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Ecosystem

Action PlanNotesQuestionsMock-Test
Study Action Plan (Sorted by Difficulty)
Trophic Levels, Standing Crop and 10 Percent Law
Accuracy: 14%
Total Attempted7
Total Correct1
Total Incorrect6
Difficulty Level:
High
Factors Affecting Decomposition
Accuracy: 38%
Total Attempted8
Total Correct3
Total Incorrect5
Difficulty Level:
High
Nutrient Cycling
Accuracy: 43%
Total Attempted7
Total Correct3
Total Incorrect4
Difficulty Level:
High
Limitations of Ecological Pyramids
Accuracy: 58%
Total Attempted12
Total Correct7
Total Incorrect5
Difficulty Level:
Medium
Productivity in Ecosystems
Accuracy: 60%
Total Attempted30
Total Correct18
Total Incorrect12
Difficulty Level:
Medium
Pond Ecosystem as a Self-Sustainable Unit
Accuracy: 62%
Total Attempted13
Total Correct8
Total Incorrect5
Difficulty Level:
Medium
Ecological Pyramids
Accuracy: 64%
Total Attempted25
Total Correct16
Total Incorrect9
Difficulty Level:
Medium
Decomposition Process
Accuracy: 70%
Total Attempted23
Total Correct16
Total Incorrect7
Difficulty Level:
Medium
Food Chains and Webs
Accuracy: 74%
Total Attempted27
Total Correct20
Total Incorrect7
Difficulty Level:
Medium
Energy Flow in Ecosystems
Accuracy: 80%
Total Attempted25
Total Correct20
Total Incorrect5
Difficulty Level:
Low
Ecosystem Structure and Function
Accuracy: 85%
Total Attempted20
Total Correct17
Total Incorrect3
Difficulty Level:
Low
Biosphere Productivity and Ocean Productivity
Accuracy: 100%
Total Attempted6
Total Correct6
Total Incorrect0
Difficulty Level:
Low

Learning Objectives

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Learning Objectives

  • Define the concept of an ecosystem and its components.
  • Describe the structure and function of ecosystems, including abiotic and biotic factors.
  • Explain the processes of productivity, decomposition, energy flow, and nutrient cycling in ecosystems.
  • Differentiate between gross primary productivity (GPP) and net primary productivity (NPP).
  • Identify the roles of producers, consumers, and decomposers in an ecosystem.
  • Discuss the significance of ecological pyramids and their limitations.
  • Analyze energy transfer through trophic levels and the implications of the 10 percent law.
  • Illustrate the decomposition process and its importance in nutrient recycling.

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Revision Notes & Summary

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Chapter 12: Ecosystem

12.1 Ecosystem - Structure and Function

  • An ecosystem is a functional unit of nature where living organisms interact with each other and the physical environment.
  • Ecosystems vary in size from small ponds to large forests or seas.
  • Two basic categories of ecosystems:
    • Terrestrial: Forests, grasslands, deserts.
    • Aquatic: Ponds, lakes, wetlands, rivers, estuaries.
  • Man-made ecosystems include crop fields and aquariums.

Key Components of Ecosystems

  1. Productivity: Input of solar energy and biomass production.
  2. Decomposition: Breakdown of organic matter.
  3. Energy Flow: Transfer of energy through food chains/webs.
  4. Nutrient Cycling: Movement of nutrients through the ecosystem.

12.2 Productivity

  • Primary Production: Amount of biomass produced by plants during photosynthesis, expressed in gm⁻² or kcal m⁻².
  • Gross Primary Productivity (GPP): Total production of organic matter.
  • Net Primary Productivity (NPP): Biomass available after respiration losses (NPP = GPP - R).
  • Secondary Productivity: Rate of formation of new organic matter by consumers.

12.3 Decomposition

  • Decomposers break down complex organic matter into inorganic substances.
  • Steps in Decomposition:
    1. Fragmentation: Breakdown of detritus into smaller particles.
    2. Leaching: Water-soluble nutrients leach into the soil.
    3. Catabolism: Degradation of detritus by bacterial and fungal enzymes.
    4. Humification: Formation of humus, a nutrient reservoir.
    5. Mineralisation: Release of inorganic nutrients.

12.4 Energy Flow

  • Energy flow is unidirectional, moving from producers to higher trophic levels.
  • Only 10% of energy is transferred to each successive trophic level.

12.5 Ecological Pyramids

  • Types of Ecological Pyramids:
    • Pyramid of Numbers: Represents the number of individuals at each trophic level.
    • Pyramid of Biomass: Shows the dry weight of organisms at each level.
    • Pyramid of Energy: Illustrates energy flow through the food chain.

Example Data for Pyramid of Numbers

Trophic LevelNumber of Individuals
Tertiary Consumers (TC)3
Secondary Consumers (SC)354,000
Primary Consumers (PC)708,000
Producers (P)5,842,000

Example Data for Pyramid of Biomass

Trophic LevelDry Weight (kg m⁻²)
Tertiary Consumers (TC)1.5
Secondary Consumers (SC)11
Primary Consumers (PC)37
Producers (P)809
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

Decomposition

B.

Primary productivity

C.

Nutrient cycling

D.

Energy flow
Correct Answer: B

Solution:

Primary productivity involves the conversion of inorganic substances into organic material through photosynthesis by autotrophs.

Chapter Concept:

Pond Ecosystem as a Self-Sustainable Unit

A.

