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o flalgae. Ans: Microorganisms are very useful such as: (i) Curd or dahi contains a bacterium called Lactobacillus acidophilus. Question 7: Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. Neutralization is an irreversible process. When some acidic substance like lemon juice or vinegar is added to milk, the milk protein gets tangled into solid masses called as curd. The curd formed has a different taste than the original substance. The composition of curd (lactic acid) is different from milk (fats and proteins). The milk is stirred and is set aside for a few hours at a warm place. | EduRev Class 7 Question is disucussed on EduRev Study Group by 142 Class 7 Students. Lactobacillus and Streptococcus. Curd is formed when milk is pasteurised and fermented by a combination of lactic acid bacteria and a protease.Curdsare a dairy product obtained bycurdling(coagulating) milk with rennet or an edible acidic substance such as lemon juice or vinegar, and then draining off the liquid portion (called whey). o a fungus called Penicillium. Answered. How do you think the pH will change as it turns into curd? Setting of a curd is a chemical change because curd cannot be converted into milk again. o viruses. 1) Formation of curd: When a small amount of curd (known as starter) is added to milk, the bacteria known as Lactobacillus, convert the milk into curd. These bacteria convert the lactose sugar of milk into lactic acid which coagulates and partially digests milk protein casein. formation of curd. Question 7: Explain why burning of wood and cutting it into small pieces is considered as two different types of changes. The lesson covers the complete explanation of class 8 Chapter 2 Microorganisms.Topics covered are Introduction to Micro-organisms and microbiology, different types of Micro-organisms, Useful and Harmful Micro-organisms. So this is an irreversible change. During fermentation, the bacteria use enzymes to produce energy (ATP) from lactose. Setting of curd is a chemical change because a new substance (lactic acid) is formed. Question 1. Following changes lead to the formation of curd from milk: A small amount of curd (starter) is added to milk Lactobacillus (present in curd) converts sugars in milk (Lactose) into lactic acid Lactic acid imparts a sour taste to curd The water separated out is known as whey and which is drained off to retain only the curd. When a little of pre-made curd is added to warm milk,then Lactobacilli bacteria present in curd multiply in milk and convert the lactose sugar into lactic acid. Jun 13,2021 - Change of milk to curd is a:a)physical changeb)chemical changec)Both physical and chemical changed)Neither physical nor chemical changeCorrect answer is option 'B'. Explain how microbes are useful to us in our day to day life. It is an irreversible change. Curd formed from milk cannot be changed into milk again. Polio, chickenpox and AIDS are caused by different o bacteria. Formation. Class 5 Maths; Class 5 EVS; NCERT Solutions for Class 4. Curd has improved nutritional quality due to increased vitamin B 1 2 . How is milk converted into curd? Class 7 Maths; Class 7 Science; NCERT Solutions for Class 6. Formation of new substance and irreversible process shows that setting of curd is a chemical change. Topperlearning. Match the following Name the groups in which microorganisms are broadly classified. The curd forms because of the chemical reaction between the lactic acid bacteria and casein. Curd contains several micro-organism including Lactobacilli bacteria. Bacteria are also involved in the making of cheese, pickles and many other food items. The starter added in the milk is the small amount of curd. III. Formation of new substance and irreversible process shows that setting of curd is a chemical change. Milk is converted into curd or yogurt by the process of fermentation. Milk consists of globular proteins called casein. The curd forms because of the chemical reaction between the lactic acid bacteria and casein. NCERT Exemplar for Class 7 Science Chapter 5 Acids, Bases and Salts Explanation: It is a chemical reaction where an acid and base reacts with each other quantitatively. Question 3. An important ingredient of rava (sooji ) idlis and bhaturas is curd. (iii) Explain the role of LAB in human body. “A zwitterion is a molecule that has both positive and negative regions of charge.” In the solid state, amino acids exist as dipolar ions called zwitterions. Answer: All you need of Class 8 at this link: Class 8. Lactic acid present in it reduces its pH value. This is an irreversible process that means milk cannot be made from curd. Milk turns into curd because of the action of o bacteria called Lactobacilli o a protozoan called Paramecium. Foot and mouth disease of cattle is caused by a virus. Answer: 1. algae 2. algae, fungus 3. microscope 4. How Is Milk Curd Formed? 1 Content. Milk curd is the strained byproduct of coagulated milk. ... 2 Formation. Milk curd forms when an acid is introduced into milk. ... 