Essential Knowledge 2.A.1

All living systems require constant input of free energy.

Life requires a highly ordered system. Order is maintained by constant free energy input into the system. Loss of order or free energy flow results in death. Increased disorder and entropy are offset by biological processes that maintain or increase order.

Living systems do not violate the second law of thermodynamics, which states that entropy increases over time. Order is maintained by coupling cellular processes that increase entropy (and so have negative changes in free energy) with those that decrease entropy (and so have positive changes in free energy). Energy input must exceed free energy lost to entropy to maintain order and power cellular processes. Energetically favorable exergonic reactions, such as ATP --> ADP, that have a negative change in free energy can be used to maintain a positive free energy change.

Energy-related pathways in biological systems are sequential and may be entered at multiple points in the pathway. Illustrative examples include:

• Krebs cycle
• Glycolysis
• Calvin Cycle
• Fermentation

Organisms use free energy to maintain organization, grow and reproduce. Organisms use various strategies to regulate body temperature and metabolism. Illustrative examples include:

• Endothermy (the use of thermal energy generated by metabolism to maintain homeostatic body temperatures)
• Ectothermy (the use of external thermal energy to help regulate and maintain body temperature)
• Elevated floral temperatures in some plant species

Reproduction and rearing of offspring require free energy beyond that used for maintenance and growth. Different organisms use various reproductive strategies in response to energy availability. Illustrative examples include:

• Seasonal reproductiion in animal and plants
• Life-history strategy (biennial plants, reproductive diapause)

There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms -- generally, the smaller the organisms, the higher the metabolic rate. Excess acquired free energy versus required free energy expenditure results in energy storage or growth. Insufficient acquired free energy versus required free energy expenditure results in loss of mass and, ultimately, the death of an organisms.

Changes in free energy availability can result in changes in population size.

Changes in free energy availability can result in disruptions to an ecosystem. Illustrative examples include:

• Change in the producer level can affect the number and size of other trophic level.
• Change in energy resources levels such as sunlight can affect the number and size of the trophic levels.

Students should be able to:

LO 2.1 Explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce.

LO 2.2 Justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems.

LO 2.3 Predict how changes in free energy availability affect organism, populations and ecosystems.