Q. Define Ecology and Ecosystem? Describe Various Factors Or Components of an Ecosystem

Chapter 2. Ecosystem

Q. Define ecology and ecosystem? Describe various factors or components of an ecosystem.

or Describe biotic and abiotic components of an ecosystem. or Describe various components of a typical ecosystem. What are the components of ecosystem?

Ans:

ECOLOGY:

The subject that deals with the study of interrelationship between living organisms to its abiotic environment is known as ecology.

ECOSYSTEM:

The natural habitat or unit comprising the living and the non-living components, interacting and exchanging materials between them, form a self sufficient and self dependent ecological unit called ecosystem. Ernest Haeckel (1866) first define ecosystem and The term ecosystem was given by A. G. Tansley (1935).

Components of Ecosystem :

These are divided into 2 groups ­

(A) Biotic or living and

(B) Abiotic or non-living

(A) Biotic or living components: The living organisms present in an ecosystem are called biotic component. These are of the following types -

(1) Producer:

These include all autotrophic organisms. They synthesize their own food utilizing solar energy, thus they are also called as transducer. Eg. Photosynthetic bacteria ,plants etc

(2) Consumers:

The biotic components which feed upon autotrophs are called consumers. Consumers are of 3 types -

1. Primary consumers: These are herbivores and they derive their food directly from the autotrophs. These are heterotrophs. They are also known as secondary producer as they produce proteins in their body as become food for the next order. Examples: Rabbit, Insects, Grasshopper, Elephant, Cattles etc .
2. Secondary Consumers: They feed upon primary consumers. They are carnivores. They are also known as key industry animals. Examples: Wolf, Frog, Snake etc.
3. Tertiary Consumers: These are the top order carnivores. They feed upon secondary consumers, Examples : Lion, Tiger etc.

(3) Decomposers :

These are saprotrophic micro-organisms which depend on dead organic matters for food and decompose organic substances of the dead plants or animals and convert them into inorganic minerals. Examples : Bacteria and Fungi.

(B) Abiotic or Non-living components: The abiotic components are mainly of 2 types, the physical or climatic factors and the chemical factors including inorganic and organic substances

[a] Physical factors:

They include sunlight, temperature, humidity, atmospheric pressure prevailing in all the areas of the biosphere viz. atmosphere, lithosphere, hydrosphere.

(b) Chemical factors:

They include the inorganic elements like carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur, calcium, magnesium etc which are primarily present in the soil and constitute the bio-geo chemical cycles like carbon cycle, oxygen cycle, nitrogen cycle.

Q. What are the abiotic factors of an environment? Illustrate with an example how light affects the life process of an organism. [H.S. '97J 3

Q. What are the different abiotic factors of an ecosystem? Discuss the effects of light and temperature on animal life. (H.S. 1st yr. '99] 2+6=8

Ans: The non-living components of an ecosystem are called abiotic components. They are further classified into two groups :

(1) Physical Abiotic Components : These include temperature, light, humidity, wind, soil etc.

(2) Chemical Abiotic Components : These include oxygen, carbon, nitrogen, sulphur, salinity of water, pH etc.

Effect of light on life processes:

In plants:

1. Light is said to be the most important factor determining the growth of plants as it forms the energy to be used during photosynthesis Light is the fundamental necessity of life as sunlight is the source of all energy.

2. Growth and development of plants depend on light.

3 Light is also essential for many other physiological processes of plants. For example plants are classified as Long Day plant Short Day plant and Day neutral plant depending upon the duration of light required for flowering.

4. Intensity and source of light has great effect on plant movement. The phototrophic movement and phototactic movements are such types.

In animals:

1. In animals the colour vision of the ability to differentiate light colours in well marked. Eg Salamander is eye less and Shark and Cattles are colourblind.
2. Growth and developments of animals are indirectly influenced by light. Altitude and precipitation affect the intensity of light and thereby organisms living in such conditions are affected by light.

