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SUBTOPIC 2.2: ENERGY AND BIOMASS IN ECOSYSTEMS
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Subtopic 2.2 focuses on the interactions among organisms and their
environment, examining principles like food webs, trophic levels, and
energy flow within ecosystems. This subtopic explores how ecological
IBDP Environmental Systems
and Societies (2017)
interactions shape the distribution and abundance of organisms,
underlining the importance of biodiversity and the dynamics of
IBDP Environmental Systems
and Societies (2024)
populations and communities within ecosystems. T
Statistical Anaylsis
he study of ecology in this context helps understand the scientific
principles governing natural systems, providing a foundation for
ESS Extended Essay
analyzing environmental issues and human impacts on these systems.
Official IB ESS Glossary
Grade 10 MYP Biology
SL/HL
​This unit will take a minimum of 6 hours
Grade 9 MYP Biology
MYP Laboratory Guidance
Guiding Questions
How can flows of energy and matter through ecosystems be modelled?
IB Command Terms
How do human actions affect the flow energy and matter, and what is the impact on ecosystems?
Guide To Exam Success
ecosystems?
How do changes in land use affect the biogeochemical cycles and what are the implications for ecosystem
Scientific Dictionary
health and sustainability?
Scientific Method
About Me
What strategies can be employed to mitigate human impacts on the natural cycles of energy and matter in
Understanding
ECOSYSTEM PRODUCTIVITY AND ENERGY FLOW
2.2.1 Ecosystems are sustained by supplies of energy and matter.
List three components that make up an ecosystem
Outline the process of energy flow in an ecosystem.
Describe how matter is recycled within an ecosystem.
Explain why ecosystems are considered open systems
Ecosystems are open systems, continuously exchanging energy and matter with their surroundings. This exchange
supports the ecosystem’s balance, health, and resilience.
Open System Dynamics:
Energy Exchange: Energy flows from the sun to producers (e.g.,
plants) and then through various trophic levels (herbivores,
carnivores, decomposers).
Energy Transformation: Solar energy is transformed into
chemical energy via photosynthesis, supporting the food
chain.
Energy Loss: Energy is released as heat during metabolic
activities and lost through decomposition.
Matter Cycling: Unlike energy, matter (e.g., carbon,
nitrogen) is recycled within ecosystems.
Biogeochemical Cycles: Essential elements circulate
through cycles (e.g., carbon cycle) allowing reuse by all
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organisms.
Role of Decomposers: Decomposers break down organic matter, returning elements like carbon to the
soil or atmosphere.
Importance of Energy and Matter Balance:
Ecosystem Stability: Balanced energy flow and matter recycling are essential for ecosystem productivity and
stability.
Human Impact: Activities like deforestation, pollution, and climate change disrupt these natural flows, affecting
ecosystem health and sustainability.
Energy Literacy Essential Prin…
Prin…
Ecosystems Episode 1: What i…
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2.2.2 The first law of thermodynamics states that as energy flows through ecosystems, it can be
transformed from one form to another but cannot be created or destroyed.
Outline the first law of thermodynamics
Explain how the first law of thermodynamics apply to a food chain and an energy production system. Use a
systems diagram to aid in your explanation.​
The First Law of Thermodynamics (law of conservation of
energy) states that energy can change forms but cannot be
created or destroyed. In ecosystems, energy undergoes various
transformations as it moves through different trophic levels,
while the total amount remains constant.
http://www.bradjbrennan.ca/13-energy-balanceequilibria.html
Importance of the First Law in Ecosystems:
Solar Energy as the Foundation: Solar energy is the primary input that sustains ecosystems. Without it, life
processes would halt.
Energy Conservation: While energy is conserved, usable energy decreases with each transfer due to losses,
mostly as heat during metabolic processes.
Energy Transformations in Ecosystems:
Photosynthesis: Producers (plants) capture sunlight and convert it into chemical energy.
Energy Flow Through Trophic Levels: Chemical energy is passed through food webs as organisms consume
one another.
Heat Loss: At each trophic level, some energy is lost as heat, making energy transfers less efficient with each
level.
Systems Approach to Energy Flow:
Modeling Energy Flow: A systems approach visualizes ecosystems as open systems, tracking energy from
sunlight to its final form as heat.
Interconnectedness: This approach illustrates how energy flows between ecosystem components and
emphasizes the efficiency and limitations of energy transfer in food webs.
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​ or example, consider a simple food chain: sunlight is captured by plants (producers), which are eaten by herbivores
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(primary consumers). Herbivores are then consumed by carnivores (secondary consumers). At each stage, energy is
transferred and transformed. While energy remains conserved according to the first law of thermodynamics, the usable
energy decreases with each transfer due to heat loss.
Importance of the First Law of Thermodynamics in Ecosystems
Ecosystems rely on a constant input of solar energy to sustain life processes.
Without solar energy, the energy transformations supporting life would cease, leading to ecosystem breakdown.
The principle of conservation of energy dictates that energy cannot be created or destroyed but only
transformed from one form to another.
Solar energy absorbed by plants is converted into stored chemical energy, which fuels ecosystem functioning.
A guide to the energy of the Earth - Jos…
Jos…
​2.2.3 Photosynthesis and cellular respiration transform energy and matter in ecosystems.
Describe photosynthesis and respiration in terms of inputs, outputs and energy transformations.
The transformation of energy and matter within ecosystems is crucial for
sustaining life. Photosynthesis and cellular respiration are
complementary processes that drive these transformations.
Photosynthesis:
Definition: Photosynthetic organisms (plants, algae, some bacteria)
convert light energy into chemical energy stored in glucose.
Location: Takes place in chloroplasts, where chlorophyll captures
sunlight.
Equation: Carbon dioxide + Water + Light energy → Glucose +
Oxygen.
Inputs: Sunlight, carbon dioxide, water.
Process: Chlorophyll traps sunlight, splits water, and combines
hydrogen with CO₂ to produce glucose.
Outputs: Glucose (energy source and building block) and oxygen
https://www.sciencefacts.net/photosynthesisand-cellular-respiration.html
(released to the atmosphere).
Transformation: Light energy is converted to stored chemical energy.
Cellular Respiration:
Definition: The process of breaking down glucose to release stored energy for cellular activities, occurring in
the mitochondria.
Equation: Glucose + Oxygen → Carbon dioxide + Water + Energy.
Inputs: Glucose and oxygen.
Process: Oxidation within cells releases energy for cellular functions.
Outputs: Energy for cellular work, CO₂, and water.
Transformation: Stored chemical energy in glucose is converted to kinetic energy and heat.
The Interconnected Cycle of Photosynthesis and Cellular Respiration:
Complementary Processes:
Photosynthesis produces oxygen and glucose, which are used in cellular respiration.
Cellular respiration produces CO₂ and water, which are used in photosynthesis.
Cycle of Energy and Matter:
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Photosynthesis stores energy in glucose and assembles matter into organic compounds.
Cellular respiration releases energy from glucose for cell functions and recycles matter back into simpler
forms.
Application of skills: Create system diagrams from a set of data of ecosystems showing transfers and
transformations of energy and matter.
​2.2.4 Photosynthesis is the conversion of light energy to chemical energy in the form of glucose,
some of which can be stored as biomass by autotrophs.
Define photosynthesis.
List the main products of the photosynthesis process.
Outline the role of chlorophyll in photosynthesis.
Describe how glucose produced in photosynthesis is used by autotrophs.
Explain the importance of photosynthesis in the flow of energy within an ecosystem.
Define the term "autotroph" and give two examples.
Photosynthesis is a vital process that converts solar energy into
chemical energy, supporting life and driving energy flow within
ecosystems.
Basic inputs and outputs of the photosynthesis process.
(Olha Pohorielova/iStock/Getty)
Role of Autotrophs (Primary Producers):
Definition: Autotrophs, or primary producers (plants, algae, certain bacteria), perform photosynthesis to create
their own energy.
Foundation of Food Webs: By producing organic matter, autotrophs form the base of the food web, supporting
herbivores and higher trophic levels.
Basics of Photosynthesis:
Location: Takes place in chloroplasts, where chlorophyll captures sunlight.
Equation: Carbon dioxide + Water + Light energy → Glucose + Oxygen.
Process:
Light energy is converted into chemical energy stored in glucose.
CO₂ and water are transformed into glucose and oxygen.
Glucose and Biomass Production:
Immediate Energy: Glucose provides energy for cellular activities within the plant.
Storage: Some glucose is stored as starch, used later when the plant needs energy.
Biomass Formation: Glucose is converted into other compounds (e.g., cellulose, proteins, lipids), contributing
to the plant's biomass.
Biomass Definition: Biomass represents the stored energy and nutrients in living matter, which can be
transferred through the food web.
Importance of Photosynthesis in Ecosystems:
Energy Flow: Primary means of introducing solar energy into ecosystems, fueling all life.
Oxygen Production: Produces oxygen, essential for the respiration of most organisms.
Carbon Cycle Contribution: Helps regulate atmospheric CO₂ levels, playing a significant role in the carbon
cycle.
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The simple story of photosynthesis an…
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ENERGY TRANSFER AND EFFICIENCY
2.2.5 Producers form the first trophic level in a food chain.
Define the term "producer" in the context of an ecosystem.
List three types of producers found in ecosystems.
Outline the process of photosynthesis in producers.
Describe the role of producers in a food chain.
Explain why producers are essential for the sustainability of ecosystems.
Define the term "trophic level" and identify the trophic level at which producers are found.
Producers, or autotrophs, are essential for ecosystem
sustainability as they provide energy and organic matter for
all other living organisms, forming the first trophic level in a
food chain.
Role of Producers:
Foundation of Energy Flow: Producers capture and
convert solar energy into chemical energy, which is
then passed through the food chain.
Photosynthesis: Producers use sunlight, CO₂, and water to produce glucose and oxygen, storing energy in
chemical bonds that support growth, reproduction, and life processes.
Types of Producers:
Plants: Terrestrial primary producers, capturing sunlight through
leaves, crucial for land ecosystems.
Algae: Primary producers in aquatic systems, providing food and
oxygen in freshwater and marine ecosystems.
Photosynthetic Bacteria: Microorganisms like cyanobacteria
perform photosynthesis, especially important in nutrient-poor
environments.
https://www.sciencefacts.net/autotrophsprimary-producer.html
Importance of Producers:
Energy Source: Producers supply energy to all other trophic levels, supporting herbivores, carnivores, and
decomposers.
Oxygen Production: Release oxygen into the atmosphere, essential for most organisms' respiration.
Carbon Dioxide Removal: Absorb CO₂ for photosynthesis, helping regulate atmospheric levels and mitigate
climate change.
Food Web Foundation: Form the base of food webs, promoting ecosystem stability and biodiversity.
Hydrological Cycle Regulation: Release water through transpiration, contributing to atmospheric water and
precipitation cycles.
Habitat Formation: Create habitats for various species, with roots stabilizing soil and preventing erosion.
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https://www.scithrill.com/10-examples-of-producers-in-food-chain/
​ .2.6 Cellular respiration releases energy from glucose by converting it into a chemical form that can easily be
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used in carrying out active processes within living cells.
Define cellular respiration.
