IB DP Biology Transfers of energy and matter Study Notes
IB DP Biology Transfers of energy and matter Study Notes
IB DP Biology Transfers of energy and matter Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- What is the reason matter can be recycled in ecosystems but energy cannot?
- How is the energy that is lost by each group of organisms in an ecosystem replaced?
C4.2.1 – Ecosystems as Open Systems in Which Both Energy and Matter Can Enter and Exit
🔄 Ecosystems as Open Systems
- An ecosystem is an open system because:
Both energy and matter can enter and leave. - Examples:
Energy input: sunlight entering the ecosystem.
Energy output: heat energy lost to the environment.
Matter input: nutrients carried in by water or air.
Matter output: organic matter carried away by animals or water flow.
🚫 Closed Systems vs Open Systems
| System Type | Energy Flow | Matter Flow |
|---|---|---|
| Open System | Energy can enter and exit | Matter can enter and exit |
| Closed System | Energy can enter and exit | Matter cannot enter or exit |
Example of a closed system: a sealed terrarium, where only energy passes through, but matter is recycled internally.
⚠️ Why Ecosystems Must Be Open Systems
Energy constantly flows in (sunlight) and out (heat).
Matter cycles through living and non-living components (e.g., carbon, nitrogen).
Without matter exchange, ecosystems would run out of nutrients or build up wastes.
Ecosystems are open systems allowing both energy and matter exchange with their surroundings. Closed systems only allow energy transfer, but no matter exchange.
C4.2.2 – Sunlight as the Principal Source of Energy That Sustains Most Ecosystems
🌱 Sunlight: The Main Energy Source
- Almost all ecosystems depend on sunlight as the primary energy source.
- Photosynthetic organisms (mainly plants, algae, and some bacteria) capture sunlight to make organic molecules – this is the base of the food chain.
- Energy flows from sunlight → producers → consumers → decomposers.
🕳️ Exceptions to Sunlight-Based Ecosystems
- Some ecosystems do not rely on sunlight, such as:
– Caves — no sunlight; energy comes from organic matter washed in or chemoautotrophic bacteria.
– Deep ocean zones (below light penetration levels, >200 m) – ecosystems rely on:
• Organic matter falling from above (marine snow)
• Chemosynthesis by bacteria near hydrothermal vents (use chemical energy from Earth’s interior)
📚 Nature of Scientific Laws (NOS – Nature of Science)
- Scientific laws:
- Describe consistent patterns or relationships in nature (e.g., energy flow in ecosystems).
- Are generalized principles or “rules of thumb” – no explanation for why, only what happens.
- Are predictive – allow us to predict outcomes under certain conditions.
- Different from scientific theories, which explain why phenomena occur.
✅ Features of Useful Scientific Generalizations
- Consistent across observations and experiments.
- Simple and easy to apply.
- Predictive of new outcomes.
- Testable through experiments or observations.
Sunlight is the main energy input for most ecosystems, but some, like deep-sea vents or caves, rely on other energy sources. Scientific laws describe these natural patterns reliably but do not explain their causes.
C4.2.3 – Flow of Chemical Energy Through Food Chains
🍽️ What is Chemical Energy in Ecology?
Chemical energy is stored in organic molecules like carbohydrates, fats, and proteins.
This energy originally comes from sunlight captured by plants during photosynthesis.
🔄 How Does Energy Flow in a Food Chain?
| Step | Explanation |
|---|---|
| Producer | Plants convert sunlight to chemical energy (glucose). |
| Primary Consumer | Eats plants and obtains chemical energy from plant tissues. |
| Secondary Consumer | Eats primary consumers and gains their stored energy. |
| Tertiary Consumer | Eats secondary consumers, continuing energy transfer. |
At each step, chemical energy is transferred as one organism feeds on another.
Example: Grass (producer) → Grasshopper (primary consumer) → Frog (secondary consumer) → Snake (tertiary consumer)
⚠️ Important Points About Energy Transfer
- Energy transfer is not 100% efficient:
– Some energy is lost as heat during respiration.
