Ecosystem Structure and Energy Flow

Ecosystem Structure and Energy Flow

An ecosystem is a functional unit of nature in which living organisms interact with one another and also interact with the non-living components of their environment.

Simple words में, ecosystem में biotic components (जीवित घटक) और abiotic components (अजीवित घटक) एक-दूसरे के साथ interact करते हैं। Energy और nutrients ecosystem के different components के बीच transfer और circulate होते हैं।

1. Components of an Ecosystem

An ecosystem has two major components:

• Abiotic components – non-living physical and chemical factors.
• Biotic components – living organisms.

2. Abiotic Components

Abiotic components are the non-living components of an ecosystem.

Component	Examples
Physical factors	Light, temperature, water, soil
Chemical factors	Minerals, gases, salts, nutrients
Climatic factors	Rainfall, humidity, wind and temperature

3. Biotic Components

Biotic components are the living organisms present in an ecosystem.

They are broadly classified into:

• Producers
• Consumers
• Decomposers

4. Producers

Producers are organisms that prepare their own food, mainly through photosynthesis.

Green plants are the major producers in terrestrial ecosystems, while algae and phytoplankton are important producers in aquatic ecosystems.

Producers are also called autotrophs because they synthesise organic food from inorganic substances.

5. Consumers

Consumers are organisms that obtain food from other organisms.

They are also called heterotrophs.

Type	Meaning	Example
Primary consumers	Feed directly on producers	Deer, rabbit, grasshopper
Secondary consumers	Feed on primary consumers	Frog, small fish
Tertiary consumers	Feed on secondary consumers	Snake, large fish
Top consumers	Occupy the highest trophic position	Eagle, tiger

6. Decomposers

Decomposers are organisms that break down complex organic matter into simpler substances.

Bacteria and fungi are the major decomposers.

Decomposition releases nutrients back into the environment, where they can again be used by producers.

7. Ecosystem Functions

The major functions of an ecosystem include:

• Productivity
• Decomposition
• Energy flow
• Nutrient cycling

8. Productivity

Productivity refers to the rate of biomass production in an ecosystem.

It is generally expressed in terms of mass per unit area per unit time.

9. Primary Productivity

Primary productivity is the rate at which producers synthesise organic matter through photosynthesis.

It is divided into:

• Gross Primary Productivity (GPP)
• Net Primary Productivity (NPP)

10. Gross Primary Productivity

Gross Primary Productivity (GPP) is the total rate of production of organic matter by producers through photosynthesis.

इसमें वह पूरा organic matter शामिल होता है जो producers photosynthesis के द्वारा बनाते हैं, respiration में उपयोग होने वाला हिस्सा भी इसी total production का part होता है।

11. Net Primary Productivity

Net Primary Productivity (NPP) is the amount of organic matter remaining after the producers have used some of the produced food for respiration.

The relationship is:

NPP = GPP − Respiration

12. Secondary Productivity

Secondary productivity refers to the rate of formation of new organic matter by consumers.

Consumers obtain organic matter by feeding on plants or other organisms and convert part of it into their own biomass.

13. Decomposition

Decomposition is the breakdown of complex organic matter into simpler inorganic substances by decomposers.

Dead plant and animal matter, collectively called detritus, provides material for decomposition.

14. Major Steps of Decomposition

According to NCERT, decomposition involves several important processes:

• Fragmentation
• Leaching
• Catabolism
• Humification
• Mineralisation

15. Fragmentation

Fragmentation is the process in which detritivores break detritus into smaller particles.

Earthworms are important detritivores that contribute to fragmentation.

16. Leaching

Leaching is the process by which water-soluble inorganic nutrients move down into the soil.

Rainwater can carry soluble substances from dead organic matter into deeper layers of soil.

17. Catabolism

Catabolism is the enzymatic breakdown of complex organic compounds into simpler compounds by bacterial and fungal decomposers.

18. Humification

Humification leads to the formation of a dark-coloured amorphous substance called humus.