List the main products of cellular respiration.
Outline the basic steps involved in cellular respiration.
Describe the role of glucose in cellular respiration.
Explain how cellular respiration contributes to energy release in living cells.
Define the term "aerobic organism" and explain its relevance to cellular respiration.
Cellular respiration is the process by which cells break down glucose
to release energy, essential for all aerobic life.
https://www.scithrill.com/10-examples-of-producers-infood-chain/
Basics of Cellular Respiration:
Process: Takes place in the mitochondria, where glucose is oxidized with oxygen to release energy.
Equation: Oxygen + Glucose → Energy + Carbon Dioxide + Water.
Steps:
Oxidation: Glucose loses electrons, releasing chemical energy.
Role of Oxygen: Helps break down glucose, producing CO₂ and water.
Energy Release: Energy is converted to a usable form (ATP) for cellular functions; heat is also released
as a by-product, which cannot be reused by the organism
Energy Use in Cells:
Muscle Contraction: Powers muscle movement.
Cell Division: Fuels growth and replication of cells.
Active Transport: Provides energy for moving molecules across membranes against their gradient.
Biosynthesis: Supports the synthesis of proteins, nucleic acids, and other vital molecules.
Importance of Cellular Respiration:
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Energy Supply: Provides essential energy for cells to perform vital functions.
Sustaining Life: Without cellular respiration, organisms couldn’t grow, reproduce, or respond to their
environment.
Connection to Photosynthesis:
Cycle of Energy Transformation: Photosynthesis stores solar energy in glucose, while cellular respiration
releases this energy for cellular use.
Ecosystem Energy Flow: This cyclical relationship maintains energy flow across producers, consumers, and
decomposers, sustaining ecosystem dynamics.
Relationship between Photosynthesis …
​2.2.7 Some of the chemical energy released during cellular respiration is transformed into heat.
List the main byproducts of cellular respiration.
Outline the reasons why heat is generated during cellular respiration.
Describe how heat produced during cellular respiration is used in warm-blooded animals.
Explain why cellular respiration is not 100% efficient in transferring energy from glucose.
Define the term "exergonic reaction" and explain its relevance to cellular respiration.
Cellular respiration releases energy for cellular activities but
is not completely efficient, resulting in some energy being
lost as heat.
Inefficiency and Heat Production:
Energy Loss as Heat: The breakdown of glucose during cellular respiration primarily produces ATP, a chemical
energy source, but some energy is inevitably lost as heat due to inefficiencies in energy transfer.
Energy Conversion Process:
Chemical to Heat Energy: As glucose is broken down, some chemical energy is not captured and is
released as heat.
Exergonic Reactions: The reactions involved release energy (exergonic), producing heat as a natural
byproduct.
Why Heat is Generated:
Energy Transfer Inefficiency: Not all energy from glucose can be stored in ATP; some escapes as heat.
Non-Recoverable Heat: Once energy is lost as heat, it cannot be converted back into usable chemical energy,
as it dissipates into the environment.
Implications for Energy Flow in Ecosystems:
Energy Flow and Heat Loss: Energy flows from the Sun to producers, which convert it into chemical energy. As
energy moves through trophic levels, heat is lost at each stage, reducing the available energy for higher levels.
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Need for Continuous Energy Input: The inefficiency of energy transfer and heat loss highlight the need for a
constant influx of solar energy to maintain life processes and ecosystem stability.
Heat is released during Respiration
2.2.8 The second law of thermodynamics states that energy transformations in ecosystems are
inefficient.
Outline the second law of thermodynamics
The second law of thermodynamics states that every energy
transformation results in energy degradation—some energy is inevitably
lost as heat, making energy transfers less efficient. This concept is
central to understanding ecosystem energy dynamics.
Summary of the Second Law of Thermodynamics:
Energy Transformation Losses: Whenever energy is
transformed, part of it is lost as heat, reducing the efficiency of
energy transfer.
Energy Inefficiency in Ecosystems:
Cellular Respiration:
When organisms break down glucose, not all chemical energy is converted to usable energy. A portion is
lost as heat, which dissipates and cannot be reused.
Energy Transfers in Food Chains:
Typically, only about 10% of the energy is passed to the next trophic level, while the remaining 90% is
lost as heat during metabolic processes.
This inefficiency limits the number of trophic levels in a food chain, as less energy is available to support
organisms at higher levels.
Implications of the Second Law of Thermodynamics in Ecosystems:
Energy Degradation: With each transfer, energy becomes less useful. A continuous input of solar energy is
essential to maintain life.
Energy Pyramids: Energy pyramids show the decreasing energy available at each trophic level due to these
losses, resulting in a pyramid structure that limits energy for higher trophic levels.
Ecosystem Productivity: Primary productivity (energy captured by producers) determines the ecosystem's
productivity. The efficiency of energy capture and transfer affects ecosystem biomass and overall energy
availability.
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image from faculty.ycp.edu
This occurs when energy is transferred between trophic levels as illustrated in a food chain When one animal feeds off
another, there is a loss of heat (energy) in the process. Additional loss of energy occurs during respiration and
movement. Hence, more and more energy is lost as one moves up through trophic levels. This fact lends more
credence to the advantages of a vegetarian diet. For example, 1350 kilograms of corn and soybeans is capable of
supporting one person if converted to beef. However, 1350 kilograms of soybeans and corn utilized directly without
converting to beef will support 22 people!
Thermodynamics, 1st and 2nd Laws - 1…
1…
TROPHIC LEVELS AND ENERGY EFFICIENCY
2.2.9 Consumers gain chemical energy from carbon (organic) compounds obtained from other organisms.
Consumers have diverse strategies for obtaining energy-containing carbon compounds.
Define the term "consumer" in the context of an ecosystem.
List three types of consumers and provide one example for each type.
Outline the process by which herbivores obtain energy from plants.
Describe the role of detritivores in an ecosystem.
Outline the importance of saprotrophs in nutrient cycling.
​Consumers are organisms that gain chemical energy from carbon (organic) compounds obtained from other
organisms. They play a critical role in the flow of energy through ecosystems by transferring energy and nutrients from
one trophic level to another. Consumers have developed diverse strategies for obtaining energy-containing carbon
compounds, each adapted to their ecological niches. These strategies include herbivory, detritivory, predation,
parasitism, saprotrophy, scavenging, and decomposition.
Types of Consumers and Their Energy Acquisition Strategies
Herbivores
Definition: Herbivores are consumers that feed primarily on plants and other photosynthetic organisms.
Energy Source: Herbivores obtain energy by consuming leaves, stems, seeds, and roots of plants. The
chemical energy stored in plant tissues, primarily as carbohydrates, is converted into usable energy
through cellular respiration.
Examples: Deer, rabbits, and caterpillars.
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https://www.activewild.com/examples-of-herbivores/
Detritivores
Definition: Detritivores are consumers that feed on dead
organic matter, particularly plant detritus
Energy Source: Detritivores break down plant litter and
other dead organic material, recycling nutrients and
obtaining energy from decomposing matter.
Examples: Earthworms, millipedes, and woodlice.
https://lizzieharper.co.uk/image/detritivores-soillitter-invertebrates/
Predators
Definition: Predators are consumers that hunt,
capture, and kill other animals for food.
Energy Source: Predators obtain energy by
consuming the flesh of their prey, which
provides proteins, fats, and carbohydrates
necessary for their survival and reproduction.
Examples: Lions, eagles, and spiders.
https://warnercnr.source.colostate.edu/apex-predators-notquick-fix-for-restoring-ecosystems/
Parasites
Definition: Parasites are consumers that live on or
inside a host organism, deriving nutrients at the host's
expense.
Energy Source: Parasites extract nutrients directly
from the tissues or bodily fluids of their hosts, often
causing harm but not immediately killing the host.
Examples: Tapeworms, fleas, and mistletoe.
https://microbeonline.com/parasitic-infections-sourceof-infection-mode-of-transmission-and-prevention/
Saprotrophs
Definition: Saprotrophs are organisms that feed on
decaying organic matter by secreting digestive
enzymes and absorbing the resulting nutrients.
Energy Source: Saprotrophs decompose dead
organic material, breaking it down into simpler
substances and absorbing the released nutrients and
energy.
https://www.geeksforgeeks.org/saprophytes/
Examples: Fungi, bacteria, and molds.
Scavengers
Definition: Scavengers are consumers that feed on dead animals and plant material.
Energy Source: Scavengers consume carrion and decomposing organic matter, playing a vital role in
cleaning the environment and recycling nutrients.
Examples: Vultures, hyenas, and crabs.
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Decomposers
Definition: Decomposers are organisms, primarily
fungi and bacteria, that break down dead organic
material into simpler inorganic substances.
Examples: Mushrooms, soil bacteria, and
actinomycetes.
Energy Source: Decomposers obtain energy by
breaking down complex organic compounds into
simpler molecules, which are then returned to the soil
and atmosphere, making nutrients available for
primary producers.
https://newtondesk.com/why-bacteria-fungi-calleddecomposers/
Importance of Consumers in Ecosystems
Energy Transfer: They facilitate the flow of energy from primary producers to higher trophic levels, ensuring
that energy captured by photosynthesis is distributed throughout the ecosystem.
Nutrient Recycling: By breaking down and consuming organic matter, consumers contribute to the recycling of
nutrients, which are essential for the growth of primary producers.
Population Control: Predators and parasites help regulate the population sizes of other organisms, preventing
overpopulation and promoting biodiversity.
2.2.10 Because producers in ecosystems make their own carbon compounds by photosynthesis, they are at the
start of food chains. Consumers obtain carbon compounds from producers or other consumers, so form the
subsequent trophic levels.
List the types of organisms that are typically considered producers in an ecosystem.
Outline the process of photosynthesis and its importance for producers.
Describe the role of primary consumers in a food chain.
Explain how energy flows from primary producers to tertiary consumers in a food chain.
Define the term "trophic level" and identify the trophic levels occupied by producers, primary consumers,
secondary consumers, and tertiary consumers.
List the main differences between herbivores, carnivores, and omnivores in terms of their feeding strategies.
A food chain illustrates the sequential transfer of energy and nutrients among organisms within an ecosystem,
showcasing how energy moves from one organism to another according to their feeding interactions. Arrows are
employed to indicate the direction of energy flow.
Flow of Organic Matter in Food Chains
The flow of organic matter in a food chain follows a unidirectional path from producers to various levels of consumers.
This can be summarized as:
Primary Producers: Capture light energy and convert it into chemical energy in the form of glucose. They form
the base of the food chain.
Primary Consumers (Herbivores): Consume producers and obtain energy stored in plant tissues.
Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers, transferring energy further up
the food chain.
Tertiary Consumers: Higher-level predators that feed on secondary consumers, maintaining the balance of the
ecosystem.
Decomposers: Break down dead organic matter from all trophic levels, recycling nutrients back into the
ecosystem.
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Importance of Food Chains in Ecosystems
Food chains are crucial for understanding the flow of energy and matter in ecosystems. They illustrate how energy
captured by producers is transferred through different trophic levels, sustaining various forms of life. Additionally, food
chains highlight the interdependence of organisms and the importance of each trophic level in maintaining the balance
and health of an ecosystem.
