SCIENCE NCERT FOR UPSC PRELIMS 2020

• Carbohydrates, proteins, fats, vitamins and minerals are components of food. 
• These components of food are necessary for our body and are called nutrients. 
• Nutrition is the mode of taking food by an organism and its utilisation by the body. 
• The mode of nutrition in which organisms make food themselves from simple substances is called autotrophic (auto = self; Trophos = nourishment) nutrition. plants are called autotrophs. 
• Animals and most other organisms take in readymade food prepared by the plants. They are called heterotrophs (heteros =other). 
• The bodies of living organisms are made of tiny units called cells. 
• Cells can be seen only under the microscope. 
• Some organisms are made of only one cell. 
• The cell is enclosed by a thin outer boundary, called the cell membrane.
• Most cells have a distinct, centrally located spherical structure called the nucleus. 
• The nucleus is surrounded by a jelly-like substance called cytoplasm. 
• Carbon dioxide from air is taken in through the tiny pores present on the surface of the leaves. 
• These pores are surrounded by ‘guard cells’. Such pores are called stomata. 
• The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water. 
• Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis (Photo: light; synthesis: to combine). 
• So we find that chlorophyll, sunlight, carbon dioxide and water are necessary to carry out the process of photosynthesis. 
• During photosynthesis, chlorophyll-containing cells of leaves in the presence of sunlight use carbon dioxide and water to synthesize carbohydrates. 
• During the process, oxygen is released. 
• The carbohydrates ultimately get converted into starch. 
• The presence of starch in leaves indicates the occurrence of photosynthesis. 
• The starch is also a carbohydrate. You often see slimy, green patches in ponds or in other stagnant water bodies. 
• These are generally formed by the growth of organisms called algae. 
• They contain chlorophyll which gives them the green colour. 
• Algae can also prepare their own food by photosynthesis. 
• The carbohydrates are made of carbon, hydrogen and oxygen. 
• These are used to synthesise other components of food. 
• Proteins are nitrogenous substances which contain nitrogen. 
• The soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. 
• These soluble forms are absorbed by the plants along with water. 
• Farmers adding fertilisers rich in nitrogen to the soil. 
• In this way, the plants fulfil their requirements of nitrogen along with the other constituents. 
• Plants can then synthesise components of food other than carbohydrates such as proteins and fats. 
• Humans and animals such plants depend on the food produced by other plants. 
• They use the heterotrophic mode of nutrition. 
• Yellow tubular structures twining around the stem and branches of a tree? This is a plant called Cuscuta (Amabel). 
• It does not have chlorophyll. 
• It takes readymade food from the plant 
• The plant on which it climbs is called a host. 
• Pitcher plant showing lid and pitcher 
• The apex of the leaf forms a lid which can open and close the mouth of the pitcher. 
• Inside the pitcher, there are hairs which are directed downwards. 
• When an insect lands in the pitcher, the lid closes and the trapped insect gets entangled into the hair. 
• The insect is digested by the digestive juices secreted in the pitcher. Such insect-eating plants are called insectivorous plants.

• Cotton-like threads spread on the piece of bread 
• These organisms are called fungi. 
• They have a different mode of nutrition. 
• They secrete digestive juices on the dead and decaying matter and convert it into a solution. 
• Then they absorb the nutrients from it. 
• This mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter is called saprotrophic nutrition. 
• Plants which use the saprotrophic mode of nutrition are called saprotrophs. 
• Fungi also grow on pickles, leather, clothes and other articles that are left in hot and humid weather for a long time 
• Some organisms live together and share shelter and nutrients. This is called a symbiotic relationship. 
• For example, certain fungi live in the roots of trees. 
• The tree provides nutrients to the fungus and, in return, receives help from it to take up water and nutrients from the soil. 
• This association is very important for the tree. 
• In organisms called lichens, a chlorophyll-containing partner, which is an alga, and a fungus live together. 
• The bacterium called Rhizobium can take atmospheric nitrogen and convert it into a soluble form. 
• But Rhizobium cannot make its own food. 
• So it lives in the roots of a gram, peas, moong beans and other legumes and provides them with nitrogen. 
• Most of the pulses (dals) are obtained from leguminous plants. 

• Animal nutrition includes the nutrient requirement, mode of intake of food and its utilisation in the body. 
• The components of food such as carbohydrates are complex substances. 
• These complex substances cannot be utilised as such. 
• So they are broken down into simpler substances. 
• The breakdown of complex components of food into simpler substances is called digestion. 
• Starfish feeds on animals covered by hard shells of calcium carbonate.

• The food passes through a continuous canal which begins at the buccal cavity and ends at the anus. 
• The canal can be divided into various compartments: (1) the buccal cavity, (2) food pipe oesophagus, (3) stomach, (4) small intestine, (5) large intestine ending in the rectum and (6) the anus. 
• These parts together form the alimentary canal (digestive tract).  The digestive tract and the associated glands together constitute the digestive system. 
• The saliva breaks down the starch into sugars. 
• The swallowed food passes into the food pipe or oesophagus. 
• The stomach-widest part of the alimentary canal.
• The inner lining of the stomach secretes mucous, hydrochloric acid and digestive juices. 
• The mucous protects the lining of the stomach. 
• The acid kills many bacteria that enter along with the food and makes the medium in the stomach acidic. 
• The digestive juices break down the proteins into simpler substances 
• The small intestine-The small intestine is highly coiled and is about 7.5 metres long. 
• It receives secretions from the liver and the pancreas. Besides, its wall also secretes juices. 
• The liver is a reddish-brown gland situated in the upper part of the abdomen on the right side. 
• It is the largest gland in the body. 
• It secretes bile juice that is stored in a sac called the gall bladder.
• The bile plays an important role in the digestion of fats. 
• The pancreas is a large cream coloured gland located just below the stomach. 
• The pancreatic juice acts on carbohydrates and proteins and changes them into simpler forms. 
• The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption. 
• The inner walls of the small intestine have thousands of finger-like outgrowths. These are called villi (singular villus). 
• The large intestine is wider and shorter than the small intestine. 
• About 1.5 metres in length. Its function is to absorb water and some salts from the undigested food material. 
• The remaining waste passes into the rectum and remains there as semi-solid faeces. 
• The faecal matter is removed through the anus from time-to-time. This is called egestion. 

