Photosynthesis and Respiration

Overview of Energy Conversion in Living Organisms

Photosynthesis and respiration are fundamental biological processes that enable organisms to convert energy from the sun into usable chemical energy and subsequently utilize it for cellular activities. These processes are central to energy flow in ecosystems.

• Producers/Autotrophs use solar energy to synthesize glucose through photosynthesis.

• Glucose produced is used for two main purposes:

  • Cellular respiration (to make ATP)

  • Building body structures (biomass)

Photosynthesis

• Definition: The process by which plants, algae, and some bacteria convert light energy, water, and carbon dioxide into glucose and oxygen.

• General Equation:

• Example: Green plants in a forest use photosynthesis to produce the glucose needed for growth and energy.

Respiration

• Definition: The process by which organisms break down glucose in the presence of oxygen to release energy (ATP), carbon dioxide, and water.

• General Equation:

• Example: Animals and plants use respiration to convert stored glucose into usable energy for cellular functions.

Energy Flow and Trophic Levels

Transfer of Energy Through Food Chains

Energy moves through ecosystems via food chains, from producers to various levels of consumers. At each trophic level, only a fraction of the energy is transferred, with the rest lost as heat or used for metabolic processes.

• Only about 10% of the energy from one trophic level is transferred to the next.

• Example: A caterpillar eats 200J of energy:

  • 100J is excreted as waste

  • 67J is lost to cellular respiration (CR)

  • 33J is retained for growth and biomass

• Decomposers recycle nutrients and energy throughout the ecosystem.

• From the sun, about 90% of energy is not absorbed by the primary producer.

Energy Pyramid Table

This table summarizes the decrease in dry mass and energy at each trophic level.

Each tier represents total dry mass per trophic level. Water is not included; 1g dry mass ≈ 5 KCal.

Ecological Pyramids

Types and Significance

Ecological pyramids visually represent the distribution of energy, biomass, or numbers among trophic levels in an ecosystem. The most important pyramids are those of energy and biomass, which typically show a sharp decrease from producers to consumers.

• Energy Pyramid: Shows energy flow and loss at each trophic level.

• Biomass Pyramid: Illustrates the total mass of living matter at each level.

• Numbers Pyramid: Represents the number of organisms at each level.

• Primary producers (plants, algae) have the greatest influence on ecosystem structure and function.

Productivity in Ecosystems

Gross and Net Primary Production

Productivity measures the rate at which energy is converted into biomass in an ecosystem. It is a key indicator of ecosystem health and capacity to support life.

• Gross Primary Production (GPP): Total amount of photosynthesis and glucose made in an ecosystem.

• Net Primary Production (NPP): GPP minus the energy used for cellular respiration by primary producers.

• Units: Energy per unit area per unit time (e.g., J/m2/yr).

• Example: Tropical rainforests and coral reefs have high NPP, while deserts and open oceans have low NPP.

Calculating Energy Efficiency

Production Efficiency in Ecosystems

Production efficiency is the percentage of assimilated energy that is converted into new biomass. It is calculated as follows:

• Formula:

• Application: Used to compare how efficiently different organisms convert energy into growth.

Summary Table: Key Concepts in Energy Flow

Additional info: Academic context and definitions have been expanded for clarity and completeness.