Application of skills: Create a food chain from given data.
The Food Chain
https://www.ahmadcoaching.com/2023/09/define-food-chain-in-science-ecology.html
2.2.11 Carbon compounds and the energy they contain are passed from one organism to the next in
a food chain. The stages in a food chain are called trophic levels.
Outline the process by which primary consumers obtain energy from primary producers.
List three roles of decomposers in an ecosystem.
Explain the significance of decomposers in maintaining the flow of energy and cycling of nutrients within an
ecosystem.
​In ecosystems, carbon compounds and the energy they contain are transferred from one organism to the next through a
sequence of feeding relationships known as a food chain. The different stages in a food chain are referred to as trophic
levels. Each trophic level represents a step in the transfer of energy and matter through the ecosystem.
Trophic Levels in Food Chains
Primary Producers: These are the autotrophs, such as plants, algae, and photosynthetic bacteria, that produce
their own food using sunlight through photosynthesis. They form the first trophic level and are the primary
source of energy and carbon compounds for all other organisms in the ecosystem.
Primary Consumers: These are herbivores that feed directly on the primary producers. They occupy the
second trophic level. Examples include deer, rabbits, and caterpillars.
Secondary Consumers: These are carnivores and omnivores that feed on primary consumers. They occupy
the third trophic level. Examples include frogs, spiders, and lions.
Tertiary Consumers: These are higher-level carnivores that feed on secondary consumers. They occupy the
fourth trophic level. Examples include eagles, sharks, and large predators.
Quaternary Consumers: In some ecosystems, there may be an additional trophic level consisting of apex
predators that have no natural predators. Examples include orcas and large cats like tigers.
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https://raider.pressbooks.pub/biology2/chapter/16trophic-interactions/
Role of Decomposers
Traditionally, decomposers are not included in linear food chains because they do not fit neatly into the sequence of
primary, secondary, and tertiary consumers. Decomposers, such as fungi and bacteria, gain carbon compounds from a
variety of sources, including dead plants, animals, and waste products. However, their role in energy transformations
and nutrient cycling is crucial for the health and sustainability of ecosystems.
Energy Recycling: Decomposers break down dead organic matter, releasing energy and nutrients back into the
ecosystem. This process ensures that energy is not lost entirely but is made available for primary producers to
capture once again through photosynthesis.
Nutrient Cycling: By decomposing organic matter, decomposers convert complex organic compounds into
simpler inorganic forms, such as nitrogen, phosphorus, and potassium, which are essential nutrients for plant
growth. This nutrient recycling maintains soil fertility and supports plant life.
Detrital Food Webs: Decomposers form the base of detrital food webs, where energy and matter flow from
dead organic material to detritivores and other organisms that consume decomposers. These detrital food webs
are interconnected with traditional grazing food webs, creating a complex and interdependent ecosystem.
Breaking Down Toxins: Some decomposers can break down and detoxify harmful substances in the
environment, contributing to the overall health of the ecosystem.
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Energy Flow in Food Webs
Energy flows through an ecosystem in a unidirectional manner from the Sun to producers and then through the various
trophic levels of consumers. The flow of energy along the food chain is in the direction of the arrows and points towards
where the energy is going, and not where it has come from. E
​ cosystems are more complex than what is represented in
simple food chains. In reality, organisms usually do not feed on only one other type of organism
2.2.12 There are losses of energy and organic matter as food is transferred along a food chain.
List the main reasons why not all food available at a given trophic level is harvested.
Describe how digestion and absorption contribute to energy losses in a food chain.
Explain why not all absorbed energy is stored as biomass in an organism.
Define the term "trophic efficiency" and explain its significance in an ecosystem.
Energy and organic matter flow through ecosystems via food chains, but at each trophic level, significant losses occur.
These losses are due to various biological and ecological processes, impacting the efficiency and sustainability of
energy flow in ecosystems.
Energy and Organic Matter Losses at Each Trophic Level:
1. Availability and Harvesting:
1. Uneaten Food: Some plants or animals remain uneaten due to inaccessibility, unpalatability, or
defenses like thorns or toxins.
2. Predation and Competition: Not all available food is harvested due to competition and predator
interactions within each trophic level.
2. Consumption:
1. Partial Ingestion: Organisms often consume only part of their food source, leaving indigestible materials
(e.g., bones, shells, or plant fibers).
2. Waste: Animals discard certain parts, contributing to organic matter that isn’t fully consumed or passed
on.
3. Absorption and Digestion:
1. Incomplete Absorption: Not all ingested nutrients are absorbed; some food exits as waste because the
digestive system does not extract all nutrients.
2. Digestive Efficiency: Differences in digestive efficiency mean some species convert food to energy
more effectively than others.
4. Utilization and Storage:
1. Immediate Metabolic Use: Much of the absorbed energy is used directly for activities like growth,
movement, and cellular repair, rather than stored.
2. Heat Loss: Cellular respiration results in energy loss as heat, which cannot be reused and dissipates
into the environment.
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Implications for Ecosystems:
Reduced Energy Transfer Efficiency: With only about 10% of energy passed to the next trophic level,
ecosystems are limited in the number of trophic levels they can sustain.
Energy Pyramid Structure: The inefficiency of energy transfer results in a pyramid structure, with fewer
organisms supported at higher trophic levels.
PRODUCTIVITY
​2.2.13 Gross productivity (GP) is the total gain in biomass by an organism. Net productivity (NP) is the amount
remaining after losses due to cellular respiration.
Define gross productivity (GP) and net productivity (NP).
List the main differences between GP and NP.
Outline the process by which net productivity is calculated from gross productivity.
Define the term "maximum sustainable yield" in the context of net productivity.
List the factors that could affect the gross productivity of primary producers in an ecosystem.
​ nderstanding the concepts of gross productivity (GP) and net productivity (NP) is essential for analyzing the
U
energy dynamics within ecosystems. These metrics help quantify the energy gain and loss by organisms, providing
insights into the sustainability and efficiency of energy transfer across trophic levels.
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Gross Productivity (GP)
Definition: Total gain in biomass by an organism or trophic level over time.
Producers: GP is the total energy captured from sunlight and converted into chemical energy
(photosynthesis).
Consumers: GP is the total energy obtained from ingested food.
Net Productivity (NP)
Definition: Biomass remaining after accounting for energy lost through respiration (R); represents the energy
available for growth, reproduction, and consumption by the next trophic level
Formula: NP=GP−R
Producers: NP is the energy remaining after plants use some captured energy for metabolic processes.
Consumers: NP is the energy remaining after animals use part of the ingested energy for metabolic
activities like movement and digestion.
Differences Between Producers and Consumers
Producers: Lower respiration rates relative to GP lead to a higher NP, as plants mainly use energy for growth
and basic metabolic functions.
Consumers: Higher respiration rates relative to GP result in a lower NP, as animals expend more energy on
movement, thermoregulation, and complex metabolic processes.
Importance of NP in Ecosystems
Sustainability: NP reflects the maximum sustainable yield that can be harvested without depleting resources. It
indicates the biomass that can be removed (e.g., by grazing or predation) without impacting the ecosystem's
regenerative capacity.
Applications of GP and NP Values
High GP and NP in Producers: Indicates a healthy ecosystem base, supporting a strong food web.
Low NP in Consumers: Highlights high energy losses due to metabolic demands, showing the need for
efficient energy conservation.
Example Calculation
Scenario: A plant captures 100 units of energy (GP) and uses 40 units for respiration (R).
Calculation: NP=GP−R. 100−40 = 60 units.
Interpretation: The 60 units of NP represent energy available for growth, reproduction, and
consumption by herbivores.
​2.2.14 The number of trophic levels in ecosystems is limited due to energy losses.
​List the main reasons why energy is lost at each trophic level in a food chain.
Describe how cellular respiration contributes to energy losses in a food chain.
Explain why only a small percentage of energy is transferred from one trophic level to the next.
Define the term "food chain" and explain why the length of food chains is limited in ecosystems.
Energy flow in ecosystems is guided by the second law of thermodynamics, which emphasizes that energy
transformations are inefficient, leading to energy losses, mainly as heat, at each trophic level.
Key Concepts in Energy Flow
Primary Energy Source: Energy enters an ecosystem through primary producers (plants, algae, and
photosynthetic bacteria) that capture solar energy and convert it into chemical energy via photosynthesis.
Energy Transfer Through Trophic Levels:
Energy flows from primary producers to various consumer levels: primary consumers (herbivores),
secondary consumers (carnivores that eat herbivores), and tertiary consumers (top predators).
At each level, energy is lost due to cellular respiration and metabolic heat loss, reducing the energy
available to higher trophic levels.
Major Causes of Energy Loss
1. Cellular Respiration: Organisms use energy for growth, reproduction, movement, and maintaining
homeostasis. During cellular respiration, energy is converted into ATP for these functions, but a substantial
portion is lost as heat, which dissipates into the environment and is not available for further biological use.
2. Heat Loss: The second law of thermodynamics explains that energy transformations are never fully efficient. As
energy is transferred from one trophic level to the next, a significant amount is lost as heat, which cannot be
recaptured.
Calculating Energy Efficiency
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The efficiency of energy transfer in ecosystems can be calculated using a hypothetical example:
Suppose the Sun provides 20,000 units of energy to primary producers.
Primary producers pass on 2,500 units of energy to primary consumers.
To calculate ecological efficiency (the percentage of energy received by one trophic level that is passed on to the
next), use the following formula:
This calculation shows that approximately 12.5% of the energy received by primary producers is transferred to primary
consumers. This is slightly higher than the commonly cited figure of 10%, which is a generalized approximation. In
reality, the efficiency of energy transfer between trophic levels can vary widely depending on the ecosystem, the species
involved, and specific environmental conditions.
Impact on Trophic Levels and Food Chain Length
10% Rule: Typically, only about 10% or less of the energy at one trophic level is passed on to the next. This low
transfer efficiency results from energy losses primarily due to heat from metabolic processes.
Limit on Food Chain Length: Because so little energy is transferred from one level to the next, food chains
rarely extend beyond four or five trophic levels. By the time energy reaches top predators, it is significantly
reduced, limiting the sustainability of additional trophic levels.
Top Predators: Organisms at the highest trophic levels are typically fewer in number. They have large energy
demands, which require them to consume a substantial biomass from lower levels to meet their energy needs.
This results in a lower population density and a higher vulnerability to changes in the ecosystem.
Application of skills: Work out the efficiency of transfer between trophic levels.
The 10 Percent Rule
2.2.15 Food webs show the complexity of trophic relationships in communities.
Define the term "food web" and explain how it differs from a food chain.
List the different trophic levels that can be found in a food web and provide an example organism for each level.
Outline the role of arrows in a food web and what they represent.
Describe how energy flows through a food web, starting from primary producers to top predators.
Explain why species in a food web may feed at more than one trophic level.
Food webs provide a detailed and interconnected representation of the trophic relationships within ecological
communities. Unlike simple food chains, which depict a linear sequence of energy transfers from one organism to
another, food webs illustrate the complex network of feeding interactions among various species in an ecosystem.
Understanding food webs is crucial for grasping the intricate dynamics of ecosystems and the flow of energy and
biomass.
