, and R explains A correctly.

---

2.
Assertion (A): Observation is important for developing scientific thinking.
Reason (R): Scientific thinking depends only on memorising theories.
Answer: (c) A is true, but R is false.

---

3.
Assertion (A): Curiosity is the starting point for scientific investigation.
Reason (R): Curiosity leads to asking questions and planning experiments to find answers.
Answer: (a) Both are true, and R explains A.

---

4.
Assertion (A): Scientific temperament means not accepting beliefs without questioning.
Reason (R): This helps save time and avoid unnecessary experiments.
Answer: (c) A is true, but R is false (scientific thinking may require experiments, not avoiding them).

---

III. Fill in the blanks

1. The process of testing an idea through practical work is called an experiment.
2. Scientific investigation requires recording data so that results can be analysed later.
3. Curiosity often begins with simple questions in daily life.
4. In the ice melting experiment, the ice cube on the metal plate melted the fastest because it is a good conductor of heat.
5. The Moon does not produce its own light but reflects sunlight.

---

IV. Arrange the jumbled words

1. SCOMRIBE → MICROBES
2. SHPASE → PHASES
3. NTOSLIUO → SOLUTION
4. MEESSCOTY → ECOSYSTEM

---

V. True or False 

1. In the ice melting experiment, the ice cube on the metal plate melted the fastest because metal is a poor conductor of heat.
   False
   Correction: Metal is a good conductor of heat.

---

2. Some microbes help in digestion and medicine-making, while others can cause diseases.
   True

---

3. In gases, particles are tightly packed and can only vibrate in place.
   False
    Correction: In gases, particles are far apart and move freely.

---

4. Human activities have no effect on Earth’s balance.
   False
   Correction: Human activities do affect Earth’s balance.

---

5. Observing, measuring and experimenting can help us address climate change.
   True

---

B. Understanding Ideas

1. List three qualities a person needs to develop a scientific temperament.
Answer: Curiosity, observation, and logical thinking.

2. Why is evidence important in science?
Answer:  Evidence helps us to prove whether an idea is correct or not and makes scientific conclusions reliable.

3. How does recording observations help in scientific investigations?
Answer: It helps in analysing results, comparing findings, and verifying conclusions later.

4. Give one example of how an everyday observation can lead to scientific investigation.
Answer:  Example: Noticing that food spoils faster in summer can lead to studying the effect of temperature on food preservation.

5. Why should scientists question their own results?

Answer:  Scientists should question their own results to check for mistakes, ensure accuracy, and confirm that the conclusions are reliable. This helps make scientific findings trustworthy.

6. How are human actions affecting Earth’s balance?

Answer:  Human activities like deforestation, pollution, burning fossil fuels, and overuse of resources disturb Earth’s balance. These actions lead to problems such as climate change, global warming, and loss of biodiversity.

---

II. Case-based Question

1. Are all microbes harmful? Explain.
Answer:  No, all microbes are not harmful. Some microbes are useful, such as microbes that help in digestion and making medicines, while others can cause diseases.

2. Name one helpful role of microbes in our body.
Answer:  Microbes in our gut help in digesting food.

3. Identify a product produced through the use of microbial processes.
Answer:   Antibiotics (medicines) are produced using microbes.

(Other examples: curd, bread)

4. Give one example of a harmful microbe.
Answer:   Bacteria that cause diseases. Diseases like tuberculosis and cholera are caused by bacteria.

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. Cholera is caused by the bacterium Vibrio cholerae.

5. How can we protect ourselves from harmful microbes?

Answer:  We can protect ourselves by:

• Maintaining personal hygiene
• Washing hands regularly
• Eating clean and properly cooked food
• Getting vaccinated

---

C. Analysing, Evaluating and Creating

1. Analyse the role of conductors and insulators in daily life. Give two situations where each is useful.

Conductors: Materials that allow heat/electricity to pass through.
Examples:

• Metal utensils used for cooking
• Electric wires made of copper

Insulators: Materials that do not allow heat/electricity to pass easily.
Examples:

• Plastic covering on wires to prevent electric shock
• Wooden handles of utensils to protect from heat

---

2. Evaluate the statement: “Human activities are the main cause of imbalance in Earth’s climate.”

Answer: This statement is true. Human activities like:

• Burning fossil fuels → increases greenhouse gases
• Cutting trees → reduces oxygen and increases CO₂
• Pollution → harms air, water, and soil

These actions lead to global warming, climate change, and environmental imbalance.