3 Techniques for Curdling Milk. Many make milk curd by simply adding edible acids such as lemon juice to milk and waiting for the curds to form, then straining the whey ... Microorganisms are beneficial to us in various ways; they not only prepare curd, bread, cake, wine and medicines for us but also used to increase soil fertility by fixing atmospheric nitrogen. Ans. If milk is incubated with curd, LAB will grow and produce lactic acid. Physical and Chemical Changes NCERT Solutions for Class 7 Science Chapter 6 Class 7 Science Chapter 6 Physical and Chemical Changes Textbook Exercise Questions and Answers. So, this an irreversible (cannot be reversed) change. Taste and texture of curd is different from milk. Malaria is caused by o protozoan. When rainwater goes back on the earth, no new product is formed. 2) Nitrogen fixation: The bacteria known as Rhizobium live in the root nodules of leguminous plants. Microorganisms Class 8 Science Chapter 2 as per NCERT Book used in CBSE and other Schools. Q10: Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. 4. Fig. (i) Complete the flowchart. o blue-green algae. Curd formed from milk cannot be changed into milk again. The byproduct of ATP production is lactic acid. Explain the process of curd formation? Bacteria are also involved in the making of cheese, pickles and many other food items. This gas makes the dough rise and fluffy. Viruses 5. carbon dioxide 6. malaria 7. Write the beneficial action of : (a) Bacteria (b) Fungi (c) Algae Answer: (a) Bacteria: Bacterium Lactobacillus help in the formation of curd from milk. The setting of curd is a chemical change because the property of milk and curd are different. It multiplies in milk and converts it into curd. (ii) Cheese and paneer are milk products prepared by using the bacteria. ... 7th Class … Question 5. Explain why rusting of iron objects is faster in coastal areas than in deserts. When milk is acidified, the protein and fat that is normally suspended in the milk begins to curdle, or become entangled. Write a use of yeast. Write the name of a bacterium that helps in the formation of curd. Curd contains several micro-organism including Lactobacilli bacteria. It promotes the formation of curd from milk. When a little of pre-made curd is added to warm milk,then Lactobacilli bacteria present in curd multiply in milk and convert the lactose sugar into lactic acid. This lactic acid then converts milk into curd. In the stomach of the young of many species is an enzyme called rennin which specifically hydrolyzes part of the casein micelle resulting in formation of a curd. Give some examples from daily life where expansion of metal by heating is used. Explain. When the milk’s pH drops (it might be due to any reasons like souring naturally or by adding extra acid), the negatively charged casein starts attracting another molecule and begin to form clumps. Bonds between hydrophobic sites start to develop and are enforced by calcium bonds that develop as the water molecules in the micelles start to … A classic precipitation method for casein in cow milk which is done in the laboratory is to slowly add HCl (0.1 N) to lower the milk pH to 4.6. Milk contains many microorganisms. 4. Lactobacillus promotes the formation of curd. Hyphae 10. unicellular 11. heterotrophic 12. viruses 13. penicillin 14. Answer: Yeast contains enzymes zymase and invertase which ferment the dough and releases carbon dioxide gas. The process of formation of curd from milk is known as the _____ of milk. (b) The milk takes time to set as curd because the milk is basic and acids produced are neutralized by … Also, once the curd is formed, milk cannot be re-obtained from it. CBSE Science Class 7- Chapter 6- Physical and Chemical changes- NCERT Exercise Solution (Question-Answer) is provided below. The starter or inoculum contains millions of LAB, which at suitable temperatures multiply, thus converting milk to curd. Ans: There are some microorganisms that cause disease in animals also like anthrax is a very dangerous human and cattle disease caused by a bacterium. When a small amount of pre-made curd is added into warm milk, then lactobacillus bacterium present in curd multiplies in milk and converts it into curd. In a few hours, the milk changes into curd. Lactic acid acts on the globular proteins present in the milk and denatures them. Class 8 Maths; Class 8 Physics; Class 8 Chemistry; Class 8 Biology; NCERT Solutions for Class 7. Decomposers 15. curdling. Curd cannot be turned back to the milk. Answer: (a) When carbon dioxide is passed through limewater, it turns milky due to the formation of __calcium carbonate (CaCO 3)_. In a few hours the milk changes into curd. Q20: Write short notes on diseases causing microorganisms in plants. Also the change is irreversible (you cannot convert curd into milk). It causes the. This contains a large number Lactobacilli (LAB) which convert milk into curd. Phytoplanktons 5. ... in the formation of curd from milk. Moreover, a new substance, curd is formed which is completely different in taste and properties from the milk. The solution is (a) basic (b) acidic (c) neutral How to avoid spreading of Micro-organisms has been discussed. Solution: Rusting of … Of these, the bacterium Lactobacillus promotes the formation of curd. Answer: The LAB bacteria grows in milk and convert it into curd, thereby digesting the milk protein casein. Formation of manure from leaves is a physical change. Name the type of microorganism that is smaller than bacteria. 