Temperature:

In plants:

1. In plants temperature is a factor which determine the distribution of species
2. The morphology, reproductive behavior etc of plants differ on the basis of climate and temperature.

In animals:

1. An organism can perform only within a certain range of temperature as the life activities to come to a stop beyond or below certain range of temperature. Temperature is known to influence metabolism as the enzymatic reactions in the body can occur within a definite range of temperature only. Animals exhibiting hibernation, aestivation, migration, metabolism, pigmentation, movements, mutation, sex-ratio and reproductive behaviour are all influenced by temperature.

Q.6. Differentiate between abiotic and biotic factors. 2 (AMET '95J

Ans: Organisms are surrounded by matters and forces. These are basically divisible into abiotic and biotic. The main differences between them are -

(i) Abiotic factors are non living and biotic factors are living components of an ecosystem.

(ii) Light, temperature, water, soil etc. are abiotic factors, whereas micro­organisms, plants and animals are biotic factors.

(iii) Biotic factors are subjected to natural death but the abiotics have no such death rather they are recycled by cyclic transformations.

(iv) Biotic components can exist within a specific set-up of the abiotic factors but abiotic factors have no such requirement.

(v) Abiotic factors do not require extra source of matter and energy but the biotic components must have inputs of matter and energy for their existence.

(vi) The existence of abiotic factors in absence of biotic factor is possible but the reverse is not possible.

Q. Define Food Chain and Food Web. What are the types of Food Chain? What are the differences between Food Chain and Food Web?

Ans:

FOOD CHAIN

DEFINITION: The linear food-predator relationship exhibited by a series of organisms in an ecosystem is termed as food chain.

Or

The entire series of organisms through which food energy moves in an ecosystem by the process of eating and being eaten constitute food chain. The food levels of a food chain are known as trophic level.

[1] Types of Food Chain: There are two types of food chairs. viz.

[A] Grazing food chain; [B] Detritus food chain. [C] Parasitic food chain.

[A] Grazing food chain: The food chain comprising of green plants as producers, herbivores as primary consumers and carnivores as secondary consumers and terminated in carnivores. eg: The food chain of a grassland ecosystem

[B] Detritus food chain. The food chain comprising of detritus organisms growing on dead organic wastes is known as detritus food chain. The organisms feeding on detritus (organic matter) are known as detrivores or detritus consumers eg algae, fungi, bacteria, protozoa, insects, molluscs, crustaceans, annelids and nematodes. They constitute the detritus food chain. Characteristics of Detritus food chain:

(i) Maximum energy flows through the detritus food chain.

(ii) Major part of this energy is stored within the detritus itself, outside the detrivores.

(iii) The energy flow in detritus food chain is a continuous process and not a stepwise process as observed in grazing food chain.

[C] Parasitic food chain: the organisms can also survive in living host and constitute a Parasitic food chain.

FOOD WEB : The food chains remaining in an interconnected state forming a complex, branched state is known as food web. The food web is regarded as a complex of food chains.

FOOD CHAIN FOOD WEB

1. Food chain is straight and simple1. Food web is complex, branched

aggregation of food chains

1. No preference of food is present2. Preference of food is present
2. If one organism is removed it hampers3. No major problem arise if one

organism is removed

1. Rare is nature4. Present in nature.

Q. Define Ecological pyramids? What are its types?

Ans:

ECOLOGICAL PYRAMIDS: The pyramidal representation of an ecosystem denoted by Charles Elton (1927) is known as Ecological pyramid. It is also called Eltonian pyramid. It represents the position of the producers and successive consumers in an ecosystem.

TYPES OF ECOLOGICAL PYRAMID

Elton denoted three types of ecological pyramids and they are as follows:

[1] Pyramid of Numbers:

The numerical relationship between the members of different trophic levels in an ecosystem constitutes the pyramid of numbers. In general, the number of producers is maximum and gradually the number of herbivores and carnivores are reduced. So the pyramid shows progressive reduction ill the number of the organisms from base to the apex. In pond ecosystem, the pyramid of number is upright but the pyramid of number may be inverted in certain cases where the producer is a big tree and primary consumers are small insects.

