Board Paper of Class 12-Science 2012 Biology (SET 3) - Solutions

Explain the work carried out by Cohen and Boyer that contributed immensely in biotechnology.

(a) State the difference between meiocyte and gamete with respect to chromosome number.

(b) Why is a whiptail lizard referred to as parthenogenetic? 

Draw a neat labeled sketch of a replicating fork of DNA. (2)

Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples.

(a) State the role of DNA ligase in biotechnology.

(b) What happens when Meloidegyne incognitia consumes cells with RNAi gene?

Where is sporopollenin present in plants? State its significance with reference to its chemical nature.

Mention the importance of Lactic acid bacteria to humans other than setting milk into curd. (2)

OR

How do methanogens help in producing biogas?

(a) Name the Protozoan parasite that causes amoebic dysentery in humans.

(b) Mention two diagnostic symptoms of the disease.

(c) How is this disease transmitted to others? (2)

(a) Highlight the role of thymus as a lymphoid organ.

(b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity. 

Why do clown fish and sea anemone pair up? What is this relationship called? (2)

(a) Construct a complete transcription unit with promoter and terminator on the basis of the hypothetical template strand given below:

(b) Write the RNA strand transcribed from the above transcription unit along with its polarity.

OR

How are the structural genes inactivated in lac operon in E. coli? Explain

Write the function of each of the following: (3)

(a) Seminal vesicle

(b) Scutellum

(c) Acrosome of human sperm.

Study a part of the life cycle of malarial parasite given below. Answer the questions that follow: 

(a) Mention the roles of ‘A’ in the life cycle of the malarial parasite.

(b) Name the event ‘C’ and the organ where this event occurs.

(c) Identify the organ ‘B’ and name the cells being released from it.

Draw a schematic sketch of pBR 322 plasmid and label the following in it:

(a) Any two restriction sites.

(b) Ori and rop genes.

(c) An antibiotic resistant gene.

State the theory of Biogenesis. How does Miller’s experiment support this theory?

Given below is the representation of amino acid composition of the relevant translated portion of β-chain of haemoglobin, related to the shape of human red blood cells.

(a) Is this representation indicating a normal human or a sufferer from certain related genetic disease? Give reason in support of your answer.

(b) What difference would be noticed in the phenotype of the normal and the sufferer related to this gene?

(c) Who are likely to suffer more from the defect related to the gene represented the males, the females or both males and females equally? And why?

(a) Why are the colourful polystyrene and plastic package used for protecting the food, considered an environment menace?

(b) Write about the remedy found for the efficient use of plastic waste by Ahmed khan of Bangalore. (3)

Name the genes responsible for making Bt cotton plants resistant to bollworm attack. How do such plants attain resistance against bollworm attacks? Explain. (3)

Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water.

Explain the carbon cycle with the help of a simplified model. (5)

OR

Explain how does:

(a) a primary succession start on a bare rock and reach a climax community?

(b) the algal bloom eventually choke the water body in an industrial area?

The following is the illustration of the sequence of ovarian events (a − i) in a human female.

(i) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.

(ii) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.

(iii) Explain the changes that occur in the uterus simultaneously in anticipation.

(iv) Write the difference between ‘c’ and ‘h’.

(v) Draw a labeled sketch of the structure of a human ovum prior to fertilization.

OR

How does the megaspore mother cell develop into 7-celled, 8 nucleate embryo sac in an angiosperm? Draw a labeled diagram of a mature embryo sac.

Name the scientists who proved experimentally that DNA is the genetic material. Describe their experiment. (5)

OR

(a) List of three different allelic forms of gene 'I'in humans. Explain the different phenotypic expressions, controlled by these three forms.

(b) A woman with blood group ‘A’ marries a man with blood group ‘O’. Discus the possibilities of the inheritance of the blood group in the following starting with “yes” or “no” for each:

(i) They produce children with blood group “A” only.

(ii) They produce children some with “O” blood group and some with “A” blood group.