Biology: CBSE Sample Question Paper- 6 | Sample Papers for Class 12 Medical and Non-Medical PDF Download

 Page 1


d o n e Biology - Sample Paper-6
1) What does movement of alleles into different gametes demonstrate?
Answer:
The movement of alleles into different gametes demonstrates segregation.
2)
Name the sex determination mechanism in followings.
(i) Mammals
(ii) Birds
Answer:
(i) Mammals-XX-XY Type. (ii) Birds -ZZ-ZW Type
3) Name two methane producing bacteria.
Answer:
Methanococcus, and Methanobacter
4) While doing a PCR, 'denaturation' step is missed. What will be its effect on the process?
Answer:
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension
will take place, hence no amplification will occur.
5) Give the name of a selectable marker for E. coli.
Answer:
Ampidllin (Amp).
6)
Differentiate between linkage and recombination.
OR
Life originated from inorganic atom earlier but it is not possible today. Give reasons.
Answer:
The main differences between linkage and recombination are as follows:
Linkage Recombination
(i) Cause of inheritance. Cause of variation.
(ii) Tendency of genes to stay together.      Tendency of genes to segregate.
(iii) Accounts for parental combination. Accounts for recombinants.
(iv) Ratio remain fixed. Ratio variable depending on % of recombination.
OR
Life originated from inorganic atoms earlier but it is not possible today because
(i) Presence of
(ii) Absence of high temperature and other climatic factors that was present in primitive atmosphere but not present today.
7) Name of man-made cereal? Trace how it was developed and where it is used?
Answer:
Triticale is the first man made cereal derived by crossing wheat and rye.   This cereal gives better bread than rye and well
adapted to grow in sandy soils where bread wheat cannot be grown.
                    
  
Page 2


d o n e Biology - Sample Paper-6
1) What does movement of alleles into different gametes demonstrate?
Answer:
The movement of alleles into different gametes demonstrates segregation.
2)
Name the sex determination mechanism in followings.
(i) Mammals
(ii) Birds
Answer:
(i) Mammals-XX-XY Type. (ii) Birds -ZZ-ZW Type
3) Name two methane producing bacteria.
Answer:
Methanococcus, and Methanobacter
4) While doing a PCR, 'denaturation' step is missed. What will be its effect on the process?
Answer:
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension
will take place, hence no amplification will occur.
5) Give the name of a selectable marker for E. coli.
Answer:
Ampidllin (Amp).
6)
Differentiate between linkage and recombination.
OR
Life originated from inorganic atom earlier but it is not possible today. Give reasons.
Answer:
The main differences between linkage and recombination are as follows:
Linkage Recombination
(i) Cause of inheritance. Cause of variation.
(ii) Tendency of genes to stay together.      Tendency of genes to segregate.
(iii) Accounts for parental combination. Accounts for recombinants.
(iv) Ratio remain fixed. Ratio variable depending on % of recombination.
OR
Life originated from inorganic atoms earlier but it is not possible today because
(i) Presence of
(ii) Absence of high temperature and other climatic factors that was present in primitive atmosphere but not present today.
7) Name of man-made cereal? Trace how it was developed and where it is used?
Answer:
Triticale is the first man made cereal derived by crossing wheat and rye.   This cereal gives better bread than rye and well
adapted to grow in sandy soils where bread wheat cannot be grown.
                    
  
would it affect your experiment?
Answer:
In a gene cloning experiment, first a recombinant DNA molecule is constructed, where the gene of interest is ligated to the vector
and introduced inside the host cell (transformation). Since, not all the cells get transformed with the recombinant/plasmid DNA,
in the absence of selectable marker, it will be difficult to distinguish between transformants and non-transformants. Because the
role of selectable marker is in the selection of transformants.
9)
(i) What is a parasitic food chain?
(ii) What is the function of decomposers?
Answer:
(i)  A parasitic food chain is one which starts from host (plants and animals) and ends in parasites. 
(ii) Decomposers breakdown the dead organic matter into simple inorganic substance.
10) What is photochemical smog? How does smog effect biological world?
Answer:
Photochemical smog is an example of secondary pollutants, it is formed in traffic congested metropolitan cities where warm
conditions and intense solar radiations are present. It is mainly composed of ozone and peroxy acyi nitrate (PAN)
and . Effect on biological world: Smog damages plant as well as animal life. In plants, main damage is caused to
leaves. Ozone activates lung disease in humans and also corrodes the heritage buildings. In human, PAN causes irritation of eyes.