• Actually, they quickly swallow the grass and store it in a separate part of the stomach called the rumen. 

Diarrhoea 

• Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhoea. 
• Caused by an infection, food poisoning or indigestion. 
• Very common in India, particularly among children. 
• Under severe conditions, it can be fatal because of the excessive loss of water and salts from the body. 
• Diarrhoea should not be neglected. 
• Even before a doctor is consulted the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS). 
• Food partially digested and is called cud. 
• But 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. 
• The grass is rich in cellulose, a type of carbohydrate. 
• Many animals, including humans, cannot digest cellulose. 
• Ruminants have a large sac-like structure between the small intestine and large intestine. 

• Amoeba is a microscopic single-celled organism found in pond water. 
• Amoeba has a cell membrane, a rounded, dense nucleus and many small bubble-like vacuoles in its cytoplasm. 
• Amoeba constantly changes its shape and position. 
• It pushes out one, or more finger-like projections, called pseudopodia or false feet for movement and capture of food. 
• Amoeba feeds on some microscopic organisms. 
• When it senses food, it pushes out pseudopodia around the food particle and engulfs it. 
• The food becomes trapped in a food vacuole. 
• Digestive juices are secreted into the food vacuole. 
• They act on the food and break it down into simpler substances. 
• Gradually the digested food is absorbed. 
• The absorbed substances are used for growth, maintenance and multiplication. 
• The undigested residue of the food is expelled outside by the vacuole. 
• The basic process of digestion of food and release of energy is the same in all animals. 
• In a later chapter, you will learn about the transport of food absorbed by the intestine to the various parts of the body. 

• Our sense of touch is not always a reliable guide to the degree of hotness of an object. 
• Temperature is a measure of the degree of hotness of an object. 
• The thermometer is a device used for measuring temperatures. 
• Clinical thermometer is used to measure our body temperature. The range of this thermometer is from 35°C to 42°C. For other purposes, we use laboratory thermometers. The range of these thermometers is usually from –10°C to 110°C. 
• The normal temperature of the human body is 37°C. 
• The 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. These are conduction, convection and radiation. 
• In solids, generally, the heat is transferred by conduction. In liquids and gases, the heat is transferred by convection. No medium is required for transfer of heat by radiation. 
• The materials which allow heat to pass through them easily are conductors of heat. 
• The materials which do not allow heat to pass through them easily are called insulators. 
• Dark-coloured objects absorb radiation better than light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer. 

• Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids. 
• The chemical nature of such substances is acidic. The word acid comes from the Latin word acere which means sour. 
• The acids in these substances are natural acids. 
• Baking Soda– it does not taste sour it means, that it has no acids in it. It is bitter in taste. 
• If you rub its solution between fingers, it feels soapy. 
• Substances like these which are bitter in taste and feel soapy on touching are known as bases. The nature of such substances is said to be basic. 
• Special types of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. 
• The indicators change their colour when added to a solution containing an acidic or a basic substance. 
• Turmeric, litmus, China rose petals (Gudhal), etc., are some of the naturally occurring indicators. 
• Name of acid Found 

• Acetic acid —- Vinegar 
• Formic acid —- Ant’s sting 
• Citric acid —- Citrus fruits such as oranges, lemons, etc. 
• Lactic acid —- Curd 
• Oxalic acid —- Spinach 
• Ascorbic acid —- Amla, Citrus fruits (Vitamin C) 
• Tartaric acid —- Tamarind, grapes, unripe mangoes, etc. 

•  All the acids mentioned above occur in nature Name of base Found in Calcium hydroxide 
• Lime water Ammonium hydroxide Window cleaner Sodium hydroxide/ Soap Potassium hydroxide Magnesium hydroxide Milk of magnesia. 
• The most commonly used natural indicator is litmus. It is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper. 
• The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. 
• These substances are neither acidic nor basic. 
• Turmeric is another natural indicator. 
• China Rose as Indicator turns acidic solutions to dark pink (magenta) and basic solutions to green. 
• The rain containing an excess of acids is called acid rain. 
• The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in raindrops to form carbonic acid, sulphuric acid and nitric acid respectively. 
• Acid rain can cause damage to buildings, historical monuments, plants and animals. 
• It is evident that when the solution is basic, phenolphthalein gives a pink colour. On the other hand, when the solution is acidic, it remains colourless. 
• When an acidic solution is mixed with a basic solution, both the solutions neutralise the effect of each other. 
• When an acid solution and a base solution are mixed in suitable amounts, both the acidic nature of the acid and the basic nature of the base are destroyed. 
• The resulting solution is neither acidic nor basic. 
• In a neutralisation reaction, heat is always produced or evolved. 
• The evolved heat raises the temperature of the reaction mixture. 
• In a neutralisation reaction, a new substance is formed. This is called salt. 
• Salt may be acidic, basic or neutral in nature. 
• The reaction between an acid and a base is known as neutralisation. 
• Salt and water are produced in this process with the evolution of heat. 
• The stomach contains hydrochloric acid. It helps us to digest food.
• 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 (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.