ENVIRONMENT AND ENVIRONMENTAL PROBLEMS - III : LONG ANSWERS

GIVE ANSWER IN DETAIL

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1. Describe sources of air pollution in brief.
   

   ANS :

   
   
   • The two types of sources of air pollution are : Natural sources and man-made sources.
   • Natural sources(factors) polluting the atmosphere are : volcanoes, forest fires, decaying plants, storms, pollen grains, lightening-induced chemicals, etc.
   • Man-made sources of pollution are : Burning of firewood, burning of fossil fuels, automobile smoke, aeroplanes, power stations, industrialisation, agriculture, wars, atomic explosions, deforestation, mining, oil refineries, etc.
     

   
   

   
   
2. Mention harmful effects of water pollution.
   

   ANS :

   
   
   • Mercury mixed with water causes the disease Minamata. It is a poisonous disease and may cause death. It was first observed in coastal area of Minamata city of Japan.
   • Chemicals like mercury, cadmium, cobalt, etc. present in water cause diarrhoea.
   • Biological Oxygen Demand(BOD) of clean water is less. BOD of polluted water increases and harms aquatic organisms, sometimes causing their destruction.
   • Accumulation of domestic sewage and fertilisers results in the increase of nitrates and phosphates in water. These promote the growth of algae and other microorganisms. Thus, there is excessive loading of aquatic ecosystem with nutrients and algal growth, a phenomenon called eutrophication. Due to eutrophication BOD increases and organisms die.
     

   
   

   
   
3. Describe the interrelationship between population, environment and development.
   

   ANS :

   
   
   • Exploding population at increasing speed has become a major problem to environment and development at global level.
   • Increase in population leads to increase in demand for food. This leads to increase in the use of fertilisers and pesticides.
   • Excessive use of fertilisers and pesticides causes pollution which has direct and indirect effect on human health.
   • Increasing demand for space due to population explosion results in encroachment of fertile and agricultural land, forests and habitat of wild life.
   • To maintain the existence of human life, the balance between population, environment and development must be maintained.
     

   
   

   
   
4. List out different laws for environmental protection.
   

   ANS :For the protection and conservation of environment, following laws have been enacted by the Government of India :
   

   
   
   • Environment (Protection) Act, 1986
   • Forest (Conservation) Act, 1980
   • Water (Prevention and Control of Pollution) Act, 1974
   • Wildlife (Protection) Act, 1972
   • The Motor Vehicle Act, 1983
   • Prevention of Cruelty to Animals Act, 1966
   • Air (Prevention and Control of Pollution) Act, 1981
   • The Insecticide Act, 1968
     

   
   

   
   
5. Describe harmful effects of air pollution.
   

   ANS :

   
   
   • Burning sensation in eyes, nose and throat.
   • Diseases of lungs like bronchitis, asthma, etc. caused by pollutant gases like SO₂ and NO₂.
   • Diseases of respiratory system spread through dust particles. Silicosis is caused by silica and asbestosis is caused by asbestos.
   • Cancer caused by carcinogenic pollutants.
   • Heavy metals inhaled through air cause poisonous effects.
   • Increase in ultraviolet radiation reaching earth due to depletion of ozone layer causes skin cancer, damage to eyes and damage to immune system.
   • Dissolution of atmospheric gases like SO₂, SO₃, NO₂ in moisture results in formation of sulphuric acid and nitric acid. This causes acid rain which harms organisms, various monuments and buildings.
   • Carbon dioxide and methane absorb heat and increase the temperature of earth's atmosphere. This is known as Greenhouse effect. This increase in temperature results in melting of ice on polar regions and causes sea level to rise.
     

   
   

   
   
6. Write a descriptive note on Prevention and Control of Air Pollution.
   

   ANS :Two types of methods are used for prevention and control of air pollution :

   
   
   1. Methods for controlling gaseous pollutants :
      
      
      1. Combustion : This method is used for pollutants in the form of organic gases or vapours. These pollutants are converted into water vapour and relatively less harmful products such as CO₂ by flame combustion or catalytic process.
      2. Absorption : In this technique, the gaseous effluents are passed through specific scrubbers or absorbers. The gaseous pollutants are absorbed and air is purified.
         
      
      
   2. Methods for controlling particulate emissions :
      
      
      1. Wet Scrubbers : Wet scrubbers are used in chemical, mining and metallurgical industries to trap SO₂, NH₃, metal fumes, etc.
      2. Electrostatic Precipitators : The gas or air stream containing aerosols in the form of dust, fumes or moisture is passed between two electrodes. The aerosol particles get precipitated on the electrodes.
         
      
      

   
   

   
   
   
   NOTE : The diagram in the textbook showing WET SCRUBBER is actually the diagram of BAG FILTER.
   
7. Describe prevention and control of water pollution.
   

   ANS :Sewage treatment and Oxidation pond are the two methods of controlling water pollution.
   

   
   
   1. SEWAGE TREATMENT :
      
      
      • This method involves three steps.
      • During first step, large components and suspended matter are isolated by sedimentation and converted into harmless matter which can be used as fertiliser.
      • During second stage, air containing oxygen and bacteria is passed through water in an aeration tank. The bacteria degrade organic substances. Then chlorination is performed.
      • During tertiary(third) stage, substances like nitrates and phosphates are removed to obtain clean water.
        
      
      
   2. OXIDATION POND :
      
      
      • This method, developed by National Environment Engineering Research Institute(NEERI), Nagpur, is used to treat industrial effluents and sewage.
      • Oxidation pond is a shallow pond where domestic as well as industrial waste matter is stored.
      • This water is mixed with microorganisms and algae which oxidise carbonic components present in water and water gets purified.
        
      
      

   
   

   
   
8. 
   

   ANS :
   

   
   

ENVIRONMENT AND ENVIRONMENTAL PROBLEMS - II : BRIEF ANSWERS

ANSWER IN BRIEF

*INDEX-TOPIC SEARCH

1. Mention types of environment with examples.
   

   ANS:

   
   
   • Physical environment : atmosphere, lithosphere, hydrosphere.
   • Biological environment : plants, animals, microorganisms.
   • Cultural environment : social traditions, economic, political.
     

   
   

   
   
2. Draw a chart showing types of environment.
   

   ANS:[SEE THE CHART]
   

   
   
   
3. Mention various environmental problems.
   

   ANS:Various environmental problems include :
   

   
   
   1. Decrease in habitat of wildlife
   2. Wastage of water
   3. Deforestation
   4. Soil erosion
   5. Desertification
   6. Depletion in biodiversity
      

   
   

   
   
4. Write a few sentences on air pollution.
   

   ANS:

   
   
   • The transparent layer of gases surrounding the earth is called atmosphere.
   • In balanced atmosphere the ratio of various gases is fixed.
   • When this balance is disturbed due to any reason, it is called air pollution.
   • The major reasons for air pollution are population explosion, urbanisation, industrialisation and heavy transportation.
     

   
   

   
   
5. Mention natural sources of air pollution.
   

   ANS:Natural sources of air pollution are : volcanoes, forest fire, storms, pollen grains, dust particles, decaying plants, lightening-induced chemical reactions, etc.
   

   
   
6. Mention man-made sources of air pollution.
   

   ANS:Man-made sources of air pollution are : Burning of firewood, burning of fossil fuels, industrialisation, agriculture, smoke from automobiles, aeroplanes, wars, atomic tests, deforestation, power stations, mining, oil refineries, etc.
   

   
   
7. Explain : Acid rain.
   

   ANS:

   
   
   • Combustion of fuels and industrial smoke add pollutant gases like NO₂, SO₂, etc. in the atmosphere.
   • These gases dissolve in moisture present in air and form acids like nitric acid and sulphuric acid.
   • When these acids come back to earth through rain, it is called Acid Rain.
   • Acid rain harms various organisms, monuments and buildings.
     

   
   

   
   
8. Explain : Greenhouse effect.
   

   ANS:

   
   
   • Gases like CO₂ and methane have the property of absorbing heat.
   • These gases, when present in atmosphere, absorb the heat of the sun rays reflected by the earth.
   • This results in the warming of earth's atmosphere.
   • This is called Green-House Effect.
   • Due to Greenhouse effect, the ice on polar regions may melt increasing the sea level.
     