11)
(i) Make a comparison between mammalian sperm and ovum.
(ii) Explain the permanent methods of birth control
OR
What is polyembryony? Give two reasons of polyembryony.
Answer:
(i) Following table shows the comparison between mammalian sperm and ovum:
Sperm Ovum
(i) Minute and motile gamete, (i) Large and non-motile
(ii) Narrow and elongated (ii) Rounded in shape
(iii) Covered by plasma membrane (iii) Covered by corona radiata
(iv) Three Body division: head middle piece and tail (iv) No such body divisions 
(ii) Sterilisation provides a permanent birth control. It is called vasectomy in men and tubectomy in women. It involves the removal of a short
segment of each vas deferens or oviduct and tying up of the remaining ends tightly with the surgical thread.
OR
Polyembryony is the phenomenon of development of more than one embryo in the same seed (1719) in Citrus.
The reasons are:
(a) Presence of more than one embryo in the same seed   
(b) Cleavage of one embryo into two or more embryos 
12) Discuss Down's syndrome.
Answer:
Down's Syndrome 
- Occur due to Trisomy of 21st chromosome.
- Characterized with rounded face, flaccid muscle, protruding tongue, broad neck, etc.
- Also called Mongoloid syndrome.
- Survivors of down syndrome have higher chances of catching leukaemia & Alzheimers disease.
13) How chromosome number is maintained during sexual reproduction?
Page 3


d o n e Biology - Sample Paper-6
1) What does movement of alleles into different gametes demonstrate?
Answer:
The movement of alleles into different gametes demonstrates segregation.
2)
Name the sex determination mechanism in followings.
(i) Mammals
(ii) Birds
Answer:
(i) Mammals-XX-XY Type. (ii) Birds -ZZ-ZW Type
3) Name two methane producing bacteria.
Answer:
Methanococcus, and Methanobacter
4) While doing a PCR, 'denaturation' step is missed. What will be its effect on the process?
Answer:
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension
will take place, hence no amplification will occur.
5) Give the name of a selectable marker for E. coli.
Answer:
Ampidllin (Amp).
6)
Differentiate between linkage and recombination.
OR
Life originated from inorganic atom earlier but it is not possible today. Give reasons.
Answer:
The main differences between linkage and recombination are as follows:
Linkage Recombination
(i) Cause of inheritance. Cause of variation.
(ii) Tendency of genes to stay together.      Tendency of genes to segregate.
(iii) Accounts for parental combination. Accounts for recombinants.
(iv) Ratio remain fixed. Ratio variable depending on % of recombination.
OR
Life originated from inorganic atoms earlier but it is not possible today because
(i) Presence of
(ii) Absence of high temperature and other climatic factors that was present in primitive atmosphere but not present today.
7) Name of man-made cereal? Trace how it was developed and where it is used?
Answer:
Triticale is the first man made cereal derived by crossing wheat and rye.   This cereal gives better bread than rye and well
adapted to grow in sandy soils where bread wheat cannot be grown.
                    
  
would it affect your experiment?
Answer:
In a gene cloning experiment, first a recombinant DNA molecule is constructed, where the gene of interest is ligated to the vector
and introduced inside the host cell (transformation). Since, not all the cells get transformed with the recombinant/plasmid DNA,
in the absence of selectable marker, it will be difficult to distinguish between transformants and non-transformants. Because the
role of selectable marker is in the selection of transformants.
9)
(i) What is a parasitic food chain?
(ii) What is the function of decomposers?
Answer:
(i)  A parasitic food chain is one which starts from host (plants and animals) and ends in parasites. 
(ii) Decomposers breakdown the dead organic matter into simple inorganic substance.
10) What is photochemical smog? How does smog effect biological world?
Answer:
Photochemical smog is an example of secondary pollutants, it is formed in traffic congested metropolitan cities where warm
conditions and intense solar radiations are present. It is mainly composed of ozone and peroxy acyi nitrate (PAN)
and . Effect on biological world: Smog damages plant as well as animal life. In plants, main damage is caused to
leaves. Ozone activates lung disease in humans and also corrodes the heritage buildings. In human, PAN causes irritation of eyes.
11)
(i) Make a comparison between mammalian sperm and ovum.
(ii) Explain the permanent methods of birth control
OR
What is polyembryony? Give two reasons of polyembryony.