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​Understanding Food Webs
Complexity of Relationships:
Multiple Interactions: Each species connects with multiple others, reflecting the complexity of natural
ecosystems where organisms have diverse diets and interactions.
Interconnectedness: Food webs highlight species interdependence for energy and nutrients,
demonstrating ecosystem resilience and stability.
Direction of Energy Flow:
Arrows: Arrows show the direction of energy flow from food source to consumer, tracing energy as it
moves through the ecosystem.
Energy Transfer: Arrows indicate the transfer of organic matter from producers to various consumers,
eventually reaching decomposers.
Feeding at Multiple Trophic Levels:
Variable Trophic Positions: Some species, like omnivores, feed at multiple trophic levels, acting as
both primary and secondary consumers.
Diet Flexibility: The ability to feed at multiple levels allows species to adapt to food availability changes,
enhancing ecosystem stability.
Importance of Food Webs in Ecosystems
Energy Dynamics:
Comprehensive View: Food webs offer a detailed view of energy pathways, showing the complex flow
of energy and nutrients in ecosystems.
Ecosystem Stability: Interconnected food webs enhance stability, as impacts from population changes
or species removal can be lessened by alternative pathways for energy flow.
Biodiversity and Ecosystem Health:
Indicator of Biodiversity: A complex food web generally signals high biodiversity and ecosystem
health.
Impact of Changes: Food webs help ecologists predict the effects of species population shifts, such as
extinctions or introductions, on the ecosystem’s structure and function.
Management and Conservation:
Ecosystem Management: Food webs are valuable for predicting outcomes of environmental changes
and human impact on ecosystems.
Conservation Strategies: Insights into species roles and interactions in a food web inform conservation
practices to protect endangered species and maintain ecological balance.
Example of a Simple Food Web
Consider a terrestrial ecosystem consisting of plants, herbivores, carnivores, and decomposers:
Primary Producers: Grass, plants, trees (convert solar energy into biomass through photosynthesis)
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Primary Consumers: Rabbits, deer, insects (herbivores that eat plants)
Secondary Consumers: Frogs, birds, small mammals (carnivores and omnivores that eat herbivores)
Tertiary Consumers: Hawks, foxes, snakes (top predators that eat secondary consumers)
Decomposers: Fungi, bacteria, earthworms (break down dead organic matter, recycling nutrients back into the
ecosystem)
Application of skills: Create a food web from given data.
Exploring Ecosystems: Coastal Food W…
W…
2.2.16 Biomass of a trophic level can be measured by collecting and drying samples.
Define the term "biomass" in the context of an ecosystem.
​Outline the process of drying samples to measure biomass.
Describe how the dry mass of samples approximates the biomass of an organism.
Biomass is the total mass of living or recently living organisms
within a given trophic level, reflecting ecosystem productivity
and energy flow.
Methods of Measuring Biomass
1. Collection and Drying of Samples:
1. Sample Collection: Collect representative
samples of organisms (plants, herbivores, etc.)
from the ecosystem.
2. Drying Samples: Dry samples in an oven at a
constant temperature until they reach a stable weight, removing all moisture to obtain the dry mass.
3. Calculating Biomass: Extrapolate the dry mass to estimate the biomass of the entire trophic level within
a defined area or volume.
2. Measuring Energy Content in Biomass:
1. Combustion of Samples:
1. Burn dried samples to release chemical energy stored in organic matter as heat.
2. Calorimetry:
1. Use a calorimeter to capture and measure the heat released during combustion. This involves
measuring the temperature change in water, which reflects the sample’s energy content.
3. Extrapolation: Scale up the energy content data to estimate the total energy in the trophic level’s
biomass.
Importance of Biomass and Energy Measurements
Ecosystem Productivity:
High biomass and energy content at the primary producer level indicate high ecosystem productivity,
supporting diverse and abundant consumers.
Energy Flow Analysis:
Understanding biomass and energy distribution across trophic levels shows energy availability at each
level and efficiency of energy transfer.
Conservation and Management:
Accurate biomass and energy data support ecosystem management, resource allocation, habitat
protection, and sustainable harvesting practices.
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​ .2.17 Ecological pyramids are used to represent relative numbers, biomass or energy of trophic levels in an
2
ecosystem.
Define the term "ecological pyramid" and explain its purpose in studying ecosystems.
List the three types of ecological pyramids and describe the main characteristic of each type.
Outline the process of constructing a pyramid of biomass.
Describe how a pyramid of energy differs from a pyramid of number.
Define the term "standing crop" and explain its significance in pyramids of number and biomass
Ecological pyramids are graphical representations that illustrate the relative amounts of different parameters—such as
numbers, biomass, or energy—across the various trophic levels within an ecosystem. These pyramids help visualize the
structure and function of ecosystems, making it easier to understand the distribution of organisms and the flow of
energy.
Types of Ecological Pyramids
Pyramids of Number:
Definition: Pyramids of number display the number of individual organisms at each trophic level in an
ecosystem.
Characteristics: These pyramids can vary greatly in shape. For example, in some ecosystems, there
may be a large number of primary producers (e.g., grasses), followed by fewer herbivores (e.g., insects),
and even fewer predators (e.g., birds).
Example: In a grassland ecosystem, the base of the pyramid would be broad, representing numerous
grasses, while the top would be narrow, representing fewer top predators like hawks.
Shape Variations in Pyramids of Number:
Inverted Pyramids: Some pyramids of number can be inverted. For instance, a single tree (one
primary producer) can support numerous herbivorous insects, which in turn support fewer
predators.
Irregular Pyramids: Variations occur due to the size and reproductive rate of organisms. For
example, a large number of small insects feeding on a single plant.
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Pyramids of Biomass:
Definition: Pyramids of biomass represent the total dry mass of all organisms at each trophic level at a
specific time.
Characteristics: These pyramids typically have a more regular shape, with a broad base representing a
large biomass of primary producers and progressively narrower levels representing smaller biomasses
of consumers.
Example: In a forest ecosystem, the base might be wide, indicating a large biomass of trees, with
narrower levels above representing the biomass of herbivores (e.g., deer) and even narrower levels for
predators (e.g., wolves).
Shape Variations in Pyramids of Biomass:
Inverted Biomass Pyramids: In some aquatic ecosystems, inverted pyramids of biomass can
occur where the biomass of primary consumers (zooplankton) exceeds that of the primary
producers (phytoplankton). This happens because phytoplankton reproduce rapidly and are
consumed quickly, maintaining a lower biomass at any given time.
Regular Biomass Pyramids: Typically, in terrestrial ecosystems, pyramids of biomass have a
broad base and narrow top, reflecting the accumulation of biomass at the producer level and
decreasing biomass at higher trophic levels.
https://commons.wikimedia.org/wiki/File:Biomass_Pyramid.svg
Pyramids of Energy (Pyramids of Productivity):
Definition: Pyramids of energy show the amount of energy flowing to each trophic level per unit area
and per unit time, usually measured in kilojoules per square meter per year (kJ m⁻² year⁻¹).
Characteristics: These pyramids always have a traditional pyramid shape because energy transfer
between trophic levels is inefficient (approximately 10% efficiency), leading to a significant decrease in
available energy at each successive level.
Example: In any ecosystem, the base of the pyramid would represent the primary producers with the
highest energy capture, and the top would represent tertiary consumers with the least energy available.
Shape Variations in Pyramids of Energy:
Consistent Shape: Pyramids of energy are always upright and never inverted because energy
transfer is unidirectional and inefficient. Energy is lost at each trophic level due to metabolic
processes and heat loss.
Importance: These pyramids provide a clear picture of the energy dynamics and the efficiency
of energy transfer within ecosystems.
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Importance of Ecological Pyramids
Ecosystem Analysis: Ecological pyramids help ecologists analyze the structure and function of ecosystems by
visualizing the distribution of organisms, biomass, and energy.
Conservation and Management: Understanding the flow of energy and distribution of biomass aids in
ecosystem management and conservation efforts, helping to identify critical trophic levels and potential impacts
of changes.
Educational Tool: These pyramids serve as effective tools for teaching ecological concepts and illustrating the
principles of energy flow and trophic relationships.
Application of skills:
Create pyramids of numbers, biomass and energy from given data.
Follow experimental procedures on how to find biomass and energy from biological samples (plant material
only).
Ecological Pyramids
POLLUTANTS AND HUMAN IMPACT
2.2.18 Pollutants that are non-biodegradable, such as polychlorinated biphenyl (PCB),
dichlorodiphenyltrichloroethane (DDT) and mercury, cause changes to ecosystems through the processes of
bioaccumulation and biomagnification.
Define the term "non-biodegradable pollutant" and provide two examples.
Define the term "biomagnification" and explain its significance in an ecosystem.
Outline the differences between bioaccumulation and biomagnification.
List the processes through which non-biodegradable pollutants enter and persist in ecosystems.
List the potential ecological and health impacts of bioaccumulation and biomagnification.
Non-biodegradable pollutants are substances that do not break down naturally in the environment. They resist
decomposition by natural processes and, as a result, can persist for long periods. These pollutants persist in the
environment and can cause significant ecological harm through the processes of bioaccumulation and biomagnification
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Polychlorinated Biphenyls (PCBs):
Industrial chemicals used in electrical equipment, which are highly persistent and toxic.
Dichlorodiphenyltrichloroethane (DDT):
A pesticide that, despite its ban in many countries, remains in the environment due to its stability and
persistence.
Mercury:
A heavy metal released from industrial processes and mining, which is highly toxic and accumulates in
living organisms.
https://capemaywhalewatch.com/blog/biomagnification-and-persistence-of-chemical-marine-pollution/
Bioaccumulation refers to the gradual build-up of non-biodegradable pollutants in an organism or trophic level over
time. This occurs because these pollutants are absorbed faster than they are excreted or metabolized. As a result, their
concentration increases within the individual organism.
Process:
Organisms absorb pollutants from their environment (water, soil, air) or through their diet. Since the
pollutants are non-biodegradable, they accumulate in the tissues, especially in fat and other lipid-rich
tissues.
Examples:
Fish in contaminated waters may accumulate mercury in their tissues.
Birds that ingest prey exposed to DDT may accumulate the pesticide in their bodies.
Biomagnification refers to the increasing concentration of non-biodegradable pollutants as they move up the food
chain. This occurs because predators consume multiple prey items, each containing the pollutant, leading to higher
concentrations in the predator's body.
Process:
At each trophic level, organisms consume others that have accumulated pollutants. Since energy
transfer between trophic levels is inefficient (only about 10% of energy is passed on), the biomass at
higher levels is much lower. However, the pollutants are not metabolized or excreted effectively, resulting
in higher concentrations in the predator's tissues.
Examples:
Small aquatic organisms like plankton absorb pollutants from the water. Small fish eat large quantities of
plankton, accumulating higher pollutant levels. Larger fish, birds, or mammals then eat these fish,
leading to even higher concentrations.
Top predators, such as eagles or polar bears, may exhibit extremely high levels of pollutants like PCBs
or DDT in their tissues, affecting their health and reproduction.
