Biology_Today_-_October_2016

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.

4. 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