   
   

   
   
9. Describe the methods for controlling gaseous pollutants.
   

   ANS:[Refer to Long Answer about prevention and control of air pollution]
   

   
   
10. Describe the methods for controlling particulate emissions.
    

    ANS:[Refer to Long Answer about prevention and control of air pollution]
    
    

    
    
11. Mention sources of water pollution.
    

    ANS:The sources of water pollution are :

    
    
    1. Industries
    2. Population explosion
    3. Sewage
    4. Pesticides and fertilisers
    5. Radioactive waste
    6. Oil(spillage of oil)
    7. Heavy metals
    8. Harmful microorganisms.
       

    
    

    
    
12. Describe sewage treatment.
    

    ANS:[Refer to Long Answer about prevention and control of water pollution]
    

    
    
13. Describe Oxidation Pond method.
    

    ANS:[Refer to Long Answer about prevention and control of water pollution]
    

    
    
14. List out pollutants causing land pollution.
    

    ANS:Pollutants causing land pollution are : fertilisers, ashes, coal, domestic waste, paper, card board, plastics, rubber, clothes, metals, glass, construction materials, dead bodies of animals, insecticides, radioactive waste, etc.
    

    
    
15. Mention effects of land pollution.
    

    ANS:

    
    
    • Agricultural land becomes less fertile.
    • Insoluble pesticides like DDT decrease the secretion of sex hormones as well as the calcium level.
    • Soil erosion occurs. The amount of soil washed out in 6 months can be sufficient to make bricks needed to construct houses of entire world.
      

    
    

    
    
16. Describe the main points for prevention and control of land pollution.
    

    ANS:

    
    
    • The pollutants can be decomposed and removed through biological processes.
    • They can be converted into organic fertilisers.
    • Non-decomposable waste can be used to fill up the pits.
    • Specific incinerators can be used for final disposal of waste.
      

    
    

    
    
17. Write about biodegradable pollutants.
    

    ANS:

    
    
    • The pollutants which can be decomposed by microorganisms are known as biodegradable pollutants.
    • Faecal matter, solid sewage waste, domestic waste, agricultural waste, paper, wood, clothes, etc. are biodegradable.
      

    
    

    
    
18. Write about non-biodegradable pollutants.
    

    ANS:

    
    
    • The pollutants which cannot be decomposed by microorganisms are known as non-biodegradable pollutants.
    • Pesticides like DDT, mercury, lead, aluminium, arsenic, plastics, etc. are non-biodegradable.
    • These pollutants remain for a long time in environment and enter the organisms through food chain and biogeochemical cycle.
    • Then they get accumulated in large amount in their bodies, a phenomenon called biomagnification.

    
    

    
    
19. Write a few points about environmental balance.
    

    ANS:

    
    
    • Environmental balance is essential for all organisms including man.
    • Pollution leads to the loss of environmental balance.
    • Environmental imbalance causes harmful effects on life of organisms.
    • Judicious use of non-renewable sources is necessary for the maintenance of environmental balance.
    • Personal as well as social awareness regarding environment like keeping one's surroundings clean automatically helps in the maintenance of balanced environment.
      

    
    

    
    
20. Write some points about conservation and protection of environment.
    

    ANS:

    
    
    • Conservation of environment means prevention of excessive use of such activities which provide individual and commercial benefits and lead to environmental damage.
    • Almost all countries in the world have made laws for the conservation of environment. These laws help protect and Conserve environment.
    • One should be aware of such laws to make it possible to protect and conserve environment.
      

    
    

    
    
21. Describe environmental problems.
    

    ANS:

    
    
    • Activities of man continuously disturb the environment and create various problems.
    • Population explosion, industrialization and other human activities create following problems :
      
      
      1. Decrease in habitat of wildlife
      2. Wastage of water
      3. Deforestation
      4. Soil erosion
      5. Desertification
      6. Depletion in biodiversity
         
      
      

    
    

    
    
22. Why do aquatic animals die in polluted water ?
    
    ANS: Due to pollution of water by domestic sewage and fertilizers there is an increase in nitrate and phosphate components. these components cause many fold growth of algae and other micro-organisms. This is called eutrophication and due to it the biological oxygen demand (BOD) of the aquatic ecosystem increases and the organisms die.
    

ENVIRONMENT AND ENVIRONMENTAL PROBLEMS - I : MCQs & SHORT ANSWERS

*INDEX-TOPIC SEARCH

MULTIPLE-CHOICE QUESTIONS

SELECT THE CORRECT ALTERNATIVE:

1. Which of the following is a greenhouse gas ?
   
   
   
   1. Methane
   2. Oxygen
   3. Nitrogen
   4. Hydrogen
      
   
   
2. ______ is used to convert organic pollutants into water vapour and CO₂.
   
   
   
   1. Electrostatic precipitator
   2. Flame combustion
   3. Absorption
   4. Wet-scrubber
      
   
   
3. ______ are used in electrostatic precipitators.
   
   
   
   1. Catalysts
   2. Absorbers
   3. Electrodes
   4. Chemicals
      
   
   
4. Biological oxygen demand of ______ is the least.
   
   
   
   1. sewage
   2. sea water
   3. pure water
   4. polluted water
      
   
   
5. Compounds of ______ cause Minamata disease.
   
   
   
   1. mercury
   2. cadmium
   3. cobalt
   4. fertilisers
      
   
   
6. Due to eutrophication______.
   
   
   
   1. BOD increases
   2. BOD decreases
   3. algae are destroyed
   4. water becomes less harmful
      
   
   
7. ______ is the first step of sewage treatment.
   
   
   
   1. Precipitation
   2. Chlorination
   3. Sedimentation
   4. Aeration
      
   
   
8. World Environment Day is celebrated every year on ______.
   
   
   
   1. 5th March
   2. 15th April
   3. 15th May
   4. 5th June
      
   
   
9. We and our surroundings together are called...
   
   
   
   1. environment
   2. atmosphere
   3. lithosphere
   4. hydrosphere
      
   
   
10. Which of the following is not an environmental problem ?
    
    
    
    1. Wastage of water
    2. Conservation of water
    3. Deforestation
    4. Land erosion
       
    
    
11. Volcano is ______ source of pollution.
    
    
    
    1. artificial
    2. natural
    3. both
    4. man-made
       
    
    
12. Which rays strike on earth due to depletion of ozone layer ?
    
    
    
    1. Ultraviolet
    2. Infrared
    3. Visible light
    4. Microwaves
       
    
    
13. Which method is used for the removal of sulphur dioxide and ammonia from the polluted air ?
    
    
    
    1. Wet scrubbers
    2. Absorption
    3. Gravitational method
    4. Electrostatic precipitator
       
    
    
14. BOD is ______ in polluted water and ______ in potable water.
    
    
    
    1. more, less
    2. less, medium
    3. medium, more
    4. less, more
       
    
    
15. Which of the following is responsible for acid rain ?
    
    
    
    1. Hydrogen
    2. Oxygen
    3. Sulphur dioxide
    4. Methane
       
    
    
16. Which pollutants are responsible for bronchitis ?
    
    
    
    1. O₂, CO₂
    2. CO, CO₂
    3. SO₂, NO₂
    4. Cl₂, H₂S
       
    
    
17. Which method is used to control pollutants of particulate nature ?
    
    
    
    1. Combustion
    2. Absorption
    3. Electrostatic precipitators
    4. Oxidation pond
       
    
    

ANSWERS TO MCQs

(1) A (2) B (3) C (4) C (5) A (6) A (7) C (8) D (9) A (10) B (11) B (12) A (13) A (14) A (15) C (16) C (17) C (18)

SHORT QUESTIONS

ANSWER IN SHORT:

1. What does 'environment' mean ?
   
        ANS :The social, economical, physical and chemical factors surrounding an organism are collectively known as 'environment' for that organism.
   
2. What is studied in environmental biology ?
   
        ANS :The interrelationship between organisms as well as between living and nonliving components is studied in environmental biology.
   
3. Mention types of environment.
   
        ANS :Types of environment are : (i)Physical environment (ii)Biological environment (iii)Cultural environment.
   
4. Mention the major reason for environmental problems.
   
        ANS :Population explosion is the major reason for environmental problems.
   