Answer:
(i) Following table shows the comparison between mammalian sperm and ovum:
Sperm Ovum
(i) Minute and motile gamete, (i) Large and non-motile
(ii) Narrow and elongated (ii) Rounded in shape
(iii) Covered by plasma membrane (iii) Covered by corona radiata
(iv) Three Body division: head middle piece and tail (iv) No such body divisions 
(ii) Sterilisation provides a permanent birth control. It is called vasectomy in men and tubectomy in women. It involves the removal of a short
segment of each vas deferens or oviduct and tying up of the remaining ends tightly with the surgical thread.
OR
Polyembryony is the phenomenon of development of more than one embryo in the same seed (1719) in Citrus.
The reasons are:
(a) Presence of more than one embryo in the same seed   
(b) Cleavage of one embryo into two or more embryos 
12) Discuss Down's syndrome.
Answer:
Down's Syndrome 
- Occur due to Trisomy of 21st chromosome.
- Characterized with rounded face, flaccid muscle, protruding tongue, broad neck, etc.
- Also called Mongoloid syndrome.
- Survivors of down syndrome have higher chances of catching leukaemia & Alzheimers disease.
13) How chromosome number is maintained during sexual reproduction?
Answer:
The gametes are usually formed by the meiotic divisions. Therefore, these are haploid, having half or (n) number of
chromosomes. In sexual reproduction, male and female gametes fuse to form a single cell called zygote. This process is called
fertilisation. The zygote formed by the fusion of two haploid gametes is thus diploid or having (2n) number of chromosomes. So,
we can say that meiosis and fertilisation are the two important events in sexual reproduction that keep the number of
chromosome constant from generation to generation.
14)
(i) Cleistogamy can favour only autogamy. Justify.
(ii) Why emasculation is not required in unisexual flowers?
Answer:
(i) In cleistogamy, flowers never open at all. Hence, foreign pollen will not land on the stigma of such
flowers. So, cleistogamy can favour only self-pollination or autogamy.
(ii) In unisexual flowers, emasculation is not needed because the female flowers are bagged before the
flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and
the flowers are rebagged.
15)
(i) Discuss the Louis Pasteur's view about the origin of life.
(ii) Define the following:
(a) Gene frequency
(b) Genetic drift.
Answer:
(i)  Louis Pasteur disapproved the spontaneous generation of life. Louis Pasteur by careful
experimentation demonstrated that life comes only from pre-existing life. He showed that in presterilised
flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose
from 'killed yeast'. Spontaneous generation theory was dismissed once and for all. However, this did not
answer how the first life form came on earth.
(ii) (a) Gene frequency is the frequency with which a particular allele occurs in a population.
(b) Genetic drift refers to a change in the population of alleles in the gene pool.
16) Write an account of the original atmosphere on primitive earth.
Answer:
The original atmosphere on the earth was very different from that existing at present. It probably contained hydrogen, nitrogen,
carbon dioxide and water vapour derived from the cosmic cloud. As the atmosphere and earth cooled, much of water vapour
condensed into droplets and came down as rain on the earth. The gases interacted with each other
and with carbides, nitrites and sulphide of earth's crust, producing methane, ammonia, hydrogen sulphide and hydrogen cyanide.
There was no free in the primitive atmosphere.
17) Define operon. What is the organization of/acoperon?
Answer:
A group of genes including an operator, a common promoter and one or more structural genes that are controlled as a unit to
produce messenger RNA (mRNA).   The lac operon consists of one regulatory gene (the; gene - here the term; does not refer to
inducer, rather it is derived from the word inhibitor) and three structural genes (z,y and a). The z gene codes for the represser of
the lac operon. The z gene codes for beta-galactosidase (|3-gal), which is primarily responsible for the hydrolysis of the
disaccharide, lactose into its monomeric units, galactose and glucose. They gene codes for permease, which increases
permeability of the cell to P-galactosides. The a gene encodes of transacetylase.
18) A mixture of fragmented DNA was electrophoresed in agarose gel. After staining the gel with ethidium bromide, no DNA
bands were observed. What could be the reason?
Answer:
Page 4


d o n e Biology - Sample Paper-6
1) What does movement of alleles into different gametes demonstrate?
Answer:
The movement of alleles into different gametes demonstrates segregation.
2)
Name the sex determination mechanism in followings.
