CBSE Class 12 exams 2019: Boards for class 12th is a month away. In this highly stressed-out time it really becomes difficult to analyse an year long preparation. During the duration of three hour, every students’ capability  and hard-work is being tested. The mind deals with lots of questions like how we will score good marks, what is the trick to crack difficult set of questions or  whether will get a good college or not after Boards. This becomes all more complicated if you are half prepared. Therefore, after pre- boards, every student runs for the improvement. The best trick to improve is to take the sample papers test. 

The students  of PCB or PCMB background can check mentioned below Biology sample paper. It is written by R K Gupta.   

SECTION A
1. Name the phase, all organisms have to pass through before they can reproduce sexually.

2. What causes speciation according to Hugo de Vries?

3. Name the technique used for separating DNA fragments in the laboratory?
4. Write the percentage of homozygous and heterozygous population in the F2 generation of a typical Mendelian monohybrid cross

5. Why are engineered vectors preferred in genetic engineering?

SECTION B

6. A woman with blood group O married a man with AB group. Show the possible blood groups of the progeny. List the alleles involved in
this inheritance.

OR

6. A mother of one year old daughter wanted to space her second child. Her docter suggested Cu T. Explain its contraceptive actions.

7. Following are the features of genetic codes. What does each one indicate?
Stop codon; Universal codon; Unambiguous codon; Degenerate codon.

8. Name a genus of baculo virus. Why are they considered good bio-control agents?

9. Explain the relationship between CFC’s and Ozone in the stratosphere.
-2-

10. Why is ‘starter’ added to set the milk into curd? Explain.

SECTION C

11. Morgan carried out several dihybrid crosses in Drosophila and found F2 ratios deviated very significantly from the expected Mendelian ratio. Explain his findings with the help of an example.

12. Describe endosperm development in angiosperm.

OR

a. Mention the problems that are taken care of by Reproduction and Child Health Care programme.

b. What is amniocentesis and why is a statutory ban on it?

a. Mention the problems that are taken care of by Reproduction and Child Health Care programme.

b. What is amniocentesis and why is a statutory ban on it?

13. With the help of a schematic diagram, explain the location and the role of the following in a transcription unit: Promotor; Structural gene; Terminator.

14. Draw a labelled sketch of a typical biogas plant.

15. a. What do ‘Y’ and ‘B’ stand for in YAC and BAC used in Human Genome Project [HGP] Mention their role in the project.

b. Expand SNPs identified by scientist in HGP.

c. Write the percentage of the total human genome that codes for proteins and the percentage of the discovered genes whose functions are known as observed during HGP.
16. a. It is generally observed that the children who had suffered from chicken-pox in their childhood may not contract the same disease in their adulthood. Explain giving reasons the basics of such immunity in an individual.

Name this kind of immunity.

b. What are interferons? Mention their role.

17. Draw a labelled diagram of sectional view of a human ovary showing various stages of follicles growing in it.

18. Plasmid is a boon to biotechnology. Justify this statement quoting the production of human insulin as an example.
19. Explain the efforts which must be put in to improve health, hygiene and milk yield of a cattle in a dairy farm.

20. Explain enzyme-replacement therapy to treat adenosine deaminase deficiency. Mention two disadvantages of this procedure.
21. Name and explain the type of interaction that exists in mycorrhizae and between cattle ergot and cattle.

22. How does activated sludge get produced during sewage treatment? Explain how this sludge is used in biogas production.

SECTION D

23. A son persuades his father to replace his old mobile phone with the latest model launched in the market. He also shares the latest features it has and explains how it can be of a help to him in the modern technological world.

Father is reluctant in buying a new one and tries to explain about its environmental impact.
How do you think, the biologist father would try to convince his son?

Justify the arguments of father and son both, by mentioning positive aspects of the behavior displayed by both of them in the situation concerned [three each]

SECTION E

24. a. Trace the development of pollen grains up to their release from the pollen mother cells. Draw diagrams of transformation of a microspore into a pollen grain.
b. Why are the pollens well preserved as fossils?

OR

Trace the development of a human zygote up to implantation in the uterus. Draw diagrammatic sketches of the stages of development.

25. DNA replication is semi-conservative. Name the scientists who proposed it and who proved it?
Explain.

OR
a. Colourblindness in humans is a sex linked trait. Explain with the help of a cross.
b. In human beings, the sex of the child is determined by the father and not by the mother. Explain.

26. a. Construct an ideal pyramid of energy in a grassland, where 100,000 joules of solar energy is available to the produces. Label all the trophic levels.
b. What is humus? Mention two of its characteristics.
c. Write two ways of measuring the standing crop in a trophic level.

OR
a. Explain with the help of a graph the population growth curve when resources are;
(i) Limiting (ii) Not limiting.
b. ‘Nature has a carrying capacity for a species’. Explain.

 The teacher is a PGT Biology, VidyaGyan School, Sitapur 

 

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