5. Define : Pollution.
   
        ANS :Pollution is an undesirable change in the physical, chemical or biological characteristics of air, water and soil.
   
6. Mention common pollutants.
   
        ANS :Various gases, heavy metals, pesticides, fertilisers, radioactive materials, high temperature, etc. are major pollutants.
   
7. Mention types of pollution.
   
        ANS :Air pollution, water pollution and land(soil) pollution.
   
8. What is atmosphere?
   
        ANS :The transparent layer of gases surrounding the earth's surface is called atmosphere.
   
9. Mention common causes for air pollution.
   
        ANS :Urbanisation, population explosion, industrialisation and heavy transportation are common causes for air pollution.
   
10. Mention respiratory diseases caused due to air pollution.
    
         ANS :Asthma, bronchitis, silicosis and asbestosis are diseases caused due to air pollution.
    
11. Mention pollutants causing asthma and bronchitis.
    
         ANS :SO₂ and NO₂ are pollutants causing asthma and bronchitis.
    
12. What are carcinogens ?
    
         ANS :Substances causing cancer are called carcinogens.
    
13. What rae the effects of depletion of ozone layer ?
    
         ANS :Depletion of ozone layer increases the amount of ultraviolet radiation reaching the earth which, in turn, causes skin cancer and damages eyes and immune system.
    
14. What is Greenhouse Effect ?
    
         ANS :The warming up of earth's atmosphere due to absorption of heat by gases like CO₂ and methane present in the atmosphere is called Greenhouse Effect.
    
15. Which type of pollutants cause air pollution ?
    
         ANS :Gaseous and particulate pollutants cause air pollution.
    
16. What is water pollution ?
    
         ANS :The mixing of undesirable chemical, physical or biological components with pure water is called water pollution.
    
17. What is the full form of BOD ?
    
         ANS :The full form of BOD is Biological Oxygen Demand.
    
18. What is Eutrophication ?
    
         ANS :The pollution caused due to growth of algae and other microorganisms under the influence of nutrients is called Eutrophication.
    
19. Which components promote algal growth in water ?
    
         ANS :Compounds having nitrates and phosphates promote algal growth in water.
    
20. What is the full form of NEERI ?
    
         ANS :NEERI stands for National Environment Engineering Research Institute.
    
21. Mention prime causes for land pollution.
    
         ANS :Urbanisation, population explosion and industrialisation are prime causes for land pollution.
    
22. Mention solid waste pollutants causing land pollution.
    
         ANS :Faeces of humans and other animals, dead bodies and domestic waste are solid pollutants causing land pollution.
    
23. How are pollutants classified ?
    
         ANS :Pollutants are classified as biodegradable and non-biodegradable pollutants.
    
24. What is meant by biodegradable pollutants ?
    
         ANS :The pollutants which can be decomposed by microorganisms are called biodegradable pollutants.
    
25. What is meant by non-biodegradable pollutants ?
    
         ANS :The pollutants which cannot be decomposed by microorganisms are called non-biodegradable pollutants.
    
26. Give examples of biodegradable pollutants.
    
         ANS :Faecal matter, solid sewage waste, domestic waste, agricultural waste, paper, wood, clothes, etc. are biodegradable pollutants.
    
27. Give examples of non-biodegradable pollutants.
    
         ANS :Pesticides like DDT, mercury, lead, aluminium, arsenic, plastics, etc. are examples of non-biodegradable pollutants.
    
28. What is Biomagnification ?
    
         ANS :The accumulation of harmful non-biodegradable substances in the bodies of organisms through the foodchains and biogeochemical cycle is called Biomagnification.
    
29. Demand of what increases due to population explosion ?
    
         ANS :Demand of space and food increases due to population explosion.
    
30. What is conservation of environment ?
    
         ANS :Conservation of environment means such activities which provide individual or commercial benefits by preventing excessive use leading to environmental damage.
    
31. Mention the effects due to depletion of ozone layer.
    
         ANS :Increase in ultraviolet radiation reaching earth due to depletion of ozone layer causes skin cancer, damage to eyes and damage to immune system.
    
32. What work has been done by NEERI for water pollution ?
    
         ANS :NEERI has developed Oxygen Pond method for the treatment of industrial effluents and sewage.
    
33. 
    
         ANS :
    
    

HEREDITY AND EVOLUTION - III : LONG ANSWERS

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1. Explain : Heredity and variation.
   

   ANS :
   HEREDITY :
   

   
   
   • Transmission of characters from parents to offsprings is known as heredity.
   • Fertilised egg or zygote carries hereditary information.
   • The zygote develops into a particular type of offspring only.
   • Thus, eggs laid by a sparrow hatch into sparrows and a dog reproduces to give birth to pups only.
     

   
   VARIATION :
   

   
   
   • Variation means some individual diversity in the organism of one generation from that of the parental generation.
   • Variation passes from generation to generation.
   • In sexual reproduction, both similarities and variation are clearly observed among the offsprings of same parents.
   • Due to variation, any two persons rarely show complete similarity.
     

   
   

   
   
2. Explain : Mendel's concept of heredity.
   

   ANS :
   

   
   
   • Mendel proposed that for regulation of every character in an organism there is a pair of factors.
   • During Mendel's time, nothing was known about chromosomes and DNA.
   • T.Boveri and W.S.Sutton proved that a gene is a part of chromosome.
   • Thus, Mendel indicated the path of transmission of factors from parental generation to offsprings through gamates.
   • Both Mendelian factors(genes) as well as chromosomes are present in pairs. They get separated from each other during meiosis when a haploid(n) gamate is formed.
   • During fertilisation, gamates fuse to form a zygote(2n) carrying characters which later on get transmitted to the offspring.
     

   
   

   
   
3. Write a note on sex determination and chromosomes OR Explain the role of chromosomes in sex determination.
   

   ANS :
   

   
   
   • The phenomenon determining whether the developing embryo will be a male or a female is known as sex determination.
   • During the investigation on grasshoppers, one additional unpaired chromosome was observed in the male. This additional chromosome is called X-body and is known as sex chromosome since it is associated with sex determination.
   • The second sex chromosome is called X-chromosome if it is similar to the previous one and is called Y-chromosome if it differs from the X-chromosome.
   • In humans, the female has 2A + XX chromosomes and all the ova are A + X type.
   • The human male has 2A + XY chromosomes. This leads to 50% sperms of A + X type and 50% of A + Y type.
   • The fertilisation of an ovum by a sperm of A + X type produces a female whereas the fertilisation of an ovum by a sperm of A + Y type produces a male.
   • In some species, like turtle Chrysema Picta and lizard Agama agama, the sex determination is regulated by environmental factors.
     
     

   
   

   
   
4. What is biological evolution ? Mention the evidences supporting evolution and different theories of evolution.
   

   ANS :
   

   
   
   • The sequential and well-organised process of gradual structural changes in species is called biological(organic) evolution.
   • Evidences of comparative anatomy, comparative embryology, vestigial organs, fossils, connecting links, physiology and taxonomy support biological evolution.
   • The various theories of evolution are :
     
     
     
     1. Lamarck's theory of inheritance of acquired characters.
     2. August Weismann's Germplasm theory.
     3. Darwin's theory of Natural Selection.
     4. Hugo De Vries' Mutation theory.
        
     
     

   
   

   
   
5. Explain : Chromosome is the physical basis of heredity.
   

   ANS :
   

   
   
   • The discovery of the process of sexual reproduction involving gamates established the concept of transmission of genetic material.
   • Mendel proposed that there is a pair of factors for regulation of every character though during his time little was known about chromosomes and DNA.
   • T.Boveri and W.S.Sutton experimentally proved that gene is a part of chromosomes.
   • Mendelian factors(genes) as well as chromosomes are found in pairs but they get separated during meiosis forming haploid(n) gamates.
   • During fertilisation, gamates fuse to form zygote(2n) in which the characters are stored and transmitted to the offspring.
   • It was proved that the genes are located on chromosomes and the number of chromosomes is fewer than that of genes because the number of characters in an organism is very large. Thus, there are 23 pairs of chromosomes in human being but the total number of genes present on them is about 30,000 to 40,000.
   • It has been established that gene is a segment of a large molecule called DNA(DeoxyriboNucleic Acid).
   • DNA is the important component for the expression of genetic information from one generation to the other. Every chromosome possesses one molecule of DNA.
   • In some viruses, RNA(RiboNucleic Acid) is the genetic material. Such viruses are called retrovirus. The virus causing AIDS in human beings is a retrovirus.
   • Thus, chromosome is the physical basis of heredity.
     

