oxygen to the air. Both the organism and the
environment are affected by the interactions
On a global scale, plants and other photosynthetic
organisms have generated all the oxygen in the air.
Interactions between organisms ultimately result in the
cycling of nutrients in ecosystems.
Humans also interact with out environment, but
sometimes our interactions have drastic consequences.
The burning of fossil fuels has been increasing at
an ever-accelerating pace, and this practice
releases gaseous compounds into the
atmosphere, including CO2.
This global warming, a major aspect of global
climate change, has already had dire effects on
life-forms and their habitats all over planet Earth.
Scientists predict that even if we stopped burning
fossil fuels today, it would take several centuries
to return to preindustrial CO2 levels.
Theme: Life requires energy transfer and transformation
o The input of energy from the sun makes life possible: A
fundamental characteristic of living organisms is their use of
energy to carry out life’s activities.
o In the business of living, organisms often transform one form
of energy to another.
Chlorophyll molecules within the tree’s leaves
harness the energy of sunlight and use it to drive
photosynthesis, converting CO2 and water to
sugar and oxygen. The chemical energy in sugar
is then passed along by plants and other
photosynthetic organisms (producers) to
An animal’s muscle cells use sugar as fuel to
power movements, converting chemical energy to
kinetic energy, the energy of motion. The cells in