Energy Flow in Ecosystems Obeys the first and second laws of thermodynamics Energy passes through an ecosystem unidirectionally – meaning it is non-reversible. Terminates its functional use in an ecosystem as heat Follows a variety of paths through an ecosystem that can be generalized by the characterization of a food chain or food web.

First law of thermodynamics: Energy cannot be created or destroyed, only transferred or transformed. An organism may absorb energy from its surroundings, or may give up energy to its surroundings, but the total energy content of an organism and its surroundings is the same. The amount of mass/energy present in the universe when it formed 18 bya equals the amount of energy present in the universe today. An organism cannot create the energy it requires to live. It must capture its energy from the environment to use for biological work. This process involves the transformation of energy from one form to another.

Second law of thermodynamics: entropy in an isolated system not in equilibrium will increase over time. As each energy transformation occurs, some energy is changed to heat that is released into cooler environments. No other organism can ever reuse this energy for biological work. It is lost from the biological point of view. The amount of usable energy available to do work in the universe decreases over time. In a sense, as the energy becomes less usable it becomes more diffuse, or disorganized. A measure of this disorganization is called ENTROPY.

-continued……. Entropy is a measure of the degree of randomness, or disorder in a system. Entropy is always increasing in the universe….. As energy transformations occur according to the first law of thermodynamics heat is lost during the transformation, which results in an increase in entropy in the universe. When a primary consumer chows on a lunch of grass, nearly 90% of the energy originally manifest in the grass is lost to entropy. Only 10% goes into ‘building’ the biological base of the primary consumers.

The implications of this fundamental law of nature….. Ecological pyramid – a graphic display that shows the trophic inter-relationships of an ecosystem. Trophic – pertaining to the position of an organism in a food chain.

The relative volume/area of each trophic level in an ecological pyramid is reflective of the relative quantities of: Energy Biomass Population

Some important considerations Mass and energy work their way up a food chain. However, 80-95% of energy is lost in the process of being transferred to a higher trophic level. So, a salad that you consume may present an original amount of energy of 300 kcal, only 30 kcal of the energy will end up being used to make biomolecules. The rest is lost as heat. This represents the second law of thermodynamics in action.