Topic 1: Systems and Models Energy in systems Describe how the first and second laws of thermodynamics are relevant to environmental systems Explain the nature of equilibria

Systems exhibit entropy. The world always has the same amount of energy, it just changes form. In systems energy is transformed or transferred. Definition: Entropy is a measure of disorder in a system. Heat energy is highly disordered.) Real world comparison of entropy levels: Orderly system: Sandcastle – has low entropy (more organized) Disorderly system: Pile of sand – has high entropy (less organized) Describe how the first and second laws of thermodynamics are relevant to environmental systems.

First Law of Thermodynamics* Energy is neither created or destroyed. (*a.k.a conservation of energy.) *In your own words, describe what is happening to energy. - In a simple food chain, energy is transferred from sunlight to the plants, to the zebra and then to the carnivore. Solar energy is transformed into chemical energy (food molecules) in the plant during photosynthesis. When the plant is eaten, the food energy is transferred to the zebra, which is eaten by the lion and the food energy is transferred again. With each transfer some energy is transformed into heat. The total amount of energy in the form of heat or food that is transferred each time is the same.

Second Law of Thermodynamics The entropy of a system that is not in equilibrium will increase over time. Energy conversions are never 100%, some energy is lost to the environment as heat. Example: Food Chain – At each stage of the food chain most of the energy is lost in heat. Plants convert solar energy into food at only 1-2% efficiency. Plant to herbivores and herbivores to carnivores is only 10%. Energy = work + heat

- In a simple food chain, energy is transferred from sunlight to the plants, to the zebra and then to the carnivore. Solar energy is transformed into chemical energy (food) in the plant during photosynthesis with about 1-2% efficiency, most is lost as heat. Food is transferred from plant to consumer, that consumer is eaten by another with 90% of the energy lost as heat during each transfer. *In your own words, describe what is happening to energy.

Explain the nature of equilibria. A state of balance exists among all of the components of a system in equilibrium. – Systems do change, but the changes tend to be within limits. Equilibrium: the tendency of a system to return to a balanced, self-regulating state following disturbance.

Steady state equilibrium - there is continuous input and output of energy and matter, but the system remains in a constant state. There are short term fluctuations, but no long- term changes

Back to the Forest System… For example, if a forest is in steady-state equilibrium energy is entering and leaving, and matter is being recycled. However, there are no long term changes. Transpiration – evaporation of water when during plant respiration. Leaching – the downward movement of soluble material including nutrients such as minerals.

Static Equilibrium is not in Living Systems Static-state equilibrium: there is no change over time. Example: most non-living systems, such as a pile of rocks. NOT in living systems (life involves exchange of energy and matter with the environment). Stable equilibrium – when a system returns to a previous equilibrium after a disturbance. Ex.) mature forest → fire! → back to mature forest Unstable equilibrium – when a system reaches a new equilibrium after a disturbance Ex.) native prairie grassland → introduction of invasive species → invasive species grassland

Vocabulary Set I. Entropy Equilibrium Steady-state Equilibrium Static-state Equilibrium Nutrient leaching Transpiration (aka evapotranspiration)