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Ecological and Health Impacts
The processes of bioaccumulation and biomagnification can have severe consequences for ecosystems and the
organisms within them:
Health Effects:
High concentrations of pollutants can cause toxic effects, including reproductive failure, immune system
suppression, and developmental abnormalities in wildlife. For example, DDT exposure has been linked
to eggshell thinning in birds, leading to reduced reproductive success.
Ecosystem Changes:
Pollutant accumulation can alter species composition and abundance, disrupting food webs and
ecosystem stability. Predators with high pollutant loads may experience population declines, affecting
the entire ecosystem structure.
Mitigation and Management
Addressing the impacts of non-biodegradable pollutants requires comprehensive strategies, including:
Regulation and Bans:
Many countries have banned or restricted the use of harmful chemicals like DDT and PCBs to reduce
their release into the environment.
Cleanup Efforts:
Contaminated sites, such as polluted rivers or industrial areas, require cleanup and remediation to
remove or neutralize pollutants.
Monitoring and Research:
Continuous monitoring of pollutant levels in the environment and research on their effects help inform
policy decisions and conservation efforts.
Bioaccumulation and Biomag…
Biomag…
Biomagnification and the Trou…
Trou…
​2.2.19 Non-biodegradable pollutants are absorbed within microplastics, which increases their transmission in
the food chain.
Define the term "microplastics" and explain their origin.
List the sources of microplastics in the environment.
Outline the process by which microplastics absorb non-biodegradable pollutants.
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Describe how microplastics are ingested by organisms in lower trophic levels.
​ lastics are materials that can be shaped when soft and retain that shape when hardened. Plastic can be synthetic or
P
naturally occurring and are polymers. A polymer is like a chain of individual components linked together.
Understanding Microplastics
Definition and Sources:
Microplastics are tiny plastic particles less than 5 mm in diameter.
They originate from:
Breakdown of larger plastics.
Microbeads in personal care products.
Synthetic fibers shed from clothing.
Various industrial processes.
Persistence and Environmental Impact:
Microplastics are non-biodegradable, meaning they do not easily decompose and can persist in
ecosystems for long durations.
They absorb and concentrate pollutants, which increases the risk of transmission through the food chain.
Studies show that microplastics can carry persistent organic pollutants (POPs), enhancing their impact
on marine environments.
Absorption of Non-Biodegradable Pollutants
Pollutant Absorption:
Microplastics can absorb harmful chemicals, including:
Heavy metals.
PCBs (polychlorinated biphenyls).
DDT (dichlorodiphenyltrichloroethane).
These chemicals adhere to or become embedded in the plastic particles.
Transport and Transmission:
Pollutant-laden microplastics can be transported through environmental pathways such as water
currents and wind.
As they travel, they pose a risk of entering food chains and impacting marine life and ecosystems.
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The Story of Microplastic
Microplastics in Food Chains
Ingestion by Organisms:
Lower Trophic Levels: Small organisms like plankton and fish often ingest microplastics, mistaking
them for food. This results in the accumulation of microplastics and pollutants within their bodies.
Higher Trophic Levels: Predators that consume these smaller organisms ingest the microplastics as
well, leading to bioaccumulation (increasing concentration in an organism) and biomagnification
(increasing concentration up the food chain).
Ecological and Health Impacts
Ecological Effects:
Toxicity: Absorbed pollutants can be toxic, causing growth and reproductive issues, and higher mortality
in affected species. Physical blockages from microplastics can damage digestive systems.
Biodiversity Loss: The combined effects of toxicity and physical harm can reduce biodiversity,
destabilizing ecosystems and disrupting natural functions.
Human Health Concerns:
Seafood Contamination: Humans consuming seafood may ingest microplastics and pollutants, with
potential health risks, including chemical exposure and digestive issues.
Long-Term Impacts: Long-term health effects are still under study, but concerns include links to cancer,
endocrine disruption, and other chronic conditions.
Mitigation and Management
Pollution Control:
Reducing Plastic Waste: Bans on single-use plastics, improved waste management, and recycling can
reduce microplastic pollution.
Cleanup Efforts: Cleaning up plastic debris in oceans, rivers, and coastal areas can reduce microplastic
sources.
Research and Monitoring:
Monitoring Programs: Tracking microplastic pollution and its impacts on ecosystems and human health
supports informed decision-making.
Scientific Research: Ongoing research is essential for understanding the impacts of microplastics and
developing effective mitigation policies.
Example of Microplastic Pollution:
Case Study: Marine Ecosystems:
Primary Producers and Primary Consumers: In marine ecosystems, microplastics are ingested by
small organisms like plankton and small fish. These primary consumers accumulate both the
microplastics and the absorbed pollutants.
Secondary and Tertiary Consumers: Larger fish, seabirds, and marine mammals that feed on the
contaminated primary consumers accumulate higher concentrations of microplastics and pollutants. For
instance, fish such as anchovies and sardines can ingest significant amounts of microplastics, which are
then passed on to predators like tuna, seals, and seabirds.
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2.2.20 Human activities, such as burning fossil fuels, deforestation, urbanization and agriculture, have impacts
on flows of energy and transfers of matter in ecosystems.
Define the term "deforestation" and explain its impact on primary productivity in ecosystems.
List three human activities that affect the flows of energy and transfers of matter in ecosystems.
Outline the process by which burning fossil fuels can both increase and decrease primary productivity.
Describe the effects of urbanization on natural ecosystems and food webs.
Explain how agriculture can lead to the disruption of energy flows and matter transfers in ecosystems.
​Human activities, including burning fossil fuels, deforestation, urbanization, and agriculture, significantly affect the flows
of energy and transfers of matter within ecosystems. These activities disrupt natural processes, leading to changes in
ecosystem structure, function, and productivity.
Burning Fossil Fuels
​Burning fossil fuels releases CO2 into the atmosphere and causes global warming as well as air
pollution ​
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Increased CO2 for Photosynthesis:
Positive Impact:
Enhanced Photosynthesis: The release of CO₂ from fossil fuel combustion can increase the
CO₂ available to plants, potentially enhancing photosynthesis and boosting primary productivity.
Negative Impacts:
Pollutant Effects: Fossil fuel combustion releases other harmful pollutants like sulfur dioxide
(SO₂), nitrogen oxides (NOx), and particulate matter, which can damage plant tissues and reduce
photosynthetic efficiency.
Global Warming: Increased atmospheric CO₂ contributes to global warming, leading to extreme
weather events, shifting growing seasons, and potential decreases in overall primary productivity.
Ecosystem Disruption: Altered weather patterns and growing conditions can impact plant
growth and food webs, disrupting entire ecosystems and reducing biodiversity.
How does photosynthesis respond to c…
c…
Global Warming:
Climate Change:
Enhanced Greenhouse Effect:
Increased CO₂ levels amplify the
greenhouse effect, leading to global
warming and altering climate
patterns.
Ecosystem Impact: Shifts in
temperature and weather patterns
affect ecosystems by changing
species distributions, reducing
ecosystem health, and potentially
lowering photosynthetic rates and
primary productivity.
https://www.researchgate.net/figure/Atmospheric-CO2-level-andSeawater-pH-in-the-North-Pacific-8_fig2_336813938
Ocean Acidification:
CO₂ Absorption by Oceans: As atmospheric CO₂ rises, oceans absorb more CO₂, leading to
increased acidity.
Impact on Marine Life: Acidification harms marine organisms with calcium carbonate structures
(e.g., corals, shellfish), weakening their shells and skeletons.
Ecosystem Disruption: Acidification impacts marine biodiversity and food webs, potentially
reducing marine productivity and affecting species reliant on these ecosystems.
Deforestation
Deforestation involves removing trees from a wide area of land. The purpose could be to clear the land for farming,
make way for mining activities, or to use the wood for timber or manufacturing​
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Loss of Biomass and Photosynthesis:
Reduced Primary Productivity: Deforestation involves the removal of large areas of forest, leading to a
significant loss of biomass and a decrease in the area available for photosynthesis. This reduces the
overall primary productivity of the ecosystem.
Carbon Sequestration: Forests act as carbon sinks, sequestering CO2 from the atmosphere.
Deforestation reduces this capacity, leading to higher atmospheric CO2 levels and contributing to global
warming.
Disruption of Food Webs:
Habitat Loss: The removal of trees and other vegetation destroys habitats, leading to the displacement
or extinction of species. This disruption of food webs affects the flow of energy and the transfer of matter,
altering ecosystem dynamics and reducing biodiversity.
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Urbanization
Urbanization involves the movement of people from rural to urban areas and the associated activities of building human
settlements. This process involves removing or disrupting ecosystems to make space for human-construction
Alteration of Natural Landscapes
Land Conversion:
Urbanization: Natural landscapes are replaced by buildings, roads, and infrastructure, reducing
areas available for photosynthesis and primary productivity.
Fragmentation:
Habitat Isolation: Urban development fragments habitats, creating isolated patches that disrupt
animal movement, breeding, and feeding patterns, ultimately impacting food webs and energy
flow within ecosystems.
Pollution and Waste
Air and Water Pollution:
Urban Emissions: Pollutants from vehicles and industry harm plant and animal health, reduce
photosynthesis, and disrupt ecosystems by affecting food webs and biodiversity.
Waste Generation:
Contamination: Increased waste from urban areas leads to soil and water pollution, impacting
plant growth and animal health and contributing to broader ecosystem degradation.
Effects of Urbanization on Str…
Str…
Urbanization and the Environ…
Environ…
Agriculture
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Agriculture involves growing crops for food or other purposes such as clothes. This usually involves clearing land to
grow crops. The food webs and other plants that are native to the environment are removed and destroyed.
Land Use and Biomass:
Conversion of Natural Ecosystems: Agricultural activities often involve clearing natural ecosystems to
create farmland, leading to a loss of biomass and a reduction in primary productivity.
Monoculture: The practice of monoculture (growing a single crop over a large area) reduces
biodiversity, making ecosystems more vulnerable to pests, diseases, and extreme weather events.
Chemical Inputs:
Fertilizers and Pesticides: The use of fertilizers and pesticides can lead to nutrient runoff and
contamination of water bodies, causing eutrophication and harming aquatic life. These chemicals can
also disrupt soil health and microbial communities, affecting nutrient cycling and energy flows.
Irrigation:
Water Use: Irrigation practices can deplete water resources, affecting the availability of water for natural
ecosystems. Over-irrigation can lead to soil salinization, reducing soil fertility and plant productivity.
What is the Environmental Impact of F…
F…
HL ONLY
This unit will take a minimum of 2 hours
​2.2.21 Autotrophs synthesize carbon compounds from inorganic sources of carbon and other elements.
Heterotrophs obtain carbon compounds from other organisms.
Define the term "autotroph" and provide two examples.
Define the term "heterotroph" and explain how heterotrophs obtain their carbon compounds.
List the main differences between photoautotrophs and chemoautotrophs.
Outline the process by which autotrophs synthesize carbon compounds from inorganic sources.
Describe the role of heterotrophs in an ecosystem.
Explain how autotrophs contribute to the carbon cycle.
Classification of Organisms by Carbon Acquisition
In ecosystems, organisms are categorized based on how they obtain carbon compounds, either as autotrophs (selfsustainers) or heterotrophs (consumers), each playing a critical role in energy flow and nutrient cycling.
