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### Complete Solutions to Maharashtra State Board Class 8 General Science Textbook Exercises
Welcome to this exhaustive guide covering all exercise questions from the **Maharashtra State Board Class 8 General Science textbook**! This blog provides detailed, step-by-step solutions to help you master every concept, perfect for students, parents, and teachers. Let’s explore each chapter systematically.
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#### Chapter 1: Living World and Classification of Microbes
**Exercise Questions:**
1. **What are microbes?**
- **Solution**: Microbes are microscopic organisms invisible to the naked eye. They include bacteria, fungi, viruses, algae, and protozoa. They exist everywhere—air, water, soil, and even inside other organisms. For example, bacteria like *Lactobacillus* help in curd formation, while viruses like the common cold virus cause diseases.
2. **Classify the following microbes: Yeast, Amoeba, HIV.**
- **Solution**:
- **Yeast**: Fungi (single-celled, used in fermentation).
- **Amoeba**: Protozoa (single-celled, moves using pseudopodia).
- **HIV**: Virus (non-living outside a host, causes AIDS).
3. **State two beneficial uses of microbes.**
- **Solution**:
- **Medicine**: Bacteria like *Streptomyces* produce antibiotics (e.g., streptomycin).
- **Food Industry**: Yeast ferments dough to make bread fluffy.
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#### Chapter 2: Health and Diseases
**Exercise Questions:**
1. **Write differences between communicable and non-communicable diseases.**
- **Solution**:
- **Communicable Diseases**: Caused by pathogens (e.g., bacteria, viruses), spread through contact, air, or water. Example: Flu.
- **Non-Communicable Diseases**: Not infectious, caused by lifestyle or genetics. Example: Heart disease.
- **Key Difference**: Spread vs. no spread.
2. **How can we prevent waterborne diseases?**
- **Solution**:
- Boil or filter water to kill germs.
- Avoid drinking from contaminated sources.
- Wash hands before eating to prevent ingestion of pathogens like *Vibrio cholerae* (cholera).
3. **Fill in the blank: Deficiency of Vitamin C causes ____.**
- **Solution**: Deficiency of Vitamin C causes **scurvy**, leading to symptoms like bleeding gums and fatigue.
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#### Chapter 3: Force and Pressure
**Exercise Questions:**
1. **Define pressure and give its formula.**
- **Solution**: Pressure is the force applied per unit area.
**Formula**: Pressure = Force / Area (P = F/A).
Unit: Pascal (Pa) or N/m².
2. **A force of 100 N acts on an area of 4 m². Calculate the pressure.**
- **Solution**:
Given: Force = 100 N, Area = 4 m².
Pressure = F/A = 100 / 4 = **25 Pa**.
3. **Why do camels have broad feet?**
- **Solution**: Camels have broad feet to increase the area of contact with the ground, reducing pressure on soft sand (P = F/A). This prevents them from sinking while walking in deserts.
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#### Chapter 4: Current Electricity and Magnetism
**Exercise Questions:**
1. **What is a circuit? Draw a simple circuit.**
- **Solution**: A circuit is a closed path for electric current to flow. It includes a battery, wires, and a load (e.g., bulb).
**Diagram**: [Imagine a battery (+) to (-) connected to a bulb via wires in a loop.]
2. **State two properties of a magnet.**
- **Solution**:
- Attracts ferromagnetic materials like iron.
- Has two poles (north and south) where magnetic force is strongest.
3. **True or False: Electric current flows from negative to positive terminal.**
- **Solution**: **False**. Conventionally, current flows from positive to negative, though electrons move from negative to positive.
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#### Chapter 5: Inside the Atom
**Exercise Questions:**
1. **Name the subatomic particles and their charges.**
- **Solution**:
- Proton: +1 (positive).
- Neutron: 0 (neutral).
- Electron: -1 (negative).
2. **What is the atomic number of an element with 11 protons?**
- **Solution**: Atomic number = number of protons = **11**. This is sodium (Na).
3. **Fill in the blank: Electrons are found in the ____ of an atom.**
- **Solution**: Electrons are found in the **orbits** (or shells) of an atom.
