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Class 8th Science NCERT Notes and Solutions (Non-Rationalised)
1. Crop Production And Management
This chapter focuses on the practices involved in growing crops to provide food for the population, especially relevant in agrarian societies like India. It covers essential agricultural steps such as preparation of soil (ploughing, levelling), sowing seeds, adding manure and fertilisers to enrich soil, irrigation methods, protecting crops from weeds and pests, harvesting the mature crop, and proper storage of grains to prevent spoilage. Understanding these steps is crucial for efficient and sustainable agriculture.
2. Microorganisms : Friend And Foe
Microorganisms are tiny living creatures, some beneficial, others harmful. This chapter explores various types of microbes like bacteria, fungi, protozoa, and viruses. It discusses their positive roles, such as in making curd and bread, producing antibiotics, cleaning the environment through decomposition, and increasing soil fertility. It also highlights their negative impact as agents causing diseases in humans, plants, and animals, and methods to prevent and cure such diseases caused by microbes.
3. Synthetic Fibres And Plastics
This chapter introduces synthetic fibres (like rayon, nylon, polyester, acrylic), which are man-made materials with properties often superior to natural fibres for specific uses. It also discusses plastics, their types, properties (lightweight, durable, non-reactive), and uses in various everyday objects. The chapter raises concerns about the non-biodegradable nature of plastics and their impact on the environment, emphasizing responsible use and disposal methods.
4. Materials : Metals And Non-Metals
This chapter explores the properties of materials, categorizing them as metals and non-metals. It discusses the physical properties that distinguish them, such as lustre, hardness, malleability (ability to be hammered into sheets), ductility (ability to be drawn into wires), conductivity of heat and electricity, and state at room temperature. Chemical properties, including reactions with oxygen, water, acids, and bases, are also covered, along with the displacement reaction between metals.
5. Coal And Petroleum
Coal and petroleum are fossil fuels formed from the remains of ancient organisms, serving as major energy sources globally and in India. This chapter explains their formation process over millions of years, how they are obtained (mining for coal, drilling for petroleum), and their processing to get various products like coke, coal tar, petrol, diesel, kerosene, etc. It stresses that these are finite resources and need to be used judiciously.
6. Combustion And Flame
Combustion is the chemical process of burning a substance in the presence of oxygen to produce heat and light. This chapter identifies combustible substances and the conditions required for combustion (presence of fuel, oxygen, and achieving the ignition temperature). It discusses different types of combustion and the structure of a flame, seen during the burning of gaseous fuels, explaining its different zones and properties. It also touches upon controlling fire.
7. Conservation Of Plants And Animals
This chapter highlights the importance of preserving biodiversity and natural habitats. It discusses the causes and consequences of deforestation, such as soil erosion, desertification, and climate change. Concepts like species (endangered, extinct), flora, fauna, endemic species, and migratory birds are introduced. Methods of conservation, including establishing national parks, wildlife sanctuaries, and biosphere reserves in India, are discussed to protect forests and wildlife.
8. Cell — Structure And Functions
This chapter introduces the cell as the basic structural and functional unit of life. It explains the discovery of the cell and discusses the diversity in cell number, shape, and size. Key components of a cell, including the cell membrane, cell wall (in plants), cytoplasm, nucleus, chromosomes, and various organelles (like chloroplasts in plants), are described with their basic functions. Differences between plant and animal cells are also highlighted.
9. Reproduction In Animals
This chapter explains how animals produce new individuals to ensure the continuation of their species. It describes both asexual reproduction (like binary fission in Amoeba and budding in Hydra) and sexual reproduction, which involves the fusion of male and female gametes. **Fertilisation**, internal and external, is discussed, along with the development of the embryo and different stages of animal life cycles, such as metamorphosis in frogs and silkworms.
10. Reaching The Age Of Adolescence
Adolescence is the period of transition from childhood to adulthood, marked by significant physical and psychological changes. This chapter explores these changes, including growth spurts, alterations in body shape, voice change, increased activity of sweat and sebaceous glands, and development of secondary sexual characteristics. It discusses the role of hormones in initiating puberty and the importance of proper hygiene and nutrition during this critical developmental stage.
11. Force And Pressure
This chapter introduces **force** as a push or a pull that can change an object's state of motion or shape. It discusses types of forces (contact and non-contact, e.g., muscular, frictional, magnetic, electrostatic, gravitational) and their effects. **Pressure**, defined as force acting per unit area ($\textsf{Pressure} = \frac{\textsf{Force}}{\textsf{Area}}$), is explained, along with pressure exerted by liquids and gases. Examples illustrate how pressure depends on both force and area.
12. Friction
Friction is a force that opposes motion between surfaces in contact. This chapter explains the nature and causes of friction (interlocking of surface irregularities). Different types of friction – static, sliding, and rolling – are discussed, noting that rolling friction is usually less than sliding friction. The chapter explores how friction can be both useful (allowing us to walk, grip) and disadvantageous (causing wear and tear), and methods to increase or decrease it.
13. Sound
Sound is produced by vibrations and requires a medium to travel. This chapter explains the production and propagation of sound through solids, liquids, and gases. It introduces characteristics of sound, such as amplitude (related to loudness), frequency (related to pitch), and speed. Differentiating between musical sound and noise, the harmful effects of noise pollution, and methods to control it are also discussed.
14. Chemical Effects Of Electric Current
This chapter explores the chemical changes that can occur when electric current passes through certain liquids. It introduces the concept of electrolytes and the process of **electrolysis**, where current causes decomposition. Experiments demonstrating this effect are discussed. Applications like **electroplating** (depositing a thin layer of one metal on another for decoration or protection) and its uses in various industries are highlighted, showing the practical significance of these chemical effects.
15. Some Natural Phenomena
This chapter examines two powerful and sometimes destructive natural phenomena: **lightning** and **earthquakes**. It explains how lightning is caused by the accumulation and discharge of electric charges in the atmosphere, discussing lightning safety measures. Earthquakes are described as vibrations in the Earth's crust caused by tectonic plate movements, mentioning the Richter scale for measuring magnitude and safety precautions during an earthquake. The chapter creates awareness about these natural hazards.
16. Light
This chapter delves into the nature of light and how we see. It explains reflection (bouncing back of light) and introduces the laws of reflection. Image formation by plane mirrors and spherical mirrors (concave and convex) is discussed using ray diagrams. It also covers the structure and working of the **human eye**, common eye defects and their correction, and the importance of eye donation, reflecting a civic sense perspective.
17. Stars And The Solar System
This chapter takes you on a journey through space, exploring celestial objects visible in the night sky. It introduces stars and constellations. The **Solar System**, comprising the Sun, planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), asteroids, comets, and meteoroids, is discussed. The Moon, its phases, and artificial satellites are also covered, providing a basic introduction to astronomy and the vastness of the universe.
18. Pollution Of Air And Water
This chapter addresses the critical environmental issue of pollution, focusing on air and water. It identifies major air pollutants (e.g., sulfur dioxide, nitrogen oxides, particulate matter) and their sources (vehicles, industries, burning fuels) and harmful effects (acid rain, respiratory problems). Water pollution, its causes (sewage, industrial waste, agricultural runoff), and consequences are discussed. The chapter stresses the need for measures to prevent and control air and water pollution for a healthier environment.