Limnetic zone
Euphotic zone
Disphotic zone
Benthic zone
Aphotic / Profundal zone
Fig.: Light zones in deep lake and ocean
Soil Low
Littoral
zone
It is open water zone where water
is very deep. Amount of oxygen
and light decreases with depth.
High
It is the lower part
of the photic zone,
(twilight zone), receives
light at or below the
compensation point.
It is upper part of
limnetic zone to which
light can penetrate.
It is shallow coastal region. Light is
able to pass through shallow water
and reach the bottom. Therefore,
producers occur throughout from
surface to bottom.
Light and oxygen levels
Lowermost zone, include sediment surface.
It is the upper part of photic
zone, receives light more than
compensation point.
Photic Zone
It is the zone below photic
zone. Producers do not occur,
only consumers are found.
- Soil
s Soil is the upper, weathered humus containing part of earth’s surface which sustains terrestrial plant life. A soil profile consists
of several soil horizons.
O
A
B
C
O-horizon
s Surface layer of organic matter, rich in humus.
A-horizon
s Uppermost horizon of soil, called top soil.
s Rich in organic matter. Typically dark colour.
s This horizon is rich in microorganisms and has high biological activity.
B-horizon
s Also called subsoil and zone of accumulation.
s May contain soluble minerals, rich in plant nutrients.
s Poor in aeration and biological activity.
C-horizon
s Unweathered bedrock.
s Bedrock lies below the soil profile.
Horizons
Fig.: Soil profile
Clayey soil
High water holding capacity, poor
aeration, rich in inorganic nutrients
Loamy soil
Good mineral nutrition, aeration,
hydration. Best soil for plant growth
Sandy soil
Loose and porous soil, poor water holding
capacity, rainwater percolates quickly
Types of soil
texture
Response to Abiotic Factors
Regulate
Organisms which maintain constant body temperature
and osmotic concentration, despite changes in the
external environment, e.g., birds and mammals.
Conform
Conformers are organisms in which temperature and
osmotic concentration changes according to external
environment, e.g., Asterias
Migrate
During unfavourable conditions, organisms migrate to favourable
areas, and return when unfavourable period is over, e.g., birds from
Siberia migrate to Rajasthan during winters.
Suspend
Organisms stop their development to survive unfavourable conditions,
e.g., Bacteria, fungi and lower plants develop thick walled spore
during unfavourable conditions and germinate in suitable conditions.
Polar bears undergo hibernation to escape cold, snails undergo
aestivation and zooplanktons enters diapause stage.
Methods by
which living
organisms cope
with stressful
conditions