Humus is highly resistant to microbial decomposition and serves as an important reservoir of nutrients in the soil.

19. Mineralisation

Mineralisation is the process by which inorganic nutrients are released from organic matter during decomposition.

These mineral nutrients can subsequently become available to plants.

Process	Main Meaning
Fragmentation	Breaking detritus into smaller particles
Leaching	Movement of water-soluble substances into soil
Catabolism	Enzymatic breakdown of complex organic matter
Humification	Formation of humus
Mineralisation	Release of inorganic nutrients

20. Factors Affecting Decomposition

Decomposition is influenced by several environmental factors.

• Temperature
• Moisture
• Oxygen availability
• Chemical composition of detritus
• Soil conditions

Warm and moist conditions generally favour decomposition, while low temperature and anaerobic conditions can slow it down.

21. Energy Flow in an Ecosystem

Energy flow refers to the transfer of energy from one trophic level to another in an ecosystem.

The ultimate source of energy for most ecosystems is the Sun.

Producers capture solar energy and convert it into chemical energy stored in organic compounds.

22. Energy Flow is Unidirectional

Energy flow in an ecosystem is unidirectional, meaning energy moves in one direction and does not return to the Sun or previous trophic level.

For example:

Sun → Plants → Herbivores → Carnivores

At each trophic level, a significant amount of energy is lost as heat through metabolic activities.

23. Trophic Levels

A trophic level represents a specific feeding position in a food chain.

Trophic Level	Organisms
First trophic level	Producers
Second trophic level	Primary consumers
Third trophic level	Secondary consumers
Fourth trophic level	Tertiary consumers

24. Food Chain

A food chain represents the sequence of organisms through which food and energy pass from one trophic level to another.

Example:

Grass → Grasshopper → Frog → Snake → Eagle

Organism	Trophic Level
Grass	First
Grasshopper	Second
Frog	Third
Snake	Fourth
Eagle	Fifth

25. Grazing Food Chain

A grazing food chain starts with living green plants and passes through herbivores to carnivores.

Example:

Grass → Deer → Tiger

Here:

• Grass = Producer
• Deer = Primary consumer
• Tiger = Secondary consumer

26. Detritus Food Chain

A detritus food chain begins with dead organic matter or detritus.

Example:

Dead leaves → Earthworm → Bird

Detritus food chains are particularly important in ecosystems where a large proportion of energy enters through dead organic matter.

27. Food Web

A food web is a network of interconnected food chains.

In nature, an organism usually has more than one food source and may itself be eaten by several organisms. इसलिए ecosystem में simple linear food chain की बजाय interconnected food web अधिक common है।

28. Ecological Pyramids

Ecological pyramids are graphical representations of the relationship between organisms at different trophic levels.

They may represent:

• Pyramid of number
• Pyramid of biomass
• Pyramid of energy

29. Pyramid of Number

A pyramid of numbers represents the number of organisms at each trophic level.

Its shape may be upright or inverted depending on the ecosystem.

For example, in a grassland ecosystem, producers are generally much more numerous than herbivores, so the pyramid is upright.

30. Pyramid of Biomass

A pyramid of biomass represents the total biomass present at each trophic level.

It may be upright or inverted.

In many terrestrial ecosystems it is upright, whereas in some aquatic ecosystems it can be inverted because the standing crop of phytoplankton at a given moment may be lower than that of consumers.

31. Pyramid of Energy

A pyramid of energy represents the amount of energy available at successive trophic levels.

The pyramid of energy is always upright because energy decreases at each successive trophic level.

32. Ten Percent Law

According to the 10% law, only about 10% of the energy available at one trophic level is transferred to the next trophic level.

The remaining energy is mainly lost as heat through respiration and other metabolic activities.

Example:

Trophic Level	Approximate Energy
Producers	10,000 units
Primary consumers	1,000 units
Secondary consumers	100 units
Tertiary consumers	10 units

इसलिए food chain में ऊपर जाते-जाते available energy कम होती जाती है।

33. Why Food Chains are Usually Short

Because only a small fraction of energy is transferred to the next trophic level, the amount of available energy decreases rapidly at higher trophic levels.

