When you eat, you are putting energy, or calories, into your body. Where does the energy originate?
Energy enters most ecosystems in the form of sunlight. Organisms, called producers, convert the sunlight into chemical energy using a process called photosynthesis . All organisms who cannot make their own energy are called consumers and they are directly or indirectly dependant on the output of the producers. However, there are exceptions; the deep sea does not receive sunlight so bacteria at these depths are capable of producing food from chemicals.
A food chain is the pathway along which food is transferred from one organism to another. Organisms are divided into trophic levels to help us determine where they fit into an ecosystem. Producers will always be positioned in the first trophic level. Primary consumers, those that consume only producers, are located at the second trophic level . Secondary consumers are at the third trophic level, and so on.
Decomposers (e.g., worms, maggots, bacteria) are a special type of consumer that break down organic wastes and the remains of dead organisms at all of the trophic levels. Decomposers often form a major link between the primary producers and the consumers.
The amount of energy in an ecosystem (biomass) is dependent on:
How much sunlight it receives.
Seasonal changes in the environment (precipitation, temperature, etc.).
The availability of inorganic nutrients.
These conditions control what type of ecosystem can form (tropical rainforest vs. desert). These types of ecosystems are called biomes.
The amount of energy that is transferred along a food chain decreases considerably from trophic level to trophic level. Only about 10% of the energy available at each trophic level is converted to new biomass. The other 90% of available energy is used as energy for respiration and body functions, or it is lost as waste.
This decrease in available energy for new biomass limits the number of organisms at higher trophic levels resulting in fewer individuals of a species as you move along.
A pyramid of numbers is a graphical representation indicating the population at each level in a food chain. The pyramid shape is produced as there are generally fewer organisms at each successive trophic level. With this representation it is clear that the populations at higher trophic levels are limited by the numbers of species (potential food resources) at lower trophic levels.
Another factor that will affect the populations of species particularly at higher trophic levels is the accumulation of toxins. Poisons can be passed along a food chain. The concentration of toxins, especially those that are fat soluble, increase in higher order carnivores in a process called bioaccumulation. Top carnivores (e.g., ospreys, falcons) at the ends of longer food chains suffered declines in population size in the 1970's due to the accumulation of a fat soluble pesticide called DDT. DDT has since been banned here in Canada.
All living organisms require carbon to make carbohydrates, fats, and proteins. Plants begin the process by using carbon dioxide (CO2) from the air to produce sugars. Animals then consume the sugars for energy. Photosynthesis is important in that it harnesses the Sun's energy to convert carbon dioxide and water into sugars which are then used by animals as an energy source. The process is a relatively complicated one taking place inside of small disc-like chloroplasts found in plant cells. The following word equation summarizes the photosynthesis reaction: carbon dioxide + water + sunlight glucose + oxygen The following chemical equation summarizes the photosynthesis reaction: 6CO2 + 6H2O + light energy $\rightarrow$ C6H12O6 + 6O2
Cellular respiration is the process that occurs within the cells of living organisms and should not be confused with breathing. Within the cells, glucose is broken down in the presence of oxygen releasing energy, carbon dioxide, and water. The following word equation summarizes the cellular respiration reaction: glucose + oxygen carbon dioxide + water + energy The following chemical equation summarizes the cellular respiration reaction: C6H12O6 + 6O2 $\rightarrow$ 6CO2 + 6H2O + energy
Carbon cycles through the environment naturally, and has done so for billions of years. However, since humans first appeared, we have been slowly altering the carbon cycle, particularly in the last 100 years.
Fossil fuel burning and deforestation have had the biggest impacts on the carbon cycle resulting in an increase of carbon dioxide in the atmosphere. This has contributed to the greenhouse effect, also known as global warming. When we travel, cook, use electricity, mine, and manufacture products, fossil fuels are burned and therefore more rapidly move carbon into the atmosphere than what is removed naturally. By clearing forests, there is a double impact because the forests are no longer capable of removing carbon dioxide. The processes of removing, harvesting, and burning trees also release carbon dioxide into the atmosphere.