Set-3

EXAM DATE: 15/03/2019

Code No. 57/1/3

Class XII BIOLOGY (Theory) (CBSE 2019)

Time: 3 Hrs.

Max. Marks: 70

GENERAL INSTRUCTIONS:

1. There are total 27 questions and four sections in the question paper. All questions are compulsory.
2. Section A contains question number 1 to 5, very short answer type questions of one mark each.
3. Section B contains question number 6 to 12, short answer type-I questions of two marks each.
4. Section C contains question number 13 to 24, short answer type-II questions of three marks each.
5. Section D contains question number 25 to 27, long answer type questions of five marks each.

1. 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.

1. Wherever necessary, the diagram drawn should be neat and properly labelled.

Section-A

1. At what stage does the meiosis occur in an organism exhibiting haploidic life cycle and mention the fate of the products thus produced? [1]
2. Write the number of chromosomes body cells of honey bee workers and drone have. [1]
3. What are 'flocs', formed during secondary treatment of sewage? [1]

OR Write any two places where methanogens can be found.

1. Name the layer of the atmosphere that is associated with 'good ozone'. [1]

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

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. [1]

Section-B

1. It is said apomixes is a type of asexual reproduction. Justify. [2]
2. Mention four significant services that a healthy forest ecosystem provide. [2]

OR

Substantiate with the help of one example that in an ecosystem mutualists (i) tend to co-evolve and

1. are also one of the major causes of biodiversity loss. [2]

1. Write the steps in sequence as carried in multiple ovulation embryo transfer technology. [2]
2. What is an origin of replication in a chromosome? State its function. [2]
3. List any four ways by which GMO's have been useful for enhanced crop output. [2]
4. How is a continuous culture system maintained in bioreactors and why? [2]
5. How would the gene flow or genetic drift affect the population in which either of them happen to take place? [2]

Section-C

1. How does a bisexual flowering plant ensures cross pollination? Explain.

$[3]$

1. 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. [3]
2. 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? [3]

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.

ATGCATGCATGC 5'- "RNA molecule"

1. (a) Write two differences between Homo erectus and Homo habilis.

$[3]$

1. Rearrange the following from early to late geologic periods :

Carboniferous, Silurian, Jurassic.

1. List six advantages of "ex-situ" approach to conservation of biodiversity.

[3]