– Energy is also used for movement, growth, reproduction, and lost in waste.
– Only a small fraction of energy passes on to the next level, limiting the number of trophic levels.
🔍 Real-World Example: Grassland Food Chain
| Organism | Role | Energy Source |
|---|---|---|
| Grass | Producer | Photosynthesis (sunlight) |
| Grasshopper | Primary Consumer | Eats grass |
| Frog | Secondary Consumer | Eats grasshoppers |
| Snake | Tertiary Consumer | Eats frogs |
Chemical energy flows through food chains as organisms feed on others, starting from producers and moving up consumers. However, energy decreases at each step due to losses in metabolism and heat.
C4.2.4 – Construction of Food Chains and Food Webs
🔍 What Is a Food Chain?
- A food chain shows a simple, linear sequence of organisms where each one is eaten by the next.
- It represents the flow of energy and biomass from one organism to another.
- Arrows (→) point in the direction of energy transfer – from the food (prey) to the eater (predator).
- Example:
Grass → Grasshopper → Frog → Snake → Hawk
🕸️ What Is a Food Web?
- A food web is a more complex diagram showing multiple interconnected food chains in a community.
- It illustrates how organisms have varied diets and how energy flows through many pathways.
- Food webs better represent real ecosystems because organisms often eat more than one type of food.
🔄 Arrows in Food Chains and Webs
Arrows always point from the organism being eaten to the organism eating it.
This shows the transfer of energy and biomass.
🏡 Local Community Example
Suppose a local pond community:
- Algae (producer) → Water flea (primary consumer)
- Water flea → Small fish (secondary consumer)
- Small fish → Larger fish (tertiary consumer)
- Larger fish → Bird (quaternary consumer)
In a food web, the bird may also eat insects, and small fish may eat different zooplankton, showing interconnected feeding relationships.
Food chains and food webs represent who eats whom in a community. Arrows point from the food to the eater, showing energy flow. Food webs are complex and more realistic than food chains.
C4.2.5 – Supply of Energy to Decomposers as Carbon Compounds in Organic Matter
🔑 What Are Decomposers?
Decomposers are organisms such as bacteria and fungi that break down dead organic material.
They play a crucial role in recycling nutrients in ecosystems.
🍃 Sources of Energy for Decomposers
Decomposers obtain energy from carbon compounds found in:
- Faeces: Waste products from animals containing undigested organic matter.
- Dead Parts of Organisms: Leaves, bark, and other parts shed or fallen from plants and animals.
- Dead Whole Organisms: Entire plants or animals that have died and become organic matter.
🔄 Role in Ecosystems
Decomposers break down these carbon compounds through respiration, releasing energy for their growth and activity.
This decomposition process returns nutrients like carbon, nitrogen, and phosphorus back to the soil and atmosphere, making them available for plants again.
Decomposers get energy by breaking down carbon compounds from faeces, dead parts, and dead organisms. This process recycles nutrients and sustains ecosystem health.
C4.2.6 – Autotrophs: Organisms Synthesizing Carbon Compounds Using External Energy
🧬 What Are Autotrophs?
Autotrophs are organisms that make their own food by converting simple inorganic substances (like CO₂ and water) into organic carbon compounds.
They are the primary producers in ecosystems, providing energy and organic matter for all other organisms.
☀️ Types of Autotrophs
| Type | Energy Source | Process | Examples |
|---|---|---|---|
| Photoautotrophs | Light energy (sunlight) | Photosynthesis | Plants, algae, cyanobacteria |
| Chemoautotrophs | Chemical energy from inorganic compounds (e.g., H₂S, NH₃) | Chemosynthesis | Bacteria in deep-sea vents, volcanic springs |
⚡ Energy Use in Autotrophs
- Energy is required to:
– Fix carbon dioxide into organic molecules (carbon fixation).
– Drive anabolic reactions that build complex macromolecules (like carbohydrates, proteins, lipids). - This energy comes from:
– Sunlight for photoautotrophs.
– Chemical reactions for chemoautotrophs.
🌱 Why Are Autotrophs Important?
