carbon dioxide concentration, the availability of water, and temperature.
Cellular Respiration
Organisms dependent on photosynthetic organisms (autotrophs) are called
heterotrophs. In general, cellular respiration is the opposite of photosynthesis. In
respiration, glucose is oxidized by the cells to produce carbon dioxide, water,
and chemical energy. This energy is then stored in the molecule adenosine
triphosphate (ATP).
C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy Food Webs and Trophic LevelsPrimary producers (autotrophs) are plants that convert solar energy into chemical
energy through photosynthesis. Primary consumers are heterotrophs (herbivores
—plant eaters) and get their energy by consuming primary producers. Primary
consumers have developed defense mechanisms against predation, some of
which include speed, flight, quills, tough hides, camouflage, and horns and
antlers.
Secondary (and higher) consumers are also heterotrophs and may be either
strictly carnivores (meat eaters) or omnivores (eat both plants and animals).
Ecological Pyramids and the 10% Rule
During the transfer of energy from one trophic level to the next, only about 10%
of the energy is used to convert organic matter into tissue. The remaining energy
is generally lost in the form of heat during respiration, metabolic processes,
temperature regulation, incomplete digestion (e.g., elephants only digest 40% of
the material they consume), decay of waste products, and so on.
Sunlight is the ultimate source of energy required for most biological
processes. A little over 50% of solar energy is absorbed in the atmosphere and
scattered into space. Of the sun’s energy that reaches Earth, 35% is spent to heat
water and land areas and to evaporate water. Of the approximately 8% of light
energy striking a leaf’s surface, about 15% is reflected, 5% is transmitted, and
80% is absorbed as heat; only about 1% of the total light energy that strikes a
leaf is used for photosynthesis. The amount of available energy decreases
approximately 10% from one stage to the next with the majority of energy being
lost in the form of heat.