   
   

   
   
6. Describe the structure of chromosome.
   

   ANS :
   

   
   
   • Chromosomes are carriers of genes.
   • Chromosomes can be identified by staining.
   • In prokaryotes only one chromosome occurs whereas in eukaryotes many chromosomes occur in pair.
   • The paired structure of chromosomes is known as diploid(2n) and is seen in somatic cells. They are called homologous chromosomes as both the chromosomes of a pair are exactly similar.
   • The number of diploid chromosomes is fixed for a species.
   • In reproductive cells the chromosomes are haploid(n), i.e. they are half in number.
   • During cell division(metaphase), different chromosomes get separated from each other and their morphological study becomes possible.
   • A group of minimum two chromatids forms one chromosome.
   • The diameter of each chromatid is 60 A°.
   • Chromatids are joined with each other by a dark region called centromere or primary constriction. Some chromosomes have additional secondary constriction.
   • Variation can be seen in position and number of centromere.
   • The length of chromosomes is 0.2 - 5.0μ (micron) andtheir diameter ranges from 0.2 - 2.0μ.
     

   
   
   
   

   
   
7. Write a note on types of chromosomes.
   

   ANS :
   

   
   
   • Chromosomes are classified depending on the position of the centromere.
   • There are four types : (i)Metacntric (ii)Sub-metacentric (iii)Acrocentric (iv)Telocentric.
   • Metacentric :
     
     
     • The centromere is present exactly in the centre.
     • All four arms of chromatids are equal in length.
       
     
     
   • Sub-metacentric :
     
     
     • The centromere is situated slightly away from the centre.
     • The two arms of chromatids on one side are long and the other two arms are short.
       
     
     
   • Acrocentric :
     
     
     • The centromere is located far from the centre near one end.
     • The two arms of chromatids on one side are very long and the other two arms are very short.
       
     • In some chromosomes, a small filamentous structure possessing a round tip is present on the distal end of short arms. This part is known as satellite.
     • A short filament called nucleolar organiser region connects satellite with the short arm.
       
     
     
   • Telocentric :
     
     
     • The centromere is situated at the tip of the chromosome.
     • The two arms are located only on one side.
       
     
     

   
   

   
   
   
   
8. Describe Watson-Crick model for structure of DNA.
   

   ANS ::

   
   
   • In 1953, Watson and Crick proposed a model showing molecular structure of DNA.
   • In the molecule of DNA two polynucleotide chains run in antiparallel directions and twist around each other to form a spiral helical structure.
   • One nucleotide is linked with another nucleotide by a phospho-diaster bond.
   • In the chain, sugar and phosphate are linked with their nitrogenous bases.
   • Purine type nitrogenous base of one nucleotide links with pyrimidine type of nitrogenous base by weak hydrogen bonds.
   • Adenine(A) links with Thymine(T) by two weak hydrogen bonds whereas Guanine(G) links with Cytosine(C) by three weak hydrogen bonds. Such pairing is known as complimentary pairing.
   • The purine to pyrimidine ratio in each DNA molecule is always 1 : 1.
   • The length of one helix is 34 A° and each helix possesses 10 nitrogenous base pairs.
   • The distance between two adjacent nucleotides is 3.4 A° and the distance between two opposite chains is 20 A°.
     

   
   
   
   

   
   
9. Explain different evidences supporting biological evolution.
   

   ANS ::

   
   
   • Comparative anatomy, comparative embryology, vestigial organs and fossils are major evidences supporting biological evolution.
   • COMPARATIVE ANATOMY :
     
     
     • A number of common features of different kinds of organisms favour evolution.
     • Homologous organs like forelimb of humans, fins of fishes, wings of birds, limb of frog and forelimb of lizard perform different functions but show structural similarities.
     • All these organs might have evolved from a common ancestor from which these organisms have evolved.
     • Analogous organs like wings of birds and wings of insects perform same function of flying but their origins differ. Wings of birds are modifications of forelimb but wings of insects are ectodermal derivatives(i.e they have originated from skin).
       
     
     
   • COMPARATIVE EMBRYOLOGY :
     
     
     • Embryology provides strong evidence of evolution for the origin of different organisms.
     • During the early stage of development, the embryos of different vertebrates show similarities.
     • Later, their development results in clearly visible differences.
     • This is an evidence of the fact that the vertebrates have a common ancestor and origin.
     • Based on this fact Ernst Hackel proposed the 'Recapitulation Theory' which states that "Ontogeny recapitulates phylogeny".
       
     
     
   • VESTIGIAL ORGANS :
     
     
     • Morphological studies have identified some organs which have lost their functions. These organs might have been functional in their ancestors. Such organs are called vestigial organs.
     • Vermiform appendix associated with large intestine is a vestigial organ in humans but it is functional in herbivores like rabbit.
     • Nictitating membrane of eye is a vestigial organ in humans but it is functional in birds and gives protection to the eyes.
     • Thus, vestigial organs support evolution.
       
     
     
   • FOSSILS :
     
     
     • Fossils provide some evidence to support evolution.
     • Fossils of Archaopteryx(now extinct) show that it looked like a bird but it had maximum reptilian characters. This indicates that birds have evolved from reptiles.
       
     
     

   
   
   

   
   
10. 
    

    ANS :
    

    
    

HEREDITY AND EVOLUTION - II : BRIEF ANSWERS

ANSWER IN BRIEF

*INDEX-TOPIC SEARCH

1. Explain : Heredity.
   

   ANS:
   

   
   
   • Transmission of characters from parents to offsprings is known as heredity.
   • Fertilised egg or zygote carries hereditary information.
   • The zygote develops into a particular type of offspring only.
   • Thus, eggs laid by a sparrow hatch into sparrows and a dog reproduces to give birth to pups only.
     

   
   

   
   
2. Explain : Variation.
   

   ANS:
   

   
   
   • Variation means some individual diversity in the organism of one generation from that of the parental generation.
   • Variation passes from generation to generation.
   • In sexual reproduction, both similarities and variation are clearly observed among the offsprings of same parents.
   • Due to variation, any two persons rarely show complete similarity.
     

   
   

   
   
3. Explain : The number of chromosomes is fewer than the number of genes.
   

   ANS:
   

   
   
   • Genes are located on chromosomes.
   • Genes are responsible for specific characters of an organism.
   • The number of chromosomes in an organism is small but the number of characters of an individual organism is very large.
   • For example, there are 23 pairs of chromosomes in a human cell but the number of characters is very large requiring a large number of genes(30,000 to 40,000).
   • Thus, the number of chromosomes is fewer than that of genes.
     

   
   

   
   
4. Explain : Mutation.
   

   ANS:
   

   
   
   • Gene is a segment of DNA and is a unit of inheritance.
   • The nature of a gene is maintained generation after generation but sometimes it undergoes sudden inheritable changes known as mutation.
   • Mutation is one of the reasons of variation among individuals and species.
     

   
   

   
   
5. Describe the role of environmental factors in sex determination.
   

   ANS:
   

   
   
   • In some species, the sex determination is regulated by environmental factors.
   • For example, in turtle Chrysema Picta, high incubation temperature results into development of a female.
   • In a lizard, Agama agama, high incubation temperature results into development of a male.
     

   
   

   
   
6. Mention various theories of evolution.
   

   ANS:
   

   
   
   • Lamarck's theory of Inheritance of acquired characters.
   • August Weismann's Germplasm theory.
   • Darwin's theory of Natural Selection.
   • Hugo De Vries' Mutation theory.
     

   
   

   
   
7. Write a few points on Darwin's theory of Natural Selection.
   

   ANS:
   

   
   
   • Darwin's theory of Natural Selection describes biological evolution.
   • It explains how evolution takes place with the help of variation.
   • It fails to explain how variation occurs.
     

   
   

   
   
8. Explain : Homologous organs with example.
   

   ANS:
   

   
   
   • The organs showing similarities in origin but performing different functions are called homologous organs.
   • Forelimbs of human beings, fins of fishes, wings of birds, limbs of frog and forelimbs of lizard have structural similarities due to same origin but they perform different functions.
     

