| Science NCERT Exemplar Solutions (Class 6th to 10th) | ||||||||||||||
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| Science NCERT Exemplar Solutions (Class 11th) | ||||||||||||||
| Physics | Chemistry | Biology | ||||||||||||
| Science NCERT Exemplar Solutions (Class 12th) | ||||||||||||||
| Physics | Chemistry | Biology | ||||||||||||
Class 8th Science NCERT Exemplar Solutions
1. Crop Production And Management
This chapter details the systematic agricultural practices followed to cultivate crops and ensure sufficient food supply for the population, highly relevant in India. It covers essential steps like **preparation of soil** (ploughing, levelling), **sowing** of seeds, providing **nutrients** through manure and fertilisers, **irrigation** methods, protecting crops from weeds and pests, **harvesting** the mature crop, and proper **storage** of produce to prevent spoilage and wastage. Understanding these steps is crucial for improving agricultural yield and efficiency.
2. Microorganisms : Friend And Foe
Microorganisms are tiny living beings found everywhere, some beneficial to humans and others harmful. This chapter explores various types of microbes including bacteria, fungi, protozoa, and viruses. It discusses their positive roles, such as in making curd, bread, and cheese, producing antibiotics, decomposing organic matter, and increasing soil fertility (e.g., nitrogen-fixing bacteria). It also highlights their negative impact as disease-causing agents in humans, plants, and animals, and introduces methods to prevent diseases and food spoilage caused by them.
3. Synthetic Fibres And Plastics
This chapter introduces **synthetic fibres** (man-made fibres like nylon, rayon, polyester, acrylic), discussing their properties (e.g., strength, durability, wrinkle resistance) and wide range of uses in clothing, ropes, and other items. It also explores **plastics**, their types (thermoplastics, thermosetting plastics), properties (lightweight, corrosion-resistant, easily mouldable), and applications. The chapter raises significant environmental concerns regarding the **non-biodegradable** nature of plastics and the need for responsible use, recycling, and managing plastic waste for a sustainable future.
4. Materials : Metals And Non-Metals
This chapter classifies common materials into **metals** and **non-metals** based on their distinct physical and chemical properties. Physical properties discussed include lustre, hardness, malleability, ductility, conductivity of heat and electricity, and state at room temperature. Chemical properties cover their reactions with oxygen, water, acids, and bases. The chapter also introduces the **Reactivity Series** of metals, explaining why some metals displace others from their compounds, crucial for understanding chemical reactions and metallurgical processes.
5. Coal And Petroleum
Coal and petroleum are major **fossil fuels**, non-renewable energy sources formed over millions of years from the remains of ancient organisms. This chapter explains their formation, extraction (mining for coal, drilling for petroleum), and the various products obtained from their processing (e.g., coke, coal tar, petrol, diesel, kerosene, LPG). The chapter emphasizes that these resources are **finite** and need to be conserved, highlighting the urgency to explore and utilize alternative sources of energy for future sustainability.
6. Combustion And Flame
This chapter focuses on **combustion**, the chemical process of burning a substance in the presence of oxygen to produce heat and light. It identifies **combustible substances** and the conditions necessary for combustion (fuel, oxygen, ignition temperature). Different types of combustion (rapid, spontaneous, explosion) are discussed. The structure of a **flame**, observed when gaseous substances burn, is explained with its different zones and temperatures. The chapter also touches upon controlling fires by removing one or more of the necessary conditions for combustion.
7. Conservation Of Plants And Animals
This chapter highlights the critical need to protect **biodiversity** and natural ecosystems. It discusses the causes and consequences of **deforestation**, including soil erosion, desertification, and climate change. Concepts like **endangered species**, extinction, flora, and fauna are introduced. Measures for **conservation** are explained, including the establishment of wildlife sanctuaries, national parks, and biosphere reserves in India to protect habitats and species. The chapter emphasizes the importance of human efforts in preserving the rich natural heritage for ecological balance and future generations.
8. Cell — Structure And Functions
This chapter introduces the **cell** as the basic structural and functional unit of all living organisms. It describes the discovery of the cell and the diversity in cell number, shape, and size. Key components of a cell, including the **cell membrane**, **cell wall** (in plants), **cytoplasm**, and **nucleus**, are discussed. Various **cell organelles** like vacuoles, plastids, mitochondria, and ribosomes, located within the cytoplasm, are introduced with their basic functions, providing a microscopic view of life and the differences between plant and animal cells.
