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Latest Class 8th Science NCERT Concepts & Solutions
1. Crop Production And Management
This chapter focuses on the systematic agricultural practices crucial for large-scale food production. It details the entire process, starting with the preparation of soil through ploughing and levelling, followed by the selection and sowing of healthy seeds. It explains the importance of replenishing soil nutrients by adding organic manure and chemical fertilisers. The chapter covers various irrigation methods, the removal of unwanted plants (weeds), and the protection of crops from pests. Finally, it discusses the processes of harvesting, threshing, winnowing, and the critical need for proper storage of grains to prevent spoilage and ensure food security.
2. Microorganisms : Friend And Foe
Microorganisms are tiny living beings, invisible to the naked eye, that are found everywhere. This chapter explores their diverse world, categorising them into major groups: bacteria, fungi, protozoa, algae, and viruses. It highlights their dual nature. As friends, they are crucial for making curd and bread (fermentation), producing antibiotics and vaccines, and decomposing organic waste. As foes, these microbes, also known as pathogens, cause diseases in humans, plants, and animals, such as typhoid, malaria, and the common cold. The chapter also discusses food preservation techniques to prevent spoilage by harmful microbes.
3. Coal And Petroleum
Coal and petroleum are vital fossil fuels, which are exhaustible natural resources formed from the remains of dead organisms over millions of years. This chapter explains the formation of coal through the slow process of carbonisation and its various uses. It describes how petroleum (crude oil) is formed and extracted, and details the process of refining it to obtain useful products like petrol, diesel, kerosene, and LPG. The chapter strongly emphasizes that these energy sources are finite and their combustion contributes to air pollution, stressing the urgent need for their judicious use and conservation.
4. Combustion And Flame
Combustion is a chemical process in which a substance reacts with oxygen to produce heat and light. This chapter explores the essentials of burning, identifying combustible and non-combustible substances. It explains that three conditions are necessary for combustion: the presence of a fuel, a supply of oxygen (air), and attaining the substance's ignition temperature. It discusses different types of combustion (rapid, spontaneous, explosion) and fire control methods. The chapter also provides a detailed explanation of the structure of a candle flame, describing its three distinct zones: the dark innermost zone, the yellow luminous middle zone, and the blue non-luminous outer zone.
5. Conservation Of Plants And Animals
Protecting our planet's rich biodiversity is crucial for ecological balance. This chapter discusses the importance of conserving plants and animals. It explains the causes of deforestation and its devastating consequences, such as soil erosion, desertification, and climate change. The chapter introduces key concepts like endemic species (found only in a particular area) and endangered species (facing extinction). It highlights conservation efforts through the establishment of protected areas like Wildlife Sanctuaries, National Parks, and Biosphere Reserves, which aim to preserve natural habitats and their flora and fauna.
6. Reproduction In Animals
Reproduction is the fundamental biological process by which organisms produce offspring, ensuring the continuation of a species. This chapter explains the two main modes of reproduction in animals. It details asexual reproduction, where a single parent is involved, with examples like budding in Hydra and binary fission in Amoeba. It then provides a comprehensive look at sexual reproduction, which involves the fusion of specialized male and female cells called gametes (sperm and ovum). The process of fertilisation—the fusion of gametes to form a zygote—is explained, differentiating between internal and external fertilisation.
7. Reaching The Age Of Adolescence
Adolescence is the transitional period between childhood and adulthood, marked by significant physical and psychological changes. This chapter delves into the process of puberty, which leads to reproductive maturity. It explains the role of hormones secreted by endocrine glands in triggering these changes, such as a sudden increase in height, changes in body shape, and voice modulation. The development of secondary sexual characteristics is detailed for both boys and girls. The chapter also emphasizes the importance of a balanced diet, personal hygiene, and emotional well-being during this critical stage of growth.
8. Force And Pressure
A force is a push or a pull that can change an object's state of motion, speed, direction, or shape. This chapter introduces the concept of force and its various effects. It differentiates between contact forces (like muscular force and friction) and non-contact forces (like magnetic, electrostatic, and gravitational forces). The chapter then explains pressure, defined as the force acting on a unit area ($\textsf{Pressure} = \frac{\textsf{Force}}{\textsf{Area}}$). It explores how pressure is exerted by solids, liquids, and gases, and introduces the concept of atmospheric pressure, illustrating its applications in our daily lives.
9. Friction
Friction is a force that opposes the relative motion between surfaces in contact. This chapter explains that friction is caused by the interlocking of irregularities on the two surfaces. It discusses the different types of friction: static (on a stationary object), sliding, and rolling, highlighting that rolling friction is the smallest. The chapter describes friction as a "necessary evil"—it is essential for actions like walking and writing, but also causes undesirable wear and tear. Methods to reduce friction using lubricants or ball bearings, and ways to increase it for better grip, are also explored.
10. Sound
Sound is a form of energy produced by vibrating objects. This chapter explores how sound is produced and how it propagates as waves through a medium (solid, liquid, or gas). A key concept is that sound cannot travel through a vacuum. It discusses the essential characteristics of sound: amplitude, which determines its loudness (measured in decibels), and frequency, which determines its pitch (measured in Hertz). The chapter explains the structure and function of the human ear, and distinguishes between audible and inaudible sounds, pleasant musical sounds, and unpleasant noise.
11. Chemical Effects Of Electric Current
When electric current passes through certain conducting liquids, called electrolytes, it can cause chemical reactions. This chapter introduces these chemical effects. The process of decomposing an electrolyte using electricity is known as electrolysis. The chapter demonstrates this with simple experiments, showing how electrodes attract ions. It then focuses on a major practical application: electroplating. This is the process of depositing a layer of a desired metal onto another material by means of electricity, used for purposes like preventing corrosion (coating iron with zinc) or for appearance (coating objects with silver or gold).
12. Some Natural Phenomena
This chapter examines two powerful and destructive natural phenomena: lightning and earthquakes. It explains lightning as a massive electric discharge occurring between clouds, or between clouds and the Earth, due to the accumulation of static charges. It also discusses safety measures and the function of a lightning conductor. The chapter then describes earthquakes as sudden shaking or trembling of the Earth's crust caused by disturbances deep inside it. It introduces the concept of seismic waves, the Richter scale for measuring earthquake magnitude, and highlights crucial safety precautions to take during an earthquake.
13. Light
This chapter expands on the properties of light. It revisits the laws of reflection and discusses different types of reflection (regular and diffused). It introduces refraction, the bending of light as it passes from one medium to another. The chapter explains the functioning of lenses, differentiating between convex lenses (converging) and concave lenses (diverging). It provides a detailed look at the structure and working of the human eye, explaining how it forms an image on the retina. Finally, it explains the phenomenon of dispersion—the splitting of white light into its seven constituent colours (VIBGYOR), as seen in a rainbow.