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Organisms and Populations Class 12 Biology Chapter 13 Questions And Answers Maharashtra Board

Class 12 | Biology Maharashtra Board Textbook Solutions

21 Apr 2026

Organisms and Populations Class 12 Biology Chapter 13 Questions And Answers Maharashtra Board

Q. 1. Multiple choice questions 1. Which factor of an ecosystem includes plants, animals and microorganisms?(a) Biotic factor(b) Abiotic factor(c) Direct factor(d) Indirect factor Answer. (a) Biotic factor 2. An assembladge of individuals of different species living in the same habitat and having functional interactions is …………….a. Biotic communityb. Ecological nichec. Populationd. Ecosystem Answer. (a) Biotic community 3. Association between sea anemone and Hermit crab in gastropod shell is that of ………………..(a) Mutualism(b) Commensalism(c) Parasitism(d) Amensalism Answer. (b) Commensalism 4. Select the statement which explains best parasitism.a. One species is benefited.b. Both the species are benefited.c. One species is benefited, other is not affected.d. One species is benefited, other is harmed. Answer. (d) One species is benefited, other is harmed. 5. Growth of bacteria in a newlly innoculated agar plate shows …………….a. exponential growthb. logistic growthc. Verhulst-Pearl logistic growthd. zero growt Answer. (c) Verhulst-Pearl logistic growth Q. 2. Very short answer questions. 1. Define the following terms : a. Commensalism Answer. The interaction between two species in which one species gets benefits and the other is neither harmed nor benefited is called commensalism. b. Parasitism Answer. The interaction between two species in which one parasitic species derives benefit from the other host species by harming it is called parasitism. c. Camouflage Answer. Camouflage is the disguising colouration or behaviour to merge with the surrounding so that prey or predator can remain hidden. 2. Give one example for each : a. Mutualism Answer. Lichen is composed of alga (cyanobacteria) and fungus. They cannot survive independently. Their association is mutualistic alga synthesises food by photosynthesis and fungus does the absorption of moisture. b. Interspecific competition Answer. Leopard and lion competing for a same prey. Sheep and cow competing for grazing in the same land. 3. Name the type of association: a. Clown fish and sea anemone Answer. Commensalism b. Crow feeding the hatchling of Koel Answer. Brood parasitism c. Humming birds and host flowering plants Answer. Mutualism 4. What is the ecological process behind the biological control method of managing with pest insects? Answer. Protocooperation: Q. 3. Short answer questions. 1. How is the dormancy of seeds different from hibernation in animals? Answer. In dormancy seed is not showing any metabolic activities. It can come back to life if and only if it gets suitable moisture and sunlight. Hibernation is suspended state, in which metabolic reactions do take place but at a very reduced pace. Animal arouses on its own after the winter sleep is over. This arousal is spontaneous and depends upon the ambient temperature. Dormant seed does not show such change unless it is planted or thrown in to moist place. 2. If a marine fish is placed in a fresh water aquarium, will it be able to survive? Give reason. Answer. Marine fish has its own osmoregulation which is different from the osmoregulation seen in fresh water fish. In marine water, the ambient salinity is more than the concentration of ions in the body. But in fresh water reverse is the case. Therefore, marine fish has different machinery to cope up with high saline environment. Therefore, it cannot survive in fresh water as its osmoregulation is not possible in less saline waters. 3. Name important defense mechanisms in plants against herbivores. Answer. Some important defence mechanisms in plants against herbivores are thorns, toxic chemicals, secondary metabolites, etc. Herbivores feed on plants and thus they are predators for the vegetations.Plants therefore have evolved variety of morphological and chemical defences against herbivores, which are as follows : 1. Thorns : Thorns seen in Cactus or Acacia make the plant inedible and thus this is the most common morphological means of defence. 2. Toxic chemicals : Many plants produce and store chemicals that are toxic and unpalatable, affecting feeding herbivores. When these secretions are consumed, they inhibit feeding or digestions in the predator, disrupt reproduction, or even kill it. 3. Secondary metabolites : Plants like Calotropis produce highly poisonous cardiac glycosides which can act toxic to the grazers. A wide variety of chemical substances such as nicotine, caffeine, quinine, strychnine, opium, etc. are secondary metabolites produced by plants which act as defences against grazers and browsers. 4. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree? Answer. 5. Distinguish between the following: a. Hibernation and Aestivation Answer. Hibernation Aestivation 1. Hibernation is winter sleep shown by some warm-blooded and some cold-blooded animals. 1. Aestivation is the type of summer sleep, shown by cold-blooded animals. 2. It is for the whole winter. 2. It is of short duration. 3. The animals look out for the warmer place to enter into hibernation. 3. Animals search for the moist, shady and cool place to sleep. 4. Metabolic activities of hibernators slowdown in this dormant stage. 4. Metabolic activities of aestivators remain low during aestivation period. 5. Hibernation helps in maintaining the body temperature and prevents any internal body damage due to low temperatures.E.g. Bats, birds, mammals, insects, etc. show hibernation. 5. Aestivation helps in maintaining the body temperature by avoiding the excessive water loss and thus prevents any internal body damaged due to high temperatures.E.g. Bees, snails, earthworms, salamanders, frogs, earthworms, crocodiles, tortoise, etc. show aestivation. b. Ectotherms and Endotherms Answer. Ectotherms Endotherms 1. Ectotherms do not have ability to generate heat in the body. 1. Endotherms possess the ability to generate their own body heat. 2. Ectotherms depend on the environmental sources to heat their bodies. E.g sunlight. 2. Endotherms do not depend upon outside sources to generate heat. 3. Most ectotherms are confined to warmer parts of the world. 3. Endotherms inhabit coldest parts of the earth. 4. Body temperature of ectotherms fluctuate according to ambient temperature. 4. Body temperatures of endotherms remain constant and do not show fluctuations as per ambient temperatures. 5. Metabolic rate of ectotherms is low.E.g. Amphibians and reptiles. 5. Metabolic rate of endotherms is high.E.g. Mammals and birds c. Parasitism and Mutualism Answer. Parasitism Mutualism 1. Parasitism is the