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Autotrophs (Primary Producers)
Definition: Organisms that create their own organic compounds from inorganic sources using environmental
energy.
Types of Autotrophs
1. Photoautotrophs:
1. Use light energy to perform photosynthesis, converting CO₂ and H₂O into glucose and O₂.
2. Examples:
1. Plants: Trees, grasses, shrubs.
2. Algae: Unicellular (phytoplankton) and multicellular (seaweeds).
3. Photosynthetic Bacteria: Cyanobacteria (blue-green algae).
2. Chemoautotrophs:
1. Use the oxidation of inorganic molecules like H₂S or NH₃ to create organic compounds.
2. Examples:
1. Sulfur Bacteria: Found in deep-sea hydrothermal vents.
2. Nitrifying Bacteria: Soil bacteria involved in the nitrogen cycle.
Role in Ecosystems
Primary Production: Form the foundation of the food web by producing organic compounds.
Energy Conversion: Convert solar or chemical energy into a form usable by heterotrophs.
Carbon Fixation: Capture CO₂ from the atmosphere, helping regulate CO₂ levels.
Heterotrophs (Consumers)
Definition: Organisms that acquire organic carbon by consuming other organisms or organic matter.
Types of Heterotrophs
1. Herbivores: Feed directly on autotrophs (plants/algae).
1. Examples: Deer, rabbits, caterpillars.
2. Carnivores: Consume other animals.
1. Examples: Lions, eagles, sharks.
3. Omnivores: Eat both plants and animals.
1. Examples: Humans, bears, pigs.
4. Detritivores: Consume dead organic material (detritus).
1. Examples: Earthworms, millipedes, woodlice.
5. Saprotrophs: Decompose organic material by secreting enzymes and absorbing nutrients.
1. Examples: Fungi, many bacteria.
Role in Ecosystems
Energy Transfer: Move energy through trophic levels by consuming other organisms.
Nutrient Recycling: Detritivores and saprotrophs break down dead material, recycling nutrients.
Population Control: Predators and parasites help regulate population sizes, maintaining balance.
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https://www.sciencefacts.net/heterotroph.html
Autotrophs and Heterotrophs
2.2.22 Photoautotrophs use light as an external energy source in photosynthesis. Chemoautotrophs use
exothermic inorganic chemical reactions as an external energy source in chemosynthesis.
Define the term "photoautotroph" and provide two examples.
List the main differences between photoautotrophs and chemoautotrophs.
Outline the process of photosynthesis in photoautotrophs, including the key reactants and products.
Describe the role of chemoautotrophs in ecosystems where light is scarce or absent.
In ecosystems, autotrophs are essential primary producers, creating organic matter from inorganic sources. They can
be divided into two main types based on their energy source: photoautotrophs, which rely on sunlight, and
chemoautotrophs, which utilize chemical energy from inorganic compounds.
Photoautotrophs
Energy Source: Light energy from the Sun.
Photosynthesis Process:
Light Energy Capture: Use pigments like chlorophyll to capture sunlight.
Inputs: Carbon dioxide (CO₂) from the atmosphere and water (H₂O) from the soil.
Outputs: Produce glucose (C₆H₁₂O₆) as a stored energy source and release oxygen (O₂) as a byproduct.
Equation
6 CO2+6 H2O+light energy→C6H12O6+6 O2
Examples of Photoautotrophs:
Plants: All green plants, such as trees, shrubs, and grasses.
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Algae: Both unicellular (e.g., phytoplankton) and multicellular (e.g., seaweeds) forms.
Photosynthetic Bacteria: Cyanobacteria, also known as blue-green algae.
Role in Ecosystems:
Primary Producers: Photoautotrophs form the base of most terrestrial and aquatic food webs, providing
energy and organic matter for heterotrophs.
Oxygen Production: They produce oxygen, which is essential for the respiration of aerobic organisms.
https://www.mdpi.com/1996-1944/14/11/3027
Chemoautotrophs are organisms that use exothermic inorganic chemical reactions as an external energy source to
drive the process of chemosynthesis. They convert inorganic molecules into organic molecules in environments where
light is scarce or absent.
Process of Chemosynthesis:
Chemical Energy: Chemoautotrophs obtain energy by oxidizing inorganic substances such as hydrogen
sulfide (H₂S), ammonia (NH₃), or ferrous iron (Fe²⁺).
Carbon Dioxide and Inorganic Molecules: They use CO₂ as a carbon source and inorganic molecules
as electron donors to produce organic compounds.
Equation: A general equation for chemosynthesis by sulfur bacteria is:
CO2+O2+4H2S→CH2O+4S+3H2O\text{CO}_2 + \text{O}_2 + 4\text{H}_2\text{S} \rightarrow
\text{CH}_2\text{O} + 4\text{S} + 3\text{H}_2\text{O}CO2​+O2​+4H2​S→CH2​O+4S+3H2​O
Examples of Chemoautotrophs:
Sulfur Bacteria: Found in deep-sea hydrothermal vents and hot springs.
Nitrifying Bacteria: Found in soil, involved in the nitrogen cycle (e.g., Nitrosomonas and Nitrobacter).
Iron-Oxidizing Bacteria: Found in environments with high levels of iron, such as acid mine drainage.
Role in Ecosystems:
Primary Producers in Dark Environments: Chemoautotrophs are the principal source of energy in
ecosystems where there is little or no light, such as deep-sea hydrothermal vents, underground caves,
and sulfur-rich hot springs.
Support Unique Food Webs: In these environments, chemoautotrophs support unique and diverse
communities of organisms that rely on chemical energy rather than sunlight
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Chemosynthetic Life
Importance of Photoautotrophs and Chemoautotrophs
Energy Conversion:
Photoautotrophs: Convert solar energy into chemical energy, making it accessible to other organisms
in the ecosystem.
Chemoautotrophs: Convert chemical energy from inorganic molecules into organic molecules,
sustaining ecosystems in the absence of light.
Ecosystem Productivity:
Both types of autotrophs are essential for the productivity and stability of ecosystems, providing the
energy foundation for food webs.
Adaptation to Diverse Environments:
Photoautotrophs thrive in environments with abundant light, such as forests, grasslands, and ocean
surfaces.
Chemoautotrophs are adapted to extreme environments with harsh conditions where light is unavailable,
showcasing the diversity of life strategies on Earth.
2.2.23 Primary productivity is the rate of production of biomass using an external energy source and inorganic
sources of carbon and other elements.
Define the term "primary productivity" and explain its significance in an ecosystem.
Define the term "net primary productivity" and explain its role in energy transfer within an ecosystem.
List the differences between gross primary productivity (GPP) and net primary productivity (NPP).
Outline the process of measuring primary productivity in a laboratory setting using photosynthesizing samples.
Primary productivity is a critical ecological metric that quantifies the rate at which biomass is produced by autotrophs
(primary producers) using external energy sources and inorganic materials. It provides insights into the energy available
to support food webs and the overall health and functioning of ecosystems.
Primary Productivity refers to the rate at which primary producers, such as plants, algae, and some bacteria, convert
inorganic carbon (CO₂) and other elements into organic compounds using an external energy source. This process is
fundamental to the creation of biomass that fuels ecosystems.
Gross Primary Productivity (GPP): The total rate of photosynthesis, including the energy used by plants for
respiration.
Net Primary Productivity (NPP): The rate of biomass accumulation after accounting for the energy expended
on plant respiration. It represents the energy available to consumers in the ecosystem.
Units of Measurement:
Primary productivity is often measured in kg carbon m-2 yr-1. This unit quantifies the amount of carbon fixed into
biomass over a specific area and time period.
Measuring Productivity
Laboratory Measurements:
Photosynthesizing Samples: In a controlled laboratory environment, primary productivity can be
estimated by measuring the rate of photosynthesis in samples of primary producers.
Oxygen Production: One common method involves measuring the amount of oxygen produced by
plants or algae, as oxygen is a byproduct of photosynthesis.
Carbon Dioxide Uptake: Another approach is to measure the uptake of CO₂, which is directly related to
the production of organic carbon.
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Field Measurements:
Biomass Change Over Time: In the field, primary productivity can be estimated by measuring the
change in biomass of primary producers over time. For example, in a grassland ecosystem, researchers
can measure the biomass of grass at the beginning and end of a growing season to estimate
productivity.
Harvest Method: This involves harvesting plant material from a known area, drying it to remove water
content, and weighing it to determine the biomass produced.
Non-Destructive Methods: These include measuring plant height, density, and coverage as proxies for
biomass, allowing continuous monitoring without destroying the samples.
Importance of Productivity
Energy Availability:
Productivity determines the amount of energy available to support all other trophic levels in an
ecosystem. Higher productivity typically indicates a more robust and diverse ecosystem.
Ecosystem Health:
Monitoring productivity helps ecologists assess the health and functioning of ecosystems. Declines in
productivity can indicate environmental stress or degradation.
Carbon Cycling:
Productivity plays a crucial role in the global carbon cycle, as it represents the rate at which CO₂ is
removed from the atmosphere and fixed into organic matter.
Management and Conservation:
Understanding productivity is essential for managing natural resources, conserving biodiversity, and
predicting the impacts of environmental changes such as climate change.
https://www.quora.com/In-environmental-science-what-is-gross-primary-productivity
2.2.24 Secondary productivity is the gain in biomass by consumers using carbon compounds absorbed and
assimilated from ingested food.
Define the term "secondary productivity" and explain how it is calculated.
Define the term "assimilation" and explain its significance in secondary productivity.
List the main processes involved in secondary productivity.
Outline the importance of secondary productivity in food webs.
Describe the role of faecal waste in the calculation of secondary productivity.
Explain how secondary productivity contributes to nutrient cycling within an ecosystem.
Secondary productivity represents the gain in biomass by consumers (heterotrophs) as they absorb and assimilate
carbon compounds from their food. This process is fundamental for understanding energy and nutrient flow within food
webs.
Definition:
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Secondary productivity is the accumulation of biomass by consumers through the ingestion, digestion,
and assimilation of carbon compounds from other organisms.
Importance in Food Webs:
It supports higher trophic levels by transferring energy and nutrients up the food chain.
Maintains ecosystem dynamics by enabling energy flow from producers to various levels of consumers.
Role in Ecosystem Dynamics:
Provides energy for growth, reproduction, and maintenance of organisms in higher trophic levels.
Contributes to the stability of food webs by ensuring energy availability across trophic interactions.
Net Secondary Productivity (NSP) measures the rate at which consumers generate biomass or energy per unit area
per unit time, after accounting for losses due to respiration. NSP provides a clearer picture of the actual energy or
biomass available to higher trophic levels within an ecosystem.
Definition:
NSP = GSP - R, where:
GSP (Gross Secondary Productivity) is the total
energy assimilated by consumers from ingested
food.
R is the energy lost to cellular respiration.
Significance of NSP:
More Accurate Measure: Unlike GSP, NSP accounts for
energy lost through respiration, making it a more
meaningful indicator of the energy truly available to
organisms at higher trophic levels.
https://collegedunia.com/exams/productivity-inecosystem-biology-articleid-1356
Ecosystem Productivity: NSP indicates the net gain in
consumer biomass, which sustains predators and decomposers within food webs.
