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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.

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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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29. How do m-RNA, t-RNA and ribosomes help in the process of translation?

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30.
(a) List the different attributes that a population has and not an individual organism.

(b) What is population density ? Explain any three different ways the population density can be measured, with the help of an example each.

(a) Following are the attributes that a population has but an individual organism does not have:

Birth rate: per capita births. It represents the increase in number with respect to the population.
Death rate: per capita deaths. It represents the decrease in number with respect to the population.
Sex ratio: Ratio of number of males to females in a given population.
Age distribution: A population at any given time is composed of individuals of different ages.

(b) Population density means number of individuals present per unit area. Population density can be measured by determining the population size. The different methods to study population size are as follows:

(1) Indirect method: In this method the population density is measured without actually counting or seeing the organism. For examples – the tiger consensus in our national park and tiger reserves are often based on the pug marks and fecal pellets of the tiger.
Example: The number of Parthenium plants in a given area can be measured using the quadrat method.

(2) Direct observation: It involves the counting of organisms in the given area.
Example: In order to determine the number of bacteria growing in a Petri dish, their colonies are counted.

(3)Relative densities: When the population is too large to be counted then relative density is taken into account . For example: The number of fishes caught per trap gives the measure of their total density in a given water body.

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