Board Paper of Class 12-Science 2019 Biology Delhi(Set 1) - Solutions

General Instructions :

(i) There are total 27 questions and four sections in the question paper. All questions are compulsory.

(ii) Section A contains questions number 1 to 5, very short answer type questions of one mark each.

(iii) Section B contains questions number 6 to 12, short answer type I questions of two marks each.

(iv) Section C contains questions number 13 to 24, short answer type II questions of three marks each.

(v) Section D contains question number 25 to 27, long answer type questions of five marks each.

(vii) There is no overall choice in the question paper, however, an internal choice is provided in two questions of one mark, two questions of two marks, four questions of three marks and all the three questions of five marks. In these questions, an examinee is to attempt any one of the two given alternatives.

(vii) Wherever necessary, the diagram drawn should be neat and properly labelled.

Question 1
British geneticist R.C. Punnett developed a graphical representation of a genetic cross called "Punnett Square". Mention the possible result this representation predicts of the genetic cross carried. VIEW SOLUTION

Question 2
State the two principal outcomes of the experiments conducted by Louis Pasteur on origin of life. VIEW SOLUTION

Question 3

Name the layer of the atmosphere that is associated with 'good ozone'.

OR

Mention the term used to describe a population interaction between an orchid growing on a forest tree.
VIEW SOLUTION

Question 4

What are 'flocs', formed during secondary treatment of sewage?

OR

Write any two places where methanogens can be found.
VIEW SOLUTION

Question 5
At what stage does the meiosis occur in an organism exhibiting haploidic life cycle and mention the fate of the products thus produced. VIEW SOLUTION

Question 6
You are conducting artificial hybridization on papaya and potato. Which on of them would require the step of emasculation and why ? However for both you will use the process of bagging. Justify giving one reason. VIEW SOLUTION

Question 7
How would the gene flow or genetic drift affect the population in which either of them happen to take place? VIEW SOLUTION

Question 8
Differentiate between the roles of B-lymphocytes and T-lymphocytes in generating immune responses.

OR

Principle of vaccination is based on the property of "memory" of the immune system. Taking one suitable example, justify the statement. VIEW SOLUTION

Question 9
Explain the relevance of "Totipotency" and "Somaclones" in raising healthy banana plants from virus infected banana plants. VIEW SOLUTION

Question 10
How is a continuous culture system maintained in bioreactors and why? VIEW SOLUTION

Question 11
List any four ways by which GMO's have been useful for enhanced crop output. VIEW SOLUTION

Question 12
Mention four significant services that a healthy forest ecosystem provide.
OR
Substantiate with the help of one example that in an ecosystem mutualists (i) tend to co-evolve and (ii) are also one of the major causes of biodiversity loss. VIEW SOLUTION

Question 13
Pollen banks are playing a very important role in promoting plant breeding programme the world over. How are pollens preserved in the pollen banks ? Explain. How are such banks benefitting our farmer ? Write any two ways. VIEW SOLUTION

Question 14

Draw a labelled diagram to show interrelationship of four accessory ducts in a human male reproductive system.

OR

Draw a sectional view of the human ovary showing the different stages of developing follicles, corpus luteum and ovulation.
VIEW SOLUTION

Question 15
Compare in any three ways the chromosomal theory of inheritance as proposed by Sutton and Bovery with that of experimental results on pea plant presented by Mendel.
OR
(a) Explain linkage and recombination as put forth by T.H. Morgan based on his observations with Drosophila melanogaster crossing experiment.
(b) Write the basis on which Alfred Sturtevant explained gene mapping. VIEW SOLUTION

Question 16
Explain the mechanism of DNA replication with the help of a replication fork. What role does the enzyme DNA-ligase play in a DNA replication fork?

OR
Construct and label a transcription unit from which the RNA segment given below has been transcribed. Write the complete name of the enzyme that transcribed this RNA.
VIEW SOLUTION

Question 17
(a) Write two differences between Homo erectus and Homo habilis.
(b) Rearrange the following from early to late geologic periods :
Carboniferous, Silurian, Jurassic. VIEW SOLUTION

Question 18
Name the group of bacteria involved in setting milk into curd. Explain the process they carry in doing so. Write another beneficial role of such bacteria. VIEW SOLUTION

Question 19
Bee keeping practice is a good income generating industry. Write the different points to be kept in mind for successful bee keeping. Write the scientific name of the most common Indian species used for the purpose. VIEW SOLUTION

Question 20

(a) Match the microbes listed under Column-A with the products mentioned under Column-B.

Column –A	Column –B
(H) Penicillium notatum	(i) Statin
(I) Trichoderma polysporum	(ii) ethanol
(J) Monascus purpures	(iii) antibiotic
(K) Saccharomyces cerevisiae	(iv) Cyclosporin-A

(b) Why does 'Swiss Cheese' develop large holes? VIEW SOLUTION

Question 21
Describe the formation of recombinant DNA by the action of EcoRI.
OR
Describe the process of amplification of "gene of interest" using PCR technique. VIEW SOLUTION

Question 22
Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl A was provided enzyme-replacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.
(a) Name the ailments the two girls were suffering from ?
(b) Why did the treatment provided to girl A required repeated visits ?
(c) How was the girl B cured permanently ? VIEW SOLUTION

Question 23
List six advantages of "ex-situ" approach to conservation of biodiversity. VIEW SOLUTION

Question 24
While on a visit to a pond in the city-neighbourhood, the visitors were delighted to find large expanse of water covered with colourful algal mass.
(a) As a student of biology, do you agree with their delight? Give reasons in support of your answer.
(b) Explain the cause of such algal growth. VIEW SOLUTION

Question 25
(a) Explain one application of each one of the following :
(A) Amniocentesis
(B) Lactational amenorrhea
(C) ZIFT

(b) Prepare a poster for the school programme depicting the objectives of :

"Reproductive and Child Health Care Programme".

OR

(a) Explain any two ways by which apomictic seed can develop.

(b) List one advantage and one disadvantage of a apomictic crop.
(c) Why do farmers find production of hybrid seeds costly? VIEW SOLUTION

Question 26
Differentiate between incomplete dominance and co-dominance. Substantiate your answer with one example of each.
OR
(a) Write the contributions of the following scientists in deciphering the genetic code.

Georce Gamow ; Hargobind Khorana ; Marshall Nirenberg ; Severo Ochoa

(b) State the importance of a Genetic code in protein biosynthesis. VIEW SOLUTION

Question 27
(a) What is "population" according to you as a biology student?
(b) "The size of a population for any species is not a static parameter." Justify the statement with specific reference to fluctuations in the population density of a
region in a given period of time.
OR
(a) What is hydrarch succession?
(b) Compare the pioneer species and climax communities of hydrarch and xerarch succession respectively.
(c) List the factors upon which the type of invading pioneer species depend in secondary hydrarch succession. Why is the rate of this succession faster than that of primary succession? VIEW SOLUTION

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