Biology Today — January 2018

(Jacob Rumans) #1
(iv) Application of stringent pollution level norms for vehicles


  1. Differences between in situ and ex situ conservation are as
    follows:
    In situ conservation Ex situ conservation
    (i) It is the conservation
    of endangered
    species in their
    natural habitats.


It is the conservation
of endangered species
outside their natural
habitats.
(ii) The endangered
species are protected
from predators.

The endangered species
are protected from all
adverse factors.
(iii) The population
recovers in natural
environment.

Offspring produced in
captive breeding are
released in natural habitat
for acclimatisation.
OR
Differences between net primary productivity and gross
primary productivity are as follows :
Net primary
productivity

Gross primary
productivity
(i) It is the amount of
organic matter stored
by producers per unit
time per unit area.

It is the amount of
organic matter synthe-
sised by producers per
unit time per unit area.
(ii) Net primary productivity
is equal to organic
matter synthesised by
photosynthesis minus
utilisation in respiration
and other losses.

Gross primary
productivity is equal to
rate of increase in body
weight of producers
plus loss suffered
through respiration and
damages.
(iii) It depends upon gross
primary productivity
as well as amount
of consumption of
photosynthates.

It depends upon
photosynthetic
efficiency of producers,
availability of solar
energy as well as
organic nutrients.


  1. (a) Predation (b) Commensalism
    (c) Protocooperation (d) Mutualism

  2. The pyramid of energy is always upright in shape as there is
    always a gradual decrease in the energy content at successive
    trophic levels from producers to various consumers. This is
    because some energy is used at each trophic level for various
    metabolic activities and some energy is lost as heat, so only
    10% of the energy is available to the next trophic level
    (Lindeman’s 10% law).

  3. DDT is a pesticide that keeps on moving from water to different
    living components of the ecosystem in an aquatic food chain.
    DDT passes into food chain and increase in amount per unit
    weight of organisms with the rise in trophic level due to their


accumulation in fat. This phenomenon is known as biological
magnification or biological amplification. The flow chart
showing biomagnification of DDT in an aquatic food chain is
given below:


  1. Communities with more species tend to be more stable
    than those with less species as it is able to resist occasional
    disturbance. This has been confirmed experimentally by
    David Tilman. He raised plots with different diversities in
    Minnesota grassland and subjected them to various stresses
    so as to carry out long term ecosystem experiments. He
    found that plots with more species showed less year to year
    variation in total biomass. He also showed in his experiments,
    that increased diversity contributed to higher productivity.

  2. Xerarch succession occurs on bare rocks. The habitat
    lacks soil, has intense light, fluctuations of temperatures
    and winds. The species that invade a bare area are called
    pioneer species. In primary succession on rocks, lichens are
    usually the pioneer species which are able to secrete acids
    to corrode rock surface and thus, helping in weathering and
    soil formation. These pave the way for some small plants
    like bryophytes, which are able to take hold in the small
    amount of soil. They are, with time, succeeded by herbs
    stage, followed by shrub stage and then bigger plants, and
    ultimately a stable climax community, i.e., forest is formed.
    The climax community remains stable as long as the
    environment remains unchanged. With time, the xerophytic
    habitat gets converted into a mesophytic one. The steps in
    xerarch succession are :
    Lichens (Pioneer community)
    p
    Bryophytes
    p
    Herbaceous plants
    p
    Shrubs
    p
    Trees (Climax community)

  3. Loss of soil productivity by erosion of top soil results in the
    desert formation. Deserts are spreading in all continents,
    destroying the fertile land. Various human activities that
    cause desertification are:
    (i) Human establishment : Forest areas have been cleared
    for building more residential complexes and industrial
    townships for ever increasing human population.

Free download pdf