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Maharashtra Board

25 Feb 2026

Carbon : An important element Class 9 Science Chapter 13 Questions And Answers Maharashtra Board

1. Select the proper option and complete the statements(single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent) a. A carbon atom forms a …….… bond with other atoms. In this bond the two atoms ……..electrons.b. All the carbon bonds in a saturated hydrocarbon …….…. electrons.c. At least one carbon bond in an unsaturated hydrocarbon is ……….d. ………. is the essential element in all the organic compounds.e. The element hydrogen is present in ………. organic compound. Answer. (a) covalent, share (b) share (c) multiple (d) Carbon (e) all 2. Answer the following questions a. Why are carbon and its compounds used as fuels ? Answer. (i) The name ‘carbon’ is derived from Latin word ‘carbo’meaning coal. In the earth’s crust, carbon is present to an extent of approximately 0.27% in the form of carbonate, coal and petroleum. One of the non-crystalline and amorphous form of carbon is coal. Coal is a fossil fuel. (ii) Peat, lignite, bituminous and anthracite are the four types of coal in the increasing order of their carbon content and heat produced respectively. Charcoal and coke are the other amorphous forms of carbon used as fuel. (iii) Compounds of carbon such as hydrocarbons consist of carbon and hydrogen and they are easily combustible. For example, methane (CH4) which occurs in natural gas is highly inflammable. It bums by reacting with oxygen to give a bluish flame. In this reaction, 213 Kcal/mol of heat is given out. Methane bums completely. Chemical reaction:CH4 + 2O2 → CO2 + 2H2O + Heat (iv) Thus when hydrocarbons are burnt in air, large amount of heat is evolved with formation of carbon dioxide (CO2) and water (H2O). Due to evolution of heat on combustion, carbon and its compounds are used as fuels. b. In which compound forms does carbon occur ? Answer. Carbon in its combined state exists as various compounds such as: c. Write the uses of diamond. Answer. Uses of diamonds are: 3. Explain the difference: a. Diamond and graphite. Answer. Diamond Graphite (i) Diamond is a brilliant, hard and crystalline allotrope of carbon. (i) Graphite is a black, soft, brittle and slippery crystalline allotrope of carbon. (ii) In diamonds, every carbon atom is bonded to four neighbouring atoms by covalent bonds forming tetragonal three dimensional structure which makes it very hard. (ii) In graphite, every carbon atom is bonded to three other carbon atoms by covalent bonds in such a way that a hexagonal layered structure is formed. A graphite crystal is made of many such layers of carbon atoms. These layers slip over each other on applying pressure. (iii) Density of diamond is 3.5 g/cm3. (iii) Density of graphite is 1.9 to 2.3 g/cm3. (iv) Diamond is a bad conductor of electricity as it does not have free electrons. (iv) Inside each layer of graphite, free electrons move continuously within the entire layer. Hence, graphite is a good conductor of electricity. b. Crystalline and non-crystalline forms of carbon. Answer. Crystalline forms of carbon Non-crystalline forms of carbon (i) A crystalline form has a regular and definite arrangement of atoms.(ii) They have high melting points and boiling points.(iii) A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.(iv) Diamond, graphite and fullerene are different crystalline forms of carbon. (i) A non-crystalline form does not have a regular and definite arrangement of atoms.(ii) They have low melting points and boiling points.(iii) They are amorphous, hence, they do not have definite geometrical shape.(iv) Coal, charcoal and coke are different noncrystalline/amorphous forms of carbon. 4. Write scientific reasons a. Graphite is a conductor of electricity. Answer. b. Graphite is not used in ornaments. Answer. c. Limewater turns milky when CO2 is passed through it. Answer. d. Biogas is an eco-friendly fuel. Answer. 5. Explain the following. a. Diamond, graphite and fullerenes are crystalline forms of carbon. Answer. b. Methane is called marsh gas. Answer. c. Petrol, diesel, coal are fossil fuels. Answer. (i) A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms. Fossil fuels contain high percentage of carbon. The word carbon is derived from the Latin word ‘Carbo’ meaning coal. (ii) Coal is formed from the remains of trees and other vegetation. Approximately 350 million years ago, these remains were trapped on the bottom of swamps, accumulating layer after layer and creating a dense material called peat. As this peat was buried under more and more ground, the high temperature and pressure transformed it into coal. (iii) Petrol and diesel are obtained from mineral oil. Mineral oil also called as crude oil or petroleum oil is formed from the remains of plants and animals that lived in the seas millions of years ago. This plant and animal matter has been drawn down and subjected to extremes of temperature and pressure over millions of years ago. (iv) Mineral oil is commonly formed in rocks under the sea bed. The word petroleum is derived from Latin word ‘Rock oil’. Petrol and Diesel are obtained from mineral oil by the process called as fractional distillation.Thus petrol, diesel and coal are fossil fuels. d. Uses of various allotropes of carbon. Answer. e. Use of CO2 in fire extinguisher. Answer. f. Practical uses of CO2. Answer. Practical uses of CO2 are: 6. Write two physical properties each. a. Diamond Answer. Properties of diamond are: b. Charcoal Answer. c. Fullerene Answer. 7. Complete the following Chemical reactions. 1. ………………..+………………..→ CO2 + 2H2O + Heat2. ………………..+………………..→ CH3Cl + HCl3. 2 NaOH + CO2 →………………..+……………….. Answer. 8. Write answers to the following in detail. a. What are the different types of coal? What are their uses? Answer. Coal is a fossil fuel. It contains carbon, hydrogen and oxygen. It also contains nitrogen, phosphorus and sulphur. It occurs in the solid state. It is of four types. Uses of coal: b. How will you prove experimentally that graphite is good conductor of electricity? Answer. Apparatus required: Lead pendi, electrical wires, battery/cell, small bulb, etc. Step-I: Remove the lead from

