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CBSE Class 12 biology Solved Question Paper 2011

Short Answer Type

1. Write the importance of cryopreservation in conservation of biodiversity.

Cryopreservation is used in storing the gametes of endangered species that can be fertilized in-vitro followed by propagation through tissue culture methods. Similarly, seeds can be preserved in seed banks for long periods using cryopreservation techniques.

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2. Normally one embryo develops in one seed but when an orange seed is squeezed many embryos of different shapes and sizes are seen. Mention how it has happened.

In orange seeds the nucellus cells divide and protrudes into the embryo sac to develop into embryos. Hence, each ovule contain several embryos and the condition is called polyembryony. This is why embryos of different shapes and sizes are seen when an orange seed is squeezed.

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3. Why is CuT considered a good contraceptive device to space children?

CuT or Copper T is considered to be good contraceptive device because Cu ions released suppress sperm motility and the fertilising capacity of sperms. In addition, it makes the uterus unsuitable for implantation and the cervix hostile to the sperms. Its success rate is the highest and is safe.

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How can bacterial DNA be released from the bacterial cell for biotechnology experiments?

Lysozyme enzyme is used to break open the bacterial cell and release the bacterial DNA from the bacterial cell for biotechnology experiments.

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5. Name the event during cell division cycle that results in the gain or loss of chromosome.

Aneuploidy results in the loss or gain of chromosome during cell division.

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6. Mention the role of the codons AUG and UGA during protein synthesis.

AUG is the start codon that initiates the protein synthesis. UGA is the stop codon that signals for the termination of protein synthesis.

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Name the type of cell division that takes place in the zygote of an organism exhibiting haplontic life cycle.

The type of cell division occurring in the zygote of an organism exhibiting haplontic life cycle is meiosis.

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How do histones acquire positive charge?

Histones are rich in the basic amino acid residues lysines and arginines both of which carry positive charges in their side chains. The presence of these positive amino acids histone acquires positive charge.

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