21. DNA is the better genetic material than RNA. Justify the statement with three comparative reasons.
The 2-OH group present at every nucleotide in RNA is reactive and makes RNA labile and
degradable. But, DNA is less reactive and structurally more stable.
The presence of Thymine in place of Uracil in DNA confers its additional stability. Onemajor problem with using uracil as a base is that cytosine undergoes deamination and gets converted into uracil. This is not a rare reaction; it happens around 100 times per cell, per day. This is no major problem when using thymine (as in the case of DNA), as the cell can easily recognize that the uracil doesn't belong there and can repair it by substituting it by a cytosine again.
22. Enumerate on convergent and divergent evolution with suitable examples in plants.
A: If same structure developed along different directions due to adaptation to different needs it is called divergent evolution and results in homologous organs. Ex Thorn and tendrils of
bougainvillea and cucurbita.
If different structure evolving for the same function and hence having similarities. It is called convergent evolution. It is results in analogous organ. Ex Sweet potato (Root modification) And Potato (Stem modification)
23. What are carcinogens? Mention any two groups of carcinogens with one example each.
A: Transformation of normal cells into cancerous neoplastic cells may be induced by physical,chemical or biological agents. These agents are called carcinogens.
• Bioreactors. DURGA
ex1: Ionising radiations like x - rays and gamma rays.
ex2: Non lonising radiations like UV rays
24. a) Mention four tools required for recombinant DNA technology
• Enzymes (Restriction enzyme, DNA ligases, polymerase enzymes)
• Vector DNA
• Host organisms
b) With reference to gel electrophoresis, what is elution?
A: Elution: The separated bands of DNA are cut out from the agarose get and extracted from the gel piece.
25. Ecological pyramids have limitations. Justify the statement with three reasons.
A: 1) It does not take into account the same species belonging to two or more trophic levels.
2) It does not accommodate a food web.
3) saprophytes are not given any place in ecological pynamids.
26. Describe three factors which affect on decomposition.
A: Decomposition is largely an oxygen - requiring process. The rate of decomposition is controlled
by chemical composition of detritus and climatic factors.
a) In particular climatic condition decomposition rate is slower. If the detritus is rich in lignin and
chitin and quicker if detritus is rich in nitrogen and water soluble substances like sugars.
b) Temperature and soil moisture are most important climatic factors that regulate
decomposition through their effects on activities of soil microbes.
c) Warm and moist environment favour decomposition whereas low temperature and
anaerobiosis inhibit decomposition.
PART - D
Answer any three of the following questions.
27. What is megasporogenesis? Explain the development of eight nucleate embryosac in flowering
plants.
A: Megasporogenesis: The process of formation of megaspore from megaspore mother cell by the process of meiosis is called megasporogenesis.
The process of megasporogenesis occurs in megasporangia (ovules) present inside the ovary.
Each ovule has outer integuments enclosing the nutritive tissue called nucellus. Some cells of nucellus develop into diploid archesporial cells.
The MMC divides by meiosis to produce a linear tetrad of haploid megaspores. Out of 4 megaspores usually the upper three degenerate functional megaspore called embryosac.
28. What are Contraceptives? Explain four different non - surgical contraceptive methods.
The devices that are using for avoiding pregnancy is called contraceptives.
Non surgical contraceptive methods are:
1) Natural methods: It works on the principle of avoiding chances of ovum and sperm meeting.
a) periodic abstinence: avoiding coitus from 10 - 17day of menstrual cycle.
b) withdrawl or coitus intereptus: in this male partner withdraws his penis from vagina before ejaculation
c) Lactational Amenorrhea: When the mother is is intense l lactating ovulation and menstrual cycle does not occur up to a maximum period of 6 months following parturition.
2) Barrier method: This method prevents the physical meeting of sperm with ovum. It includes
1) condomes, 2) Diaphragms, 3) cervical caps 4) vaults 5) Spermicidal creams, jellies and foams
3) Intra Uterine devices: these are three types
a) Non medicated IUDs: Ex Lippes loop
b) Copper releasing TUDs: Ex Cut, Cu7, Multiload 375)
c) Hormone releasing IUDs: Ex Progestasert, LNG - 20)
They increase phagocytosis of sperms within uterus and the Cu ions released suppress sperm motility and fertilising capacity of sperms. The hormone releasing IUDs in addition make the uterus unsuitable for implantation and the cervix hostile to the sperms.
4) Oral Contraceptive pills: They are made up of progestogens or progestogen - estrogen combinations a) They inhibit ovulation, implantation and alter the quality of cervical mucus to prevent/ retard entry of sperms.
28. What are Contraceptives? Explain four different non - surgical contraceptive methods.
The devices that are using for avoiding pregnancy is called contraceptives.
Non surgical contraceptive methods are:
1) Natural methods: It works on the principle of avoiding chances of ovum and sperm meeting.
a) periodic abstinence: avoiding coitus from 10 - 17day of menstrual cycle.
b) withdrawl or coitus intereptus: in this male partner withdraws his penis from vagina before ejaculation
c) Lactational Amenorrhea: When the mother is is intense l lactating ovulation and menstrual cycle does not occur up to a maximum period of 6 months following parturition.
2) Barrier method: This method prevents the physical meeting of sperm with ovum. It includes
1) condomes, 2) Diaphragms, 3) cervical caps 4) vaults 5) Spermicidal creams, jellies and foams
3) Intra Uterine devices: these are three types
a) Non medicated IUDs: Ex Lippes loop
b) Copper releasing TUDs: Ex Cut, Cu7, Multiload 375)
c) Hormone releasing IUDs: Ex Progestasert, LNG - 20)
They increase phagocytosis of sperms within uterus and the Cu ions released suppress sperm motility and fertilising capacity of sperms. The hormone releasing IUDs in addition make the uterus unsuitable for implantation and the cervix hostile to the sperms.
