C4.2 Transfer of Energy & Matter
Transfer of Energy & Matter in Ecosystems
Contents
Ecosystems as Open Systems
Energy Flow in Ecosystems
Obtaining Carbon Compounds in Ecosystems
Trophic Levels
Pyramids of Energy: Skills
Energy Losses
Primary & Secondary Production
The Carbon Cycle
Nutrient Cycling
Ecosystems as Open Systems
Definition of Ecosystems
An ecosystem is defined as a group of organisms interacting with each other and with the non-living parts of the environment. Ecosystems consist of:
Biotic Components: Living organisms (plants, animals, microorganisms).
Abiotic Components: Non-living elements (temperature, light, water, minerals).
Characteristics of Ecosystems
Ecosystems vary greatly in size and scale, ranging from small ponds in a back garden to the open ocean.
Ecosystems also vary in complexity. For example, a desert is a relatively simple ecosystem, while a tropical rainforest is very complex.
Example of Ecosystems
An ocean serves as an example of a complex ecosystem with a large community of organisms including fish, crustaceans, corals, algae, and plants. The abiotic components, like salinity, pH, temperature, and light intensity, influence the community of organisms by providing habitat and nutrients essential for survival and reproduction.
Open Systems vs. Closed Systems
Ecosystems are open systems, allowing both energy and matter to enter and exit. Energy enters as sunlight and flows through as stored chemical energy, while matter enters through the arrival of organisms.
When an organism leaves, such as during migration, the matter stored in its tissues is removed.
Although ecosystems are open, they are often self-contained.
Comparison with Closed Systems
In a closed system:
Matter is recycled without entering or leaving the system.
Energy can still enter and leave.
An example of a closed system is Earth.
Energy Flow in Ecosystems
Sunlight as an Energy Source
The sun is the primary energy source for most food chains, where light energy is converted by producers into chemical energy through photosynthesis. This energy then flows through the ecosystem as organisms consume one another.
Process of Photosynthesis
Photosynthesis involves:
Conversion of light energy into chemical energy.
Production of organic molecules like glucose, which can be used in respiration or stored as starch, lipids, and amino acids.
Energy Transfer in Food Chains
Chemical energy stored in plant tissues is passed to primary consumers when they ingest plants.
Energy is further transferred up the food chain, reaching secondary consumers.
After an organism dies, its stored chemical energy is transferred to decomposers like detritivores and saprotrophs.
Constructing Food Chains
Food Chains illustrate feeding relationships, with arrows indicating energy transfer between trophic levels.
Food Webs show connections among multiple food chains, depicting the complex feeding relationships present in an ecosystem.
Obtaining Carbon Compounds in Ecosystems
Decomposers and Nutrient Cycling
Inorganic nutrients enter the food chain and are converted into carbon compounds.
Essential for cycling of nutrients, decomposition breaks down bodies of dead organisms and organic waste, releasing nutrients back to the soil.
Types of Decomposers
Detritivores: Break down tissues.
Saprotrophs: Release enzymes that decompose organic molecules, absorbing some nutrients and releasing others into the soil.
Autotrophs and Heterotrophs
Autotrophs
Autotrophs synthesize their own organic molecules from inorganic sources.
Photoautotrophs: Use light energy for photosynthesis (e.g. plants).
Chemoautotrophs: Obtain energy by oxidizing inorganic compounds.
Heterotrophs
Heterotrophs obtain carbon compounds by ingesting tissues from other organisms, which can occur both inside and outside their bodies.
Types of Heterotrophs
Consumers (herbivores, carnivores), detritivores, and saprotrophs contribute to nutrient uptake and cycling.
Trophic Levels
Description of Trophic Levels
Trophic Level | Name of Trophic Level | Description |
|---|---|---|
1 | Producers | Organisms producing their own carbon compounds. |
2 | Primary Consumers | Herbivores feeding on plant tissues. |
3 | Secondary Consumers | Carnivores preying on primary consumers. |
4 | Tertiary Consumers | Carnivores preying on secondary consumers. |
5 | Quaternary Consumers | Apex predators with no natural predators. |
Significance of Trophic Levels
Trophic levels illustrate energy transfer within a food chain and can also be identified in complex food webs.
Pyramids of Energy: Skills
Energy Representation in Pyramids
Pyramids of energy depict the amount of energy contained in biomasses at each trophic level.
Bars in the pyramid must be drawn to scale and labeled appropriately (e.g. units in kJ m^-2 year^-1).
Energy loss occurs at every trophic level due to multiple factors, including incomplete consumption and respiration.
General Rules
Roughly 10% of energy is passed on at each trophic level, causing a decrease in total energy available as one moves up the pyramid.
Energy Losses
Nature of Energy Losses
Not all energy is stored as biomass when organisms consume one another. About 90% of energy gets lost due to:
Parts of food not getting consumed.
Ineffectiveness of digestion (e.g., cellulose).
Heat loss during respiration.
Excretion of waste products.
Role of Decay Organisms
Decomposers like detritivores and saprotrophs contribute to the breakdown of organic matter, playing a crucial role in energy flow through ecosystems.
Primary & Secondary Production
Primary Production
Definition: Accumulation of biomass in autotrophs through photosynthesis, converting light energy into chemical energy.
Rates of primary production vary by biome, heavily influenced by sunlight, temperature, and rainfall (tropical forests having the highest rates).
Secondary Production
Heterotrophs store energy through secondary production by ingesting organic biomass.
The rate of secondary production is always lower than that of primary production due to respiratory losses and metabolic waste.
The Carbon Cycle
Components of the Carbon Cycle
The carbon cycle involves both organic (e.g. in living organisms) and inorganic carbon (e.g. as CO2).
Carbon stores (pools/sinks) include oceans and fossil fuels, while fluxes (transfers) involve processes like photosynthesis and combustion.
Carbon Sinks and Sources
Carbon Sink: Absorbs and stores carbon, e.g. plants during photosynthesis.
Carbon Source: Releases carbon, e.g. combustion of fossil fuels.
Human Influence
Human combustion of fossil fuels and biomass increases atmospheric CO2 levels, impacting climate. The Keeling Curve illustrates changes in atmospheric CO2 due to seasonal variances and overall human impact.
Nutrient Cycling
Interaction Between Autotrophs and Heterotrophs
Photosynthesis and respiration create a cycling relationship where CO2 is utilized by autotrophs and released by heterotrophs.
Importance of Recycling
Nutrients like Nitrogen, Phosphorus, and others are cycled through ecosystems to ensure the sustainability of living organisms.
Decomposers are critical in recycling, breaking down organic matter for use by producers again.
These comprehensive notes serve as an extensive overview of ecosystem dynamics, energy transfer, and the carbon cycle necessary for a deeper understanding in the fields of biology and environmental science.