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Class 8 | Science | Textbook Solutions | Maharashtra Board

20 Feb 2025

Class 8 | Science | Chapter 13 | Chemical Change and Chemical Bonds | Exercise Solution | Maharashtra Board

1. Complete the statement by filling the gaps using appropriate term from the terms given in the brackets:(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign) a. An ……….. is drawn in between the reactants and products while writing the equation for a chemical reaction.Answer:An arrow is drawn in between the reactants and products while writing the equation for a chemical reaction. b. Rusting of iron is a ……….. chemical change.Answer:Rusting of iron is a slow chemical change. c. The spoiling of food is a chemical change which is recognized from the generation of certain …………. due to it.Answer:The spoiling of food is a chemical change which is recognized from the generation of certain smell due to it. d. A colourless solution of calcium hydroxide in a test tube turns ………….. on blowing in it through a blow tube for some time.Answer:A colourless solution of calcium hydroxide in a test tube turns milky on blowing in it through a blow tube for some time. e. The white particles of baking soda disappear when put in lemon juice. This means that it is a ……….. change.Answer:The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change. f. Oxygen is a …………….. in respiration.Answer:Oxygen is a reactant in respiration. g. Sodium chloride is …………… compound while hydrogen chloride is compound.Answer:Sodium chloride is ionic compound while hydrogen chloride is covalent compound. h. Electron …………….. is complete in each hydrogen in a hydrogen molecule.Answer:Electron duplet is complete in each hydrogen in a hydrogen molecule. I. Chlorine (Cl2) molecule is formed by ………….. of electrons between two chlorine atoms.Answer:Chlorine (Cl2) molecule is formed by sharing of electrons between two chlorine atoms. 2. Explain by writing a word equation. a. Respiration is a chemical change.Answer:Respiration is a biological process, in this process air is inhaled, oxygen present in this inhaled air reacts with glucose present in the cells of the body forming carbon dioxide and water. Moreover, we cannot obtain glucose and oxygen from carbon dioxide and water. Hence, respiration is a chemical change.Word equation: b. Hard water gets softened on mixing with a solution of washing soda.Answer:Hard water does not form lather with soap and is brackish to taste. This is because hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state. When a solution of washing soda is added to hard water, it forms a precipitate of calcium carbonate and magnesium carbonate, which is removed by filtration thus water is softened.Word equation: c. Limestone powder disappears on adding to dilute hydrochloric acids.Answer:In the reaction of dil. HCl and limestone powder (CaCO3), limestone disappears slowly and carbon dioxide (CO2) liberates slowly.Word equation: d. Bubbles are seen on adding lemon juice to baking soda.Answer:When baking soda is added to lemon juice a chemical change takes place in citric acid present in the lemon juice and carbon dioxide gas is formed. Word equation: This is a neutralization reaction. 3. Match the pairs. Column I Column II 1. Photosynthesis a. Tendency to lose electrons 2. Water b. Reactant in combustion process 3. Sodium chloride c. Chemical change 4. Dissolution of salt in water d. Covalent bond 5. Carbon e. Ionic bond 6. Fluorine f. Physical change 7. Magnesium g. Tendency to form anion Answer: Column I Column II 1. Photosynthesis c. Chemical change 2. Water d. Covalent bond 3. Sodium chloride e. Ionic bond 4. Dissolution of salt in water f. Physical change 5. Carbon b. Reactant in combustion process 6. Fluorine g. Tendency to form anion 7. Magnesium a. Tendency to lose electrons 4. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms. a. Sodium Chloride: Answer:1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.2. Sodium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na+). 4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.5. Thus, the electron lost by sodium is taken up by chlorine. 6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP). 7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed. 8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule. b. Potassium fluoride:Answer:1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.2. Potassium atom has 1 electron in its outermost shell. 3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K+). 4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet. 5. Thus, the electron lost by potassium is taken up by chlorine. 6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F–). 7. Thus, a fluorine atom accepts one electron from