(i) Mammals
(ii) Birds
Answer:
(i) Mammals-XX-XY Type. (ii) Birds -ZZ-ZW Type
3) Name two methane producing bacteria.
Answer:
Methanococcus, and Methanobacter
4) While doing a PCR, 'denaturation' step is missed. What will be its effect on the process?
Answer:
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension
will take place, hence no amplification will occur.
5) Give the name of a selectable marker for E. coli.
Answer:
Ampidllin (Amp).
6)
Differentiate between linkage and recombination.
OR
Life originated from inorganic atom earlier but it is not possible today. Give reasons.
Answer:
The main differences between linkage and recombination are as follows:
Linkage Recombination
(i) Cause of inheritance. Cause of variation.
(ii) Tendency of genes to stay together.      Tendency of genes to segregate.
(iii) Accounts for parental combination. Accounts for recombinants.
(iv) Ratio remain fixed. Ratio variable depending on % of recombination.
OR
Life originated from inorganic atoms earlier but it is not possible today because
(i) Presence of
(ii) Absence of high temperature and other climatic factors that was present in primitive atmosphere but not present today.
7) Name of man-made cereal? Trace how it was developed and where it is used?
Answer:
Triticale is the first man made cereal derived by crossing wheat and rye.   This cereal gives better bread than rye and well
adapted to grow in sandy soils where bread wheat cannot be grown.
                    
  
would it affect your experiment?
Answer:
In a gene cloning experiment, first a recombinant DNA molecule is constructed, where the gene of interest is ligated to the vector
and introduced inside the host cell (transformation). Since, not all the cells get transformed with the recombinant/plasmid DNA,
in the absence of selectable marker, it will be difficult to distinguish between transformants and non-transformants. Because the
role of selectable marker is in the selection of transformants.
9)
(i) What is a parasitic food chain?
(ii) What is the function of decomposers?
Answer:
(i)  A parasitic food chain is one which starts from host (plants and animals) and ends in parasites. 
(ii) Decomposers breakdown the dead organic matter into simple inorganic substance.
10) What is photochemical smog? How does smog effect biological world?
Answer:
Photochemical smog is an example of secondary pollutants, it is formed in traffic congested metropolitan cities where warm
conditions and intense solar radiations are present. It is mainly composed of ozone and peroxy acyi nitrate (PAN)
and . Effect on biological world: Smog damages plant as well as animal life. In plants, main damage is caused to
leaves. Ozone activates lung disease in humans and also corrodes the heritage buildings. In human, PAN causes irritation of eyes.
11)
(i) Make a comparison between mammalian sperm and ovum.
(ii) Explain the permanent methods of birth control
OR
What is polyembryony? Give two reasons of polyembryony.
Answer:
(i) Following table shows the comparison between mammalian sperm and ovum:
Sperm Ovum
(i) Minute and motile gamete, (i) Large and non-motile
(ii) Narrow and elongated (ii) Rounded in shape
(iii) Covered by plasma membrane (iii) Covered by corona radiata
(iv) Three Body division: head middle piece and tail (iv) No such body divisions 
(ii) Sterilisation provides a permanent birth control. It is called vasectomy in men and tubectomy in women. It involves the removal of a short
segment of each vas deferens or oviduct and tying up of the remaining ends tightly with the surgical thread.
OR
Polyembryony is the phenomenon of development of more than one embryo in the same seed (1719) in Citrus.
The reasons are:
(a) Presence of more than one embryo in the same seed   
(b) Cleavage of one embryo into two or more embryos 
12) Discuss Down's syndrome.
Answer:
Down's Syndrome 
- Occur due to Trisomy of 21st chromosome.
- Characterized with rounded face, flaccid muscle, protruding tongue, broad neck, etc.
- Also called Mongoloid syndrome.
- Survivors of down syndrome have higher chances of catching leukaemia & Alzheimers disease.
13) How chromosome number is maintained during sexual reproduction?
Answer:
The gametes are usually formed by the meiotic divisions. Therefore, these are haploid, having half or (n) number of
chromosomes. In sexual reproduction, male and female gametes fuse to form a single cell called zygote. This process is called
fertilisation. The zygote formed by the fusion of two haploid gametes is thus diploid or having (2n) number of chromosomes. So,
we can say that meiosis and fertilisation are the two important events in sexual reproduction that keep the number of
chromosome constant from generation to generation.
14)
(i) Cleistogamy can favour only autogamy. Justify.
(ii) Why emasculation is not required in unisexual flowers?
