7th Class

Winds, Storms and Cyclones   Synopsis  
  • Air exerts pressure.
 
  • Moving air is known as wind. Winds are accompanied by low pressure.
 
  • Air always moves from a region of high pressure to a region of low pressure.
 
  • Air expands on heating. Warm air is lighter than cold air.
 
  • Wind currents are caused because of uneven heating of the earth.
 
  • Uneven heating of the land is a result of the variation in distances from the sun and wind movements.
 
  • Rains are caused by monsoon winds that carry water in them.
 
  • When water is heated up, it changes into vapour.
 
  • The swift movement of the falling water droplets along with the rising air create lightning and sound. It is called as thunderstorm.
 

Water : A precious Resource   Synopsis  
  • Water is the most essential thing for the existence of life. Water is an extremely stable compound. It does not decompose into its constituents, hydrogen and oxygen, easily.
 
  • Water exists in three states - solid, liquid and gas.
 
  • About \[71%\]of the earth's surface is covered with water but only \[0.006%\] of the water found on the earth is available for our use.
 
  • The continuous cycling of water among its three forms keeps the total amount of water constant. This is known as water cycle.
 
  • Though water is maintained by the water cycle, yet there is an acute scarcity of water in many parts of the globe.
 
  • There is an uneven distribution of water. Much of it has resulted from human activities.
 

Nutrition in Plants   Synopsis  
  • Green plants, synthesise their food themselves by the process of photosynthesis. They are autotrophs. Non-green plants and animals are heterotrophs.
 
  • Photosynthesis can be summarised as follows.
  \[\text{carbon}\,\text{dioxide+}\,\text{water}\xrightarrow[\text{Chlorophyll}]{\text{Sunlight}}\text{Glucose+Oxygen}\]  
  • Photosynthesis provide food and oxygen to all the living organisms.
 
  • The Sun is the ultimate source of energy for all living organisms.
 
  • Gaseous exchange in the leaves takes place through tiny pores, which are generally located on the lower surface of a leaf called stomata.
 
  • In some plants like crotons, the green colour of the chlorophyll is hidden by other pigments and appear dark red.
 
  • Some plants like pitcher plant and venus fly trap, feed on trapped insects and fulfill their nitrogen requirement. They are called insectivorous plants.
 
  • The organisms which feed on dead more...

Nutrition in Animals   Synopsis  
  • Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body.
 
  • Nutrition in animals involves five steps-ingestion, digestion, absorption, assimilation and egestion.
 
  • The human digestive system consists of the alimentary canal and digestive glands.
 
  • We have 32 permanent teeth, which are classified into incisors, canines, premolars and molars according to their shapes and specific functions.
 
  • The digestion process begins in the mouth. The saliva break down the starch into sugars.
 
  • The stomach wall secretes gastric juice, which contain hydrochloric acid and pepsin. The acid kills many bacteria that enter along with the food.
 
  • Liver secretes bile juice. The bile helps in the digestion and absorption of fats.
 
  • The pancreatic juice secreted by pancreas acts on carbohydrates, fats more...

Fibre to Fabric   Synopsis  
  • Clothes protect us from heat, cold and other adverse climatic conditions.
 
  • All clothes are made from fibres.
 
  • The fibres can be natural, i.e., of plant or animal origin, or synthetic, i.e., man-made.
 
  • Wool is obtained from the fleece or hair of sheep, goat, yak, camel, Llama and alpaca.
 
  • Silk comes from silk worms. Silk worms are caterpillars of silk moth.
 
  • Sheep hair is sheared off from the body to yield wool by the following process. Processing of fibres into wool
 
  • Shearing\[\to \]Scouring\[\to \]Sorting\[\to \]Drying\[\to \] Dyeing \[\to \] Spinning \[\to \] Weaving
 
  • A pile of cocoons is used for obtaining silk fibres.
 
  • The cocoons are kept under the sun or boiled or exposed to steam to separate out silk more...