   
   

   
   
9. Explain : Analogous organs with example.
   

   ANS:
   

   
   
   • The organs showing different origin but performing the same functions are called analogous organs.
   • For example, both birds and insects use wings to fly(same function) but their origins are different. The wings of birds are modifications of forelimbs whereas the wings of insects are ectodermal derivatives(i.e. they have originated from skin).
     

   
   

   
   
10. Write a note on components of nucleotides.
    

    ANS:
    

    
    
    • DNA is a macromolecule made up of a large number of nucleotides.
    • A nucleotide is made up of three components :
      
      
      
      1. Pentose sugar(deoxyribose sugar)
      2. Phosphate group(H₃PO₄)
      3. Nitrogenous base
    • The nitrogenous bases are of two types :
      1. Purines
      2. Pyrimidines
    • Adenine(A) and Guanine(G) are purines whereas Cytosine(C) and Thymine(T) are pyrimidines.
      

    
    

    
    
11. 
    

    ANS:
    

    
    

HEREDITY AND EVOLUTION - I : MCQs & SHORT ANSWERS

*INDEX-TOPIC SEARCH

MULTIPLE-CHOICE QUESTIONS

SELECT THE CORRECT ALTERNATIVE:

1. Variation is observed in...
   
   
   
   1. asexual reproduction
   2. sexual reproduction
   3. both asexual reproduction and sexual reproduction
   4. neither of them
      
   
   
2. The number of genes is______ the number of chromosomes.
   
   
   
   1. same as
   2. less than
   3. more than
   4. less than or equal to
      
   
   
3. In human being ______ pairs of chromosomes are present.
   
   
   
   1. 23
   2. 46
   3. 30,000
   4. 40,000
      
   
   
4. The number of genes in human being is about...
   
   
   
   1. 23
   2. 46
   3. 1,000-2,000
   4. 30,000 to 40,000
      
   
   
5. Every chromosome possesses ______ molecule/s of DNA.
   
   
   
   1. 23
   2. 4
   3. 2
   4. 1
      
   
   
6. Which of the following is true ?
   
   
   
   1. Chromopsomes are located on genes.
   2. Chromosomes are part of a chromatid.
   3. Chromotids are part of a chromosome.
   4. Prokaryotes have paired chromosomes.
      
   
   
7. What is the diameter of a chromatid ?
   
   
   
   1. 40 A°
   2. 50 A°
   3. 60 A°
   4. 70 A°
      
   
   
8. The chromatids are joined to each other by...
   
   
   
   1. chromosome
   2. centromere
   3. gene
   4. DNA
      
   
   
9. The length of a chromosome is...
   
   
   
   1. 0.2-0.5μ
   2. 60 A°
   3. 60μ
   4. 34 A°
      
   
   
10. The diameter of a chromosome is...
    
    
    
    1. 0.2-0.5μ
    2. 0.2-2.0μ
    3. 60 A°
    4. 34 A°
       
    
    
11. A satellite structure is found in ______ chromosomes.
    
    
    
    1. metacentric
    2. sub-metacentric
    3. acrocentric
    4. telocentric
       
    
    
12. The centromere is situated at the tip of ______ chromosome.
    
    
    
    1. metacentric
    2. sub-metacentric
    3. acrocentric
    4. telocentric
       
    
    
13. Which of the following is not a nitrogenous base ?
    
    
    
    1. Adenine
    2. Guanine
    3. Cytosine
    4. Deoxyribose sugar
       
    
    
14. The molecule of DNA has ______ structure.
    
    
    
    1. linear
    2. cyclic
    3. helical
    4. hexagonal
       
    
    
15. Adenine links with thymine by ______ weak hydrogen bonds in DNA.
    
    
    
    1. one
    2. two
    3. three
    4. four
       
    
    
16. Guanine links with cytosine by ______ weak hydrogen bonds in DNA.
    
    
    
    1. one
    2. two
    3. three
    4. four
       
    
    
17. In a DNA molecule adenine links with ______.
    
    
    
    1. adenine
    2. guanine
    3. cytosine
    4. thymine
       
    
    
18. Each DNA molecule contains purine and pyrimidine in the ratio ______.
    
    
    
    1. 1 : 1
    2. 1 : 2
    3. 2 : 1
    4. 2 : 3
       
    
    
19. The cells in human female have chromosomes of the type ______.
    
    
    
    1. A + X
    2. A + Y
    3. 2A + XX
    4. 2A + XY
       
    
    
20. The cells in human male have chromosomes of the type ______.
    
    
    
    1. A + X
    2. A + Y
    3. 2A + XX
    4. 2A + XY
       
    
    
21. The ovum produced by a human female is ______ type.
    
    
    
    1. A + X
    2. A + Y
    3. 2A + XX
    4. 2A + XY
       
    
    
22. If the sperm having ______ chromosome fertilises an ovum then ______ is produced.
    
    
    
    1. X, male
    2. Y, female
    3. X, female
    4. XY, female
       
    
    
23. The principle of inheritance of acquired characters was given by...
    
    
    
    1. Lamarck
    2. Weismann
    3. Darwin
    4. Hugo De Vries
       
    
    
24. ______ gave Germplasm Theory.
    
    
    
    1. Lamarck
    2. Weismann
    3. Darwin
    4. Hugo De Vries
       
    
    
25. Mutation theory was described by ______.
    
    
    
    1. Lamarck
    2. Hugo De Vries
    3. Darwin
    4. Weismann
       
    
    
26. Fossils of ______ provide evidence of evolutionas the connecting link between birds and reptiles.
    
    
    
    1. Dinosaurs
    2. Lizard
    3. Archeopteryx
    4. Ostrich
       
    
    
27. ______ gives detailed information of variation and evolution.
    
    
    
    1. Lamarckism
    2. Modern synthetic theory
    3. Recapitulation theory
    4. Darwinism
       
    
    
28. The process of inheritance of characters in living beings is called...
    
    
    
    1. heredity
    2. evolution
    3. variation
    4. migration
       
    
    
29. Individual variation means...
    
    
    
    1. heredity
    2. variation
    3. evolution
    4. similarities
       
    
    
30. The branch of biology related with heredity and variation is called...
    
    
    
    1. Genetics
    2. Evolution
    3. Taxonomy
    4. Livinglogy
       
    
    
31. Boveri and Sutton proved that...
    
    
    
    1. Factor is responsible for information of heredity.
    2. Variation is inherited generation to generation.
    3. Chromosomes are transported by gametes.
    4. Gene is a part of a chromosome.
       
    
    
32. The number of chromosomes in comparison to the number of genes is...
    
    
    
    1. less
    2. more
    3. equal
    4. more or equal
       
    
    
33. The unit of expression of genetic information from one generation to another generation is...
    
    
    
    1. DNA
    2. RNA
    3. both DNA & RNA
    4. blood
       
    
    
34. An example of retrovirus is...
    
    
    
    1. the virus responsible for AIDS
    2. TMV
    3. bacteriophage
    4. RIV
       
    
    
35. Generally, the gametes, according to the number of chromosomes, are...
    
    
    
    1. haploid
    2. diploid
    3. triploid
    4. none of three
       
    
    
36. In which type of chromosome is the centromere displaced slightly from the center ?
    
    
    
    1. Metacentric
    2. Sub-metacentric
    3. Acrocentric
    4. Telocentric
       
    
    
37. Which type of nitrogen base are Adenine and Thymine ?
    
    
    
    1. purine and pyrimidine
    2. pyrimidine and purine
    3. purine and purine
    4. pyrimidine and pyrimidine
       
    
    
38. The extra chromosome found in male insect is called...
    
    
    
    1. X-body
    2. Y-body
    3. homologous
    4. neutral
       
    
    
39. In which animal, the embryo develops into a male at high temperature ?
    
    
    
    1. turtle
    2. lizard
    3. grasshopper
    4. fish
       
    
    
40. Which principle was given by Darwin ?
    
    
    
    1. Inheritance of acquired characters
    2. Germplasm theory
    3. Mutation theory
    4. Theory of natural selection
       
    
    
41. 
    
    
    
    4. 
       
    
    
42. 
    
