BIOLOGY Case study (4 Marks)

→ Sun is the only source of energy for all ecosystems on Earth, except for the deep sea hydro-thermal ecosystem.
→ Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR).
→ We know that plants and photosynthetic bacteria (autotrophs), fix Sun's radiant energy to make food from simple inorganic materials.
→ Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.
→ So, it is very important to know how the solar energy captured by plants flows through different organisms of an ecosystem.
→ All organisms are dependent for their food on producers, either directly or indirectly.
→ The flow of energy from the sun to producers and then to consumer is unidirectional.
→ In ecosystem, flow of energy follows two important principles.
→ According to the first law of Thermodynamics, energy can neither be destroyed nor can it be created. Thus the quantum of energy is constant. Energy can be converted from one form into another.
→ According to the second law 'whenever energy is converted from one form into another, some energy is dissipated in the form of heat'.
→ Producers can only convert solar energy in to chemical energy.
→ They need a constant supply of energy to synthesise the molecules they require, to counter act the universal tendency toward increasing disorderliness.
→ The green plant in the ecosystem are called producers. In a terrestrial ecosystem, major producers are herbaceous and woody plants. Likewise, producers in an aquatic ecosystem are various species like phytoplankton, algae and higher plants.
→ The chain or web is formed because of this interdependency. The energy trapped by the producer, hence, is either passed on to a consumer at different trophic levels.
→ During conversation of energy in trophic levels, certain amount of energy is lost as a heat.

Decomposition :
→ Break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.
→ Dead plant remains such as leaves, bark, flowers and dead remains of animals, including feacal matter, constitute detritus, which is the raw material for decomposition.
Important steps for decomposition :
→ The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation.
Fragmentation :
→ Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation.
Leaching :
→ By the process of leaching, water soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
Catabolism :
→ Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as catabolism.
Humification :
→ Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate.
→ Being colloidal in nature it serves as a reservoir of nutrients.
Mineralisation :
→ The humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralisation.
Factors affecting decomposition :
→ Decomposition is largely an oxygen- requiring process.
→ The rate of decomposition is controlled by chemical composition of detritus and climatic factors.
→ In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin.
→ Decomposition rate is quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.
→ Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes.
→ Warm and moist environment favour decomposition, whereas low temperature and anaerobiosis inhibit decomposition resulting in build up of organic materials.