(b) (i) Wings of butterfly and birds show analogy as the basic
structure of the wings of the insects is different from
the wings of birds, however, their function is similar.
(ii) Vertebrates hearts show structural homology.
(iii) Thorns (not tendrils) of Bougainvillea and tendrils of
Cucurbita both arise in the axillary position thus, show
homology.
(iv) Sweet potato (root modification) and potato (stem
modification) show analogy.- A nematode Meloidogyne incognita infects the roots of
tobacco plants and causes a great reduction in yield. A
novel strategy that was adopted to prevent this infestation
was based on the process of RNA interference (RNAi), i.e.,
silencing of gene expression using a dsRNA. It involves
silencing of specific mRNA due to complementary dsRNA
molecule that binds to and prevents translation of mRNA
(silencing). Using Agrobacterium vectors, nematode-
specific genes were introduced into the host plant (tobacco
plant). The introduction of DNA was such that it produced
both sense and anti-sense RNA in the host cells. These
two RNAs being complementary to each other formed a
dsRNA (double stranded RNA) that initiated RNAi and thus,
silenced specific mRNA of the nematode.
The correct sequence of steps involved in making tobacco
plant resistant to nematode are:
(i) RNase enzyme called ‘dicer’ cuts all dsRNA molecules
into small interfering RNAs (siRNAs) (21-23 nucleotides
long).
(ii) Each siRNA complexes with ribonucleases (distinct from
dicer) to form an RNA-induced silencing complex (RISC).
(iii) The siRNA unwinds and RISC is activated.
(iv) The activated RISC targets complementary mRNA molecules.
The siRNA strands act as guides where the RISCs cut the
transcripts in an area where the siRNA binds to the mRNA.
This destroys the mRNA.
(v) When mRNA of the parasite is destroyed, no parasite
proteins are synthesised that resulted in the death of
the parasite (nematode) in the transgenic host. Thus, the
transgenic plant gets itself protected from the parasite. - (a) Yes, India has greater ecosystem diversity than Norway as
India comes under the tropical region whereas, Norway
lies in temperate region. Tropical regions account for
greater biological diversity as they have deserts, rain
forests, mangroves, coral reefs, wetlands, estuaries and
alpine meadows than temperate regions. In tropical
region more solar energy is available that also promotes
higher productivity and increased biological diversity.
(b) Differences between genetic and species biodiversity are as
follows :
Genetic biodiversity Species biodiversity
(i) It is related to the
number of genes and
their alleles found in
organisms.It is related to number
and distribution of
species found in an
area.
(ii) It is trait of the species. It is trait of a community.
(iii) It influences the
adaptability and
distribution of a species
in diverse habitats.It influences biotic
interactions and
stability of the
community.
(iv) Example : India has more
than 50,000 genetically
different strains of rice
and 1,000 varieties of
mango.Example : Western
ghats have greater
amphibian species
diversity as compared
to Eastern ghats.
OR
Urban sewage includes domestic sewage (soaps, detergents,
household wastes, feces, etc.) and industrial effluents (toxic
metals, chemicals, etc.) which flow into the river through
sewers. It also includes animal wastes, dumping of worship
materials, ashes of dead bodies, bathing of animals, etc.
Effects of sewage discharge in a river are :
(i) Water becomes unfit for bathing and drinking and also
for domestic or industrial use as it becomes coloured,
turbid with a lot of particulate matter floating on water.
(ii) Domestic sewage primarily contains biodegradable
organic matter which is rich in nitrates and phosphates.
These nitrates and phosphates encourage a thick
bloom of planktonic algae that are toxic to humans
and animals. Algal bloom also supports the growth
of floating plants such as water hyacinth that cut-off
sunlight for submerged plants. This results in organic
loading of the rivers causing, depletion of oxygen
content of the water. This suffocates the fish and other
aquatic life. Consequently, river become highly polluted.
(iii) Domestic sewage can be decomposed by microorga-
nisms in the presence of oxygen. Biochemical oxygen
demand (BOD) is the amount of oxygen required by the
microorganisms in milligrams in five days to completely
decompose the organic matter present in one litre of
polluted water at 20°C. Higher the amount of oxygen
consumed, greater is the degree of organic pollutants.
So, the input of domestic sewage increases the BOD
of the river because microorganisms consume oxygen
during aerobic decomposition of organic wastes. This
inturn decreases the dissolved oxygen in the river
leading to death of large number of aquatic animals
such as fish which disturbs numerous food chains.
Hot water is released by industries that contains a variety
of organic and inorganic residues which heavily pollute
the river water.