CBSE Class 12 Biology — Long Answer Questions

(a) (i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. [½] (ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place. [2] (iii) How does the parasite damage the human body after entering the blood stream? [1½] (iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions. [1] OR (b) (i) What are bio-fertilizers? [1] (ii) Name the different types of microorganisms used as bio-fertilizers in organic farming and explain how each contributes to soil fertility. [3] (iii) Write two advantages of using bio-fertilizers over chemical fertilizers. [1]

(a) Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place. [5] OR (b) (i) Case studies of some couples are given below. They were not able to have kids even though the parents were not taking any precautions. They also do not wish to adopt a child or take the help of donors. Study these cases and suggest an appropriate Assisted Reproductive Technology that could help them. Case I – Female – Normal Reports. Male – Normal sperms but no connection between epididymis and vas deferens. [1] Case II – Female – Normal eggs but Fallopian tube blocked. Male – Normal sperms. Male reports are normal. [1] Case III – Female – Normal Reports. Male – Low sperm count with less motility. [1] (ii) Copper releasing intrauterine devices are very effective and popular contraceptive devices. Name any two copper releasing IUDs. Write two reasons that make them effective contraceptives. [2]

(a) (i) Watson and Crick's discovery of double helical structure was based on which two findings. Also mention the name of the scientists associated with these findings. [2] (ii) Write down the salient features of double helix structure of DNA (any three points). [3] OR (b) Given below is a stretch of DNA showing the coding strand of structural gene of transcription unit. 5' - ATG ACC GTA TTT TCT GTA GTG CCC GTA CTT CAG GCA TTA 3' (i) Write the corresponding template strand and m-RNA strand that will be transcribed along with its polarity. [2] (ii) If GUA of transcribed mRNA is an intron, then depict the sequence involved in formation of mRNA / mature / processed hnRNA strand: (1) In a bacterium [1] (2) In humans [1] (iii) How many amino acids the resulting polypeptide will have after the process of translation in humans? [1]