Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Cycles and Ecosystems

Energy Flow Within and Between Living Systems
As matter and energy flow through different levels of organization of living system--cells, organs, organisms, communities--and between living systems and the physical environment, chemical elements are recombined in different ways. Each recombination results in storage and dissipation of energy into the environment as heat. Matter and energy are conserved in each change.

All matter tends toward more disorganized states. Living systems require a continuous input of energy to maintain their chemical and physical organizations. With death, and the cessation of energy input, living systems rapidly disintegrate.

The complexity and organization of organisms accommodates the need for obtaining, transforming, transporting, releasing, and eliminating the matter and energy used to sustain the organism.

Further Description:

All life, from the simplest cell to the most complex organism, requires a constant supply of energy to maintain itself. Most organisms receive their energy from sugar produced by photosynthesizing organisms.

Ecosystems as well require a continual input of energy from the sun in order to sustain community structure. The energy flow in all ecosystems sets up a food pyramid from producers to consumers. A small amount of sunlight (1% to 3%) is converted by plants (producers). Only 10% of stored energy in plants is available to herbivores (primary consumers), and only 10% of that energy is available to secondary consumers. Much of the energy consumed is dissipated as heat through respiration of organisms. The productivity of any ecosystem is based on the amount of energy stored by the producers that can be passed on to consumers. Measurements of productivity must include rates of photosynthesis in excess of respiration.

All living systems require energy to be maintained. Death of protoplasm results in a "shutdown" of enzyme systems, DNA function, and all activities that require energy, such as growth, reproduction, and metabolism. A constant supply of energy is essential to maintain the activities of living systems. Energy production involves the transfer of electrons from atoms to molecules and from molecules to compounds. Living systems are more complex than what remains after death and the processes that follow death. The degenerated remains are far simpler and reflect an increase in entropy (greater disorder).

Metabolism is based upon the activities of living protoplasm. These activities and associated metabolism account for a continual rearrangement of electrons whereby energy is converted from one form to another. The laws of thermodynamics apply to every living system, from the simplest cell to the most complex organisms on Earth.

Concepts Needed:

Grade 9

Community, respiration, productivity, energy flow, food chain, biomass

Grade 10

Entropy, biomass, productivity, trophic levels, chemical cycles

Grade 11

Pyramids, models, productivity

Grade 12

Exergonic and endergonic reactions, entropy

Empirical Laws or Observed Relationships:

First and second laws of thermodynamics

Theories or Models:

Food chains, food webs, trophic pyramids, biomass, energy flow, ten percent law, Hutchinson productivity model

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Micro-Unit Description:

Cycles and Ecosystems
Students should examine fundamental energy transfer along a typical food chain. (b) Students should examine food chain relationships and the importance of inorganic compounds. They can study the water cycle, including transpiration by plants, as an important factor in the maintenance of ecosystems.

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