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Class 7 | Science | Textbook Solutions | Maharashtra Board

8 Jul 2024

Class 7 | Science | Chapter 13 | Changes – Physical and Chemical | Maharashtra Board | Solution

1. Distinguish between the following. a. Physical change and Chemical changeAnswer: Physical changes Chemical changes 1. In a physical change material may change its 1. A change which after physical properties and shape, size, texture or state. composition also. 2. No new compound is formed. 2. New compound /substance is formed due to chemical change. 3. The change is temporary. It is reversible. 3. The change is permanent and irreversible. 4. Examples: Evaporation of water, boiling of water, melting of ice. 4. Examples: Burning of wood, paper, souring of milk, digestion of food, rusting of iron. b. Periodic changes and Non-periodic changeAnswer: Periodic changes Non-periodic change 1. Some changes occur again and again after a definite interval of time. Such changes are called periodic changes. 1. In this, certain changes will recur after one occurrence, it cannot be said for sure, even if they occur interval is not fixed. Such changes are called non-periodic changes. 2. Examples: movement of clock hands in clock showing time, change of season, day and night formation, heart beat, ripening of fruit, rising and setting of the sun. 2. Examples: volcanic eruption, occurrence of an earthquake, tsunami, forest fires, freezing of water to form ice, sneezing, rusting of iron. 3. They repeat themselves after a fixed interval of time. 3. They do not repeat themselves after a fixed interval of time. c. Natural change and Man-made changeAnswer: Natural change Man-made change 1. Changes that occur naturally on its own are called natural changes. 1. Changes that are result of human activity. Such changes are called man-made. 2. Examples ripening of a fruit, spoiling of milk, change in the climate 2. Burning of fossil fuels, deforestation, pollution of air, water and soil. 2. Under which different types can the following changes be classified? a. Conversion of milk into yoghurt.Answer:Manmade (useful). b. Bursting of cracker.Answer:Manmade (fast change). c. Occurrence of an earthquake.Answer:Non-periodic. d. Revolution of earth around the sun.Answer:Periodic. (Natural change) e. Stretching of a spring.Answer:Physical, reversible change. 3. Give reasons. a. While purchasing canned food, its expiry date should be checked.Answer: b. An iron article should be given a coat of paint.Answer: c. A Wooden article should be polished.Answer: d. Copper and brass utensils should be tinned.Answer: e. A dry handkerchief gets wet at once on dipping in water, but it takes long for a wet handkerchief to dry.Answer: 4. What will you take into account while identifying the following: a. A physical change in a substance.Answer:I will take into account the following facts. b. A chemical change in a substance.Answer:I will take into account the following facts. 5. Read the paragraph and note down the various types of changes it mentions. It was nearing six o’clock in the evening. The sun was setting. A breeze was blowing. Leaves on the tree were shaking. Sahil was sitting in the courtyard, rolling balls of wet soil and shaping them into various toys. Then he felt hungry and went into the house. Mother made a dough from wheat flour and fried purees. While eating hot purees, his attention was drawn outside the window. It had started raining. There was lighting too. Sahil was enjoying his dinner in the dim light.Answer:

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