Answer:
(i) In cleistogamy, flowers never open at all. Hence, foreign pollen will not land on the stigma of such
flowers. So, cleistogamy can favour only self-pollination or autogamy.
(ii) In unisexual flowers, emasculation is not needed because the female flowers are bagged before the
flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and
the flowers are rebagged.
15)
(i) Discuss the Louis Pasteur's view about the origin of life.
(ii) Define the following:
(a) Gene frequency
(b) Genetic drift.
Answer:
(i)  Louis Pasteur disapproved the spontaneous generation of life. Louis Pasteur by careful
experimentation demonstrated that life comes only from pre-existing life. He showed that in presterilised
flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose
from 'killed yeast'. Spontaneous generation theory was dismissed once and for all. However, this did not
answer how the first life form came on earth.
(ii) (a) Gene frequency is the frequency with which a particular allele occurs in a population.
(b) Genetic drift refers to a change in the population of alleles in the gene pool.
16) Write an account of the original atmosphere on primitive earth.
Answer:
The original atmosphere on the earth was very different from that existing at present. It probably contained hydrogen, nitrogen,
carbon dioxide and water vapour derived from the cosmic cloud. As the atmosphere and earth cooled, much of water vapour
condensed into droplets and came down as rain on the earth. The gases interacted with each other
and with carbides, nitrites and sulphide of earth's crust, producing methane, ammonia, hydrogen sulphide and hydrogen cyanide.
There was no free in the primitive atmosphere.
17) Define operon. What is the organization of/acoperon?
Answer:
A group of genes including an operator, a common promoter and one or more structural genes that are controlled as a unit to
produce messenger RNA (mRNA).   The lac operon consists of one regulatory gene (the; gene - here the term; does not refer to
inducer, rather it is derived from the word inhibitor) and three structural genes (z,y and a). The z gene codes for the represser of
the lac operon. The z gene codes for beta-galactosidase (|3-gal), which is primarily responsible for the hydrolysis of the
disaccharide, lactose into its monomeric units, galactose and glucose. They gene codes for permease, which increases
permeability of the cell to P-galactosides. The a gene encodes of transacetylase.
18) A mixture of fragmented DNA was electrophoresed in agarose gel. After staining the gel with ethidium bromide, no DNA
bands were observed. What could be the reason?
Answer:
The reasons are as follows: (a) DNA sample that was loaded on the gel may have got contaminated with nuclease (exo-or endo-
or both) and completely degraded.    (b) Electrodes were put in opposite orientation in the gel assembly that is anode towards
the wells (where DNA sample is loaded). Since DNA molecules are negatively charged, they move towards anode and hence
move out of the gel instead of moving into the matrix of gel. 
19)
(i) How is bioreactor useful for production of desired products?
(ii) How do we elute DNA of desired quality in gel electrophoresis?
Answer:
(i)  Bioreactor it provides optimum conditions for culture growth by providing optimum pH, temperature,
substrate, salt, vitamins and oxygen.
(ii) The steps in elution are -
(a) Separated DNA fragments are visualized after staining with ethidium bromide.
(b) Illumination with UV light that imparts orange colour.
(c) Cutting and separating bands of DNA looking through UV protection glasses.
20) What is accelerated eutrophication? Mention any two consequences of this phenomenon.
Answer:
Increased concentrations of phosphorus and nitrates from industries and residences, etc., in a water body act as nutrients and
accelerate the growth of algae that may form a mat on the water surface. This increased productivity is called accelerated
eutrophication.  Consequences, (i) Eutrophication leads to lowering of dissolved oxygen (DO) in water body leading to death of
aquatic life. (ii) Nitrates from fertilizers and detergents contaminate drinking water leading to decrease in oxygen carrying
capacity of haemoglobin in human beings.
21) Write a note on fermentation by microbes and its applications.
Answer:
Fermentation is the process of conversion of carbohydrates to alcohol and  with the help of
bacteria and yeast.
Microbes via fermentation are utilised for the synthesis of a number of products valuable for human
beings.
(a) Production of bread using baker's yeast.
(b) Microbes are used to ferment fish, soyabean, bamboo shoots, etc.
(c) Different varieties of cheese are produced by fermentation via microbes.
(d) Wine, beer and other alcoholic drinks are also produced by fermentation.
(e) Vinegar is also produced by fermentation.
22)
(i) Mention the useful as well as harmful drug obtained from the latex of poppy plant.