Soil   Synopsis  
  • Soil is the uppermost layer of earth's crust. It is formed of rock particles and organic matter called humus.
 
  • Soil is a good habitat. Plants depend on soil for nutrients like mineral salts and water.
 
  • We depend on soil for agricultural and construction purposes, making utensils and toys.
 
  • Soil is important for life on the earth. It supports the existence of living organisms. It is essential for agriculture.
 
  • Soil is formed by the weathering of rocks by the action of wind, water and climate. It contains coarse particles, clay, moisture and humus. Soil contains three important layers: top soil, subsoil and bed rock.
 
  • Soil profile consists of three horizons. Top soil or Horizon-A, Middle layer or Horizon-B. Third layer or Horizon-C.
 
  • Soil is of different types: Clayey, more...

Respiration in Organisms   Synopsis  
  • Respiration is essential for survival of living organisms. It releases energy from the food.
 
  • Breathing is a part of the process of respiration during which an organism takes in the oxygen rich air and gives out air rich in carbon dioxide.
 
  • Taking in of oxygen is called inspiration or inhalation. Giving out of carbon dioxide is called expiration or exhalation. During inhalation, our lungs expand and then come back to its original position as the air moves out during exhalation.
 
  • Anaerobic respiration is otherwise known as fermentation. Fermentation is a biochemical process in which certain microorganisms like fungi and bacteria oxidise carbohydrates with the evolution of \[C{{O}_{2}}\] and production of ethyl alcohol or lactic acid. Accumulation of lactic acid in muscle cells causes muscle cramps or muscle fatigue.
 

Transportation in Living Beings   Synopsis  
  • Transport system for carrying food materials and waste is must for an organism to survive. Mode of transportation could be either diffusion, osmosis, absorption or circulation of blood through blood vessels in the higher organisms.
 
  • Human circulatory system consists of blood, blood vessels and the heart.
 
  • Blood is a fluid connective tissue which consists of plasma, red blood cells, white blood cells and blood platelets. Red colour of the blood is due to the presence of the pigment hemoglobin, white blood cell protects the body from harmful microorganisms and infections.
 
  • Arteries carry pure blood from the heart to the other organs of the body and veins coiled impure blood from different parts of the body and carry to the heart.
 
  • Pulmonary artery carries impure (deoxygenated) blood from the heart to more...

Reproduction and Growth In Plants   Synopsis  
  • The phenomenon of formation of new individuals from the existing ones to increase the population is called reproduction.
 
  • Reproduction can be broadly grouped into two types: asexual reproduction and sexual reproduction.
 
  • There are several methods of asexual reproduction such as fragmentation, budding, spore formation and vegetative propagation.
 
  • Sexual reproduction involves the fusion of male and female gametes.
 
  • New plants produced from different vegetative parts such as leaves, stems and roots is called vegetative propagation.
 
  • A flower is a modified shoot, meant for reproduction. There are four whorls in a flower - Calyx (sepals) corolla (petals), androecium (stamens) and gynoecium (carpels) arranged on the thalamus called receptacle.
 
  • Calyx and corolla form the accessory whorls, while androecium and gynoecium form the reproductive whorls.
  more...

Resource on Earth-Forests and Ecosystems   Synopsis  
  • Plants and animals depend on each other and this is important for the survival of both the organisms.
 
  • Forest is a system comprising of various plants, animals and microorganisms.
 
  • In a forest; trees form the uppermost layer, followed by shrubs. The herbs form the lowest layers of vegetation.
 
  • Forests regulate the climate by bringing down the temperature and increasing rainfall. They maintain the gaseous balance in air and control pollution by absorbing dust.
 
  • Forests are sources of timber, fuel, medicines, oils, resins, cane etc. They check soil erosion, control floods and help to recharge groundwater.
 
  • Deforestation began by clearing forests so that crops could be grown. This leads to the destruction of ecosystem.
 
  • Soil erosion is caused when the top soil is carried more...


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