    
    
    4. 
       
    
    

SHORT QUESTIONS

ANSWER IN SHORT:

1. Define : Heredity.
   
        ANS :Heredity is defined as 'the transmission of characters from parents to the off-springs'.
   
2. Give the meaning of variation from biological point of view.
   
        ANS :From biological point of view, variation means some individual difference(diversity) in the organismof one generation from that of the parental generation.
   
3. What is Genetics ?
   
        ANS :Genetics is the branch of biology which studies important aspects of heredity and variation.
   
4. What did Mendel propose ?
   
        ANS :Mendel proposed that for regulation of every character(in an organism) there is a pair of factors.
   
5. What happens when a cross is made between two pea plants ?
   
        ANS :When a cross is made between two pea plnats showing different characters, only one character is seen in the offsprings but the successive generations show both characters.
   
6. Who showed that gene is a part of chromosome ?
   
        ANS :T.Boveri and W.S. Sutton showed that gene is a part of chromosome.
   
7. Where are genes located ?
   
        ANS :Genes are located on chromosomes.
   
8. Of what is a gene the segment ?
   
        ANS :A gene is a segment of DNA(deoxyribonucleic acid).
   
9. Who established the DNA as a component for expression of genetic information from one generation to the other ?
   
        ANS :Griffin, Avery, McLeod and McCarty established the DNA as a component for expression of genetic information from one generation to the other.
   
10. What is meant by homologous chromosomes ?
    
         ANS :Homologous chromosomes are chromosomes occurring in pair and the members of a pair of chromosomes are exactly identical.
    
11. What is the difference between prokaryotic and eukaryotic chromosomes ?
    
         ANS : In prokaryotes only one chromosome occurs whereas in eukaryotes many chromosomes occur in pairs.
    
12. What is the difference in number of chromosomes of somatic cells and reproductive cells ?
    
         ANS :The number of chromosomes in reproductive cells is half(haploid) of that in somatic cells(diploid).
    
13. When do chromosomes get separated from each other ?
    
         ANS :Chromosomes get separated from each other during metaphase of cell division.
    
14. Why can chromosomes be identified easily during metaphase ?
    
         ANS :Chromosomes can be identified easily during metaphase because they get separated from each other.
    
15. What is centromere (primary constriction) ?
    
         ANS :In a chromosome, the dark region which connectes two individual chromatids is known as centromere (primary constriction).
    
16. How are chromosomes classified ?
    
         ANS :Chromosomes are classified depending on the position of the centromere.
    
17. Mention the types of chromosomes.
    
         ANS :Metacentric, submetacentric, acrocentric and telocentric are the types of chromosomes.
    
18. What is nucleolar organisation region ?
    
         ANS :A short filament connecting the satellite with the arm of an acrocentric chromosome is called nucleolar organisation region.
    
19. What is the full form of DNA ?
    
         ANS :The full form of DNA is DeoxyriboNucleic acid.
    
20. What is DNA ?
    
         ANS :DNA is a macromolecule in which a large number of nucleotide units is present.
    
21. Why is DNA known as polynucleotide ?
    
         ANS :DNA is known as polynucleotide as it is a macromolecule consisting of a large number of nucleotide units.
    
22. Mention the components of a DNA nucleotide.
    
         ANS :The components of a DNA nucleotide are : (1)Pentose sugar(deoxyribose sugar),(2)Phosphate group(H₃PO₄) and (3)Nitrogenous base.
    
23. Mention the types of nitrogenous base in DNA.
    
         ANS :Purines and pyrimidines are the types of nitrogenous base in DNA.
    
24. Mention the purines present in DNA.
    
         ANS :Adenine and Guanine are the purines present in DNA.
    
25. Mention the pyrimidines present in DNA.
    
         ANS :Cytosine and Thymine are the pyrimidines present in DNA.
    
26. What is complimentary pairing ?
    
         ANS :The linking of a purine type nitrogenous base with a pyrimidine type nitrogenous base by weak hydrogen bonds in a DNA molecule is called complimentary pairing.
    
27. What is the length of each helix in a DNA molecule ?
    
         ANS :The length of each helix in a DNA molecule is 34 A°.
    
28. How many nitrogenous base pairs are present in one helix of DNA ?
    
         ANS :10 nitrogenous base pairs are present in one helix of DNA.
    
29. What is the distance between two adjacent nucleotides in a DNA molecule ?
    
         ANS :The distance between two adjacent nucleotides in a DNA molecule is 3.4 A°.
    
30. What is the distance between two opposite chains of a DNA helix ?
    
         ANS :The distance between two opposite chains of a DNA helix is 20A°.
    
31. What is the biological name of the fruit fly ?
    
         ANS :Drosophila melanogaster is the biological name of the fruit fly.
    
32. What is mutation ?
    
         ANS :A sudden inheritable change in the nature of a gene is called mutation.
    
33. Mutation is one of the reasons of variation. True or false ?
    
         ANS : TRUE
    
34. What is the effect of high incubation temperature in determining sex in a turtle, chrysema picta ?
    
         ANS :The high incubation temperature in a turtle, chrysema picta, results in the development of a female.
    
35. What is the effect of high incubation temperature in determining sex in a lizard, agama agama ?
    
         ANS :The high incubation temperature in a lizard, agama agama results in the development of a male.
    
36. Give an example of a plant showing sex determination.
    
         ANS :Coccinia indica is a plant showing sex determination.
    
37. What are the two basic factors of evolution ?
    
         ANS :Variation and heredity are the two basic factors of evolution.
    
38. How is a new species evolved ?
    
         ANS :A new species is evolved during evolution process due to small changes in the heredity of one generation which gives rise to a new generation with different characters.
    
39. Mention the types of evidence that support the biological evolution.
    
         ANS :Evidences of comparative anatomy, comparative embryology, vestigial organs, fossils, connecting links, physiology and taxonomy support biological evolution.
    
40. Which theory of evolution did Darwin give ?
    
         ANS :Darwin gave the Theory of Natural Selection.
    
41. Mention the limitation of Darwinism.
    
         ANS :Darwinism explains evolution with the help of variation but it does not explain how variation occurs.
    
42. What are homologous organs ?
    
         ANS :The organs showing similarities in origin but performing different functions are called homologous organs.
    
43. What are analogous organs ?
    
         ANS :The organs different origin but performing same functions are called analogous organs.
    
44. Who proposed recapitulation theory ?
    
         ANS :Ernst Hackel proposed recapitulation theory.
    
45. What does recapitulation theory state ?
    
         ANS :Recapitulation theory states that 'Ontogeny recapitulates phylogeny'.
    
46. What are vestigial organs ?
    
         ANS :Those organs found in an organism which are not functional but which might have been functional in ancestors are called vestigial organs.
    
47. What do you study in Genetics ?
    
         ANS :We study important aspects of heredity and variation in Genetics.
    
48. What is satellite(in a chromosome)?
    
         ANS :Satellite is around structure at the tip of the filament on the distal end of the short arm of an acrocentric chromosome.
    
49. What is retrovirus ? Give an example.
    
         ANS :Retrovirus is a virus with RNA as hereditary material. The virus causing AIDS in humans is a retrovirus.
    
50. What is organic(biological) evolution ?
    
         ANS :A natural process of structural sequential transformation of species which is slow but progressive is called organic(biological) evolution. OR The structural and well-organised process of gradual changes in species is called organic(biological) evolution.
    
51. 
    
         ANS :
    
52. 
    
         ANS :
    

REPRODUCTION IN ORGANISMS - III : LONG ANSWERS

GIVE ANSWER IN DETAIL

*INDEX-TOPIC SEARCH

1. Describe fission as a method of reproduction.
   
   ANS :Fission occurs in unicellular organisms. Binary fission and multiple fission are its two types.
   
   BINARY FISSION :
   
   
   
   • An organism produces two unicellular organisms identical to the parent cell through mitotic division.
   • Amoeba, paramoecium, etc. reproduce by binary fission.
     
   
   
   MULTIPLE FISSION :
   
   
   
   • Under certain circumstances, the nucleus of a cell divides several times within the cell forming many nuclei.
   • Each nucleus is then surrounded by cytoplasm to form a separate unit.
   • All these newly formed cells then come out of the mother cell(parent cell) by breaking the wall and behave as a new organism.
   • Plasmodium, amoeba, paramoecium, etc. exhibit such reproductive event.
     
