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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.

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.

Desert

B.

Tropical rainforest

C.

Tundra

D.

Open ocean
Correct Answer: B

Solution:

Tropical rainforests have the highest Gross Primary Productivity due to their dense vegetation and optimal conditions for photosynthesis, including high solar radiation and abundant rainfall.

Chapter Concept:

Productivity in Ecosystems

A.

Because the biomass of fishes exceeds that of phytoplankton.

B.

Because phytoplankton have a higher biomass than fishes.

C.

Because energy transfer is more efficient in aquatic ecosystems.

D.

Because of the high rate of primary productivity in oceans.
Correct Answer: A

Solution:

The pyramid of biomass in the ocean is generally inverted because the biomass of fishes far exceeds that of phytoplankton, despite the latter being the primary producers.

Chapter Concept:

Productivity in Ecosystems

A.

Energy flow is bidirectional between trophic levels.

B.

Energy flow is unidirectional from producers to consumers.

C.

Energy is recycled between trophic levels.

D.

Energy flow is not dependent on the sun.
Correct Answer: B

Solution:

Energy flow in an ecosystem is unidirectional, starting from producers who capture solar energy and moving up to consumers.

Chapter Concept:

Ecosystem Structure and Function

A.

Energy flows from producers to consumers and decomposers, with some energy lost as heat at each transfer.

B.

Energy cycles between producers and consumers with no loss.

C.

Energy is stored indefinitely at each trophic level.

D.

Energy is transferred from decomposers to producers.
Correct Answer: A

Solution:

Energy flow in an ecosystem is unidirectional, starting from the sun to producers and then to consumers and decomposers, with heat loss at each transfer.

Chapter Concept:

Energy Flow in Ecosystems

A.

10 J

B.

100 J

C.

1,000 J

D.

10,000 J
Correct Answer: B

Solution:

According to the 10 percent law, only about 10% of energy is transferred to each successive trophic level. Therefore, 10% of 1,000 J (energy available to primary consumers) is 100 J available to secondary consumers.

Chapter Concept:

Trophic Levels, Standing Crop and 10 Percent Law

A.

Cold and dry

B.

Warm and moist

C.

Hot and arid

D.

Cold and wet
Correct Answer: B

Solution:

A warm and moist environment favors decomposition by enhancing the activity of soil microbes.

Chapter Concept:

Decomposition Process

A.

1-5%

B.

2-10%

C.

20-30%

D.

50-60%
Correct Answer: B

Solution:

Plants capture only 2-10% of the incident PAR, which is the energy that sustains the entire living world.

Chapter Concept:

Energy Flow in Ecosystems

A.

2000 kcal m−2^{-2} yr−1^{-1}

B.

1000 kcal m−2^{-2} yr−1^{-1}

C.

1500 kcal m−2^{-2} yr−1^{-1}

D.

500 kcal m−2^{-2} yr−1^{-1}
Correct Answer: B

Solution:

The Net Primary Productivity (NPP) is calculated as the Gross Primary Productivity (GPP) minus the respiration loss (R). Thus, NPP = 1500 - 500 = 1000 kcal m−2^{-2} yr−1^{-1}.

Chapter Concept:

Productivity in Ecosystems

A.

Atmosphere

B.

Hydrosphere

C.

Earth's crust

D.

Biosphere
Correct Answer: C

Solution:

The Earth's crust serves as the primary reservoir for the sedimentary cycle of phosphorus.

Chapter Concept:

Nutrient Cycling

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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 of dry weight organic matter, with oceans contributing about 55 billion tons despite covering 70% of Earth's surface.

Chapter Concept :

Biosphere Productivity and Ocean Productivity

Correct Answer: True

Solution:

Energy flow in an ecosystem is unidirectional, starting from producers who capture solar energy and then transferring it to consumers through the food chain.

Chapter Concept :

Ecosystem Structure and Function

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:

In aquatic ecosystems, the biomass pyramid is often inverted because the biomass of fish and other consumers can exceed that of the phytoplankton producers due to the rapid turnover rate of phytoplankton.

Chapter Concept :

Ecological Pyramids

Correct Answer: True

Solution:

A pond is considered a self-sustainable aquatic ecosystem because it includes all necessary components: abiotic factors like water and soil, autotrophs such as phytoplankton and algae, consumers like zooplankton, and decomposers such as fungi and bacteria, which together perform all essential ecosystem functions.

Chapter Concept :

Pond Ecosystem as a Self-Sustainable Unit

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:

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

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: False

Solution:

The pyramid of energy is always upright because energy is lost as heat at each trophic level, making it impossible for higher trophic levels to have more energy than lower ones.

Chapter Concept :

Ecological Pyramids

Correct Answer: False

Solution:

Net primary productivity (NPP) is the biomass available to heterotrophs after accounting for respiration losses from gross primary productivity (GPP).

Chapter Concept :

Productivity in Ecosystems

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