4) Oral Contraceptive pills: They are made up of progestogens or progestogen - estrogen combinations
a) They inhibit ovulation, implantation and alter the quality of cervical mucus to prevent/ retard entry of sperms.
29. What is incomplete dominance? Explain it with reference to flower colour in snapdragon.
A: It is a condition in heterozygous individuals in which the dominant gene fails to suppress the recessive gene completely and undergoes blending to produce a new trait which differs from their parents.The incomplete dominance was observed by Carl Correns of Germany during hybridization experiments in Antirrhinum majus (Snapdragon). He crossed pure breeding red flowering plants (RR) with pure breeding white flowering plants (rr) and obtained all heterozygous pink flowering plants (Rr) in Figeneration. Then he self pollinated the Fıpink flowering plants
obtained the plants in the phenotypic and genotypic ratio of 1: 2: 1 in F2generation as follows.
The Phenotypic and Genotypic ratio of monohybrid cross (incomplete dominance) is 1: 2: 1 (1 (RR) Red: 2 (Rr) Pink: 1 (rr) White).
30. Explain five benefits of creating transgenic animals.
A : To study basic biological process: Transgenic animals are used to study gene regulation and its effect on normal functions of the body and its development
E.g., Study of complex factors involved in growth such as insulin –like growth factor.
Study of diseases: Transgenic animal models are used to understand the contribution of genes in the development of disease and to investigate new treatments for diseases like fibrosis, rheumatoid arthritis, Alzheimer's etc
Biological products: Transgenic were created to produce milk containing particular human proteins, (α – 1- antitrypsin) which may help in the treatment of human emphysema.
E.g., Rosie is the first transgenic cow (1997) that produced the milk enriched with human protein, α –lactalbumin (2.4g per ltr) which is nutrition-ally more balanced product for human babies than natural cow milk.
Vaccine safety : Transgenic mice are being developed for us in testing for the safety of vaccines ( polio vaccine) before they are used on human
Chemical safety testing : Transgenic animals are exposed to toxic substances to study their effects in less time
31. a) Tropical region has greater biodiversity than temperate region. Justify the statement with three reasons.
A: i) Tropical latitudes have remained relatively undisturbed for millions of years and thus had a long evolutionary time for species diversification.
ii) Tropical environments are more constant and predictable that promote niche specialization and lead to greater species diversity
iii) there is more solar energy available which contribute to higher productivity.
b) The use of CNG is better that petrol or diesel. Give four reasons.
A: i) CNG burns more effieciently
ii)In the automobiles very little of it is left unburnt iii) CNG is cheaper than petrol/diesel.
iv) it cannot be siphoned off by thieves.
33. a)Write the schematic representation of spermatogenesis
b) Write the two events that occur in the ovary and uterus during the follicular phase of menstrual cycle
A:i) During follicular phase, the primary follicles in the ovary grow to become a fully mature graafian follicle under the stimulation of FSH & LH.
ii)In the uterus endometrium regenerates through prolifaeration under the stimulation of estrogen hormone.
34. ‘DNA replication is said to be semi conservative ‘,Why? Describe the experimental proof of Messelson and stahl to show DNA replication is semi conservative.
A: The daughter DNA molecules have one parental strand and another new strand.
Matthew Meselson and Franklin Stahl (1958) performed the following experiment in E.coli to prove semi-conservative replication
They grew E.coli in a medium containing 15NH4CL(15N is the heavy isotope of nitrogen) as the only nitrogen source for many generations. The result was that 15N was incorporated into newly synthesised DNA (as well as other nitrogen containing compounds)
This heavy DNA molecule could be distinguished from the normal DNA by centrifugation in a cesium chloride density gradient
Then they transferred the cells into a medium with normal 15NH4CL and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double- stranded helices
The various samples were separated independently on gradients to measure the densities of DNA
Thus, the DNA that was extracted from the culture, one generation after the transfer from 15N to 14N medium had a hybrid or intermediate density. DNA extracted from the culture after another generation was composed of equal amounts of this hybrid DNA and of 'light' DNA.
35)Draw a neat labelled diagram of Miller’s experiment
Theory of chemical evolution was proposed by Oparin and Haldane.
i)It states that "the first form of life could have come from pre-existing non living organic molecules (like RNA, protein)
ii) The formation of diverse organic molecules from inorganic constituents".
36. Name the technology that can successfully increase the herd size of cattle in a short time and explain the steps involved in the technology
A:MOET(Multiple ovulation and Embryo Transfer)
In MOET, a cow is administered hormones with FSH-like activity, to induce follicular maturation and super ovulation to produce 6-8 eggs.
Then the cow is either mated and elite bull or artificially inseminated
The fertilized eggs at 8 – 32 cells stages, are recovered non-surgically and transferred to
surrogate mothers
The genetic mother is available for another round of super ovulation
This technology has been demonstrated for cattle, sheep, rabbits, buffaloes, mares, etc
High milk-yielding breeds of females and high quality (lean meat with less lipid) meat-
yielding bulls have been bread successfully to increase herd size in a short time
37. a)Mention four ”Evil Quartet” which cause depletion of biodiversity A: i)Habitat loss and fragmentation
ii)Over-exploitation
iii) Alien species invasions
iv) Co-extinctions
b)Write two suspended activities in animals against abiotic stresses with suitable examples
A:Hibernation(wintersleep):E.g.,Polarbear,
Diapause: Eg. Zooplanktons
Aestivation(Summersleep):Eg.Somesnailsandfish,
c)Among vertebrates ,which group of animals has the highest number in global biodiversity. A:Fishes
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