They form the base of food chains, supporting heterotrophs (organisms that consume organic matter).
They convert inorganic carbon into forms usable by all other life forms.
Autotrophs synthesize organic compounds from inorganic sources using external energy, either from sunlight (photosynthesis) or chemical reactions (chemosynthesis). This energy input drives carbon fixation and biosynthesis, supporting all other life.
C4.2.7 – Energy Sources in Photoautotrophs and Chemoautotrophs
🌞 Photoautotrophs: Using Light as an Energy Source
- Photoautotrophs capture light energy from the sun.
- This energy powers photosynthesis, where CO₂ and water are converted into organic compounds.
- Light energy excites electrons, starting a chain of reactions that produce energy-rich molecules (ATP, NADPH).
- Example: Plants, algae, cyanobacteria.
⚙️ Chemoautotrophs: Using Oxidation Reactions as an Energy Source
Chemoautotrophs gain energy by oxidizing inorganic substances.
Oxidation reactions release energy by transferring electrons from molecules like:
- Iron (Fe²⁺ → Fe³⁺)
- Hydrogen sulfide (H₂S)
- Ammonia (NH₃)
This energy is then used to fix carbon dioxide into organic molecules (chemosynthesis).
🔍 Example of Chemoautotroph: Iron-Oxidizing Bacteria
These bacteria oxidize iron ions (Fe²⁺) to obtain energy.
Found in environments like:
- Acid mine drainage
- Some freshwater and marine habitats
They play important roles in nutrient cycling and biogeochemical processes.
⚡ Why Oxidation Reactions Are Useful in Living Organisms
- Oxidation releases energy stored in chemical bonds.
- This energy can be harnessed to drive essential biochemical processes.
- Both chemoautotrophs and heterotrophs rely on oxidation for energy production.
Photoautotrophs use sunlight to power photosynthesis, while chemoautotrophs extract energy from oxidation of inorganic molecules. Oxidation reactions release energy that organisms harness to synthesize organic compounds and sustain life.
C4.2.8 – Heterotrophs: Using Carbon Compounds from Other Organisms
🧬 What Are Heterotrophs?
- Heterotrophs are organisms that cannot make their own food.
- They obtain carbon compounds by consuming other organisms (plants, animals, or decomposed material).
- They rely on organic carbon made by autotrophs or other heterotrophs.
🔄 How Heterotrophs Use Carbon Compounds
Complex molecules like proteins, nucleic acids, carbohydrates, and lipids are:
- Digested externally (e.g., fungi secreting enzymes outside their bodies).
- Or digested internally (e.g., animals breaking down food in the gut).
After digestion, smaller molecules (like amino acids, sugars) are assimilated:
Used to build new carbon compounds the organism needs.
Support growth, repair, and energy storage.
⚠️ Key Point
Heterotrophs do not directly use the carbon compounds they consume.
They break down these compounds first, then rebuild the molecules suited to their own cells.
🔍 Example: Human Digestion
Humans eat proteins and carbohydrates.
Enzymes in the gut break these into amino acids and sugars.
The body uses these to make its own proteins, DNA, and energy stores.
Heterotrophs depend on consuming organic carbon compounds. They digest complex molecules externally or internally and then assimilate the smaller building blocks to synthesize the carbon compounds they require.
C4.2.9 – Release of Energy by Oxidation of Carbon Compounds in Autotrophs and Heterotrophs
🔥 Energy Release Through Cellular Respiration
- Both autotrophs and heterotrophs release energy by oxidizing carbon compounds like glucose.
- This process is called cellular respiration.
- Energy released is stored as ATP (adenosine triphosphate), which powers cellular activities.
⚙️ Key Points
- Autotrophs produce their own organic carbon compounds (e.g., glucose) during photosynthesis and break these down for energy.
- Heterotrophs obtain organic carbon compounds by consuming other organisms and also oxidize them to release energy.
- The chemical reaction (simplified):
Glucose + O2 → CO2 + H2O + Energy (ATP) - Oxygen is needed for aerobic respiration, which is more efficient.