---

3. Create a poster showing the helpful and harmful uses of microbes.

Answer:

Title: MICROBES – FRIENDS AND FOES

Helpful microbes:

• Help in digestion
• Used to make medicines (antibiotics)
• Used in making curd and bread

Harmful microbes:

• Cause diseases (cholera, tuberculosis)
• Spoil food

---

D. Life Skill Activity

Identify 3 daily habits that can reduce your carbon footprint.

Answer:

1. Saving electricity (switching off lights/fans when not in use)
2. Using public transport or walking instead of private vehicles
3. Avoiding plastic and using reusable bags

---

Chapter 2: The invisible Living World: Beyond Our Naked Eye.

I. Select the correct option:

1. Bread mould grows best in which conditions?
(a) Dry and cold
(b) Moist and warm ✅
(c) Dry and hot
(d) Cold and sunny

---

2. Why does dough become soft and spongy after adding yeast?
(a) Yeast forms alcohol
(b) Yeast releases carbon dioxide ✅
(c) Yeast produces heat
(d) Yeast digests gluten

---

3. Which of the following is NOT a microorganism?
(a) Bacteria
(b) Algae
(c) Mould
(d) Earthworm ✅

---

4. What is the main role of decomposer microbes in soil?
(a) Absorb sunlight
(b) Cause diseases
(c) Break down dead matter ✅
(d) Make food

---

5. bacteria live in the root nodules of which plants?
(a) Wheat and rice
(b) Beans and peas ✅
(c) Mango and banana
(d) Apple and orange

---

6. is an example of
(a) Virus
(b) Protozoa
(c) Microalgae ✅
(d) Fungus

---

7. Which of these microorganisms is correctly matched with its product?

(a) Rhizobium: Alcohol
(b) Lactobacillus: Curd ✅
(c) Yeast: Oxygen
(d) Spirulina: Vinegar

---

8. Why do legumes reduce the need for chemical fertilisers?

(a) They require very little water.
(b) They have shallow roots.
(c) They trap nitrogen from the air through bacteria. ✅
(d) They grow only in rainy seasons.

---

II. Assertion and Reasoning Questions

Codes:
(a) Both A and R are true and R explains A
(b) Both A and R are true but R does not explain A
(c) A is true, R is false
(d) A is false, R is true

---

1.

Assertion (A): Bread mould can be seen as green or black patches.
Reason (R): It is a type of bacteria that grows on clean surfaces.
Answer: (c) A is true, R is false

---

2.

Assertion (A): Algae in soil are useful as they perform photosynthesis.
Reason (R): Algae are fungi that grow in dark conditions.
Answer: (c) A is true, R is false

---

3.

Assertion (A): Yeast is used in baking.
Reason (R): It kills harmful bacteria in the dough.
Answer: (c) A is true, R is false

---

4.

Assertion (A): Bacteria can be useful in farming.
Reason (R): Some bacteria help plants get nitrogen.
Answer: (a) Both A and R are true and R explains A

---

5.

Assertion (A): Microbes in pond water can be seen with naked eyes.
Reason (R): They are large enough to be seen without tools.
Answer: (d) A is false, R is true

---

III. Fill in the blanks

1. Nucleus is the part of the cell that controls all its activities.

2. The chloroplast in plant cells helps in the process of photosynthesis.

3. The process of converting sugar into alcohol using microorganisms is called fermentation.

4. Microorganisms grow best when there is enough warmth, moisture, air and nutrients.

5. In an experiment with bread slices, the one near the sink is more likely to grow mould because of higher moisture and temperature.

---

IV. Match items in Column I with those in Column II

1. Robert hooke→ (c) Micrographia
2. Antonie van Leeuwenhoek→ (d) Father of Microbiology
3. Dr. Manu Prakash→ (e) Foldscope
4. Lactobacillus→ (a) Probiotic
5. Root-like structure of a fungus → (b) Mycelium

---

V. State whether the following statements are true or false. Correct the false statement.

1. Yeast produces oxygen during fermentation, which causes balloons to inflate in test tube experiments.
   Answer: False
   Correction: Yeast produces carbon dioxide, which causes balloons to inflate.

---

2. Rhizobium bacteria in root nodules of legumes can fix atmospheric nitrogen into a form usable by plants.
   Answer: True

---

3. The nucleoid is a membrane-bound structure found only in plant cells.
   Answer: False
   Correction: The nucleoid is not membrane-bound and is found in prokaryotic cells (bacteria).