Warm and moist environment

B.

Cold and dry environment

C.

High nitrogen content in detritus

D.

Presence of earthworms
Correct Answer: B

Solution:

A cold and dry environment would slow down the rate of decomposition as it inhibits microbial activity.

Chapter Concept:

Decomposition Process

A.

Pyramid of numbers

B.

Pyramid of biomass

C.

Pyramid of energy

D.

All pyramids
Correct Answer: A

Solution:

In a tree ecosystem, the pyramid of numbers is inverted because a single tree supports many herbivores.

Chapter Concept:

Ecological Pyramids

A.

Zooplankton

B.

Phytoplankton

C.

Fungi

D.

Fish
Correct Answer: B

Solution:

Phytoplankton are the primary autotrophic components in a pond ecosystem, as they perform photosynthesis and form the base of the aquatic food web.

Chapter Concept:

Ecosystem Structure and Function

A.

To maintain the ecosystem's biodiversity.

B.

To counteract the universal tendency toward increasing disorderliness.

C.

To ensure that all trophic levels receive equal energy.

D.

To allow decomposers to function effectively.
Correct Answer: B

Solution:

According to the second law of thermodynamics, ecosystems require a constant input of energy to synthesize molecules and counteract the universal tendency toward increasing disorderliness.

Chapter Concept:

Energy Flow in Ecosystems

A.

Zooplankton

B.

Phytoplankton

C.

Fishes

D.

Benthic organisms
Correct Answer: B

Solution:

Phytoplankton are the primary producers in aquatic ecosystems, converting solar energy into chemical energy through photosynthesis.

Chapter Concept:

Ecosystem Structure and Function

A.

Energy primarily flows through the grazing food chain.

B.

Energy primarily flows through the detritus food chain.

C.

Energy flows equally through both the grazing and detritus food chains.

D.

Energy flow is not significant in terrestrial ecosystems.
Correct Answer: B

Solution:

In terrestrial ecosystems, a larger fraction of energy flows through the detritus food chain compared to the grazing food chain.

Chapter Concept:

Food Chains and Webs

A.

Leaching

B.

Fragmentation

C.

Catabolism

D.

Humification
Correct Answer: C

Solution:

Catabolism is the step where bacterial and fungal enzymes degrade detritus into simpler inorganic substances.

Chapter Concept:

Decomposition Process

A.

Leaching

B.

Fragmentation

C.

Catabolism

D.

Humification
Correct Answer: B

Solution:

Fragmentation is the process where detritivores like earthworms break down detritus into smaller particles.

Chapter Concept:

Decomposition Process

A.

It forms complex organic molecules.

B.

It releases inorganic nutrients for plant uptake.

C.

It reduces the soil's nutrient content.

D.

It increases the carbon content in soil.
Correct Answer: B

Solution:

Mineralisation is the process where inorganic nutrients are released from organic matter, making them available for plant uptake.

Chapter Concept:

Decomposition Process

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Ecosystem

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True or False

Correct Answer: True

Solution:

The annual net primary productivity of the biosphere is approximately 170 billion tons dry weight of organic matter, with oceans contributing only about 55 billion tons.

Chapter Concept :

Biosphere Productivity and Ocean Productivity

Correct Answer: True

Solution:

A pond ecosystem is a self-sustainable unit as it exhibits productivity through autotrophs like phytoplankton, decomposition by fungi and bacteria, energy flow through various trophic levels, and nutrient cycling.

Chapter Concept :

Pond Ecosystem as a Self-Sustainable Unit

Correct Answer: True

Solution:

Decomposition is a multi-step process where detritivores and decomposers break down complex organic matter into simpler inorganic substances, involving several stages including fragmentation, leaching, catabolism, humification, and mineralisation.

Chapter Concept :

Decomposition Process

Correct Answer: True

Solution:

Secondary productivity refers to the rate at which consumers in an ecosystem generate new organic matter from the biomass they consume.

Chapter Concept :

Productivity in Ecosystems

Correct Answer: True

Solution:

In terrestrial ecosystems, the detritus food chain (DFC) plays a significant role as a larger fraction of energy flows through it compared to the grazing food chain (GFC). This is due to the abundance of dead organic matter and decomposers in these ecosystems.

Chapter Concept :

Food Chains and Webs

Correct Answer: False

Solution:

Humification results in the formation of humus, a dark, amorphous substance that is resistant to decomposition. It is mineralisation, not humification, that releases inorganic nutrients from detritus.

Chapter Concept :

Decomposition Process

Correct Answer: True

Solution:

Decomposition is the process where decomposers break down complex organic matter into simpler inorganic substances like carbon dioxide, water, and nutrients.

Chapter Concept :

Decomposition Process

Correct Answer: True

Solution:

In nutrient cycling, the Earth's crust serves as the reservoir for sedimentary cycles, such as that of phosphorus.

Chapter Concept :

Nutrient Cycling

Correct Answer: False

Solution:

In a terrestrial ecosystem, a larger fraction of energy flows through the detritus food chain compared to the grazing food chain.

Chapter Concept :

Ecosystem Structure and Function

Correct Answer: True

Solution:

Energy flow in ecosystems is indeed unidirectional, starting from the sun, captured by producers, and then transferred to consumers and decomposers, with energy lost as heat at each transfer.

Chapter Concept :

Energy Flow in Ecosystems

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