Biology Today — January 2018

(Jacob Rumans) #1
(ii) By burning of fossil fuels: Fossil fuels like coal, petroleum
and natural gas are rich source of carbon. On burning,
they release carbon in the form of carbon dioxide back
into the atmosphere.


  1. (a) Metals used in catalytic converters that help in keeping
    the environment clean are platinum- palladium and
    rhodium.
    (b) Lichens are very sensitive to pollution, especially
    caused by SO 2. Air polluted with SO 2 and acid rain,
    destroy lichen population. Hence, lichens are regarded
    as pollution indicators.

  2. (a) Differences between grazing food chain and detritus
    food chain are as follows:
    Grazing food chain Detritus food chain


(i) The food chain begins
with producers at the
first trophic level.

The food chain begins
with detritivores and
decomposers at the first
trophic level.
(ii) Energy for the food
chain comes from sun.

Energy for the food chain
comes from organic
remains or detritus.
(b) In ecological context, herbivores are considered similar
to predators because they feed on plants and their
products for their food requirements just like predators
feed on prey for their food needs.


  1. (a) Mammals from colder climates generally have shorter
    ears and limbs to minimise heat loss. This is called as
    the Allen’s rule.
    (b) Photochemical smog is composed of secondary air
    pollutants. It is formed by interaction of hydrocarbons
    with nitrogen oxides. The products are ozone,
    peroxyacyl nitrate (PAN), aldehydes and phenols.
    (c) Diapause is a stage of suspended development, which
    is exhibited by many zooplankton species in lakes and
    ponds, under unfavourable conditions.
    (d) Biodiversity hotspots are the regions which are
    characterised by very high levels of species richness
    and high degree of endemism. India has three hotspots



  • Indo-Burma (North-East India), Eastern Himalayas,
    and Western Ghats.



  1. (a) CNG (Compressed natural gas) is a better fuel than
    petrol or diesel because it is (i) cheaper (ii) burns more
    efficiently, (iii) does not produce much pollution,
    (iv) cannot be siphoned off by thieves and (v) cannot be
    adulterated like petrol and diesel. The major problem of
    CNG is laying down of pipes to ensure uninterrupted
    supply of CNG to CNG pumps or distribution points.
    (b) Catalytic converters, having expensive metals namely
    platinum-palladium and rhodium as the catalysts,


are fitted into automobiles for reducing emission of
poisonous gases. As the exhaust passes through the
catalytic converter, unburnt hydrocarbons are converted
into carbon dioxide and water, and carbon monoxide
and nitric oxide are changed to carbon dioxide and
nitrogen gas, respectively. Vehicles equipped with
catalytic converter should use unleaded petrol because
lead in the petrol inactivates the catalyst.
(c) Cars seen with Bharat stage IV stickers implies that the
vehicles are complied with the new auto fuel policy to
reduce vehicular pollution. Bharat stage IV norms are
implemented in 13 mega cities of India.
(d) Rekha shows alertness, awareness, responsibility and
firmness in tackling a problem. She had the knowledge
about vehicular norms which she applied in a correct
situation.


  1. (a) The nutrient enrichment of water bodies near industrial
    area is due to passage of industrial effluents, sewage,
    etc. This cause dense growth of planktonic algae, that
    results in colouration of water called algal bloom.
    Excessive growth of it cut off light for submerged
    plants which kills the latter and causes organic loading.
    This leads to decreased oxygen level which eventually
    chokes the water body.
    (b) Organic waste and other types of waste material
    should not be dumped into the pond. Domestic wastes
    with organic nutrients must be treated before passing
    into it.
    (c) Eichhornia crassipes is also called as “Terror of
    Bengal” because it is an exotic shrub which strongly
    competes with the native species and has also
    eliminated many of them. It has beautiful flowers but
    it sometimes chokes ponds, lakes, wetlands and rivers
    resulting in imbalance of ecosystem of water bodies
    and causes death of many aquatic species of India.
    It also increases biochemical oxygen demand of the
    water body.
    OR
    Refer to answer 74, page 370, MTG CBSE Champion.

  2. Refer to answer 114, page 350, MTG CBSE Champion.
    OR
    (a) Refer to answers 84 and 82 (a), page 409, MTG CBSE
    Champion.
    (b) Refer to answer 86 (b), page 409, MTG CBSE
    Champion.

  3. Refer to answer 82, page 371, MTG CBSE Champion.
    OR
    Refer to answer 65 (a), page 368, MTG CBSE Champion.
    

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