इस energy loss के कारण ecosystems में generally food chains बहुत long नहीं होतीं।

34. Energy Flow vs Nutrient Cycling

Energy Flow	Nutrient Cycling
Energy flows through the ecosystem.	Nutrients circulate between biotic and abiotic components.
It is unidirectional.	It is cyclic.
Energy is ultimately lost as heat.	Nutrients can be reused.
Sun is the major energy source for most ecosystems.	Elements such as carbon, nitrogen and phosphorus are recycled.

35. Standing Crop

Standing crop refers to the mass of living material present in an ecosystem at a particular time.

It may be measured as biomass or as the number of individuals present at a particular trophic level.

36. Standing State

Standing state refers to the amount of nutrients present in the soil or environment at a particular time.

यह concept ecosystem में nutrient availability को समझने में useful है।

37. Ecosystem Structure – Quick Comparison

Component	Role
Producers	Convert solar energy into chemical energy
Consumers	Transfer energy by feeding on other organisms
Decomposers	Break down dead organic matter
Abiotic components	Provide physical and chemical conditions and nutrients

38. Important Differences

Producer vs Consumer

Producer	Consumer
Autotrophic	Heterotrophic
Prepare their own food	Obtain food from other organisms
First trophic level	Second or higher trophic levels

GPP vs NPP

GPP	NPP
Total primary production	Production remaining after plant respiration
Includes respiratory loss	Excludes respiratory loss
GPP is greater than NPP	NPP = GPP − Respiration

Grazing Food Chain vs Detritus Food Chain

Grazing Food Chain	Detritus Food Chain
Starts with living green plants	Starts with dead organic matter
Herbivores are the first consumers	Detritivores/decomposers participate early
Example: Grass → Deer → Tiger	Example: Dead leaves → Earthworm → Bird

39. Very Short Answer Questions

1. What is an ecosystem?
2. Name two abiotic components of an ecosystem.
3. Who are producers?
4. Who are consumers?
5. Name two decomposers.
6. What is productivity?
7. What is GPP?
8. What is NPP?
9. Write the relation between GPP and NPP.
10. What is decomposition?
11. What is detritus?
12. What is humification?
13. What is mineralisation?
14. What is a trophic level?
15. What is a food chain?
16. What is a food web?
17. What is a pyramid of energy?
18. State the 10% law.
19. What is carrying capacity?
20. Why is energy flow unidirectional?

40. Short Answer Questions

1. Describe the biotic and abiotic components of an ecosystem.
2. Explain the role of producers, consumers and decomposers.
3. Differentiate between GPP and NPP.
4. Explain the major steps of decomposition.
5. What factors affect decomposition?
6. Explain energy flow through trophic levels.
7. Differentiate between grazing and detritus food chains.
8. Differentiate between food chain and food web.
9. Why is the pyramid of energy always upright?
10. Explain the 10% law of energy transfer.
11. Differentiate between energy flow and nutrient cycling.

41. Long Answer Questions

1. Define ecosystem and describe its major components and functions.
2. Explain decomposition and describe its major steps.
3. Explain the flow of energy in an ecosystem with suitable examples.
4. Describe ecological pyramids and explain the significance of the pyramid of energy.
5. Explain productivity, including GPP, NPP and secondary productivity.
6. Explain the structure and functioning of an ecosystem.