Units:
Expressed in terms of mass or energy per unit area per unit time, commonly g m⁻² yr⁻¹ or similar.
Gross secondary productivity (GSP) measures the amount of biomass
assimilated by animals (herbivores and carnivores) after accounting
for the portion lost through feces (egestion).
Calculation of GSP:
GSP = Biomass eaten - Biomass lost as feces.
Represents the total biomass assimilated from
ingested food.
Assimilated Energy Use:
Metabolic Processes: A large portion of assimilated
energy is used for activities such as respiration,
growth, and reproduction.
New Biomass: The remaining energy is stored as new biomass that can be passed on to the next
trophic level.
Units of Measurement: Secondary productivity is typically expressed as mass per unit area per unit time, e.g.,
grams per square meter per year (g m⁻² yr⁻¹).
Processes Involved in Secondary Productivity
Ingestion:
Consumers take in food containing carbon compounds from primary producers (e.g., plants and algae)
or other consumers.
The food includes various organic materials such as carbohydrates, proteins, and fats.
Absorption and Assimilation:
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Through digestion, food is broken down into smaller molecules, which are absorbed through the gut
lining into the bloodstream.
These nutrients are then assimilated into cells and tissues, supporting growth and maintenance.
Faecal Waste:
Not all ingested food is digested and absorbed; undigested materials are excreted as faecal waste.
Faecal waste is excluded from secondary productivity calculations as it doesn’t contribute to biomass
gain.
Importance of Secondary Productivity
Energy Transfer:
Secondary productivity measures the energy available to higher trophic levels (e.g., predators and
scavengers).
It reflects the efficiency with which consumers convert energy and nutrients from food into new biomass.
Food Web Dynamics:
Secondary productivity offers insights into energy and matter flow within food webs.
It indicates ecosystem health and sustainability, showing the effectiveness of energy transfer from
producers to consumers.
Nutrient Cycling:
Processes like ingestion, digestion, absorption, and excretion contribute to nutrient cycling.
Secondary productivity aids in decomposing organic matter and recycling nutrients back into the
ecosystem, supporting overall ecosystem function.
https://old-ib.bioninja.com.au/standard-level/topic-4-ecology/42-energy-flow/ecological-productivity.html
2.2.25 Net primary productivity is the basis for food chains because it is the quantity of carbon compounds
sustainably available to primary consumers.
Define the term "net primary productivity" and explain its significance in an ecosystem.
List the main differences between gross primary productivity (GPP) and net primary productivity (NPP).
Outline the process by which NPP is calculated from GPP and respiration.
Describe the role of NPP in supporting primary consumers in a food chain
Net Primary Productivity (NPP) is the biomass produced by primary producers that remains available for
consumption by primary consumers after accounting for energy used in respiration. This measure is essential for
understanding energy flow, ecosystem dynamics, and sustainable resource use.
Units: NPP is typically expressed as mass per unit area per unit time (e.g., g m⁻² yr⁻¹).
Formula: NPP = Gross Primary Productivity (GPP) - Respiration (R)
Importance of Net Primary Productivity
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Basis for Food Chains:
Energy Source: NPP is the primary energy source for herbivores (primary consumers), which in turn
support higher trophic levels in the food chain.
Sustainable Yield: Represents the amount of biomass available for herbivores without depleting primary
producer levels, ensuring ecosystem productivity over time.
Sustainable Harvesting:
Natural Ecosystems: NPP indicates the biomass herbivores can consume sustainably, supporting the
food web and ecosystem stability.
Agricultural Systems: In agriculture, NPP guides sustainable crop yields, supporting food and feed
production without degrading the soil or ecosystem health.
Forestry (Silvicultural Systems): In forestry, NPP measures the sustainable yield of timber and forest
products, aiding in forest health and preventing resource depletion.
Implications of Net Primary Productivity
Ecosystem Health:
Indicator of Productivity: High NPP values reflect robust primary production, supporting diverse
consumer populations and indicating ecosystem vitality.
Environmental Change Detection: Variations in NPP may reflect shifts in climate, nutrient levels, or
environmental disturbances like deforestation or pollution.
Resource Management:
Sustainable Practices: Understanding NPP helps inform sustainable practices in agriculture, forestry,
and conservation, aligning harvesting rates with ecosystem regenerative capacity.
Biodiversity Conservation: Maintaining high NPP supports biodiversity by ensuring energy and habitat
for a wide range of species, enhancing ecosystem resilience.
Global Carbon Cycle:
Carbon Sequestration: NPP sequesters CO₂ from the atmosphere, storing it in biomass, which is
crucial for mitigating climate change and stabilizing atmospheric CO₂ levels.
Application of skills: Use laboratory and field techniques for measuring primary and secondary productivity and
work out GP and NP from data.
Net Primary Productivity
2.2.26 Maximum sustainable yields (MSYs) are the net primary or net secondary productivity of a system.
Define the term "maximum sustainable yield" (MSY) and explain its significance in resource management.
List the differences between net primary productivity (NPP) and net secondary productivity (NSP) in the context
of MSYs.
Outline the process of determining MSY in a forest ecosystem.
Describe how MSY is applied in fisheries management.
Explain the importance of environmental stability for maintaining MSY in natural ecosystems.
MSY represents the highest rate at which biomass can be harvested from an ecosystem without affecting its ability to
regenerate over time. This concept balances resource extraction with the long-term sustainability of ecosystems and
applies to both primary and secondary productivity:
Net Primary Productivity (NPP): MSY in plant-based systems, indicating the maximum harvestable biomass of
plants or algae.
Net Secondary Productivity (NSP): MSY in animal-based systems, like the maximum sustainable harvest of
fish, livestock, or wildlife.
MSYs in Natural Ecosystems
Forests:
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Timber Harvesting: Ensures that tree cutting aligns with natural regeneration rates.
Non-Timber Products: Involves sustainable collection of forest products like fruits, nuts, and medicinal
plants.
Wildlife:
Game Management: Sets hunting quotas to maintain stable wildlife populations.
Fisheries:
Fish Stocks: Establishes catch quotas based on fish reproductive rates to avoid overfishing.
Marine Ecosystems: Maintains fish population health and marine ecosystem balance through
sustainable practices.
http://ib.bioninja.com.au).
Maximum Sustainable Yield (MSY) - EX…
EX…
MSYs in Agricultural Systems
Crop Production:
Sustainable Harvesting: Maximizes crop yield without depleting soil nutrients or damaging land.
Soil Health: Preserves soil structure and nutrients through crop rotation, cover cropping, and organic
amendments.
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Livestock:
Grazing Management: Manages grazing intensity to prevent overgrazing, using rotational grazing and
appropriate stocking rates.
Animal Health: Ensures livestock productivity through adequate nutrition, healthcare, and living
conditions.
MSYs in Silvicultural Systems
Timber Plantations:
Sustainable Forestry: Harvests trees at a rate that allows for continuous growth, maintaining steady
timber supplies.
Selective Logging: Harvests only certain trees, helping to preserve biodiversity and ecosystem stability.
Non-Timber Forest Products:
Sustainable Harvesting: Applies to products like resin or rubber, ensuring that collection allows for
regeneration.
Key Considerations for Determining MSYs
Environmental Conditions: Stable conditions are essential for sustainable yields; factors like climate change
and habitat quality can impact MSY stability.
Ecosystem Dynamics: Predator-prey relationships, competition, and nutrient cycling need to be understood to
set sustainable MSYs.
Monitoring and Adaptation: Regular stock and environmental monitoring allow for adjustments to MSYs as
conditions change.
Socioeconomic Factors: Balances ecological sustainability with the needs of local communities and
economies to support well-being and livelihoods.
2.2.27 Sustainable yields are higher for lower trophic levels.
List the environmental impacts associated with high levels of meat consumption and animal farming.
Describe the environmental benefits of consuming plant-based foods over animal-based foods from higher
trophic levels.
Explain how land and water requirements differ between plant-based food production and animal-based food
production.
Sustainable yields are the harvest rates that allow resources to replenish and remain available in the future. Achieving
higher sustainable yields is more feasible at lower trophic levels, particularly with plant-based foods, due to greater
energy efficiency, reduced resource use, and lower environmental impact.
Why Sustainable Yields Are Higher at Lower Trophic Levels
Energy Efficiency:
Energy Transfer: Only about 10% of energy at one trophic level is passed to the next, making energy
capture most efficient at the primary producer level (plants).
Lower Energy Loss: Directly consuming plants requires fewer energy transfers, making it more efficient
than consuming animals that feed on plants.
Resource Use:
Land and Water: Growing plants generally requires less land and water than raising livestock,
especially larger animals.
Feed Conversion Ratios: Animals require substantial amounts of plant-based food to produce meat,
while plants are consumed directly, maximizing resource efficiency.
Environmental Impact:
Greenhouse Gas Emissions: Plant-based food production emits fewer greenhouse gases than animalbased systems, with livestock, especially ruminants, contributing significant methane emissions.
Pollution: Intensive animal farming can lead to water contamination and pollution, whereas plant
farming typically has a lower environmental footprint.
Biodiversity and Ecosystem Health:
Habitat Conservation: Plant farming can support biodiversity, especially through integrated practices
like agroforestry.
Sustainable Practices: Techniques like crop rotation and permaculture improve soil health and help
maintain ecosystem services, supporting higher sustainable yields over time.
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Implications for Sustainable Food Production
Dietary Choices:
Plant-Based Diets: Shifting toward plant-based diets lowers ecological footprints by supporting more
efficient energy use and conserving resources.
Reduced Meat Consumption: Decreasing meat consumption, especially from higher trophic levels,
conserves natural resources and reduces environmental harm.
Agricultural Practices:
Sustainable Farming: Emphasis on organic farming, regenerative practices, and precision agriculture
enhances productivity while preserving ecosystems.
Innovation in Crop Production: Advances in crop breeding, biotechnology, and water management
improve sustainable yields in plant-based foods.
Policy and Education:
Promoting Sustainability: Policies that support sustainable farming practices and public awareness
can help increase sustainable yields.
Consumer Awareness: Educating consumers on the benefits of lower trophic level foods drives
demand for sustainable products, supporting environmental goals.
How does your diet affect the environ…
environ…
2.2.28 Ecological efficiency is the percentage of energy received by one trophic level that is passed on to the
next level.
Define ecological efficiency and explain its significance in energy flow within ecosystems.
Describe how ecological efficiency is calculated and discuss factors that may influence its value in different
ecosystems.
Compare and contrast ecological efficiency in a terrestrial ecosystem with that in an aquatic ecosystem,
Ecological efficiency measures the percentage of energy transferred from one trophic level to the next in an
ecosystem. This transfer ratio varies among ecosystems, trophic levels, and species, providing insights into energy flow
and the structure of food webs.
Key Points on Ecological Efficiency
Energy Transfer:
Energy transfers between trophic levels are generally inefficient, with a significant portion of energy lost
at each level.
The typical efficiency of energy transfer is around 10%, known as the "10% rule," meaning only about
10% of the energy at one level is available to the next.
Variation Among Ecosystems:
Different ecosystems exhibit varying levels of ecological efficiency. For example, aquatic ecosystems
often have slightly higher efficiencies compared to terrestrial ecosystems due to factors like lower energy
costs for mobility in water.