   
   
   
   
   
   
   
2. Describe budding as a method of reproduction.
   
   ANS :
   
   
   
   • Budding is observed in both unicellular and multicellular organisms.
   • In unicellular organisms, some part of the body swells out at one point and developes into a 'bud' due to the formation of nucleus and cytoplasm within it. This bud then separates from the parent cell and behaves as an independent organism. Sometimes the buds form a chain before being separated. Example : yeast.
   • In multicellular organisms like hydra, a part of its cylindrical body swells and develops into a bud. This bud then grows and separates from the mother's body to develop as an independent daughter animal.
     
   
   
   
   
   
   
   
3. Describe spore formation as a method of reproduction.
   
   ANS :
   
   
   
   • Spore formation is the most common method of asexual reproduction in majority of bacteria and fungi.
   • During spore formation, a structure called sporangium develops from fungal hypha which is a filamentous structure.
   • The nucleus in sporangium divides several times and forms many nuclei.
   • Each nucleus gets surrounded by cytoplasm and forms small unicellular structure called spore.
   • When sporangium bursts, the spores spread into the surrounding environment and germinate into new hypha forming mycellium which behaves as new organism.
   • Mucor and Rhizopus reproduce by this method.
     
   
   
   
   
   
4. Describe regeneration as a method of reproduction.
   
   ANS :
   
   
   
   • Regeneration is the ability of an organism to reproduce the lost parts of its body.
   • When some body part of an organism breaks suddenly, a new part similar to the lost (broken) part is created at the point of breaking after some time.
   • All broken parts thus develop into new organisms.
   • Hydra, planaria, sponge and starfish reproduce by regeneration.
   • Some filamentous algae increase their number by this method. Algae filaments break frequently and each broken piece develops into independent algae. This is called fragmentation.
     
   
   
   
   
   
5. Describe role of sex hormones in humans.
   
   ANS :
   
   
   
   • Once a male reaches puberty, testes start producing sex hormone testosterone. Similarly, in females, ovaries start producing sex hormones estrogen and progesterone.
   • These hormones play an important role in the regulation of the processes of spermatogenesis (in male) and oogenesis (in female).
   • Sex hormones are also responsible for the structural development, maintenance and functions of accessory sex organs.
   • They induce secondary sexual characters at proper age.
   • The secondary sexual characters in male include : growth of hair on face, chest and other body parts; change in voice, aggressive behaviour and mental agitation.
   • Those in female include : changes in face and body, development of mammary glands, change in the pitch of voice, vigilant behaviour and sentimental approach.
     
   
   
   
6. What is the difference between menstruation and menopause ?
   
   ANS :When a woman (girl) attains puberty, her reproductive system becomes functional. As a result the ovary starts releasing ovum and this phenomenon is repeated after a definite period as a cycle. When an ovum is released the uterine wall gets ready for the implantation of fertilised ovum (zygote). If the ovum is not fertilised within certain period, it gets destroyed and the uterine wall disintegrates resulting in the breaking of blood vessels. The disintegrated tissue along with blood flows out through vagina. This flow of blood continues for about 3-5 days and is called menstruation.
   
   Menstruation, as a part of sexual cycle, starts at the age of about 10-12 years and its commencement indicates that the reproductive system of the woman has become active. The reproductive system then remains active up to the age of about 45-50 years and then becomes non-functional. The sexual cycle stops and menstruation ceases. This is called menopause. Thus, menopause marks the end of reproductive period of a woman.
   
   
7. Describe vegetative propagation in detail.
   
   ANS :
   
   
   
   • Development of a new plant from root, stem or leaf is called vegetative propagation.
   • Some higher plants exhibit this method of reproduction.
   • Examples : (i)Development of buds from the root of sweet potato.(ii)Development of buds on potato tuber.(iii)Development of buds on the margin of bryophyllum leaf.
   • Besides natural method, artificial vegetative propagation is also used to increase production. Cutting, layering and grafting are commonly used methods of artificial vegetative propagation.
     
   
   
   
   
   
8. Describe various methods of artificial vegetative propagation.
   
   ANS :
   
   
   
   1. CUTTING :
      
      
      
      • In this method, a piece of root, stem, leaf or sometimes a bud is sown in soil which develops into a new plant.
      • The piece of the plant sown in the soil develops roots downwards in the soil and aerial organs in the external environment.
      • this method is useful for large scale production which is greatly economical and profitable.
      • Example : sugarcane, grapes, rose, phalsa.
        
      
      
      
      
   2. LAYERING :
      
      
      
      • In this method, a branch of stem of a plant is bent towards the soil in such a way that some part of the branch remains inside the soil and its tip remains outside.
      • The part covered by the soil develops roots.
      • When this part is detached from the parent plant, it grows independently into a new daughter plant.
      • Example : Lemon, guaua, hibiscus, jasmine and bougainvillaea.
      • In plants like strawberry and raspberry, sometimes a branch comes into contact of the soil naturally and develops as a daughter plant after producing roots.
        
      
      
      
      
   3. GRAFTING :
      
      
      
      • Grafting is a method in which two parts of different plants are joined together in such a way that they unite to grow as one plant.
      • A part of an adult (mature) plant is tied up with a unit of soft plant to get early flowering in the soft plant.
      • The portion of the plant having roots on which grafting is performed is called 'stock'.
      • The portion of the plant which is grafted on the other plant is called 'scion'.
      • By this method, desirable characteristics of different plants can be combined.
      • This method is very useful for plants whose seeds have long dormancy period and poor germination capacity.
      • Example : On the stock of lemon, a scion of lemon or orange can be grafted. This method is widely used to increase the production of mango.
        
      
      
      
      
   
   
   
9. Describe reproductive system in human male.
   
   ANS :
   
   
   
   • A pair of testes is the main reproductive organ in human male.
   • Vas deferens and penis are the accessory reproductive organs.
   • Seminal vesicle, prostate gland and bulbourethral gland are the accessory reproductive glands.
   • The two testes lie in a muscular sac called scrotum outside the abdominal cavity in the region between legs.
   • The temperature in the scrotum is 3°C lower than that of the body. This temperature is suitable for the process of spermatogenesis.
   • The sperms produced in the testes are transported through vas deferens to the penis.
   • Sperms mix with the semen which is formed by the secretions of reproductive glands.
   • Semen provides movement to sperms so that they can reach the egg cell(ovum).
   • In male, urine and sperms get released through the same path called urinogenital path.
     
   
   
   
   
   
10. Describe reproductive system in human female.
    
    ANS :
    
    
    
    • The main reproductive organ in human female is a pair of ovaries located in the abdominal cavity.
    • The reproductive system includes ovaries, fallopian tube (oviduct), uterus, cervix, vagina and vaginal opening.
    • Accessory reproductive organs include labia major, labia minor and clitoris.
    • Ovaries possess many ovarian follicles which become mature at puberty stage and form graffian follicle. Graffian follicle form the structure of ovum.
    • Generally, one ovarian follicle becomes active alternately and forms one ovum.
    • The free end of the oviduct towards ovary is fimbricated and funnel shaped. It is known as oviductal funnel.
    • The oviducts on both sides join in the middle to form inverted triangular shaped muscular sac called uterus. The mouth of uterus opens into vagina through narrow cervix.
    • Vagina opens outside the body through vaginal opening.
    • There is a separate urinary opening above the vaginal opening. Thus, in female, the urinary passage and genital passage are separate from each other.
      