42. Multiple Choice Questions

1. An ecosystem consists of:

   (A) Only plants   (B) Only animals   (C) Biotic and abiotic components   (D) Only microorganisms

   Answer: (C) Biotic and abiotic components

2. The first trophic level is occupied by:

   (A) Herbivores   (B) Carnivores   (C) Producers   (D) Decomposers

   Answer: (C) Producers

3. Which organisms are the major decomposers?

   (A) Birds and mammals   (B) Bacteria and fungi   (C) Plants and algae   (D) Reptiles

   Answer: (B) Bacteria and fungi

4. NPP is equal to:

   (A) GPP + Respiration   (B) GPP − Respiration   (C) Respiration − GPP   (D) GPP × Respiration

   Answer: (B) GPP − Respiration

5. The first step in decomposition involving breaking of detritus is:

   (A) Humification   (B) Fragmentation   (C) Mineralisation   (D) Catabolism

   Answer: (B) Fragmentation

6. Formation of humus is called:

   (A) Leaching   (B) Catabolism   (C) Humification   (D) Mineralisation

   Answer: (C) Humification

7. The ultimate source of energy for most ecosystems is:

   (A) Soil   (B) Water   (C) Sun   (D) Decomposers

   Answer: (C) Sun

8. Energy flow in an ecosystem is:

   (A) Cyclic   (B) Bidirectional   (C) Unidirectional   (D) Random

   Answer: (C) Unidirectional

9. A food chain always begins with:

   (A) Carnivores   (B) Producers in a grazing food chain   (C) Decomposers in every case   (D) Tertiary consumers

   Answer: (B) Producers in a grazing food chain

10. Which ecological pyramid is always upright?

    (A) Pyramid of number   (B) Pyramid of biomass   (C) Pyramid of energy   (D) All can be inverted

    Answer: (C) Pyramid of energy

11. Approximately what percentage of energy is transferred to the next trophic level?

    (A) 1%   (B) 5%   (C) 10%   (D) 50%

    Answer: (C) 10%

12. A food web is:

    (A) A single food chain   (B) A network of interconnected food chains   (C) A nutrient cycle   (D) A pyramid

    Answer: (B) A network of interconnected food chains

13. Detritus consists mainly of:

    (A) Living green plants   (B) Dead organic matter   (C) Minerals only   (D) Water

    Answer: (B) Dead organic matter

14. Which process releases inorganic nutrients from organic matter?

    (A) Fragmentation   (B) Humification   (C) Mineralisation   (D) Leaching

    Answer: (C) Mineralisation

15. Grass → Grasshopper → Frog → Snake represents a:

    (A) Detritus food chain   (B) Grazing food chain   (C) Nutrient cycle   (D) Decomposition pathway

    Answer: (B) Grazing food chain

43. Fill in the Blanks

1. The living components of an ecosystem are called ________ components.
2. Green plants are the major ________ of an ecosystem.
3. Bacteria and fungi are major ________.
4. Gross primary productivity is abbreviated as ________.
5. Net primary productivity is equal to GPP minus ________.
6. The first trophic level consists of ________.
7. A food chain beginning with dead organic matter is called a ________ food chain.
8. The formation of humus is called ________.
9. The pyramid of ________ is always upright.
10. Approximately ________ percent of energy is transferred to the next trophic level.

Answers:

1. Biotic
2. Producers
3. Decomposers
4. GPP
5. Respiration
6. Producers
7. Detritus
8. Humification
9. Energy
10. 10

44. Assertion and Reason

1. Assertion: Energy flow in an ecosystem is unidirectional.

   Reason: A considerable amount of energy is lost as heat at each trophic level.

   Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

2. Assertion: Pyramid of energy is always upright.

   Reason: Energy decreases at successive trophic levels.

   Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

3. Assertion: NPP is lower than GPP.

   Reason: Producers use some of the energy obtained through photosynthesis in respiration.

   Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

4. Assertion: Decomposers are important for nutrient cycling.

   Reason: They break down dead organic matter and release simpler substances and inorganic nutrients.

   Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion.

45. Match the Following

Column A	Column B
1. Producers	a. Formation of humus
2. Decomposers	b. First trophic level
3. Humification	c. Breakdown of dead organic matter
4. NPP	d. GPP − respiration
5. Pyramid of energy	e. Always upright

Answers: 1-b, 2-c, 3-a, 4-d, 5-e

46. Quick Revision

47. Must Remember for Board Exam