Influencing Factors:
Type of Organisms: Herbivores, carnivores, and decomposers exhibit different efficiencies based on
their metabolic rates and the type of food they consume.
Trophic Level: Efficiency generally decreases as you move up trophic levels, with producers usually
having the highest ecological efficiency.
Environmental Conditions: Temperature, resource availability, and ecosystem health can all impact
ecological efficiency by affecting metabolic rates and energy needs.
Importance of Ecological Efficiency
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Energy Flow: Determines energy movement through ecosystems, influencing food web structure and biomass
distribution.
Ecosystem Productivity: Higher efficiency supports greater productivity at higher trophic levels, sustaining
larger populations.
Biodiversity and Stability: Efficient energy transfer fosters biodiversity and ecosystem stability, supporting a
variety of species.
Conservation and Management: Guides sustainable harvesting, wildlife management, and habitat
conservation strategies.
​Implications of Ecological Efficiency
Limitations on Food Chain Length: Due to energy losses at each trophic level, there is a limited amount of
energy available to support higher trophic levels, restricting food chains to four or five levels.
Ecosystem Productivity: Higher ecological efficiency allows for more biomass and energy to be passed
through the food web, supporting more diverse and abundant ecosystems.
Resource Management: Understanding ecological efficiency is essential for sustainable resource
management, particularly in agriculture, fisheries, and conservation, as it helps estimate sustainable yields and
energy requirements.
Limitations and Considerations
Variability: The 10% rule is an average; actual efficiency varies widely across ecosystems and species.
Energy Losses: Significant losses occur at each trophic level due to respiration, growth, and heat, impacting
energy available for transfer.
Data Accuracy: Accurate ecological efficiency calculations depend on reliable data, necessitating careful field
studies and experiments.
Calculating Ecological Efficiency
To calculate ecological efficiency, you need data on the energy received by one trophic level and the energy transferred
to the next. Here’s an example calculation:
Given Data:
Energy received by primary consumers (herbivores) from primary producers (plants): 1000 kJ
Energy transferred to secondary consumers (carnivores) from primary consumers: 100 kJ
Calculation:
In this example, the ecological efficiency is 10%, indicating that 10% of the energy received by the herbivores is passed
on to the carnivores.
2.2.29 The second law of thermodynamics shows how the entropy of a system increases as biomass passes
through ecosystems.
Define the term "entropy" and explain its significance in the context of the second law of thermodynamics.
Outline how the second law of thermodynamics affects energy transfer between trophic levels.
Describe how cellular respiration contributes to the increase in entropy in an ecosystem.
Explain how living systems maintain a high degree of organization despite the second law of thermodynamics.
The Second Law of Thermodynamics
States that in any energy transfer, the total entropy (disorder) of a system and its surroundings increases.
Entropy: Measure of disorder; increases as energy is lost as heat during transfers, leading to less organized
energy states in ecosystems.
Energy Transfer and Entropy in Ecosystems
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Energy Loss: At each trophic level, only about 10% of energy is passed on, while the rest is lost as heat,
increasing system entropy.
Primary Producers to Consumers: Energy stored in biomass at each level decreases due to respiration and
metabolic losses, contributing to higher entropy as biomass moves through trophic levels.
Entropy and Biomass Flow
Primary Producers: Capture solar energy, reducing entropy by creating organized biomass.
Consumers: Energy transfers to herbivores, carnivores, and omnivores increase entropy, as heat loss from
cellular respiration grows at each level.
Maintaining Organization in Living Systems
Energy Input: Constant energy (sunlight for autotrophs, food for heterotrophs) is necessary to maintain low
internal entropy.
Entropy Export: Living organisms release heat to the environment, keeping internal structures organized while
adhering to the second law.
​Implications for Ecosystems
Energy Availability: Limited by entropy increases at each level; higher trophic levels support fewer individuals.
Ecosystem Productivity: Balances between photosynthetic energy capture and energy loss determine
productivity.
Biodiversity and Stability: Diverse ecosystems distribute energy more effectively, enhancing resilience and
stability.
How Entropy Powers The Earth (Big Pi…
Pi…
Correct use of terminology is a key skill in ESS. It is essential to use key terms correctly when communicating your
understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race,
speller and test to help you master the vocabulary.
Key Terms
Laws of Thermodynamics
carbon compounds sustainability
food chains
gross productivity
photosynthesis
cellular respiration
organic matter
non-biodegradable
energy transfer
​trophic levels
food webs
​equilibrium
​ nergy efficiency
e
ecological pyramids
conservation of energy
​biomass
bioaccumulation
​autotrophs
biomagnification.
energy
​energy transformation
HL
heterotrophs
producers
photoautotrophs
chemoautotrophs
secondary productivity
assimilated
net primary productivity
maximum sustainable yields
​ cological efficiency
e
entropy
Classroom Resources
Subtopic 2.2 Energy and Biomass.pptx
D
l
d Fil
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Download File
Subtopic 2.2 Energy and Biomass Workbook.docx
Download File
Energy Flow Diagram homework
Thermodynamics of Food Investigation
Activities
Activity 1: Create system diagrams from a set of data of ecosystems showing transfers and transformations of energy
and matter.
Activity 2: Individually brainstorm and select your own organisms to draw a food chain from given data. Include
decomposers and detritivores in your food chains to illustrate the complete cycle of energy and nutrients in ecosystems
Activity 3: Draw a freshwater food web based on the following information
Activity 4: Using the provided data, each group will calculate the trophic efficiency between consecutive trophic levels.
Activity 5 : Using data, draw pyramids of numbers, biomass, and energy from the given data
Activity 6: Follow experimental procedures on how to find biomass and energy from biological samples (plant material
only).
Activity 7: Bioaccumulation simulation. This experiment is based on a simulation that was generously developed and
made available to all by Virtual Biology Lab, located on the web at virtualbiologylab.org
HL
Activity 8: Use laboratory and field techniques for measuring primary and secondary productivity and work out GP and
NP from data
Activity 9: Graph the ecological efficiency between two trophic levels in both terrestrial and aquatic ecosystems
Useful links
National Geographic - Ecosystem
Khan Academy - Energy Flow in Ecosystems:
Encyclopedia Britannica - Primary Productivity:
​NOAA - Primary Productivity in the Ocean:
Photosynthesis and Cellular Respiration - Khan Academy
BBC Bitesize - Trophic Levels and Food Webs
University of Michigan - The Food Chain
houghtCo - Understanding Ecological Pyramids:​
NOAA - Biomagnification:
In The News
Tracking the Impacts of Climate Change on Food Webs in High-Latitude Ecosstems:
The New Arctic: Amid Record Heat, Ecosystems Morph and Wildlife Struggle:
A Drowned Future for Coastal Ecosystems:
Energy Flow Through an Ecosystem:
Human Impacts on Energy Flow through Natural Ecosystems, and How to Mitigate Them:
International-Mindedness
Understanding the principles of energy flow and ecological efficiency in ecosystems highlights the
interconnectedness of global environmental challenges. By recognizing the impacts of human activities such as
deforestation, urbanization, and pollution on energy transfer and ecosystem sustainability, we can foster a sense
of global responsibility and cooperation in developing sustainable practices to protect our planet's diverse
ecosystems for future generations..
TOK:
To what extent does the second law of thermodynamics challenge the sustainability of ecosystems, and how do
different ways of knowing influence our understanding and management of energy flow and entropy in these
systems?
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Video Clips
Biological processes depend on energy flow through the Earth system.
Energy Literacy Essential Principle #3
This video is about how we don't just need energy to power our lives, we need *low entropy* energy! This is also known
as "free energy", and one way of thinking about entropy is as the lack of free energy. The sun provides us with useful,
low entropy, energy in the form of photons of visible light, which are then absorbed and converted into plants, sugar,
complex molecules, etc, before being radiated back into space as heat, which has much higher entropy.
How Entropy Powers The Earth (Big Pi…
Pi…
This video explains the 1st and 2nd laws of thermodynamics as they relate to energy exchanges with environmental
systems.
Thermodynamics, 1st and 2nd Laws - 1…
1…
In this episode of Crash Course Chemistry, Hank goes over the ideas of keeping your life balance... well, your chemical
life. Equilibrium is all about balance and today Hank discusses Chemical Equilibrium, Concentration, Temperature, and
Pressure. Also, he'll chat about Le Chatalier's Principle and Fritz Habe
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Equilibrium: Crash Course Chemistry #…
#…
​Watch the following video to learn about: -Positive feedback loops -Negative feedback loops -How competing feedback
loops may influence climate change
Global Change Effects
Paul Andersen explains how ecosystems respond to disruptions. Disruptions can cause changes in the number and
variety of organisms. It can also lead to migration, extinction or even speciation.
LS2C - Ecosystem Dynamics, Functioni…
Functioni…
"A short animated film about the feedback loops likely to lead to catastrophic climate change, by Leo Murray."
Wake Up, Freak Out - then Get a Grip (H…
(H…
From time to time, ecosystems are hit by storms, fires or other types of disturbance. Resilience is the ability of an
ecosystem to resist or recover from these events. Resilience preserves ecosystem diversity, productivity and
sustainability. Disturbance has more impact on ecosystems that have lost diversity.
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Resilience
For 10,000 years, our world seemed endless. The sky was the limit. But today's world looks much smaller. We've
cleared, consumed and polluted our way across the globe. The planet is shrinking. Have we pushed Earth past the
tipping point? That's a critical issue the University of Minnesota's Institute on the Environment explores in our second
Big Question video. This three-minute multimedia feature draws on research from the article Planetary Boundaries: A
Safe Operating Space for Humanity, published this past fall in the journal Nature, and discussed in the current Scientific
America
Big Question: Is Earth past the tipping …
Earth Could Reach Devastating Ecological Tipping Point by 2025
Earth Could Reach Devastating Ecologi…
Ecologi…
This segment deals with the main positive feedback loops in action in Gaia's complex ecosystems: melting of the ice
caps, deforestation, melting of permafrost regions of the planet and the destruction of Ehux: a vital marine algae that is
a key component of the earth's climate regulation system.
The scientific evidence appears (overwhelmingly) to indicate that earth (Gaia) may be inexorably approaching or
perhaps PAST the tipping point and on it's way to a new climate regime not seen on earth for 55 million years. It will be
a climate that is, on average, much hotter, more chaotic and violent than what we have experienced for the entire tenure
of our species.
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Scorched Earth: Beyond The Tipping P…
P…
Rain Forest Tipping Point
07 Ecological tipping points rain forests
In a remote fishing village in the Philippine archipelago, coastal fishers responded to falling fish stocks by working
harder to catch them. The combination of dynamite, longer workdays, and more advanced gear caused stocks to fall
faster. On the edge of crisis, this small community decided to create a no-take marine sanctuary on 10% of its coral-reef
fishing grounds. This initiative sparked a renaissance of not only their fishery, but also their cherished way of life
Ecotipping Point - Saving a Fishery and…
and…
Plenty of people have an opinion on whether the precautionary principle is good or bad, but what exactly is it?
What is the Precautionary Principle, an…
an…
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