BackGeneral Biology Review: Ecology, Energy, and Photosynthesis (Session 1)
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Ecology and the Greenhouse Effect
The Greenhouse Effect
The greenhouse effect is a natural process that warms the Earth's surface. It occurs when certain gases in Earth's atmosphere trap heat, preventing it from escaping into space.
Greenhouse gases (such as carbon dioxide, methane, and water vapor) trap heat in the atmosphere, maintaining Earth's temperature at a level suitable for life.
Atmospheric greenhouse gases reflect some solar radiation back to space, but also absorb and re-emit infrared radiation, warming the planet.
Clouds can trap greenhouse gases in the lower atmosphere, enhancing the effect.
The ozone layer traps solar radiation in the outer atmosphere, protecting living organisms from harmful ultraviolet (UV) rays.
Example: Without the greenhouse effect, Earth's average temperature would be much colder, making it inhospitable for most current life forms.
Energy in Biological Systems
What is Heat?
Heat is a form of energy that is transferred between systems or objects with different temperatures. In biological systems, heat is often a byproduct of metabolic processes.
Heat is related to temperature, which measures the average kinetic energy of particles in a substance.
Heat is not a characteristic of life, but all living things exchange heat with their environment.
Example: During cellular respiration, some of the chemical energy from food is converted to heat, helping to maintain body temperature in warm-blooded animals.
Levels of Biological Organization
Population
A population is a group of individuals of the same species living in the same place at the same time.
Organism: An individual living thing.
Community: All the populations of different species living and interacting in an area.
Ecosystem: A community of organisms and their physical environment interacting as a system.
Example: All the oak trees in a forest make up a population of oaks.
Photosynthesis and the Calvin Cycle
Products of the Calvin Cycle
The Calvin Cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. Its main product is glucose, a simple sugar.
The chemical formula for glucose is C6H12O6.
Other products include ADP and NADP+, which are recycled in the light-dependent reactions.
Equation:
Example: The glucose produced can be used for energy or as a building block for other organic molecules.
Ecology: Keystone Species
Keystone Species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Removing a keystone species can cause dramatic changes in the structure of an ecosystem.
In San Diego County, the great horned owl may function as a keystone species due to its role as a top predator, helping to regulate populations of other species.
Other options, such as eucalyptus (an introduced plant), soil bacterium Bacillus megaterium, and rabbit, are less likely to be keystone species in this context.
Example: The removal of sea otters (a keystone species) from kelp forest ecosystems leads to an overpopulation of sea urchins, which then overgraze kelp and reduce biodiversity.
