1. Cycling of Matter C4.2

Cycling of Matter

  • Matter can be recycled in ecosystems because it is composed of elements that can be reused within various biochemical cycles.

  • Energy, in contrast, flows and is eventually lost as heat, leading to its inability to be recycled.

Heat Loss in Organisms

  • Both autotrophs (plants) and heterotrophs (animals) convert chemical energy to heat during cellular respiration.

  • Energy transfers are not 100% efficient; typically, only 10-20% of energy is usable.

  • Heat production occurs when ATP is generated and used in cells.

Trophic Levels and Energy Losses

  • Energy loss restricts the number of trophic levels in ecosystems.

  • Each successive stage in food chains generally contains fewer or smaller organisms, reducing biomass without decreasing energy content per unit mass.

Primary Production

  • Defined as the accumulation of carbon compounds in biomass by autotrophs.

  • Measured in grams of carbon per unit area per unit time (g m−2 yr−1).

  • Different biomes have varying capacities to accumulate biomass, which occurs when autotrophs and heterotrophs grow or reproduce.

Secondary Production

  • Refers to the accumulation of carbon compounds in biomass by heterotrophs.

  • Secondary production is typically lower than primary due to biomass loss during cellular respiration when carbon is converted to CO2 and H2O.

Carbon Cycle Diagrams

  • Understanding how carbon is recycled in ecosystems involves illustrating processes like photosynthesis, feeding, and respiration.

Ecosystems as Carbon Sinks/Sources

  • If photosynthesis exceeds respiration, ecosystems capture CO2 (sink).

  • Conversely, if respiration exceeds photosynthesis, they release CO2 (source).

Combustion and Carbon Dioxide Release

  • Combustion of biomass, peat, coal, oil, and natural gas releases CO2 into the atmosphere.

  • Natural combustion can occur from lightning strikes, but human activities have significantly increased these rates.

Analysis of the Keeling Curve

  • The Keeling Curve illustrates fluctuations in atmospheric CO2 levels, linking photosynthesis, respiration, and combustion.

  • Annual fluctuations and long-term trends reflect the interactions among these processes.

Dependence of Respiration and Photosynthesis

  • Aerobic respiration depends on O2 produced by photosynthesis.

  • Photosynthesis relies on CO2 produced by heterotrophs during respiration, illustrating major interactions between autotrophs and heterotrophs.

Recycling Chemical Elements

  • All chemical elements used by living organisms are recycled in ecosystems.

  • Decomposers play a crucial role in this recycling process.

  • Detailed knowledge of the nitrogen cycle and other nutrient cycles is not required.

Energy Transformations

  • Energy transformations in living organisms are inefficient, typically yielding only 10-20%, measured in kJ/year/m2.

  • Energy flow can be visually represented by pyramids of energy.

Measuring Energy Content of Biomass

  • To study energy transfer in ecosystems, biomass combustion can be measured.

  • Specific heat capacity of water aids in calculating energy from biomass.

  • Heat energy produced by burning biomass is used to raise the water temperature, allowing for energy content calculations.

Biomass Definitions

  • Biomass refers to the total mass of organisms within one trophic level, consisting of cellular structures and carbon compounds.

  • Energy losses lead to reduced biomass at higher trophic levels.

Limitations in Trophic Levels

  • Energy limitations in food chains are judged by the available energy at the start; abundant energy can support multiple levels.

Types of Productivity in Ecosystems

  • Primary Productivity: Total biomass of carbon compounds created through photosynthesis.

  • Gross Primary Productivity (GPP): Total biomass produced in plants.

  • Net Primary Productivity (NPP): GPP minus biomass lost to respiration; available to consumers.

  • Secondary Productivity: Accumulation of carbon compounds from food through heterotrophs.

Net Primary Productivity by Biome

  • Varies significantly across biomes, with tropical forests showing high productivity compared to deserts and tundras.

  • Estimates for primary production rates are often based on satellite data, indicating global primary production.

Consequences of Energy Loss in Production

  • Not all biomass is transferred to the next trophic level, leading to lower secondary production.

  • Crop production generally surpasses that of meat and animal products.

Interdependence of Photosynthesis and Respiration

  • Autotrophs depend on atmospheric O2 produced through photosynthesis while contributing CO2 through respiration.

Nutrient Cycling

  • Chemical elements essential for living organisms are sourced from the environment and recycled.

  • Autotrophs obtain nutrients (C, H, O, N, P) from abiotic sources, while heterotrophs obtain them from consumed food.

Decomposers' Role in Nutrient Recycling

  • Decomposers, including certain bacteria, break down organic matter, aiding in the recycling of nutrients within ecosystems.

  • They convert complex organic matter into simpler forms that can be reused by other organisms.

Nitrogen Cycle

  • Important cycles involve various bacteria that capture atmospheric nitrogen (N2) and convert it into forms usable by plants.

  • Nitrogen is assimilated in plant proteins and later consumed by animals.