---

4. Microorganisms can grow in extreme environments like hot springs, acidic lakes and deep oceans.
   Answer: True

---

5. Dried leaves added to compost help balance the carbon and nitrogen ratio needed for effective decomposition.
   Answer: True

---

B. Understanding Ideas

I. Answer in one word or one sentence

1. What is the basic structural and functional unit of life?
   Answer: Cell

---

2. Which organelle controls all the activities of the cell?
   Answer: Nucleus

---

3. Which type of microorganism causes diseases and can only grow inside living cells?
   Answer: Virus

---

4. Where do rhizobium bacteria commonly live?
   Answer: In the root nodules of leguminous plants

---

5. How do onion peel cells appear under a microscope?
   Answer: Rectangular (brick-like) cells arranged in rows

---

II. Answer the following questions

1. How does yeast help in making food? 

Answer: Yeast helps in making food by the process of fermentation. It converts sugar into carbon dioxide and alcohol. The carbon dioxide makes the dough rise, making bread and cakes soft and spongy.

---

2. What is the role of in curd formation? 

Answer: Lactobacillus converts milk sugar (lactose) into lactic acid. This lactic acid thickens the milk and turns it into curd.

---

3. What are viruses and how are they different from other microbes?

Answer: Viruses are microscopic organisms that can only grow and reproduce inside living cells. Unlike other microbes, they are not truly living outside a host and do not carry out life processes on their own.

---

4. How do microorganisms help in cleaning the environment?

Answer: Microorganisms act as decomposers. They break down dead plants, animals, and waste materials into simpler substances, thus cleaning the environment and recycling nutrients.

---

5. Mention two differences between plant and animal cells.

Answer: Two differences between plan and animal cells are -

1. Plant cells have a cell wall, while animal cells do not.
2. Plant cells contain chloroplasts, while animal cells do not.

---

6. Explain with examples how microbes can be both useful and harmful.

Answer: Microbes are useful in many ways. For example, helps in making curd, and yeast is used in baking. Some bacteria like improve soil fertility by fixing nitrogen.

However, microbes can also be harmful. Some cause diseases like tuberculosis and cholera. Others spoil food and cause food poisoning.

---

III. Case-based Question

One day, Arjun’s mother was making bread and added yeast to the dough. She placed it near the stove to keep it warm. After a few hours, Arjun noticed that the dough had become soft and had risen. Curious, he remembered learning in school that some microorganisms help in food preparation. Later, he saw his grandfather adding kitchen waste and dry leaves to a compost bin and explaining how tiny microbes turn waste into useful manure.

1. What caused the dough to rise in Arjun’s house?

Answer: The dough rose due to the action of yeast, which released carbon dioxide gas during fermentation, making the dough soft and fluffy.

---

2. Why was the dough kept near the stove?

Answer: The dough was kept near the stove to provide warmth, which helps yeast grow and carry out fermentation faster.

---

3. What role do microbes play in composting?

Answer: Microbes act as decomposers. They break down kitchen waste and dry leaves into simpler substances, converting them into useful manure.

---

4. Mention two beneficial uses of microorganisms shown in the case.

Answer : Two beneficial uses of microorganism are -

1. Yeast helps in making bread by fermentation.
2. Microorganisms help in composting waste into manure.

---

C. Analysing, Evaluating and Creating

1. Would you prefer using compost with the help of microbes over chemical fertilisers in farming? Why or why not?

Answer: Yes, compost is better because it is eco-friendly, improves soil structure, and adds natural nutrients without harming the environment. It also increases soil fertility in a sustainable way, unlike chemical fertilisers which may degrade soil over time.

---

2. Should microalgae be used as a food source in the future? Give one reason.

Answer: Yes, microalgae such as can be used because they are rich in nutrients like proteins and vitamins, making them a healthy food source.

---

3. Why can’t multicellular organisms survive with just one cell, like unicellular organisms do?

Answer: Multicellular organisms have specialised cells that perform different functions. A single cell cannot carry out all these complex activities, so they require many cells working together for survival.

---

Chapter 3: Health: The Ultimate Treasure.