🔍 Why This Is Important
Energy from respiration is essential for:
- Movement
- Growth
- Repair
- Active transport
- Other life processes
Both autotrophs and heterotrophs release energy by oxidizing carbon compounds during cellular respiration, producing ATP to fuel cellular functions.
C4.2.10 – Classification of Organisms into Trophic Levels
🌱 What Are Trophic Levels?
Trophic levels describe the position of organisms in a food chain based on how they obtain energy.
Organisms are grouped into levels depending on what they eat and who eats them.
⚡ Key Trophic Levels and Terms
| Trophic Level | Role in Ecosystem | Examples |
|---|---|---|
| Producer | Make their own food through photosynthesis (autotrophs) | Plants, algae, some bacteria |
| Primary Consumer | Eat producers (herbivores) | Rabbits, caterpillars |
| Secondary Consumer | Eat primary consumers (carnivores or omnivores) | Frogs, small birds |
| Tertiary Consumer | Eat secondary consumers (top predators) | Hawks, sharks |
🔄 Organisms with Varied Diets
Many organisms have mixed diets and can occupy different trophic levels in various food chains.
Example:
Omnivores (e.g., bears) can be both primary and secondary consumers.
Some fish may be primary consumers in one food chain and secondary consumers in another.
🌿 Why Understanding Trophic Levels Matters
Helps track energy flow and nutrient cycling in ecosystems.
Important for studying food webs, ecosystem stability, and human impacts.
Organisms are classified into trophic levels—producers, primary, secondary, and tertiary consumers—based on their feeding relationships. Many species can occupy multiple levels depending on their diet.
C4.2.11 – Construction of Energy Pyramids
🔋 What Is an Energy Pyramid?
- An energy pyramid is a diagram that shows:
– The amount of energy available at each trophic level.
– How energy decreases as it moves up the food chain.
Energy is measured in kilojoules per square meter per year (kJ/m²/year).
⚡ Key Features
- Producers form the base with the most energy.
- Energy decreases at each successive trophic level due to:
- Energy lost as heat (cell respiration).
- Energy lost in waste.
- Energy used for life processes.
- Usually, only 10% of energy is passed to the next level (the 10% rule).
📐 How to Construct an Energy Pyramid
- Collect data on energy content at each trophic level from research.
- Represent each level as a bar or layer proportional to energy available.
- Label trophic levels clearly: producer, primary consumer, secondary consumer, etc.
- Show energy loss visually by decreasing bar size at higher levels.
🔍 Example (Hypothetical Data)
| Trophic Level | Energy Available (kJ/m²/year) | Approximate Energy Transfer (%) |
|---|---|---|
| Producers | 10,000 | 100% |
| Primary Consumers | 1,000 | 10% |
| Secondary Consumers | 100 | 1% |
| Tertiary Consumers | 10 | 0.1% |
Energy pyramids visually represent the flow and loss of energy through trophic levels. They highlight that energy decreases significantly as it moves up the food chain, with only about 10% transferred to the next level.
C4.2.12 – Energy Losses Between Trophic Levels in Food Chains
⚡ Why Energy Decreases Along Food Chains
Energy availability reduces at each trophic level due to several types of energy loss:
- Respiration: Energy used for movement, growth, and other life processes is lost as heat.
- Waste: Not all food is digested; some energy is lost in feces and urine.
- Incomplete consumption: Not all organisms are eaten.
As a result, only about 10% of energy is transferred to the next trophic level (known as the 10% rule).
🍂 Role of Decomposers and Detritus Feeders
- These organisms (e.g., fungi, bacteria, earthworms) break down dead organic matter and waste.
- They recycle nutrients and release energy back into the ecosystem as heat.
- Not usually part of the main food chain, but crucial for energy transformation and ecosystem health.
🔍 Causes of Energy Loss
| Cause | Explanation |
|---|---|
| Respiration | Energy lost as heat during metabolic processes |
| Egestion (waste) | Energy lost through undigested materials |
| Excretion | Energy lost in urine and other waste products |
| Uneaten parts | Energy in parts of organisms not consumed by predators |
Large amounts of energy are lost at each trophic level due to respiration, waste, and incomplete consumption. Decomposers recycle nutrients and energy but are generally not included in food chains.
C4.2.13 – Heat Loss to the Environment in Autotrophs and Heterotrophs
🔥 Energy Transfer Is Not 100% Efficient
- During cellular respiration, chemical energy from carbon compounds is converted to ATP.
- Not all energy is captured as ATP, some is lost as heat.
- Heat is also produced when ATP is used by cells to perform work (e.g., muscle contraction).
⚙️ Heat Loss in Both Autotrophs and Heterotrophs
- Autotrophs (e.g., plants) produce ATP during photosynthesis and respiration.
- Heterotrophs (e.g., animals) generate ATP mainly through respiration.
- In both, energy transformations release heat, warming the organism and environment.
🌍 Why Heat Loss Matters
- Heat loss contributes to the decrease in available energy at each trophic level.
- This heat energy disperses into the environment, meaning energy flows one way through ecosystems.
- Explains why energy pyramids narrow at higher trophic levels.
Energy transfers during respiration are inefficient; chemical energy partly converts to heat. Both ATP production and usage release heat, contributing to energy loss in ecosystems.
C4.2.14 – Restrictions on Number of Trophic Levels Due to Energy Losses
⚡ Why Ecosystems Have Limited Trophic Levels
At each trophic level, energy loss means less energy is available to support organisms at the next level.
Due to this energy reduction:
- There are fewer organisms at higher trophic levels.
- Organisms tend to be smaller in size at higher levels.
📉 Biomass vs Energy Content
- Biomass (total mass of living matter) decreases at higher trophic levels.
- However, the energy content per unit of biomass remains constant.
- The energy pyramid narrows primarily because of the decrease in biomass, not energy density.
🌿 Implications
- Most ecosystems have 3 to 5 trophic levels.
- Longer food chains are rare because energy losses make higher levels unsustainable.
- This affects the structure and stability of ecosystems.
Energy loss at each trophic level limits the number of levels in a food chain. Fewer and smaller organisms exist at higher levels, reducing biomass but not energy per unit mass.
C4.2.15 – Primary Production: Accumulation of Carbon Compounds in Biomass by Autotrophs
🌱 What is Primary Production?
Primary production is the process by which autotrophs (like plants and algae) create and accumulate carbon compounds (biomass) through photosynthesis.
This biomass represents stored chemical energy available for the rest of the ecosystem.
📏 Measuring Primary Production
Units used: grams of carbon per square meter per year (g C m−2 yr−1).
It measures how much carbon is fixed into organic matter over time in a given area.
🌍 Variation Across Biomes
Different biomes have different rates of primary production because of varying:
- Temperature
- Light availability
- Water supply
- Nutrient availability
Example:
Tropical rainforests have high primary production due to warm temperatures and abundant rainfall.
Deserts have low primary production due to limited water.
🌿 Biomass Accumulation
Biomass accumulates when autotrophs grow and reproduce.
Heterotrophs (consumers) also contribute to biomass by growth and reproduction but rely on autotrophs’ primary production.
Primary production is the build-up of carbon compounds in autotroph biomass, measured in g C m−2 yr−1. Different biomes show varying production rates based on environmental conditions.
C4.2.16 – Secondary Production: Accumulation of Carbon Compounds in Biomass by Heterotrophs
🍽️ What Is Secondary Production?
Secondary production is the accumulation of carbon compounds in the biomass of heterotrophs (animals, fungi, some bacteria) as they grow and reproduce by consuming organic matter.
It represents the energy stored in consumers after feeding on producers or other consumers.
⚠️ Why Secondary Production Is Lower Than Primary Production
- During cell respiration, heterotrophs convert carbon compounds into carbon dioxide and water, releasing energy as heat.
- This causes a loss of biomass because not all the consumed carbon compounds are converted into new biomass.
- Hence, secondary production is always less than primary production in an ecosystem.
🌿 Energy Flow
- Primary production provides the energy source.
- Secondary production shows how much energy heterotrophs convert into new biomass.
- The gap between the two indicates energy loss in the ecosystem.
Secondary production is the biomass gained by heterotrophs through consumption, but it’s less than primary production due to energy loss during respiration.
C4.2.17 – Constructing Carbon Cycle Diagrams
🌍 What Is the Carbon Cycle?
The carbon cycle shows how carbon atoms move through ecosystems.
It involves the processes of photosynthesis, feeding, respiration, and decomposition.
🌿 Key Processes in the Carbon Cycle
- Photosynthesis: Autotrophs (plants, algae) take in carbon dioxide (CO₂) from the atmosphere and convert it into organic carbon compounds (like glucose).
- Feeding: Carbon compounds pass from producers to consumers when organisms eat others.
- Respiration: Both autotrophs and heterotrophs break down carbon compounds, releasing CO₂ back into the atmosphere.
- Decomposition: Dead organisms and waste are broken down by decomposers, releasing carbon back to the soil and atmosphere.
📋 How to Draw a Carbon Cycle Diagram
- Start with atmospheric CO₂ as a source.
- Show photosynthesis moving CO₂ into plants.
- Draw arrows from plants to herbivores (primary consumers), then to carnivores (secondary/tertiary consumers).
- Include respiration arrows from all organisms back to the atmosphere as CO₂.
- Add decomposers breaking down dead matter, releasing CO₂.
- Label all parts clearly.
🔍 Example Diagram Elements
| Component | Description |
|---|---|
| Atmospheric CO₂ | Source of carbon for photosynthesis |
| Producers | Convert CO₂ to organic molecules |
| Consumers | Obtain carbon by eating other organisms |
| Decomposers | Recycle carbon from dead material |
| Respiration | Releases CO₂ back into atmosphere |
Carbon cycles through ecosystems via photosynthesis, feeding, respiration, and decomposition. Diagrams show these flows and recycling between organisms and the atmosphere.
C4.2.18 – Ecosystems as Carbon Sinks and Carbon Sources
🌱 Carbon Sink
- An ecosystem is a carbon sink when photosynthesis exceeds respiration.
- This means the ecosystem absorbs more CO₂ than it releases.
- Carbon is stored in biomass (plants, soil, organic matter).
- Example: Dense forests like the Amazon rainforest act as major carbon sinks.
🌬️ Carbon Source
- An ecosystem is a carbon source when respiration exceeds photosynthesis.
- This means the ecosystem releases more CO₂ than it absorbs.
- Often happens in deforested areas, burning biomass, or decomposing organic matter.
- Example: Peatlands or areas affected by wildfires can be carbon sources.
🔄 Balance of Carbon
| Condition | Result | Effect on Atmosphere |
|---|---|---|
| Photosynthesis > Respiration | Net carbon uptake | Reduces atmospheric CO₂ |
| Respiration > Photosynthesis | Net carbon release | Increases atmospheric CO₂ |
Ecosystems can act as carbon sinks or sources depending on whether photosynthesis or respiration dominates. This balance affects atmospheric CO₂ levels and climate change.
C4.2.19 – Release of Carbon Dioxide During Combustion of Biomass and Fossil Fuels
🌿 Sources of Combustion Carbon
- Biomass: Includes wood, plant material, and organic waste.
- Peat: Partially decayed plant material stored in wetlands.
- Fossil Fuels: Coal, oil, and natural gas formed from ancient organic matter over millions of years.
💨 Carbon Release Process
Combustion burns carbon-rich materials, releasing carbon dioxide (CO₂) into the atmosphere.
This process returns stored carbon from these carbon sinks back into the atmosphere.
⚡ Natural vs Human-Induced Combustion
- Natural combustion: e.g., wildfires started by lightning strikes.
- Human activities: Deforestation, burning fossil fuels, and agricultural practices have greatly increased combustion rates.
- This accelerates CO₂ release, contributing to climate change.
⏳ Age of Carbon Sinks
- Biomass and peat represent recently fixed carbon (decades to centuries).
- Fossil fuels store ancient carbon (millions of years old).
- Burning fossil fuels releases carbon that was locked away long ago, disrupting the natural carbon cycle.
Combustion of biomass, peat, and fossil fuels releases CO₂ into the atmosphere. Human activities have accelerated this process, releasing ancient carbon and impacting climate.
C4.2.20 – Analysis of the Keeling Curve: Photosynthesis, Respiration, and Combustion
🌍 What is the Keeling Curve?
The Keeling Curve is a graph showing the changes in atmospheric carbon dioxide (CO₂) concentration over time, based on measurements at Mauna Loa Observatory.
It reveals both long-term trends and annual fluctuations in CO₂ levels.
📊 Long-Term Trend
- CO₂ levels have been steadily increasing since measurements began in the late 1950s.
- This increase is mainly due to:
– Combustion of fossil fuels (coal, oil, natural gas)
– Deforestation and land-use changes
Represents a net increase in atmospheric CO₂, contributing to global warming.
🌿 Annual Fluctuations
- CO₂ levels rise and fall within each year, creating a saw-tooth pattern on the graph.
- Spring and summer: CO₂ decreases due to photosynthesis by plants absorbing more CO₂.
- Autumn and winter: CO₂ increases as respiration and decomposition release CO₂, and photosynthesis slows down.
- This cycle reflects the seasonal balance between photosynthesis and respiration in the Northern Hemisphere, where most land plants are located.
| Feature | Cause | Effect on CO₂ Levels |
|---|---|---|
| Long-term increase | Fossil fuel combustion & deforestation | Gradual rise in atmospheric CO₂ |
| Seasonal fall | Increased photosynthesis in growing season | Decrease in CO₂ during spring/summer |
| Seasonal rise | Increased respiration & decay in autumn/winter | Increase in CO₂ during autumn/winter |
The Keeling Curve shows rising atmospheric CO₂ due to human activities, with natural seasonal fluctuations caused by photosynthesis and respiration cycles.
C4.2.21 – Interdependence of Aerobic Respiration and Photosynthesis
🌬️ Aerobic Respiration Depends on Photosynthesis
Aerobic respiration in heterotrophs uses oxygen (O₂) from the atmosphere to break down carbon compounds and release energy.
This atmospheric oxygen is produced by photosynthesis carried out by autotrophs (plants, algae).
🌱 Photosynthesis Depends on Respiration
Photosynthesis requires carbon dioxide (CO₂) from the atmosphere.
This CO₂ is produced by respiration from heterotrophs and autotrophs.
🔄 Huge Annual Fluxes
- The yearly exchange of gases between photosynthesis and respiration is massive.
- This balance maintains the atmospheric levels of oxygen and carbon dioxide.
- It represents a vital biological feedback loop sustaining life on Earth.
| Process | Uses | Produces |
|---|---|---|
| Photosynthesis | CO₂, water, sunlight | Oxygen (O₂), organic carbon |
| Aerobic Respiration | Oxygen (O₂), organic carbon | Carbon dioxide (CO₂), energy |
Photosynthesis and aerobic respiration are tightly linked processes. Photosynthesis produces the oxygen required for respiration, while respiration produces the carbon dioxide required for photosynthesis.
C4.2.22 – Recycling of Chemical Elements in Ecosystems
🌿 All Elements Are Recycled
Ecosystems recycle all chemical elements essential for life, not just carbon.
Elements like nitrogen, phosphorus, potassium, and others are continuously reused.
♻️ Role of Decomposers
- Decomposers (fungi, bacteria) break down dead organisms and waste.
- They release elements back into the soil and environment in usable forms.
- This recycling maintains nutrient availability for plants and other organisms.
🌎 Importance of Recycling
- Recycling prevents depletion of essential nutrients.
- It supports sustainable ecosystem functioning.
- Without decomposers, nutrients would become locked in dead matter.
Chemical elements are recycled in ecosystems with decomposers playing a vital role in breaking down organic matter and returning nutrients to the environment for reuse.