Energy and Matter Exchange in the Biosphere - Notes

Focusing Questions

• Why can matter be recycled in the biosphere, while energy must be supplied constantly?
• What roles do photosynthesis and cellular respiration play in the transfer of energy and the availability of matter in the biosphere?
• How do human activities and technologies affect the quality and availability of energy and matter in the biosphere?

General Outcomes

• Explain the constant transfer of energy through the biosphere and its ecosystems.
• Explain the cycling of matter through the biosphere.
• Describe energy and matter exchange in the biosphere as an open system and explain how this maintains equilibrium.

Unit Contents

• Chapter 1: Energy Transfer in the Biosphere.
• Chapter 2: Cycles of Matter.

Unit Prerequisite

• This unit builds on knowledge of the hydrologic cycle.

The Study of Ecology

• In 1866, Ernst Haeckel defined ecology from the Greek word for "house" or "home".
• Ecology Defined: The study of the relationships between living things (organisms) and their non-living surroundings (the environment).
• Ecologists study diverse events from cellular processes of bacteria to the flow of carbon atoms through the planet.
• Ecology involves observations, insights, and innovations from many areas of study.

The Biosphere— Earth’s Life System

• System: An object or group of objects chosen for study.

• Surroundings: Everything other than the system.

• Boundary: Separates systems from surroundings; can be real or arbitrary.

• Open System: Allows energy and matter to cross the system’s boundary.

• Closed System: Allows only energy to cross the boundary.

• Earth as a System:

  • Matter: Earth is essentially a closed system.
  • Energy: Earth is an open system, receiving energy from the Sun.

• Energy Flow:

  • Solar energy enters the atmosphere.
  • Some energy is reflected back into space.
  • Some energy is absorbed by the atmosphere.
  • Remaining energy reaches Earth's surface, where it is either reflected or absorbed.
  • Eventually, all absorbed energy is radiated back into space as heat.

• Biosphere: The thin layer of air, land, and water on and in which all life on Earth is found.

• Components of the Biosphere:

  • Atmosphere: The gaseous part of Earth, mainly within 10 km of the surface.
  • Hydrosphere: All of the water (solid and liquid) that exists and moves through the geosphere.
  • Geosphere: The solid, mainly rocky part of Earth (also called the lithosphere).
  • Biosphere: All areas on Earth inhabited by and supporting life.

Chapter Concepts

1. 1 How Energy Enters the Biosphere

• Producers (autotrophs) capture and store energy via photosynthesis or chemosynthesis.
• Consumers (heterotrophs) and decomposers consume autotrophs and other heterotrophs.
• Matter cycles in the biosphere, but energy follows a one-way path.

1. 2 How Energy Is Transferred in the Biosphere

• Food chains and food webs model feeding relationships and energy transfer between trophic levels.

• Ecological pyramids model relationships between trophic levels quantitatively.

• Changes affecting one trophic level affect other trophic levels due to interconnectedness.

• All organisms need energy to grow and maintain their lives.

• Energy is released from carbohydrates and other energy-rich organic molecules through cellular respiration (or fermentation in some species).

• Cellular Respiration: The process that releases energy in organisms.

  • Word Equation: carbohydrates (sugars and starches) + oxygen → carbon dioxide + water + energy
  • Chemical Equation: C6H{12}O6(s) + 6O2(g) \rightarrow 6CO2(g) + 6H2O(l) + energy

• Photosynthesis: The process by which plants, algae, and some bacteria use the Sun’s light energy to convert carbon into carbohydrates.

  • Word Equation: carbon dioxide + water + light energy → carbohydrates (sugars and starches) + oxygen
  • Chemical Equation: 6CO2(g) + 6H2O(l) + light \space energy \rightarrow C6H{12}O6(s) + 6O2(g)

• Producers (Autotrophs): Organisms that use the Sun’s energy to produce food for themselves.

• Consumers (Heterotrophs): Organisms that obtain energy by consuming other organisms or absorbing nutrients from them.

Radiant Energy

• Earth receives approximately 10^{22} J (joules) of the Sun’s radiant energy each day.

Outcomes for Radiant Energy:

• About 30% is reflected back into space from clouds, particles in the atmosphere, or from land and ocean surfaces.
  • Albedo: The measure of reflected energy. Earth’s average albedo is about 30%. Light-colored surfaces and thick cloud cover have high albedos (80-90%), while dark surfaces like forests and water have lower albedos (25% or less).
• About 19% is absorbed by atmospheric gases like water vapor and carbon dioxide, heating the atmosphere, and some is radiated back into space.
• About 51% reaches Earth’s surface, warming the planet. Some heat radiates upward into the atmosphere and out into space.
• Producers only capture a small fraction of the total energy that reaches the ground. Only 1-2% of the total radiant energy reaching Earth is converted into chemical energy through photosynthesis.
• Producers generate about 150 billion to 200 billion tonnes of organic matter each year, supporting most life on Earth.

Chemosynthetic Producers

• Chemosynthesis: The process by which some bacteria capture energy stored in the chemical bonds of molecules (e.g., hydrogen sulfide) in the absence of sunlight.
  • Unlike photosynthesis, chemosynthesis produces sulfuric acid as a byproduct instead of oxygen.
• Chemosynthetic producers have been discovered in extreme environments: deep-sea vents, cold-water seeps, hot springs, salty lakes, and deep caves.
• Nitrifying bacteria in the soil convert ammonia to other nitrogen compounds, playing an important role in the nitrogen cycle.

Consumers (Heterotrophs) Categorization

• Herbivores: Primary consumers that eat plants.
• Carnivores: Animals that eat other animals.
  • Secondary Consumers: Carnivores that eat mainly herbivores.
  • Tertiary Consumers: Carnivores that eat other carnivores.
• Decomposers: Obtain energy by eating or absorbing leftover or waste matter, including feces, dead bodies, or body parts. Decomposers recycle organic and inorganic matter back into the environment.

The Fate of Energy in the Biosphere

• Earth is essentially a closed system for matter; atoms and molecules are cycled and reused in the biosphere.
• Energy follows a one-way path through the biosphere.

Laws of Thermodynamics:

• First Law: Energy cannot be created or destroyed, only converted from one form to another or transferred from one object to another.
• Second Law: With each conversion of energy, there is less energy available to do useful work. Some energy is always dispersed as unusable heat.
• Consequences: A constant supply of energy, primarily from the Sun, is necessary to sustain life. Producers are essential because they are the means by which all organisms are connected through energy transfer.