I. Select the Correct Option:

1. Which of the following is a sign of a healthy lifestyle?
   (a) Eating junk food daily
   (b) Regular exercise and balanced diet ✅
   (c) Sleeping very late every night
   (d) Avoiding fruits and vegetables

2. Which of these is a communicable disease?
   (a) Diabetes
   (b) Tuberculosis ✅
   (c) Hypertension
   (d) Obesity

3. Which of these is a non-communicable disease?
   (a) Cholera
   (b) Chickenpox
   (c) Hypertension ✅
   (d) Influenza

4. Which one of the following is given to develop immunity against diseases?
   (a) Antibiotics
   (b) Painkillers
   (c) Vaccines ✅
   (d) Antacids

5. Antibiotics are effective against:
   (a) Viral infections
   (b) Bacterial infections ✅
   (c) Worm infestations
   (d) Fungal infections

6. Which of the following is not a healthy habit?
   (a) Washing hands before eating
   (b) Eating fresh fruits
   (c) Skipping breakfast regularly ✅
   (d) Drinking clean water

7. A disease that spreads through contaminated water is:
   (a) Cholera ✅
   (b) Hypertension
   (c) Diabetes
   (d) Obesity

8. Which organ of the body is mainly attacked by the tuberculosis bacteria?
   (a) Heart
   (b) Liver
   (c) Lungs ✅
   (d) Kidneys

9. Which of these helps in preventing non-communicable diseases like obesity and diabetes?
   (a) Eating oily food
   (b) Doing regular physical exercise ✅
   (c) Not sleeping at night
   (d) Taking antibiotics

10. The main purpose of vaccination is to:
    (a) Kill all germs inside the body
    (b) Provide energy for the body
    (c) Train the immune system to fight specific diseases ✅
    (d) Reduce body temperature.

II. Assertion and Reasoning Questions

1. Assertion (A): Diabetes is a non-communicable disease.
   Reason (R): It can spread by coughing and sneezing.
   Answer: (c) Assertion (A) is true, but Reason (R) is false. 

2. Assertion (A): Regular physical exercise helps prevent obesity.
   Reason (R): Exercise burns extra calories in the body.
   Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A). 

3. Assertion (A): Boiling water helps in reducing the risk of water-borne diseases.
   Reason (R): Boiling water makes it tasty to drink.
   Answer: (c) Assertion (A) is true, but Reason (R) is false. 

4. Assertion (A): Hypertension spreads from one person to another.
   Reason (R): It is caused by stress, unhealthy diet and lifestyle.
   Answer: (d) Assertion (A) is false, but Reason (R) is true. 

5. Assertion (A): Washing hands before eating food prevents many infections.
   Reason (R): It removes harmful germs from our hands.
   Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A). 

---

III. Fill in the blanks with a suitable word(s)

1. The immune system helps the body fight diseases by producing antibodies. 

2. Diabetes, hypertension, asthma and cancer are examples of non-communicable diseases. 

3. A pathogen is a harmful microorganism or agent that causes disease when it enters a host’s body. 

4. Non-communicable diseases often require long-term treatment and lifestyle management. 

5. Prevention saves time, money and suffering, while treatment often takes longer and may not fully restore health. 

---

IV. State whether the following statements are true or false. Correct the false statements.

1. Non-communicable diseases spread from person to person.
   False .
   Correct Statement: Non-communicable diseases do not spread from person to person. 

2. Yoga and meditation support both mental and physical health.
   True .

3. Cholera spreads through contaminated food and water.
   True .

4. Vaccines cure diseases after we fall sick.
   False .
   Correct Statement: Vaccines help prevent diseases before we fall sick. 

5. Excessive antibiotic use can cause resistance in bacteria.
   True 

V. Match items in Column I with those in Column II

1. Dr M. K. Bhan — (c) Rotavirus vaccine 
2. Alexander Fleming — (d) Penicillin 
3. Edward Jenner — (e) Smallpox vaccine 
4. Dr Kamal Ranadive — (a) Links between cancers and viruses 
5. Vaccination — (b) Measles/Chickenpox 

---

B. Understanding Ideas

I. Answer the following questions in one word or one sentence.

1. Ravi had fever and cough. The doctor confirmed Tuberculosis. What type of disease is this?
   Answer: Tuberculosis is a communicable disease. 

2. Sneha’s grandmother has diabetes. Can this disease spread to Sneha?
   Answer: No, diabetes is a non-communicable disease and does not spread from person to person. 

3. A health worker advised people in a village to boil water before drinking. Which disease does this prevent?
   Answer: It helps prevent water-borne diseases like cholera. 

