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8th Class

Pollution of Air and Water

Pollution of Air and Water   Synopsis  
  • Pollution is the introduction of harmful substances into the environment, which can harm the health, survival or activities of living organisms. Pollutants may be biodegradable or non-biodegradable. Biodegradable pollutants can be broken down by biological agents, whereas non-biodegradable pollutants cannot be broken down by any agents and remain in the environment for a long time.
 
  • The major causes of air pollution are industries and automobiles. The burning of fossil fuels releases carbon dioxide, carbon monoxide, sulphur dioxide, oxides of nitrogen, hydrocarbons and particulate matter. Industrial processes release polluting gases and particulate matter.
 
  • The oxides of nitrogen and sulphur combine with rainwater to form acid rain, which affects more...
Catgeory: 8th Class

Cell

Cell   Synopsis  
  • The structural and functional unit of living organisms is a cell. Organisms that consist of only one cell are called unicellular. A tissue is made of cells. Tissues organise to form organs which in turn form organ systems and the organism.
 
  • Cells without well organised nucleus, i.e., lacking nuclear membrane, are called prokaryotic cells and cells with definite nucleus are called eukaryotic cells.
 
  • The cell is enclosed by a cell membrane enclosing the cytoplasm, nucleus and cell organelles.
 
  • The cell membrane is selectively permeable, i.e., it lets the passage of certain substances only.
 
  • The cytoplasm contains organelles, water and many dissolved substances such as proteins, more...
Catgeory: 8th Class

Microorganisms

Microorganisms   Synopsis  
  • Microorganisms are tiny organisms that can be seen only under a microscope.
 
  • Microorganisms are classified into: bacteria, fungi, protozoa, viruses and algae.
  Useful mocroorganisms:  
  • coli bacteria produce vitamins \[{{B}_{12}}\] and K. In herbivores and in some insects, bacteria and protozoa digest cellulose.
  Decomposition and recycling of materials:  
  • Microorganisms such as bacteria, protozoa and fungi break down the harmful organic portion of raw sewage to less harmful sludge.
  Medicine and health supplements:  
  • Antibiotic penicillin is produced by a type of fungus Penicillium notatum. Insulin used for treating diabetics is produced by genetically modified bacteria, a vaccine, consisting of dead or weakened harmful microorganisms.
    • more...
Catgeory: 8th Class

Conservation of Plants and Animals

Conservation of plant and Animals   Synopsis  
  • The physical and biological world we live in is called our environment.
 
  • Biodiversity refers to the variety of living organisms in a specific area.
 
  • Plants and animals of a particular area are known as the flora and fauna of that area.
 
  • The term wildlife refers to plants and animals living in the natural conditions. It serves as a source of genes or a gene bank.
 
  • Over-exploitation of wildlife for economically useful products, deforestation, in dustrialisation and pollution resulted in extinction of several plant and animal species.
 
  • Red Data Book contains a record of endangered species. Conservation involves keeping more...
Catgeory: 8th Class

Reproduction in Animals

Reproduction in Animals   Synopsis  
  • Reproduction is the production of new individuals more or less similar to the parent organisms. This may be achieved by a number of means and serves to perpetuate increase of species.
 
  • There are two main methods in which organisms give rise to new individuals - Asexual reproduction and sexual reproduction.
 
  • Asexual reproduction is the process of producing new organism(s) from a single parent without the involvement of sex cells or gametes.
  e.g., Binary fission in amoeba, regeneration in planaria, budding in hydra.  
  • Sexual reproduction is the process of producing new organism(s) from two parents with the involvement of sex cells or gametes. Male sexual unit more...
Catgeory: 8th Class

Reaching the Age of Adolescence

Reaching the Age of Adolescence   Synopsis  
  • Humans become capable of reproduction after puberty sets in. Between the ages of 11 years and 19 years children are called adolescents.
 
  • The period of time when a person changes from a child into an adult is called puberty.
 
  • A boy reaches puberty when he is 13-14 years old. Girls reach puberty earlier than boys at the age of 11 -12 years.
 
  • During puberty, physical and emotional changes take place. These are called secondary sexual characters. In girls, puberty is marked by the onset of menstruation and the development of secondary sexual characters, namely, enlargement of breasts, widening of pelvic girdle and growth of more...
Catgeory: 8th Class

NCERT Summary - Elements

  Elements   Elements  
  • An element is a substance which can neither be broken nor built from two or more simple substances by any physical or chemical method. Or in other words an elements is a pure substance which contains only one kind of atom, e.g., Fe (Iron), Na (Sodium), etc.
  Types of Elements (a) Metals (b) Non-Metals (c) Metalloids   COMPOUNDS
  • A compound is a pure substance which contains more than one kind of elements or atom in fixed proportion by weight e.g., NaCl (Sulphur dioxide), (Sodium chloride),\[S{{O}_{2}}\]etc.
  Types of Compounds (a) Organic compounds (b) Inorganic compounds
  • The properties of a compound are completely different from those of its constituents.
  MIXTURES
  • A material containing two or more elements or compounds in any proportion is a mixture. more...
Catgeory: 8th Class

NCERT Summary - Metals Its Physical Properties

  Metals and its Physical Properties     Metals and its Physical Properties   (a) Physical Change: A physical change is a change of state only and is not accompanied by an alteration in the chemical composition, weight or chemical properties of any substance, e.g., melting of ice, magnetising a needle, etc. (b) Chemical Change: A chemical change gives rise to a new substance having composition and properties altogether different from those of the original substance, e.g., radioactive decay, rusting of iron, photosynthesis, etc. Energy is absorbed or released during a chemical change.   PHYSICAL AND CHEMICAL PROPERTIES (a) Physical Properties: The properties which do not depend on reaction with any other substance, e.g., colour, melting point, boiling point, density, etc. (b) Chemical Properties: The chemical properties of a substance are those that describe its reactions with other substances.   EMPIRICAL FORMULA
Catgeory: 8th Class

NCERT Summary - Carbon

Carbon The Carbon   The Carbon
  • Group 14 (IVA) consists of carbon, silicon, germanium, tin and lead. Carbon is a non-metal, silicon and germanium are metalloids, tin and lead are metals.
    • Carbon is a very important element. This is due to 3 reasons:
  • Carbon is a tetravalent atom. It may form four covalent bonds in different directions tetrahedrally.
    • Carbon has several allotropes, three of which are common.
(i)   Amorphous carbon is coal and soot. The carbon molecules are covalently bonded but there is no order of arrangement. (ii)   Graphite occurs when carbon forms flat covalent networks. These flat "sheets" are not bonded to each other, making them free to slide past each other. Graphite composes the "lead" in pencils. Since graphite contains free electrons, it is a good conductor of heat and electricity. Graphite is used as a more...
Catgeory: 8th Class

NCERT Summary - Man-Made Materials

Man-Made Materials   Soaps
  • Soaps are sodium or potassium salts of higher fatty acids (organic acids that have more than 16 carbon atoms in their molecules) like stearic, palmitic and oleic acids.
  • The sodium soaps are called hard soaps and the potassium soaps are known as soft soaps.
  Differences between Soaps and Detergents
Soaps Detergents
They are metallic salts of long chain higher fatty acids, These are sodium salts of long chain hydrocarbons like alky1 sulphates or alkyl benzene sulphonates.
These are prepared from vegetable oils and animals fats. They are prepared from hydrocarbons of petroleum or coal.
They cannot be used effectively in hard water as they produce scum, i.e., insoluble precipitates of more...
Catgeory: 8th Class

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