BIOLOGY 5 Marks Questions

i. Plasmid considered to be an important tool in rDNA technology as it can act as vector/can self-replicate to form multiple copies/have selectable markers/ small in size will facilitate insertion/presence of 'Ori'- E. coli, Agrobacterium tumefaciens, Salmonella typhi, Bacteria.
ii. Role of 'Ori'- this is a sequence from where replication starts/any piece of DNA when linked to this sequence can be made to replicate with in the host cells/controls copy number of linked DNA.
Role of selectable marker helps in identifying and eliminating non-transformants, and selectively permitting the growth of transformants during recombinant DNA technology.
iii. Restriction endonuclease identifies a specific palindromic sequence of DNA and cut the DNA at the specific sites in both the host as well in desired/foreign DNA, thereby creates "sticky ends" facilitating ligation to form a recombinant DNA.

i. A typical mature embryo sac of Angiosperms is a 7-celled and 8-nucleate structure.
(i) At the micropylar end, an egg apparatus is present which consists of an egg cell and 2 synergid cells. Synergids contain filiform apparatus which guides the pollen tube entry into the embryo sac during fertilisation.
(ii) At the chalazal end, three antipodal cells are present.
(iii) In the centre, two polar nuclei are present which get fused prior to fertilisation to form a diploid secondary nucleus.
Hence, 8 nuclei are constituted within 7 cells. Thus, embryo sac is 7-celled and 8-nucleate.

ii. 1. Male and Female flowers are present on different plants (dioecy)/ Self incompatibility
2. Production of unisexual flowers by the plant/ both male and female flowers are present on the same plant/Monoecious / non synchronization of pollen release and stigma receptivity/Anther and stigma are placed at different positions (Herkogamy)

i. The desirable DNA sequences are cut by using resriction endonuclease enzyme. These enzymes cut at specific palindromic sites, between same two bases on both the strands.
ii. DNA fragments formed by the use of restriction endonucleases are separated by gel electrophoresis.
a. DNA fragments are negatively charged molecules Thus, they move towards the anode under electric field through the gel medium.
b. DNA fragments separate according to their size due to sieving effect of agarose gel.
c. The separated DNA fragments can be viewed by staining the DNA with ethidium bromide followed by exposure to UV radiation
d. The separated bands of DNA are cut and extracted from gel piece. This is known as elution.
iii. The resulting fragments are joined together with vector DNA by DNA ligase enzyme. It forms phosphodiester bonds between them.

Viviparity is a condition that is presented in both animals and plants. In the case of animals; viviparity means an animal gives birth to young ones. In case of plants, viviparity means germination of the embryo on the plant itself; without the normal sequence of development of the seed. Viviparity involves too much drain of resources on the mother. In case of animals; a female has to constantly supply the nutrients and oxygen to the growing foetus if the foetus developing in the womb. Enough resources are not available to support a large litter and hence viviparity automatically limits the number of offsprings in a litter. This is true in the case of plants also because a germinating embryo on the plant would require resources from the mother plant.