Board Paper of Class 12-Science 2010 Biology (SET 3) - Solutions

Where does triple fusion take place in a flowering plant? Why is it so called? Mention its significance.

Why certain regions have declared as biodiversity “hot spots” by environmentalists of the world? Name any two “hot spot” regions of India.

A moss plant produces a large number of antherozoids but relatively only a few egg cells. Why?

Why is the introduction of genetically engineered lymphocytes into a ADA deficiency patient not a permanent cure? Suggest a possible permanent cure.

Study the given food chain and answer the questions that follow:

(i) Give reasons why there is a continuous increase in the DDT content in different trophic levels of the chain.

(ii) Name the phenomenon responsible for the increase in DDT content.

Honey collection improves when beehives are kept in crop-fields during flowering season. Explain.

OR

How does addition of a small amount of curd to fresh milk help formation of curd? Mention a nutritional quality that gets added to the curd.

Name the type of food chains responsible for the flow of larger fraction of energy in an aquatic and a terrestrial ecosystem respectively. Mention one difference between the two food chains.

Name the host and the site where the following occur in the life-cycle of a malarial parasite:

(a) Formation of gametocytes

(b) Fusion of gametocytes

Why are F₂ phenotypic and genotypic ratios same in a cross between red-flowered snapdragon and white-flowered snapdragon plants. Explain with the help of a cross.

How does the floral pattern of Mediterranean orchid Ophrys guarantee cross pollination?

During his studies on genes in Drosophila that were sex-linked T.H. Morgan found F₂ − population phenotypic ratios deviated from expected 9:3:3:1. Explain the conclusion he arrived at.

Describe the termination process of transcription in bacteria.

How does RNA interference help in developing resistance in tobacco plant against nematode infection?

Draw a longitudinal section of a post − pollinated Pistil showing entry of pollen tube into a mature embryo-sac. Label filiform apparatus, chalazal end, Hilum, antipodals, male gametes and secondary nucleus.

OR

Draw a labelled sectional view of seminiferous tubule of a human male.

Explain the efforts which must be put in to improve health, hygiene and milk yield of cattle in a dairy farm.

Explain convergent and divergent evolution with the help of one example of each.

Eco RI is used cut a segment of foreign DNA and that of a vector DNA to form a recombinant DNA. Show with the help of schematic diagrams.

(i)The set of palindronic nucleotide sequence of base pairs the Eco RI will recognise in both the DNA segments. Mark the site at which Eco RI will act and cut both the segments.

(ii)Sticky ends formed on both the segments where the two DNA segments will join later to form a recombinant DNA.

An antibody molecule is represented as H₂L₂. Explain.

Identify a, b, c, d, e and f in the table given below:

When and where are primary oocytes formed in a human female? Trace the development of these oocytes till ovulation (in menstrual cycle). How do gonadotropins influence this developmental process?

OR

(a)Explain the events taking place at the time of fertilization of an ovum in a human female.

(b)Trace the development of zygote upto its implantation in the uterus.

(c)Name and draw a labelled sectional view of the embryonic stage that gets implanted.

Draw and explain a logistic curve for a population of density (N) at time (t) whose intrinsic rate of natural increase is (r) and carrying capacity is (k).

OR

Describe the process of decomposition of detritus under the following heads: Fragmentation; leaching; catabolism; humification and mineralization.

Write the symptoms of haemophilia and sickle-cell anaemia in humans.

Explain how the inheritance pattern of the two diseases differ from each other.

OR

(a) Write Hardy-Weinberg principle.

(b) Explain the three different ways the natural selection can affect the frequency of a heritable trait in a population shown in the graph given below.