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CBSE Class 12 Biology Solved Question Paper 2015

Short Answer Type

21.

Describe any three potential applications of genetically modified plants.

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22. How do snails, seeds, bears, zooplanktons, fungi and bacteria adapt to conditions unfavourable for their survival?

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23. How did an American Company. Eli Lilly use the knowledge of r-DNA technology to produce human insulin?

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24.

With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain.

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25.

Your school has been selected by the Department of Education to organize and host an interschool seminar on 'Reproductive Health – Problems and Practices'. However, many parents are reluctant to permit their wards to attend it. Their argument is that the topic is 'too embarrassing.'
Put forth four arguments with appropriate reasons and explanation to justify the topic to be essential and timely.

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Long Answer Type

26.

(a) Plan an experiment and prepare a flow chart of the steps that you would follow to ensure that the seeds are formed only from the desired sets of pollen grains. Name the type of experiment that you carried out.

(b) Write the importance of such experiments.

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27. Describe the roles of pituitary and ovarian hormones during the menstrual cycle in a human female.

Menstrual cycle is the reproductive cycle in all primates and begins at puberty (menarche). In human females, menstruation occurs once in a month (in about 28 to 29 days). The cycle of events, starting from one menstruation till the next is called the menstrual cycle. Following are the changes that are brought about by ovarian and pituitary hormones.

The cycle starts with the menstrual phase, where the menstruation occurs. This is followed by the follicular phase. In this phase, the primary follicles mature into the Graafian follicles and the release of gonadotropins (LH and FSH) also increases. This causes follicular growth and the growing follicles produce oestrogen.
The LH and FSH are at their peak in the middle of the cycle (14th day) and cause the rupture of the Graafian follicles to release the ovum. This phase is called the ovulatory phase.
The remains of the Graafian follicles get converted into the corpus luteum that secretes progesterone for the maintenance of the endometrium.
In the absence of fertilisation, the corpus luteum degenerates; thereby, causing the disintegration of the endometrium and the start of a new cycle.

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28.

(a) Why are thalassemia and haemophilia categorized as Mendelian disorders ? Write the symptoms of these diseases. Explain their pattern of inheritance in humans.

(b) Write the genotypes of the normal parents producing a haemophilic son.

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