4. The doctor gave Meena antibiotics for her sore throat caused by bacteria. Why were antibiotics given?
   Answer: Antibiotics were given to kill or stop the growth of bacteria. 

5. During a vaccination camp in school, students were given polio drops. What is the role of vaccination here?
   Answer: Vaccination helps develop immunity against polio. 

---

II. Answer the following questions

1. Rohit eats chips and cold drinks daily, skips breakfast, and avoids exercise.

   (a) Name one disease he may develop.
   Answer: He may develop obesity. 

   (b) Write one way to prevent it.
   Answer: He should do regular physical exercise and eat a balanced diet. 

2. In a health camp, people were warned not to take antibiotics without prescription. Why is this advice important?
   Answer: Taking antibiotics without prescription can lead to antibiotic resistance in bacteria and may harm health. 

3. Seema washes her hands before eating and drinks clean water. Which type of diseases is she preventing?
   Answer: She is preventing communicable and water-borne diseases. 

4. How does air pollution affect our health?
   Answer: Air pollution can cause breathing problems, asthma, allergies and other respiratory diseases. 

5. Why do some people get sick more often than others, even in the same environment?
   Answer: Some people have weaker immunity, poor nutrition or unhealthy habits, making them fall sick more often. 

6. Why is personal hygiene important for maintaining good health? Explain with four examples of habits that protect us from diseases.
   Answer: Personal hygiene is important because it prevents the spread of germs and diseases and keeps the body healthy.

   Four healthy habits are:

   • Washing hands before eating and after using the toilet
   • Drinking clean and safe water
   • Bathing regularly and wearing clean clothes
   • Eating fresh and nutritious food 

7. What is immunity? Differentiate between natural immunity and acquired immunity with one example each.
   Answer: Immunity is the body’s ability to fight against diseases and germs.

  

III. Case-based Question:

“In Bhadrak district, a community health survey found that many families were suffering from stomach pain, diarrhoea and dehydration. The investigation showed that people were drinking water from a pond contaminated with sewage. Doctors explained that the disease was caused by bacteria entering the body through unsafe water. They advised people to boil water before drinking, wash hands properly, and maintain cleanliness. At the same time, they cautioned that antibiotics should only be taken on the advice of a doctor.”

1. Which disease is most likely spreading in this community?

(a) Diabetes
(b) Cholera
(c) Hypertension
(d) Asthma

✅ Answer: (b) Cholera

---

2. What was the main cause of the spread of this disease?

(a) Eating junk food
(b) Contaminated drinking water
(c) Lack of exercise
(d) Air pollution

✅ Answer: (b) Contaminated drinking water

---

3. Which preventive measure was suggested to the people?

(a) Washing hands and boiling water
(b) Eating more oily food
(c) Taking painkillers daily
(d) Sleeping less

✅ Answer: (a) Washing hands and boiling water

---

4. Why should antibiotics be taken only with doctor’s advice?

Answer: Antibiotics should be taken only with a doctor’s advice because wrong or unnecessary use can make bacteria resistant to medicines and may also cause side effects.

---

C. Analysing, Evaluating and Creating

1. A survey found that children in a town are suffering from tooth decay, obesity and frequent colds. They mostly eat fast food, skip breakfast and rarely wash hands. Analyse the link between their lifestyle and these health problems.

Answer:
The unhealthy lifestyle of the children is directly linked to their health problems. Eating fast food regularly contains excess sugar, oil and unhealthy fats, which can cause obesity and tooth decay. Skipping breakfast makes the body weak and reduces energy levels. Rarely washing hands allows germs to enter the body, leading to frequent colds and infections. Lack of nutritious food also weakens immunity. Therefore, healthy eating habits, regular meals and proper hygiene are necessary to maintain good health.

---

2. In a village, many people take antibiotics whenever they feel unwell, even without consulting a doctor. Evaluate this practice and predict its long-term effects.

Answer:
Taking antibiotics without consulting a doctor is a harmful practice. Antibiotics should only be used for bacterial infections and in the correct dosage. Unnecessary use may not cure the illness and can cause side effects. Overuse of antibiotics can make bacteria resistant, meaning medicines may stop working in the future. In the long term, diseases may become harder to treat, medical costs may increase, and serious infections may spread more easily. Therefore, antibiotics should always be taken only on a doctor’s advice.