Cell Energy Sources, ATP, and the Utilization of Energy
NSES Generalization
The chemical bonds of food molecules contain energy. Energy is released when the bonds of food molecules
are broken and new compounds with lower energy bonds are formed. Cells usually store this energy
temporarily in phosphate bonds of a small high-energy compound called ATP.
The energy for life primarily derives from the sun. Plants capture energy by absorbing light and using it to
form strong (covalent) chemical bonds between the atoms of carbon-containing (organic) molecules. These
molecules can be used to assemble larger molecules with biological activity (including proteins, DNA, sugars,
and fats). In addition, the energy stored in bonds between the atoms (chemical energy) can be used as sources
of energy for life processes.
The distribution and abundance of organisms and populations in ecosystems are limited by the availability of
matter and energy and the ability of the ecosystem to recycle materials.
Further Description
Of prime importance to all cell activities is the ability of the cell to convert high energy yielding
compounds, such as sugar, to a usable chemical energy. The chief source of energy in the cell is from
carbohydrates. Carbohydrates are broken down in order to produce the energy molecule ATP. The process
of conversion, referred to as cell respiration, takes place in the mitochondrion. In the presence of oxygen,
glucose is oxidized by a series of enzyme-controlled reactions that provide the energy to synthesize many
ATP molecules. ATP, in turn, will release the necessary energy for cell activities.
When oxygen is not present, this metabolic pathway is altered and glucose will yield a very small amount
of energy with end products of alcohol or lactic acid. In yeast the process of producing alcohol is called
fermentation.
The health and maintenance of a population in any ecosystem is controlled by factors that limit its survival.
Limiting factors influence a population in terms of density, range of distribution, dispersion patterns, and
niche selection. An understanding of a population’s range of tolerance to these factors becomes critical to
an understanding of its status in an environment. Physical factors that tend to become limiting in either
minimum or maximum quantities are light, temperature, water, required nutrients, atmospheric gases,
space, currents, and pressure.
Concepts Needed
Grade 9
Photosynthesis, cell respiration, carbohydrates, kilocalories, calories, temperature
Grade 10
Atmosphere, nutrients, bond energy, energy molecules, ATP, oxidation-reduction
Grade 11
Glycolysis, citric acid cycle, ATP, mitochondrion, membrane structure, oxidative phosphorylation, bond
energy
Grade 12
Niche, habitat, limiting factors, range of tolerance, populations
Empirical Laws or Observed Relationships
Law of the minimum, law of tolerance
Theories or Models
Krebs cycle, chemiosmosis, glycolysis, oxidative phosphorylation, citric acid cycle