(ii) Wrie the name of plant from which morphine is obtained.
(iii) Give the name of plant from which cocaine is obtained.
Answer:
(i)  Morphine
(ii) Papaver somniferum (poppy)
(iii) Erythroxylum coca.
23) Explain diagrammatically the age structure of expanding, stable and declining population.
Answer:
Age structure of different populations are
(i) Expanding Population: This population has more pre-reproductive and reproductive population and
less post reproductive population.
Page 5


d o n e Biology - Sample Paper-6
1) What does movement of alleles into different gametes demonstrate?
Answer:
The movement of alleles into different gametes demonstrates segregation.
2)
Name the sex determination mechanism in followings.
(i) Mammals
(ii) Birds
Answer:
(i) Mammals-XX-XY Type. (ii) Birds -ZZ-ZW Type
3) Name two methane producing bacteria.
Answer:
Methanococcus, and Methanobacter
4) While doing a PCR, 'denaturation' step is missed. What will be its effect on the process?
Answer:
If denaturation of double-stranded DNA does not take place, then primers will not be able to anneal to the template, no extension
will take place, hence no amplification will occur.
5) Give the name of a selectable marker for E. coli.
Answer:
Ampidllin (Amp).
6)
Differentiate between linkage and recombination.
OR
Life originated from inorganic atom earlier but it is not possible today. Give reasons.
Answer:
The main differences between linkage and recombination are as follows:
Linkage Recombination
(i) Cause of inheritance. Cause of variation.
(ii) Tendency of genes to stay together.      Tendency of genes to segregate.
(iii) Accounts for parental combination. Accounts for recombinants.
(iv) Ratio remain fixed. Ratio variable depending on % of recombination.
OR
Life originated from inorganic atoms earlier but it is not possible today because
(i) Presence of
(ii) Absence of high temperature and other climatic factors that was present in primitive atmosphere but not present today.
7) Name of man-made cereal? Trace how it was developed and where it is used?
Answer:
Triticale is the first man made cereal derived by crossing wheat and rye.   This cereal gives better bread than rye and well
adapted to grow in sandy soils where bread wheat cannot be grown.
                    
  
would it affect your experiment?
Answer:
In a gene cloning experiment, first a recombinant DNA molecule is constructed, where the gene of interest is ligated to the vector
and introduced inside the host cell (transformation). Since, not all the cells get transformed with the recombinant/plasmid DNA,
in the absence of selectable marker, it will be difficult to distinguish between transformants and non-transformants. Because the
role of selectable marker is in the selection of transformants.
9)
(i) What is a parasitic food chain?
(ii) What is the function of decomposers?
Answer:
(i)  A parasitic food chain is one which starts from host (plants and animals) and ends in parasites. 
(ii) Decomposers breakdown the dead organic matter into simple inorganic substance.
10) What is photochemical smog? How does smog effect biological world?
Answer:
Photochemical smog is an example of secondary pollutants, it is formed in traffic congested metropolitan cities where warm
conditions and intense solar radiations are present. It is mainly composed of ozone and peroxy acyi nitrate (PAN)
and . Effect on biological world: Smog damages plant as well as animal life. In plants, main damage is caused to
leaves. Ozone activates lung disease in humans and also corrodes the heritage buildings. In human, PAN causes irritation of eyes.
11)
(i) Make a comparison between mammalian sperm and ovum.
(ii) Explain the permanent methods of birth control
OR
What is polyembryony? Give two reasons of polyembryony.
Answer:
(i) Following table shows the comparison between mammalian sperm and ovum:
Sperm Ovum
(i) Minute and motile gamete, (i) Large and non-motile
(ii) Narrow and elongated (ii) Rounded in shape
(iii) Covered by plasma membrane (iii) Covered by corona radiata
(iv) Three Body division: head middle piece and tail (iv) No such body divisions 
(ii) Sterilisation provides a permanent birth control. It is called vasectomy in men and tubectomy in women. It involves the removal of a short
segment of each vas deferens or oviduct and tying up of the remaining ends tightly with the surgical thread.
OR
Polyembryony is the phenomenon of development of more than one embryo in the same seed (1719) in Citrus.
The reasons are:
(a) Presence of more than one embryo in the same seed   
(b) Cleavage of one embryo into two or more embryos 
12) Discuss Down's syndrome.
Answer:
Down's Syndrome 
- Occur due to Trisomy of 21st chromosome.