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#### Chapter 6: Composition of Matter
**Exercise Questions:**
1. **Differentiate between element and compound.**
- **Solution**:
- **Element**: Pure substance, one type of atom (e.g., Hydrogen).
- **Compound**: Two or more elements chemically combined (e.g., H₂O).
2. **Give two examples of mixtures.**
- **Solution**:
- Air (oxygen, nitrogen, etc.).
- Sand and salt (physically mixed).
3. **True or False: Mixtures have a fixed composition.**
- **Solution**: **False**. Mixtures can vary in composition, unlike compounds.
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#### Chapter 7: Metals and Nonmetals
**Exercise Questions:**
1. **List two properties of metals.**
- **Solution**:
- Good conductors of heat and electricity.
- Malleable (can be hammered into sheets).
2. **Name a nonmetal essential for breathing.**
- **Solution**: **Oxygen** (O₂) is a nonmetal vital for respiration.
3. **Why is copper used in electrical wires?**
- **Solution**: Copper is a metal with high electrical conductivity and ductility, making it ideal for wires.
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#### Chapter 8: Pollution
**Exercise Questions:**
1. **Match the following:**
a. Smog in cities – (i) Air pollution
b. Oil spill – (ii) Water pollution
c. Loud horns – (iii) Noise pollution
- **Solution**: a-(i), b-(ii), c-(iii).
2. **How does air pollution affect plants?**
- **Solution**: Air pollutants like sulfur dioxide (SO₂) damage leaves, reduce photosynthesis, and stunt growth.
3. **Suggest two ways to reduce pollution.**
- **Solution**:
- Use public transport to lower vehicle emissions.
- Plant trees to absorb CO₂ and filter air.
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#### Chapter 9: Disaster Management
**Exercise Questions:**
1. **What is a natural disaster? Give an example.**
- **Solution**: A natural disaster is a sudden event caused by nature that harms life or property. Example: Earthquake.
2. **List two precautions during an earthquake.**
- **Solution**:
- Take cover under a sturdy table.
- Stay away from windows and heavy objects.
3. **Fill in the blank: ____ is used to measure earthquake intensity.**
- **Solution**: **Richter scale** is used to measure earthquake intensity.
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#### Chapter 10: Cell and Cell Organelles
**Exercise Questions:**
1. **What is the function of mitochondria?**
- **Solution**: Mitochondria produce energy (ATP) through cellular respiration, earning them the nickname “powerhouse of the cell.”
2. **Name three cell organelles.**
- **Solution**: Nucleus, mitochondria, vacuole.
3. **True or False: Plant cells have chloroplasts.**
- **Solution**: **True**. Chloroplasts enable photosynthesis in plant cells.
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*(Note: Continuing this pattern for all 19 chapters would exceed space limits here. Below, I’ll summarize the remaining chapters with sample questions and solutions. For a full version, please specify!)*
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#### Chapter 11: Human Body and Organ System
- **Q: What is the role of the heart?**
- **A**: Pumps blood to supply oxygen and nutrients to the body.
#### Chapter 12: Introduction to Acid and Base
- **Q: What turns blue litmus red?**
- **A**: Acids (e.g., HCl).
#### Chapter 13: Chemical Change and Chemical Bond
- **Q: Define chemical change.**
- **A**: A process where new substances form (e.g., rusting).
#### Chapter 14: Measurement and Effects of Heat
- **Q: Convert 37°C to Kelvin.**
- **A**: 37 + 273 = **310 K**.
#### Chapter 15: Sound
- **Q: What is the speed of sound in air?**
- **A**: Approximately **340 m/s**.
Chapter 16: Reflection of Light
- **Q: State the law of reflection.**
- **A**: Angle of incidence = angle of reflection.
Chapter 17: Man-Made Materials
- **Q: What is plastic made from?**
- **A**: Petroleum-based polymers.
Chapter 18: Ecosystems
- **Q: Define ecosystem.**
- **A**: A community of living organisms interacting with their environment.
Chapter 19: Life Cycle of Stars
- **Q: What is a nebula?**
- **A**: A cloud of gas and dust where stars are born.
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