[2] Pyramid of Biomass:

The total dry weight of the organisms present in a particular trophic level is known as biomass. The ecological pyramid based on the biomass is known as the pyramid of biomass. For the terrestrial ecosystems like forest ecosystem, the pyramid is upright, but the pond ecosystem shows an inverted pyramid of biomass because the biomass of producers are much less than that of the consumers.

[3] Pyramid of Energy:

The ecological pyramid depicting the flow of energy between the members of an ecosystem at different trophic level is known as pyramid of energy. The energy trapped by the producers is highest and it is gradually reduced as it passes to the tertiary consumer. This loss of energy at each trophic level makes the pyramid of energy always upright.

Q. Describe pond as an ideal example of ecosystem.

Ans: A small, freshwater pond is a It is a classic example of fresh water lentic ecosystem. As in other ecosystems pond ecosystem also consists of biotic and abiotic components which form a balanced independent aquatic natural unit.

A. Biotic Components of Pond Ecosystem:

These are living organisms of the pond which are linked with each other through food chain. They are categorized into the following types -

(I)Producer : These are green plants which trap solar energy and convert it into chemical energy. Eg phytoplanktons like and macroscopic plants like the rooted ones (Vallisnaria, Hydrilla) and the free-floating ones like Pistia, water hyacinth.

(II)Consumers: These are animal organisms which feed on producers. They include, among others, small crustaceans, worms, insect larvae, insects and fishes. These are classified into 3 orders of consumers –

1. Primary Consumers: These are small herbivorous organisms which feed on phytoplankton. e.g. Crustaceans, Waterfleas, Cyclops etc. Other primary consumers are mosquito larvae, tadpoles, snails and tortoises etc.
2. Secondary Consumers: These are carnivores and feed on the primary consumers. eg Hydra, dragonfly larvae, water insects and small fishes.
3. Tertiary consumers: These are also carnivores and feed on the secondary consumers. They include large fishes and water birds example duck and waterfowls.

(III)Decomposers : The complex organic substances of the dead bodies of plant and animals are broken down by the bacteria and fungi of decay to simple organic and inorganic substances.

(B) Abiotic Components of Pond Ecosystem :

These are non living elements of ponds. They include -

(a) Water with dissolved gases and minerals, and. suspended organic matters.

(b) Soil at the bottom with its minerals and organic debris.

(c) Air above the surface of water containing free CO2 and O2.

(d) Sunlight.

The abiotic environment provides raw materials and energy to the biotic components for their growth and development.

Q. Explain how producers, consumers and decomposer are linked with the food chain.

Ans: In an ecosystem, solar energy is harvested by the producers and is converted into potential chemical energy. These producers are eaten by herbivores which are called primary consumers. They convert the plant products into animal products by the process of digestion, absorption an resynthesis. The herbivores are eaten up by higher group of carnivores which are known as secondary consumers and they get their energy through the food of herbivores. The secondary consumers become the food of still higher group of consumers - the tertiary consumers and after the death and decay of both plants and animals including - tertiary consumers, due to the activity of decomposers, simpler compounds are released to the atmosphere which are again utilised by producers. Thus food energy passes through all consumers through different steps till it is completely spent. Each food level in an ecosystem through which energy passes is called trophic level. The entire organisms through which food energy moves in an ecosystem from one trophic level to another by the process of eating and being eaten is called a food chain.

Q. Describe the energy flow in ecosystem?

Ans:

The linear unidirectional flow of energy from the producers to final consumers constitute energy flow.

Characteristics of Energy Flow:

(i)The solar energy is the only source of energy in an ecosystem utilized by the green plants by photosynthesis.

(ii)Only a small amount of solar energy encountered by the plant can actually be utilized during photosynthesis where the solar energy is converted to chemical energy.

(iii)The energy flow is strictly unidirectional from producers to the tertiary consumers and cannot return to the solar system.