- Characterized with rounded face, flaccid muscle, protruding tongue, broad neck, etc.
- Also called Mongoloid syndrome.
- Survivors of down syndrome have higher chances of catching leukaemia & Alzheimers disease.
13) How chromosome number is maintained during sexual reproduction?
Answer:
The gametes are usually formed by the meiotic divisions. Therefore, these are haploid, having half or (n) number of
chromosomes. In sexual reproduction, male and female gametes fuse to form a single cell called zygote. This process is called
fertilisation. The zygote formed by the fusion of two haploid gametes is thus diploid or having (2n) number of chromosomes. So,
we can say that meiosis and fertilisation are the two important events in sexual reproduction that keep the number of
chromosome constant from generation to generation.
14)
(i) Cleistogamy can favour only autogamy. Justify.
(ii) Why emasculation is not required in unisexual flowers?
Answer:
(i) In cleistogamy, flowers never open at all. Hence, foreign pollen will not land on the stigma of such
flowers. So, cleistogamy can favour only self-pollination or autogamy.
(ii) In unisexual flowers, emasculation is not needed because the female flowers are bagged before the
flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and
the flowers are rebagged.
15)
(i) Discuss the Louis Pasteur's view about the origin of life.
(ii) Define the following:
(a) Gene frequency
(b) Genetic drift.
Answer:
(i)  Louis Pasteur disapproved the spontaneous generation of life. Louis Pasteur by careful
experimentation demonstrated that life comes only from pre-existing life. He showed that in presterilised
flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose
from 'killed yeast'. Spontaneous generation theory was dismissed once and for all. However, this did not
answer how the first life form came on earth.
(ii) (a) Gene frequency is the frequency with which a particular allele occurs in a population.
(b) Genetic drift refers to a change in the population of alleles in the gene pool.
16) Write an account of the original atmosphere on primitive earth.
Answer:
The original atmosphere on the earth was very different from that existing at present. It probably contained hydrogen, nitrogen,
carbon dioxide and water vapour derived from the cosmic cloud. As the atmosphere and earth cooled, much of water vapour
condensed into droplets and came down as rain on the earth. The gases interacted with each other
and with carbides, nitrites and sulphide of earth's crust, producing methane, ammonia, hydrogen sulphide and hydrogen cyanide.
There was no free in the primitive atmosphere.
17) Define operon. What is the organization of/acoperon?
Answer:
A group of genes including an operator, a common promoter and one or more structural genes that are controlled as a unit to
produce messenger RNA (mRNA).   The lac operon consists of one regulatory gene (the; gene - here the term; does not refer to
inducer, rather it is derived from the word inhibitor) and three structural genes (z,y and a). The z gene codes for the represser of
the lac operon. The z gene codes for beta-galactosidase (|3-gal), which is primarily responsible for the hydrolysis of the
disaccharide, lactose into its monomeric units, galactose and glucose. They gene codes for permease, which increases
permeability of the cell to P-galactosides. The a gene encodes of transacetylase.
18) A mixture of fragmented DNA was electrophoresed in agarose gel. After staining the gel with ethidium bromide, no DNA
bands were observed. What could be the reason?
Answer:
The reasons are as follows: (a) DNA sample that was loaded on the gel may have got contaminated with nuclease (exo-or endo-
or both) and completely degraded.    (b) Electrodes were put in opposite orientation in the gel assembly that is anode towards
the wells (where DNA sample is loaded). Since DNA molecules are negatively charged, they move towards anode and hence
move out of the gel instead of moving into the matrix of gel. 
19)
(i) How is bioreactor useful for production of desired products?
(ii) How do we elute DNA of desired quality in gel electrophoresis?
Answer:
(i)  Bioreactor it provides optimum conditions for culture growth by providing optimum pH, temperature,
substrate, salt, vitamins and oxygen.
(ii) The steps in elution are -
(a) Separated DNA fragments are visualized after staining with ethidium bromide.
(b) Illumination with UV light that imparts orange colour.
(c) Cutting and separating bands of DNA looking through UV protection glasses.
20) What is accelerated eutrophication? Mention any two consequences of this phenomenon.
Answer:
Increased concentrations of phosphorus and nitrates from industries and residences, etc., in a water body act as nutrients and
accelerate the growth of algae that may form a mat on the water surface. This increased productivity is called accelerated
eutrophication.  Consequences, (i) Eutrophication leads to lowering of dissolved oxygen (DO) in water body leading to death of
aquatic life. (ii) Nitrates from fertilizers and detergents contaminate drinking water leading to decrease in oxygen carrying
capacity of haemoglobin in human beings.