8. Curd: Micro-organisms such as Lactobacillius and others commonly called lactic acid bacteria grow in milk and convert it into curd. It promotes the formation of curd from milk. Vibrio 8. parasites 9. Explain. Answer: Formation of clouds is a physical change. Clouds are formed by the condensation of water vapours present in the atmosphere. Curd is a dairy product obtained by curdling (coagulating) milk with an edible acidic substance such as lemon juice or vinegar and then draining off the liquid portion (called whey). The formation of the curd is due to the sudden removal of the hydrophilic macropeptides and the consequent imbalance in intermolecular forces. Best answer (i) When a small amount of curd is added as a starter to the fresh milk at a suitable temperature, a micro-organism Lactobacillus and lactic acid bacteria grows in milk in millions. So, the correct option is 'X-Lactic acid, Y-Vitamin B 1 2 ' CBSE Class 12-science - Ask The Expert. The different varieties of cheese can be made by using different kinds of bacteria. 3. Question 1. (c) Two methods by which rusting of iron can be prevented are __galvanization__ and __ painting__. Question 12. While discussing whether a substance is zwitterionic or not, the pH rangein which the information is required must be specified (because a sufficiently alkaline solution will change the zwitterion to an anion, and a sufficiently acid solution will change it to a cation). Activity 2.3 Thus we called them friendly. An important ingredient of rava (sooji) idlis and bhaturas is curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. Answer : Setting of curd is a chemical change since a new substance is formed which differs in taste from the original substance i.e. milk. Also the change is irreversible (you cannot convert curd into milk). The composition of curd (lactic acid) is different from milk (fats and proteins). In a few hours the milk changes into curd. A solution changes the colour of turmeric indicator from yellow to red. Formation of curd in milk is called 'Fermentation '. Of these, the bacterium Lactobacillus promotes the formation of curd. The milk is stirred and is set aside undisturbed for a few hours at a warm place. The pH of milk ranges between 6.4-6.8. Explain your answer. (True/False) Answer: False. They grow and multiply. o fungi. Q.1. The entanglement of milk protein and entrapment of fats within the protein lead to the separation of the milk curd from the leftover moisture and soluble protein in the form of whey. During their growth they produce enzymes which convert milk sugar lactose into lactic acid which coagulate and partially digest milk protein casein to form the curd. The result of this process of milk coagulation, or curdling, is a gelatinous material called curd. 2.5 : Viruses I saw that my mother added a little curd to warm milk to set curd for the o a bacterium. This lactic acid then converts milk into curd. 15. (a) The milkman shifts the pH of the fresh milk from 6 to slightly alkalinity because in alkaline condition milk it is not easy to become sour or to curd due to the formation of lactic acid. A small quantity of curd is added to warm milk. Question 4. Can you guess why? Can you explain this answer? Answer: pH of milk falls below 6 as it turns into curd due to the formation of lactic acid during this process. done clear. Milk curd forms when an acid is introduced into milk. Explain… (d) Changes in which only __physical__ properties of a substance change are called … Class 6 Maths; Class 6 Science; Class 6 English; NCERT Solutions for Class 5. Explain the process of curd formation from milk. Can you guess why? It multiplies in milk and converts it into curd. o a virus. Question 2. 2. A milkman adds a very small amount of baking soda to fresh milk. (b) The chemical name of baking soda is __sodium hydrogen carbonate__. Microorganisms: Friend and Foe Class 8 Extra Questions Very Short Answer Type. DIRECTIONS: Read the passage (s) given below and answer the questions that follow Passage -1 For changing milk into curd we add a small quantity of curd into milk. fresh milk has a pH of 6. This process of milk coagulating to form curd is known as curdling. Milk is a slightly acidic complex compound made up of fat and proteins together with casein. A) slow change. Curd contains several microorganisms. Some key Characteristics of Z… (ii) Expand the word LAB. The change of milk into curd is a. Milk that has been left to sour (raw milk alone or pasteurized milk with …

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