Science Class 07 part-I NCERT

1. Nutrition in plants
1. Plants are the only organisms that can prepare food for themselves. Leaves are the food factories of plants.
1. The synthesis of food in plants occurs in leaves. Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves.
2. These pores are surrounded by ‘guard cells� Such pores are called stomata. Chlorophyll helps leaves to capture the energy of the sunlight.
3. Sun is the ultimate source of energy for all living organisms
2. Besides leaves, photosynthesis also takes place in other green parts of the plant — in green stems and green branche .
1. During photosynthesis, oxygen is released.
2. The carbohydrates ultimately get converted into starch. The presence of starch in leaves indicates the occurrence of photosynthesis.
3. The starch is also a carbohydrate.
3. The leaves other than green also have chlorophyll. The large amount of red, brown and other pigments mask the green color. There are some plants which do not have chlorophyll (amarbel).
4. Mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition. Plants which use saprotrophic mode of nutrition are called saprotrophs.
5. In lichens, a chlorophyll-containing partner, which is an alga, and a fungus live together. Alga prepares the food.
6. Carbohydrates are made of carbon, hydrogen and oxygen. These are used to synthesize other components of food such as proteins and fats. But proteins are nitrogenous substances which contain nitrogen.
7. The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form. But Rhizobium cannot make its own food.
8. So it lives in the roots of gram, peas, moong, beans and other legumes and provides them with nitrogen.
2. Nutrition in animals
1. Breakdown of complex components of food into simpler substances is called digestion. Starfish feeds on animals covered by hard shells of calcium carbonate.
2. Digestion in humans - through alimentary canal. The inner walls of the stomach and the small intestine, and the various glands associated with the canal such as salivary glands, the liver and the pancreas secrete digestive juices.
3. The digestive tract and the associated glands together constitute the digestive system.
4. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. It is free at the front and can be moved in all directions. Inside the throat, air and food share a common passage
5. Food is pushed down by movement of the wall of the food pipe. The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices. The mucous protects the lining of the stomach.
6. The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic and helps the digestive juices to act. The digestive juices break down the proteins into simpler substances.
7. Small intestine is highly coiled and is about 7.5m long. It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices.
8. Liver is the largest gland in the body; secretes bile juice that is stored in a sac called the gall bladder, plays an important role in the digestion of fats.
9. Lower part of the small intestine is where the intestinal juice completes the digestion of all components of the food. The carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol, and proteins into amino acids
10. The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi; increase the surface area for absorption of the digested food. Large intestine is wider and shorter than small intestine.
11. It is about 1.5m in length. Its function is to absorb water and some salts from the undigested food material.
12. Cows quickly swallow the grass (rich in cellulose, humans can't digest) and store it in part of stomach called rumen.
13. It get partially digested and is called cud. Later the cud returns to the mouth in small lumps and the animal chews it. This process is called rumination and these animals are called ruminants.
14. Amoeba ingests its food with the help of its false feet or pseudopodia. The food is digested in the food vacuole.
3. Fiber to fabric
1. Air is a poor conductor of heat. Hair trap a lot of air. Yak wool is common in Tibet and Ladakh. Angora wool is obtained from angora goats, found in hilly regions such as J&K. Natural fleece of sheep and goats is black, brown or white in color.
2. Wool sorter’s job is risky as sometimes they g infected by a bacterium, anthrax, which causes a fatal blood disease called sorter’s disease.Silk fibers are also animal fibers. Soft silk yarn is as strong as a comparable thread of steel. Silk yarn (thread) is obtained from the cocoon of the silk moth. Silkworms are caterpillars of silk moth.
3. The process of taking out threads from the cocoon for use as silk is called reeling the silk. Most common silk moth is the mulberry silk moth.
4. Heat
1. Clinical thermometer is designed to measure the temperature of human body only. The temperature of human body normally does not go below 35°C or above 42°C.� Kink in thermometer prevents mercury level from falling on its own. The normal temperature of human body is 37°C.
Range of a laboratory thermometer is generally from –10°C to 110°C. <
1. “Dry bulb” i rument, records the temperature of the air. “Wet bulb” thermometer, sures relative humidity in the air and the results are normally lower than just the pure air temperature.
2. At 100% relative humidity, the wet-bulb temperature is equal to the air temperature (dry-bulb temperature) and is lower at lower humidity.
3. If wet bulb temperatures in our environment are at 35°C or greater, our ability to lose heat declines rapidly and eve n the fittest of people would die in around 6 hours.
2. Materials which allow heat to pass through them easily are conductors of heat. For examples, aluminum, iron and copper. The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators.
3. Heat flows from a body at a higher temperature to a body at a lower temperature. There are three ways in which heat can flow from one object to another.
4. These are conduction, convection and radiation.
5. All hot bodies radiate heat. When this heat falls on some object, a part of it is reflected, a part is absorbed and a part may be transmitted.
5. Acid, bases, salts
1. Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids.
2. Substances like baking soda which are bitter in taste and feel soapy on touching are known as bases. The nature of such substances is said to be basic.
3. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators.
4. The indicators change their color when added to a solution containing an acidic or a basic substance.
5. Most commonly used natural indicator is litmus. It is extracted from lichens.
6. Rain containing excess of acids is called an acid rain. Rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
7. The reaction between an acid and a base is known as neutralization. Salt and water are produced in this process with the evolution of heat
1. Our stomach contains hydrochloric acid. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide.
2. When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralized by rubbing moist baking soda
3. When the soil is too acidic, it is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). If the soil is basic, organic matter is added to it.
6. Physical and chemical changes
1. Rust is not iron (iron oxide). For rusting, the presence of both oxygen and water (or water vapor) is essential.
2. This process of depositing a layer of zinc on iron is called galvanization. Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese. It does not rust.