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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.

(a) Thalassaemia and haemophilia are categorised as Mendelian disorders because they occur by mutation in a single gene. Their mode of inheritance follows the principles of Mendelian genetics. Mendelian disorders can be

autosomal dominant (muscular dystrophy)
autosomal recessive (thalassaemia)
sex linked (haemophilia)

Symptoms of Thalassaemia

Thalassaemia minor results only in mild anaemia, characterised by low haemoglobin level.
Thalassaemia major is also known as Cooley's anaemia. In this disease, affected infants are normal but as they reach 6 to 9 months of age, they develop severe anaemia, skeletal deformities, jaundice, fatigue, etc.

Symptoms of Haemophilia

Person suffering from this disease does not develop a proper blood clotting mechanism.
A haemophilic patient suffers from non-stop bleeding even on a simple cut, which may lead to death.

Pattern of Inheritance of Thalassaemia
Pair of alleles Hb^A and Hb^T controls the expression of this disease.
Conditions for thalassemia:

Hb^A and Hb^A: Normal
Hb^A and Hb^T: Carrier

Hb^T and Hb^T: Diseased

Let us assume that both father and mother are the carriers (Hb^A Hb^T) of beta thalassaemia.

Parents		Hb^AHb^T (Father)	x	Hb^AHb^T (Mother)
Offsprings	Hb^AHb^A Normal child	Hb^AHb^T Carrier child with thalassaemia trait	Hb^AHb^T Carrier child with thalassaemia trait	Hb^THb^T Child with severe thalassaemia

Pattern of Inheritance of Haemophilia:
Haemophilia is an X-linked genetic disorder. Compared to females, males have higher chances of getting affected because females have XX chromosomes while males have only one X with Y chromosome. Thus, for a female to get affected by haemophilia, she has to have the mutant gene on both the X chromosomes while males can be affected if they carry it on the single X chromosome.
Conditions for haemophilia:
XY; XX: Normal
X^hY: Haemophilic
X^hX: Carrier
X^hX^h: Haemophilic
Let us assume that a carrier female (X^hX) is married to a normal male.