(iv)The energy flow is reduced substantially (minimum loss may be 10%) and maximum loss may be upto 90% at each trophic level due to utilization of energy for respiration and other metabolic activities of living species at each trophic level.

Q. Population of which type of organism is usually minimum in an ecosystem?

Ans: Tertiary consumer

Q. In an ecosystem, how does the flow of energy differ from the flow of matter?

Ans: The flow of energy in an ecosystem is unidirectional while the flow of matter is cyclic. In an ecosystem, producers conserve solar energy to chemical energy but it cannot return it back, once it is converted. Similarly, consumers acquire energy from the producers but it cannot return the same. On the other hand all materials used by organisms for building their biomass and energy are made available for repeated use.

Q. What are biogeochemical cycles? Describe briefly the nitrogen cycle. 1 + 5 = 6

Ans: Biogeochemical cycles are the cyclic path through which chemical elements move from environment to organisms and back to the environment. Through the bio geochemical cycles materials in the environment are recycled and their proportion in the environment always remain more or less constant. Due to the cyclic transformation, shortage of matter never occurs in the biosphere.

Nitrogen cycle :

The nitrogen cycle maintains the equilibrium of nitrogen in nature. It consists of five main steps -

(i)Nitrification:

It is the process by which atmospheric nitrogen is fixed to the living system by both biologically and abiologically. Biologically atmospheric nitrogen is fixed by certain bacteria (Rhizobium, Nostoc, Anabaena, Azotobacter etc.) AbiologicaIly, some· free molecular nitrogen of the atmosphere is fixed into nitrates by lightning. (ii) Nitrogen assimilation : Green plants absorb inorganic nitrogen in the form of nitrates, nitrites and ammonia and converts these into nitrogenous organic compounds.

(ii)Ammonification :

The process of conversion of dead organic nitrogeneous compounds in the soil into ammonia by ammonifying bacteria (Bacillus mycoides) is referred to as ammonification.

(iii)Nitrification:

Oxidation of ammonia to nitrites by nitrifying soil bacteria (Nitrosomonas, Nitrobacter) is known as nitrification.

(iv)Denitrification :

It is a biological process by which ammonium compounds, nitntes, nitrates are reduced to molecular nitrogen in the presence of denitrifying bacteria (Pseudomonas, Bacillus subtilis etc.)

Q. Discuss the carbon cycle in nature?

Ans:

The concentration of carbon in living matter (18%) is almost 100 times greater than its concentration in the earth (0.19%). So living things extract carbon from their nonliving environment. For life to continue, this carbon must be recycled.

Carbon exists in the nonliving environment as:

• carbon dioxide (CO2) in the atmosphere and dissolved in water (forming HCO3−)
• carbonate rocks (limestone and coral = CaCO3)
• deposits of coal, petroleum, and natural gas derived from once-living things
• dead organic matter, e.g., humus in the soil

Carbon enters the biotic world through the action of autotrophs, primarily photoautotrophs, like plants and algae, that use the energy of light to convert carbon dioxide to organic matter and to a small extent, chemoautotrophic bacteria and archaeathat do the same but use the energy derived from an oxidation of molecules in their substrate.

Carbon returns to the atmosphere and water by

• respiration (as CO2)
• burning
• decay (producing CO2 if oxygen is present, methane (CH4) if it is not.

Q. Define succession? What are its type? Describe the process of climax community formation?

Ans:

Plant Succession:

The process by which one community replaces another community in a particular habitat is known as plant succession. This ultimately results in the development of a stable community known as climax community.

Types of Plant Succession: Succession can be of 2 types, viz. Primary Succession and Secondary Succession.

[a] Primary Succession:

This succession is also called Autotrophic succession and takes place in the barren area or sterile area like barren rock or sand . They include the following stages.

(i) Nudation : The soil surface or the rock is exposed due to the physical forces of the nature.

(ii) Migration: The plant parts or propagules are transferred to that barren area.