21) Write a note on fermentation by microbes and its applications.
Answer:
Fermentation is the process of conversion of carbohydrates to alcohol and  with the help of
bacteria and yeast.
Microbes via fermentation are utilised for the synthesis of a number of products valuable for human
beings.
(a) Production of bread using baker's yeast.
(b) Microbes are used to ferment fish, soyabean, bamboo shoots, etc.
(c) Different varieties of cheese are produced by fermentation via microbes.
(d) Wine, beer and other alcoholic drinks are also produced by fermentation.
(e) Vinegar is also produced by fermentation.
22)
(i) Mention the useful as well as harmful drug obtained from the latex of poppy plant.
(ii) Wrie the name of plant from which morphine is obtained.
(iii) Give the name of plant from which cocaine is obtained.
Answer:
(i)  Morphine
(ii) Papaver somniferum (poppy)
(iii) Erythroxylum coca.
23) Explain diagrammatically the age structure of expanding, stable and declining population.
Answer:
Age structure of different populations are
(i) Expanding Population: This population has more pre-reproductive and reproductive population and
less post reproductive population.
(ii) Stable Population: In this type of population, there are nearly equal number of pre-reproductive and
reproductive individuals with a declining number of post reproductive individuals.
(iii) Declining Population: This population has larger number of post-reproductive individuals as
compared to pre-reproductive and reproductive population.
24) Nidhi attended a seminar on the topic "How to minimise the use of plastic bags to reduce environmental pollution?" In
evening she goes to a market with her mother and carried a natural fibre carry bag for shopping and decline to take good items
in polythene bags.
(i) Do you think Nidhi's action is eco-friendly? Justify.
(ii) How the use of polythene causes environmental pollution?
(iii) Compare biodegradable and non-biodegradable
pollutants.
Answer:
(i) Nidhi's action is totally eco-friendly. Since polythene bags are non-biodegradable product and their use add to the
environmental pollution. (ii) Polythene is non-biodegradable product. It exists as such in soil for year and causes water logging. It
does not allow water to pass through it. (iii) The main difference between biodegradable and non-biodegradable pollutants are:
S. No. Biodegradable pollutants Non-biodegradable pollutants
1. Pollutants decomposed by decomposer or in waste
treatment plastic, plants, e.g., livestock waste, cans
etc. muncipal sewage, etc.
They are not degraded, e.g.
polyethylene, soft drink
2. They can be recycled. They can be turned into
useful
They are not recycled.
3. They are difficult to manage, resources. 
                                                      
25)
Discuss the various chemical methods of controlling human population.
OR
What do you mean by gametogenesis? Describe the structure of a human sperm.
Answer:
Chemical methods of controlling human population are following:
(a) Birth control pills are taken through mouth. They contain combination of progestogens and estrogen.
Pills are taken daily menstruation occurs) it has to be repeated in the same pattern till the female desires
to prevent conception. They inhibit ovulation and implantation.
(b) Progestogens alone or in combination with estrogen is used as by female injections or implants under
the skin of the upper arm. Their mode of action is same as that of pills and their effective period lasts for 3
to 4 years.
(c) Spermicidal creams, tablets, jellies and paste are introduced in the vagina before the sexual
intercourse. These kill sperms.
OR
Gametogenesis carried out in gonads, is the formation of gametes for sexual reproduction. It is controlled
by gonadotrophic hormones (FSH, LH, ICSH etc.) secreted by pituitary gland. Meiosis is the most significant
part of the of gametogenesis. The male reproductive organ or testis undergo spermatogenesis and the
female reproductive organ or ovary, oogenesis. As a result of reduction division or meiosis, the sperms and
the ova produced have only half the number of chromosomes as compared to body cells of the parent.
Human sperm is microscopic in structure. It is composed of head, neck, middle piece and tail. The whole
sperm is covered by a plasma membrane. The head portion has an elongated nucleus whose anterior
portion is covered by a cap like acrosome. The acrosome is derived from the Golgi complex & contains
hydrolysing enzymes for the sperm penetration. The nucleus contain haploid set of chromosomes. The
middle piece has several mitochondria which provide energy for sperm movement. The tail helps in motility
of sperm.