9. Reproduction In Animals
This chapter explains how animals produce new individuals, a vital process for the continuation of species. It covers both **asexual reproduction**, involving a single parent (e.g., binary fission in Amoeba, budding in Hydra), and **sexual reproduction**, involving the fusion of male and female gametes (**fertilisation**). The chapter details internal and external fertilisation. The development of the embryo and the different life cycles in animals, including **metamorphosis** in organisms like frogs and silkworms, are also discussed, illustrating the various ways animals multiply.
10. Reaching The Age Of Adolescence
**Adolescence** is a significant period of transition from childhood to adulthood, marked by profound physical and psychological changes. This chapter explores the onset of puberty and the changes that occur, including growth spurts, changes in body shape and voice, increased activity of glands, and the development of secondary sexual characteristics, triggered by hormones. The chapter also discusses the importance of personal hygiene, proper nutrition, and reproductive health during this crucial stage of development, providing essential information for teenagers.
11. Force And Pressure
This chapter introduces the concepts of **force** and **pressure**. A force is defined as a push or pull that can change an object's state of motion or shape. Different types of forces, both contact (e.g., muscular, friction) and non-contact (e.g., magnetic, electrostatic, gravitational), are discussed. **Pressure** is defined as the force acting per unit area ($\textsf{Pressure} = \frac{\textsf{Force}}{\textsf{Area}}$), explaining how it depends on both the applied force and the area over which it acts. Pressure exerted by liquids and gases is also covered, illustrating its presence in everyday phenomena.
12. Friction
**Friction** is a force that opposes the relative motion between two surfaces in contact. This chapter explains the causes of friction (interlocking of irregularities on surfaces) and discusses different types of friction: static friction (opposing initiation of motion), sliding friction (opposing sliding motion), and rolling friction (opposing rolling motion), noting that rolling friction is generally the least. The chapter explores situations where friction is useful (e.g., walking, braking) and where it is undesirable (e.g., wear and tear), and discusses methods to increase or decrease friction.
13. Sound
**Sound** is a form of energy produced by **vibrations**. This chapter explains how sound is produced and requires a material medium (solid, liquid, or gas) to propagate, demonstrating that it cannot travel through a vacuum. Key characteristics of sound waves, such as amplitude (related to loudness), frequency (related to pitch), time period, and speed, are discussed. The chapter differentiates between musical sound and noise, highlighting the harmful effects of **noise pollution** and measures to reduce it, emphasizing the physical properties of sound.
14. Chemical Effects Of Electric Current
This chapter explores the **chemical changes** that can occur when electric current passes through certain liquids known as electrolytes. It introduces the process of **electrolysis**, where current decomposes a substance. Experiments demonstrating the conduction of electricity through liquids and the resulting chemical effects are discussed. The chapter highlights practical applications of these chemical effects, such as **electroplating** – depositing a thin layer of one metal onto another for protection or decoration (e.g., chrome plating on taps, gold plating on jewellery), which is common in various industries.
15. Some Natural Phenomena
This chapter focuses on understanding two significant and often destructive natural events: **lightning** and **earthquakes**. It explains how **lightning** is caused by the accumulation and discharge of electric charges in storm clouds and between clouds and the ground, discussing lightning safety. **Earthquakes** are described as sudden vibrations in the Earth's crust, their causes (plate tectonics), and how their intensity is measured (Richter scale). The chapter emphasizes precautions and safety measures to be taken during these natural calamities to minimize harm and loss of life.
16. Light
This chapter delves into the properties of **light** and how we perceive the world visually. It revisits **reflection** from surfaces and the laws of reflection. The formation of images by plane mirrors and **spherical mirrors** (concave and convex) is discussed using ray diagrams. The chapter also covers the structure and working of the **human eye**, explaining how it forms images and common vision defects like myopia and hypermetropia and their correction. The importance of eye donation is also highlighted from a social perspective.
17. Stars And The Solar System
This chapter takes you on an astronomical journey beyond Earth, exploring the celestial objects we see in the night sky. It introduces **stars**, **constellations**, and the concept of light-years as a unit of astronomical distance. The **Solar System**, comprising the Sun, eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), asteroids, comets, and meteoroids, is described. The Moon, its phases, and artificial satellites are also covered, providing a basic understanding of our place in the vast universe and the movements of celestial bodies.
18. Pollution Of Air And Water
This chapter addresses the critical environmental issue of **pollution**, focusing specifically on air and water. It identifies major sources and types of **air pollutants** (e.g., smoke, dust, gases) and their harmful effects on human health, plants, and buildings (e.g., acid rain). Similarly, sources and types of **water pollutants** (e.g., sewage, industrial waste, agricultural chemicals) and their consequences for aquatic life and human health are discussed. The chapter emphasizes the importance of reducing pollution and adopting measures to protect air and water resources for a healthy environment, relevant to India's pollution challenges.