    
    
    
    
    
11. Describe sexual cycle in human female.
    
    ANS :
    
    
    
    • The sexual cycle in female starts at puberty stage when the development of ovum starts in ovary from ovarian follicle.
    • When the ovum develops (matures) up to a definite stage it is released by rupturing of ovarian follicle. This is called ovulation.
    • During first 13 days of cycle, development of ovum occurs and ovulation takes place on the 14th day. After ovulation, the ovum enters oviduct through oviductal funnel.
    • Simultaneously, the walls of uterus get ready for the implantation of embryo.
    • If fertilisation occurs, the implantation of embryo on the walls of uterus takes place and the process of supply of nutrition to embryo starts.
    • If fertilisation does not occur, the walls of uterus that got prepared for implantation in the form of blood-filled tissues start disintegrating.
    • This results in the breakdown of blood vessels and the broken uterine wall tissues come out through vagina along with blood. This is known as Menstruation.
    • Menstruation may last for 3-5 days during which abdominal pain is experienced.
    • Then the cycle is repeated. Generally menstruation cycle is repeated every 28-32 days.
    • The secretion of sex hormones at puberty stage is responsible for the commencement of menstrual cycle. With this the female attains the ability of conception.
    • The sexual cycle generally remains functional up to the age of 45-50 years. Then gradually the sexual cycle stops due to hormonal changes and menopause starts indicating the loss of the ability of conception.
      
    
    
    
12. Describe fertilisation and embryo development in humans.
    
    ANS :
    
    
    
    • During the sexual cycle of a female ovulation occurs on the 14th day and the ovum enters the fallopian tube.
    • If copulation occurs during the period when the ovum is present in the oviduct, sperms released in semen try to reach the ovum with the help of the fluid substances present in semen.
    • If one of the sperms can reach the egg(ovum) in the oviduct, then fertilisation takes place.
    • If fertilisation occurs, then the walls of uterus start further developments.
    • The embryo(fertilised egg) reaches the walls of the uterus and gets implanted on the wall.
    • An umbilical cord develops from the embryo to the uterine wall and supplies nutrition to the embryo from mother's body.
    • For the protection of the developing embryo, a structure (amnion) filled with amniotic fluid develops.
    • The birth of the child takes place, usually, after 40 weeks or 280 days. (this is the time for the development of the embryo into a mature baby).
    • Duration from zygote formation till birth of the child is called embryo developing time.
    • When the development of the embryo is complete, a new born child comes out of the mother's body by breaking the amnion. This event is known as delivery.
    • The calculation of embryo development time starts from the first day of last menstrual cycle.
    • The normal weight of the foetus(at the time of birth) should be about 3-3.5 kg.
      
    
    
    
    
    
13. Write an explanatory note on population control.
    
    ANS :
    
    
    
    • Growth of population is one of the biggest problems in the world. The population of India has crossed 1 billion mark and it needs serious attention . Also, frequent delivery can be dangerous to both the mother and the child as it results in ill health and the birth of a weak baby.
    • Keeping the growth rate of population limited by using some scientific devices is called population control.
    • Types of such devices include : (i) Birth-control tools (ii) Chemical devices (iii) Surgical devices.
    • Birth-control tools :
      1. A condom used by males prevents the entry of semen into vagina during copulation.
      2. A copper-T or a loop used by a female prevents implantation in uterus.
         
    • Chemical devices include birth-control pills containing hormones which prevent implantation.
    • Surgical methods :
      1. In males, the vas deferens is cut and tied up to prevent the transport of sperms. The method is called Vasectomy.
      2. In females, the oviduct is cut and tied up to prevent the transport of ovum. The method is called Tubectomy.
         
    • A doctor must be consulted before following any method of population control to avoid side effects.
      
    
    
    
    
    
14. Write a note on sexually transmitted diseases (STDs).
    
    ANS :
    
    
    
    • Sexually transmitted diseases are infectious and some times they prove fatal.
    • The diseases occurring due to unsafe sexual intercourse are called Sexually Transmitted Diseases(STDs).
    • Such diseases are caused by virus, bacteria, fungi and protozoans.
    • Syphillis is caused by Treponema Palidium.
    • Gonorrhoea is caused by Neissena Gonorrhoea.
    • Symptoms of STDs :
      • Inflammation of the passage of urine.
      • Lesions on the skin of urinary tract and vagina.
      • Itching sensation in penis or vagina.
      • Lesions on genital passage.
    • STDs are curable by proper treatment, so a doctor must be consulted immediately without hesitation when any of the symptoms of STDs become visible.
    • AIDS can prove fatal. Research work is in progress to find out medicines to cure AIDS.
    • WHO has given several guidences to prevent the spread of STDs and to protect human race.
    • In India, NACO (National AIDS Control Organisation) and other NGOs (Non-Government Organisations) are functioning to create awareness about STDs.
    • Individual Care :
      
      
      • One should keep awareness about the cleanliness of the reproductive organs.
      • There must be limit in developing friendship with opposite sex.
      • Use of birth-control tools during intercourse can prevent such diseases.
      • The best one is to learn to keep control on sexual desires.
      • Morality must be imposed as religious practice.
      
      
    
    
    
15. 
    
    ANS :
    

REPRODUCTION IN ORGANISMS - II : BRIEF ANSWERS

ANSWER IN BRIEF

*INDEX-TOPIC SEARCH

1. What is reproduction ? Mention its importance.
   

   ANS:
   The process by which organisms produce new organisms similar to them is known as reproduction.
   
   The importance of reproduction is :
   

   
   
   • It maintains the existence of each species.
     
   • It transfers hereditary characteristics to the next generation.
     
   • It brings concomitant changes in evolutionary events.
     

   
   

   
   
2. What is asexual reproduction ? Mention its types(methods).
   

   ANS:The process of reproduction in which any somatic part of the body of a single organism develops into a new organism is called asexual reproduction.
   
   Its types are :
   

   
   
   • fission
   • budding
   • spore formation
   • regeneration
   • vegetative propagation
     

   
   

   
   
3. What is vegetative propagation ? Mention its different methods.
   

   ANS:Development of a new plant from the root, stem or leaf is called vegetative propagation.
   
   The different methods of vegetative propagation are :
   

   
   
   • Cutting
   • Layering
   • Grafting
     

   
   

   
   
4. Write a note on fission as a method of reproduction.
   

   ANS:
   

   
   
   • Fission occurs in unicellular organisms.
   • It is a method of asexual reproduction.
   • Binary fission and multiple fission are its two types.
   • Amoeba, paramoecium,plasmodium,etc. reproduce by fission.
     

   
   

   
   
5. Explain : Binary fission.
   

   ANS:
   

   
   
   • It is a method of asexual reproduction occurring in unicellular organism.
   • An organism produces two unicellular organisms identical to the parent cell through mitotic division.
   • Amoeba, paramoecium,etc. reproduce by binary fission.
     

   
   

   
   
6. Write a note on puberty.
   

   ANS:
   

   
   
   • Puberty is the stage in the life of a human being when the reproductive organs show gradual change in structure and they become functional.
   • A boy attains puberty at the age of 13-14 years whereas a girl attains it at the age of 10-12 years.
   • During puberty,testes in male start producing sperms and sex hormone testosterone.
   • Similarly, ovaries in female start producing ovum and sex hormones estrogen and progesterone.
     

   
   

   
   
7. Mention accessory reproductive glands and their function in human male.
   

   ANS:Seminal vesicle,prostate gland and bulbourethral gland are the accessory reproductive glands in human male. The secretions of these glands form semen which provides movement to sperms so that they can reach the egg cell easily.
   

   
   
8. Mention the requirements of fertilisation of an ovum.
   

   ANS:
   

   
   
   • Ovulation must have occurred and hence the ovum must be present in the oviduct.
   • Copulation must occur before the ovum gets destroyed.
   • A sperm must reach the ovum to fertilise it.
     

   
   

   
   
9. Why is population control needed ?
   

   ANS:Population control is needed to control population growth which is the biggest problem in the world. Also, frequent deliveries can be dangerous for the health of a female and they can result in the birth of a weak(unhealthy) child.
   

   
   
10. Mention symptoms of STDs (Sexually Transmitted Diseases).
    

    ANS:
    

    
    
    • Inflammation of urinary tract and hence pain at the time of passing urine.
    • Lesions on skin of the urinary tract.
    • Itching sensation in penis or vagina.
    • Lesions on genital passage.
      

    
    

    
    
11. What individual care should one take to prevent STDs ?
    

    ANS:
    

    
    
    • One should keep awareness about the cleanliness of reproductive organs.
    • There must be limit in developing friendship with opposite sex.
    • One should use birth-control tools during intercourse to prevent such diseases.
    • One should learn to keep control on sexual desires.
    • Morality must be imposed as a religious practice.
      

    
    

    
    
12. Distinguish between menarche and menopause.
    
    ANS:
    
    
    
13. 
    

    ANS: