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?

IBDP Biology 2025 -Study Notes -All Topics

C4.2.1—Ecosystems as open systems in which both energy and matter can enter and exit

Open Systems: Ecosystems are open systems, exchanging energy and matter with their surroundings. Energy enters ecosystems through sunlight, and matter enters through various inputs like water, minerals, and organic matter.
Energy Flow: Energy flows through ecosystems in a one-way direction, from sunlight to producers (plants) to consumers (animals) and eventually dissipating as heat.
Nutrient Cycling: Unlike energy, matter, such as nutrients like nitrogen and phosphorus, cycles within ecosystems. Decomposers break down organic matter, releasing nutrients back into the soil, where they can be taken up by plants.
Closed Systems: In contrast, closed systems, like a sealed terrarium, do not exchange matter with their surroundings. While energy can enter and exit, the amount of matter remains constant.

The understanding of ecosystems as open systems is crucial for comprehending how energy flows, nutrients cycle, and how human activities can impact these processes.

C4.2.2—Sunlight as the principal source of energy that sustains most ecosystems

Sunlight is the primary energy source for most ecosystems. Photosynthetic organisms like plants, algae, and cyanobacteria convert sunlight into chemical energy through photosynthesis. This energy fuels the food chain, supporting the growth and survival of all organisms. The availability of sunlight varies across different environments, influencing the structure and productivity of ecosystems.

C4.2.3—Flow of chemical energy through food chains

Producers: The first organisms in a food chain, typically photosynthetic organisms like plants, algae, and cyanobacteria. They convert sunlight into chemical energy through photosynthesis.
Consumers: Organisms that obtain energy by consuming other organisms. Primary consumers feed on producers, secondary consumers feed on primary consumers, and so on.
Energy Flow: Energy flows through the food chain in a one-way direction, from producers to consumers. At each trophic level, some energy is lost as heat.
Food Webs: In reality, food chains are interconnected, forming complex food webs with multiple pathways for energy flow.

The example of the Monte Desert food chain highlights the interconnectedness of organisms within an ecosystem. The tara shrub provides energy to the guanaco, which in turn provides energy to the puma. This illustrates the transfer of energy through trophic levels.

C4.2.4—Construction of food chains and food webs to represent feeding relationships in a community

Food webs are complex networks of feeding relationships within an ecosystem. They illustrate how energy flows through different trophic levels, from producers to consumers. In a food web, multiple food chains are interconnected, showing the intricate relationships between organisms. Understanding food webs is essential for comprehending the structure and dynamics of ecosystems.

C4.2.5—Supply of energy to decomposers as carbon compounds in organic matter coming from dead
organisms

Decomposers play a crucial role in recycling nutrients within ecosystems. They break down dead organic matter, such as fallen leaves, dead animals, and animal waste, into simpler substances that can be reused by other organisms. This process, known as decomposition, is essential for maintaining the balance of nutrients in the environment.

Bacteria and fungi are the primary decomposers. They secrete enzymes that break down complex organic molecules into simpler ones, which they then absorb. By breaking down dead organic matter, decomposers release nutrients like nitrogen and phosphorus back into the soil, where they can be taken up by plants and other organisms.

Without decomposers, dead organic matter would accumulate, and essential nutrients would become locked up, limiting the growth and productivity of ecosystems. Therefore, decomposers are vital for the health and functioning of ecosystems.

C4.2.6—Autotrophs are organisms that use external energy sources to synthesise carbon compounds from simple inorganic substances

Autotrophs are organisms that can synthesize their own food using simple inorganic substances like carbon dioxide and water. They are the primary producers in ecosystems, providing the foundation for all other life forms.

There are two main types of autotrophs:

Photoautotrophs: These organisms use light energy from the sun to convert carbon dioxide and water into organic compounds through photosynthesis. Examples include plants, algae, and cyanobacteria.
Chemoautotrophs: These organisms obtain energy from the oxidation of inorganic compounds, such as sulfur, hydrogen sulfide, or ammonia. This process is known as chemosynthesis. Chemoautotrophs are found in extreme environments like deep-sea hydrothermal vents and volcanic hot springs.

Autotrophs play a crucial role in the ecosystem by converting inorganic matter into organic compounds, which are essential for the survival of heterotrophic organisms. They are the base of the food chain and provide energy for all other living organisms.

C4.2.7—Use of light as the external energy source in photoautotrophs and oxidation reactions as the energy source in chemoautotrophs

Autotrophs are organisms that can synthesize their own food using simple inorganic substances like carbon dioxide and water. They need an external energy source to drive this process.

There are two main types of autotrophs:

Photoautotrophs: These organisms use sunlight as an energy source to convert carbon dioxide and water into organic compounds through photosynthesis. Examples include plants, algae, and cyanobacteria.
Chemoautotrophs: These organisms obtain energy from the oxidation of inorganic compounds, such as sulfur, hydrogen sulfide, or ammonia. This process is known as chemosynthesis. Chemoautotrophs are often found in extreme environments like deep-sea hydrothermal vents and volcanic hot springs.

Photoautotrophs utilize the vast amounts of energy emitted by the Sun to fuel photosynthesis. Chemoautotrophs, on the other hand, harness the energy released from the oxidation of inorganic compounds. Both groups of autotrophs play crucial roles in ecosystems by providing the energy and organic matter necessary for the survival of other organisms.

C4.2.8—Heterotrophs as organisms that use carbon compounds obtained from other organisms to synthesize the carbon compounds that they require

Heterotrophs are organisms that obtain their carbon compounds from other organisms. They digest the complex carbon compounds in food, breaking them down into simpler molecules. These simpler molecules are then used to build the complex carbon compounds needed for their own bodies. This process of absorbing and incorporating carbon compounds is called assimilation.

C4.2.9—Release of energy in both autotrophs and heterotrophs by oxidation of carbon compounds in cell respiration

All organisms, whether autotrophs or heterotrophs, require energy in the form of ATP for their survival and growth. This energy is obtained through the process of cellular respiration, where carbon compounds like carbohydrates and lipids are oxidized to release energy. The released energy is then used to phosphorylate ADP, producing ATP. This ATP provides the energy needed for various cellular activities, including synthesizing large molecules, active transport, muscle contraction, and maintaining body temperature in warm-blooded organisms.

C4.2.10—Classification of organisms into trophic levels

Ecologists classify organisms into trophic levels based on how they obtain energy and carbon compounds. These trophic levels represent the position of organisms in food chains.

Producers: These are autotrophic organisms that can produce their own food using external energy sources like sunlight. They form the base of food chains.
Primary Consumers: These are herbivores that consume producers.
Secondary Consumers: These are carnivores that feed on primary consumers.
Tertiary Consumers: These are carnivores that feed¹ on secondary consumers.

It’s important to note that many organisms can occupy multiple trophic levels depending on their diet. For example, a fox might eat both primary consumers (like rabbits) and secondary consumers (like mice). This flexibility in diet allows organisms to adapt to changing environmental conditions and resource availability.

C4.2.11—Construction of energy pyramids

Energy pyramids are a visual representation of the amount of energy available at each trophic level in an ecosystem. They are typically pyramid-shaped, with the base representing producers and each subsequent level representing consumers. The size of each bar in the pyramid corresponds to the amount of energy available at that trophic level.

Key points about energy pyramids:

Energy flow: Energy flows from producers to consumers in a one-way direction.
Energy loss: As energy flows through the food chain, a significant amount is lost as heat at each trophic level. This means that the amount of energy available to higher trophic levels is progressively smaller.
Pyramid shape: The pyramid shape of energy pyramids reflects the decrease in energy available at each trophic level.
Units: Energy is typically measured in units like kilojoules per square meter per year (kJ m⁻² yr⁻¹).

By understanding energy pyramids, we can appreciate the efficiency of energy transfer in ecosystems and the limitations on the number of trophic levels.

C4.2.12—Reductions in energy availability at each successive stage in food chains due to large energy losses between trophic levels

Energy flows through food chains in a one-way direction, with significant losses occurring at each trophic level. This energy loss limits the number of trophic levels in a food chain.

Three main forms of energy loss:

Incomplete consumption: Organisms at each trophic level do not consume all available energy. For example, predators often leave behind bones and other inedible parts of their prey. This energy is lost to decomposers.
Incomplete digestion: Not all ingested food is digested and absorbed. Indigestible materials, like cellulose in plants, are eliminated as waste. This energy is also lost to decomposers.
Cellular respiration: Organisms use energy from food for cellular respiration, which releases heat as a byproduct. This energy is not available to higher trophic levels.

These energy losses limit the length of food chains and the amount of biomass that can be supported at each trophic level. As a result, the top trophic levels in food chains typically have fewer individuals than the lower trophic levels.

C4.2.13—Heat loss to the environment in both autotrophs and heterotrophs due to conversion of chemical energy to heat in cell respiration

All organisms, both autotrophs and heterotrophs, convert some of their chemical energy into heat. This heat loss is an inevitable consequence of the laws of thermodynamics.

Mechanisms of Heat Loss:

Cellular Respiration: During cellular respiration, the oxidation of carbon compounds releases energy, some of which is used to produce ATP, while the rest is dissipated as heat.
Muscle Activity: When muscles contract, they generate heat as a byproduct. This is particularly noticeable in warm-blooded animals, such as birds and mammals, which maintain a constant body temperature.
Other Cellular Processes: Many cellular processes, such as active transport and protein synthesis, also generate heat as a byproduct.

The relatively low temperature of the wings suggests that heat is being lost to the environment, likely through evaporation of water from the wing surface. This helps to regulate the bird’s body temperature and prevent overheating.

C4.2.14—Restrictions on the number of trophic levels in ecosystems due to energy losses

The number of trophic levels in a food chain is limited by the amount of energy available at each level. As energy flows through the food chain, a significant portion is lost at each step due to respiration, heat loss, and incomplete consumption. This means that there is less energy available to support higher trophic levels.

Consequently, most food chains have only a few trophic levels, typically three or four. For example, a simple food chain might consist of a producer (like a plant), a primary consumer (like a herbivore), and a secondary consumer (like a carnivore). In some cases, there may be additional trophic levels, such as tertiary consumers. However, these higher-level consumers are often rare and have limited populations.

The limited number of trophic levels in food chains has important implications for ecosystem stability and energy flow. It highlights the importance of conserving biodiversity at all trophic levels to maintain the balance and functioning of ecosystems.

C4.2.15—Primary production as accumulation of carbon compounds in biomass by autotrophs

Primary production is the process by which autotrophs convert solar energy into organic matter through photosynthesis. This organic matter forms the base of food chains and supports all other life in ecosystems. Factors like sunlight, temperature, water, and nutrients influence primary production rates. Understanding primary production is essential for assessing ecosystem health and productivity.

C4.2.16—Secondary production as accumulation of carbon compounds in biomass by heterotrophs

Secondary production refers to the accumulation of organic matter by heterotrophs. Heterotrophs consume organic matter from other organisms, breaking it down into smaller molecules like amino acids and sugars. These molecules are then used to build their own bodies and tissues.

However, a significant portion of the ingested energy is lost as heat during cellular respiration. This means that the net production at each trophic level is lower than the gross production. As a result, secondary production decreases with each successive trophic level. This is why it is more efficient to consume plants directly than to consume animals that have consumed plants.

This concept has implications for food production and sustainability. Producing plant-based foods is generally more efficient than producing animal-based foods, as less energy is lost in the food chain. This is why there is growing interest in plant-based diets as a more sustainable way to feed the world’s population.

C4.2.17—Constructing carbon cycle diagrams

The carbon cycle is a biogeochemical cycle that describes the movement of carbon through Earth’s systems. It involves the exchange of carbon between the atmosphere, oceans, land, and organisms.

Key Components:

Carbon Pools: These are reservoirs of carbon, such as the atmosphere, oceans, and terrestrial ecosystems.
Carbon Fluxes: These are the processes that transfer carbon between different pools.

Main Carbon Fluxes:

Photosynthesis: Plants and other photosynthetic organisms absorb carbon dioxide from the atmosphere and convert it into organic compounds.
Respiration: Organisms¹ release carbon dioxide back into the atmosphere through respiration.
Feeding: Carbon is transferred from one organism to another through feeding.
Decomposition: Decomposers break down dead organisms and organic matter, releasing carbon dioxide into the atmosphere.

Understanding the carbon cycle is crucial for understanding how human activities, such as the burning of fossil fuels, impact the global climate. By analyzing the carbon cycle, scientists can develop strategies to mitigate climate change and protect the environment.

C4.2.18—Ecosystems as carbon sinks and carbon sources

Ecosystems can act as both carbon sinks and sources. Photosynthesis removes carbon dioxide from the atmosphere, while respiration releases it back. Factors like temperature, moisture, and nutrient availability influence an ecosystem’s role in the carbon cycle. Human activities like deforestation and fossil fuel burning can disrupt this balance, leading to increased atmospheric carbon dioxide and climate change.

C4.2.19—Release of carbon dioxide into the atmosphere during combustion of biomass, peat, coal, oil and natural gas

Biomass, peat, coal, oil, and natural gas are all carbon sinks, meaning they store carbon over long periods. When these materials are burned, the stored carbon is released into the atmosphere as carbon dioxide, contributing to greenhouse gas emissions and climate change.¹

Natural gas and oil: Formed over millions of years from the remains of marine organisms.
Coal: Formed from plant matter that accumulated in swamps and was buried under sediments.
Peat: Formed from partially decomposed plant matter in waterlogged bogs and swamps.

C4.2.20—Analysis of the Keeling Curve in terms of photosynthesis, respiration and combustion

The Keeling Curve, named after Charles Keeling, is a graph showing the continuous measurement of atmospheric carbon dioxide (CO2) concentrations at Mauna Loa Observatory in Hawaii since 1959.

Key trends observed in the Keeling Curve:

Annual Fluctuations:
- CO2 levels rise between October and May and decline between May and October.
- This seasonal variation is primarily driven by photosynthesis and respiration. During the Northern Hemisphere’s growing season (spring and summer), plants absorb CO2 through photosynthesis, leading to a decrease in atmospheric CO2 levels. In the fall and winter, as plants shed leaves and respiration rates increase, CO2 levels rise.

Long-Term Trend:
- The overall trend shows a steady increase in atmospheric CO2 concentrations. This increase is primarily attributed to human activities, such as the burning of fossil fuels and deforestation, which release large amounts of CO2 into the atmosphere.

The Keeling Curve provides compelling evidence for the impact of human activities on the global carbon cycle and the resulting climate change.

C4.2.21—Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis, and of photosynthesis on atmospheric carbon dioxide produced by respiration

Photosynthesis and respiration are two fundamental processes that are interconnected. Photosynthesis releases oxygen as a byproduct, which is essential for aerobic respiration. In turn, respiration releases carbon dioxide, which is used by photosynthetic organisms as a raw material.

Photosynthesis:

Photosynthetic organisms, such as plants, algae, and cyanobacteria, use sunlight to convert carbon dioxide and water into glucose and oxygen.¹
The oxygen released during photosynthesis is crucial for the survival of aerobic organisms, including humans and animals.²

Respiration:

Aerobic respiration is a process that uses oxygen to break down organic molecules, releasing energy in the form of ATP.
The carbon dioxide produced as a byproduct of respiration is used by photosynthetic organisms to fuel photosynthesis.

C4.2.22—Recycling of all chemical elements required by living organisms in ecosystems

Living organisms require a supply of chemical elements to survive and reproduce. Carbon, hydrogen, and oxygen are essential for building carbohydrates, lipids, and other organic compounds. Nitrogen and phosphorus are also crucial for the synthesis of proteins and nucleic acids. Additionally, around 15 other elements, such as iron, calcium, and magnesium, are needed in smaller quantities.

These elements are continuously recycled within ecosystems. Through processes like photosynthesis, respiration, decomposition, and nutrient cycling, elements are taken up by organisms, used in their bodies, and then returned to the environment. This recycling ensures a sustainable supply of essential elements for future generations of organisms.

The graphs in the image illustrate the global patterns of carbon dioxide uptake by photosynthesis (GPP), release by respiration (Reco), and net ecosystem exchange (NEE) across different latitudes. These patterns highlight the importance of ecosystems in the global carbon cycle and their role in regulating atmospheric carbon dioxide levels.

IB DP Biology Transfers of energy and matter Study Notes | New Syllabus