Short AnswerType Questions - Ecosystem

Short AnswerType Questions
43. What is an ecosystem? Write the main components of an ecosystem.
A stable, self-supporting ecological unit resulting from the interaction between biotic components and their abiotic environment is called ecosystem.
An ecosystem comprises two main components.
(1) Biotic - including plants, animals and microorganisms and •
(2) Abiotic - including substratum, water, minerals, CO2 and oxygen.
44. What are the biotic components of an ecosystem? Biotic components including living organisms which are of three types. ie. producers, consumers and decomposers.
Producers (Autotrophs) are photosynthetic organisms which fix light energy into organic molecules. Phytoplanktons and rooted plants are the chief producers. Consumers or phagotrophs are animals which generally ingest or swallow their food. They may be herbi¬vores (plant eaters) or carnivores (meat eaters).
Decomposers or saproirophs include bacteria and fungi which make dead organic matter into its simpler components.
45. What are the abiotic components of an ecosystem?
The abiotic components are of two types.
(a) Climatic factors - including temperature, light, wind, gases, humidity, rain and water.
(b) Edaphic factors-- including soil, substratum, topography, minerals and .pH.
46. Explain standing crop and standing state.
A trophic structure may be described in terms of the amount of living material present in different trophic levels at a given time This is called standing crop. The amount of nutrients, such as nitrogen;phosphorus and calcium present in the soil at any given time is re ferred to as the standing state.
Standing crop is expressed as biomass per unit area Standing states of nutrients, differ from one ecosystem to another or with seasons even in the same ecosystem.
47. Write a note on the structure of an ecosystem.
Biotic and abiotic components are physically organised to provide a characteristic structure of the ecosystem. The important structural features are species composi¬tion and stratification. Some ecosystems show tall plant canopy (tropical rain forest) and bewildering numbers of biological species, whereas an desert ecosystem shows onlya few sparsely distributed species.
48. What are the functions of an ecosystem?
Ecosystems possess a natural tendency to persist due
to a variety of functions. The important functions are
(a) productivity (b) decomposition (c) energy flow and
(d) nutrient cycle. These functions are carried out in the ecosystem through delicately 'balanced and controlled professes.
49. Write a note on productivity in an ecosystem.
The rate of biomass production is called productivity. The rate of capture of solar energy or biomass production by producers is called primary productivity, which is generally expressed in terms of grn-2year1 or kcal m-2,'
year--1. The rate of total production of organic material or capture of energy is known as Gross Primary Produc-tivity (GPP). Thd balance energy or biomass remaining after meeting the cost, of respiration of producers, is called Net Primary Productivity (NPP).
Net productivity = Gross productivity — Respiration rate.
50. Write a note on decomposition.
Decomposition involves the breakdown of complex organic components in detritus to CO2, water and inor 
ganic nutrients by decomposers. It involves mainly three
processes; such as fragmentation of detritus, leaching and catabolism. Fragmentation of detritus involves break-down of detritus by detritivores (eg. earthworm etc) into smaller par-ticles. Leeching involves removal of soluble substances. Catabolism involves enzymatic convection of the decomposing detri 
tus by bacteria and fungi to simpler components and inorganic substances.
What are the factors affecting the decomposiiion of detritus?
The rate of decomposition of detritus is regulated by the climatic factors and the chemical quality of the detritus. High temperature and moisture increases the rate of detritus decomposition. Within the same climatic conditions decomposition rate is sloWer if the detritus is rich in substances like Jignin and chitin.
52. What is food chain? What are the kinds of food chains? A nutritive interaction among biotic communities involving a producer, various levels of consumers and a de-.composer forms a food chain. Each step in a food chain is called a trophic level.
Two types of food chains can be distinguished in all ecosystems, grazing food chains and detritus food chains.
Grazing food chain extends from producers through .herbivores to carnivores. Detritus food chain begins with dead organic matter and passes through detritus - feed¬ing organisms in soil to organisms feeding on detritus feeders. Much larger fraction of energy flows through the detritus food chain.
53. What is a food web? Explain.
In natural conditions, several food chains are intercon nected with one another forming a network. This com¬plex interconnected food chains is called a food web. In a food web, there are several food chains. The food web becomes more complicated because of variability of taste and preferences, availability and compulsion and several other factors at each level.
54. What is the meaning of effect of energy in an ecosystem? Explain with examples how energyis lost at the various energy levels.
In the ecosystem, there is continuous and unidirectional flow of energy. The energy from the sun through the various energy levels finally reaches the tertiary consumers. These various energy levels Fare joined by a food chain. Many food chains overlap and form a food web. Trapped energy is fixed in the form of complex organic compounds and is used by herbivorous and carnivorous animals. But the energy does not terminate or end here. When the organism dies, the dead body gets mixed

with soil to release the energy to the decomposer level. Thus, at each level, organisms make use of energy for various life activities, and as a result some energy is lost and therefore supply of energy from the sun is continuously required.
55. The length of food chains in an ecosystem is gene ally limited to 3-4 trophic levels". Why?
Generally in an ecosystem about 1-5% of total solar radiation is utilized for biomass production. On an aver age, in different ecosystems, the herbivore assimilation or productivity approximates 10% of gross productivity of producers. The energy assimilated by herbivores is used in respiration and a fraction of assimilated energy (10%) is transferred to the next trophic level. This process goes on to the decomposer level. Because of these tremendous loss of energy at successive higher trophic levels, the residual energy is decreased to such an extend tliat no further trophic level can be supported. Therefore, the length of food chains in an ecosystem is generally limited to 3-4 trophic levels.
56. Write notes on pyramid of numbers.
The trophic structure and functions at successive trophic levels, are shown graphicaliy by means of ecological pyramids. The base of the pyfamid constitutes the pro ducer level.
A pyramid of numbers represents the number of indi viduals of various trophic levels per unit area at a given time The base represents the producers, while the apex is formed by the number of top carnivores. The intermediate consumers are placed between the two
In the case of a grassland ecosystem the pyramid is ° upright while in the case of a tree dominated ecosys tem, the pyramid is inverted because, a single tree can support many herbivores, which in turn provide food for a number of parasites. The top consumers will be still larger in number. As the number of organsims in each trophic level increases, the pyramid remains inverted.