Biosphere
Biotic vs. Abiotic
Organisms with similar needs may compete with one another for resources, including food, space, water, air, and shelter. In any particular environment, the growth and survival of organisms depend on the physical conditions including light intensity, temperature range, mineral availability, soil type, and pH. Physical or non-living factors such as these which influence living things are called abiotic factors. Living factors which influence living things are called biotic factors. Some examples of biotic factors include disease and predation.
Energy Flow
Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms or producers, to herbivores to carnivores and decomposers. The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in a food web, some energy is stored in newly made structures but much energy is lost into the environment as heat. Continual input of energy from sunlight is required to keep this process going. Energy pyramids are often used to show the flow of energy in ecosystems.
Material Cycles
The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. Carbon dioxide and water molecules used in photosynthesis to form energy-rich organic compounds are returned to the environment when the energy in these compounds is eventually released by cells through the processes of cell respiration and other life activities. The number of organisms any environment can support is called its carrying capacity. The carrying capacity of an environment is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of bacteria and fungi. Living organisms have the capacity to produce populations of unlimited size, but available resources in their environments are finite. This restricts the growth of populations and produces competition between organisms.
Organism Relationships
Organisms interactions may be competitive or beneficial. Organisms may interact with one another in several ways. Some of these relationships include producer/consumer, predator/prey, or parasite/host relationships. Other organisms interactions include those in which one organism may cause disease in, scavenge, or decompose another.
Feeding Relationships
Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms including green plants and algae, to herbivores to carnivores and decomposers. Green plants and algae are called autotrophs or producer organisms, as they capture solar energy to make sugars in the process of photosynthesis. Herbivores or primary consumers use the producer organisms to provide them with their food. Carnivores are secondary consumers as they eat the primary consumers as their source of food. Some organisms are capable of functioning as primary consumers (eating plant material) and as secondary consumers (eating animal material). These organisms are called omnivores. Humans are examples of omnivores. All consumers are examples of heterotrophic organisms, as they can not make their own food using the sun, but depend upon the ingestion of other organisms for their nutrition.
Food Chains
If an ecosystem is to be self-sustaining it must contain a flow of energy. One way of representing the flow of energy through the living components of an ecosystem is through the use of a food chain. A food chain indicates the transfer of energy from producers through a series of organisms which feed upon each other.
Food Webs
In a natural community, the flow of energy and materials is much more complicated than illustrated by any one food chain. A food web is a series of interrelated food chains which provides a more accurate picture of the feeding relationships in an ecosystem, as more than one thing will usually eat a particular species.
Energy Pyramids
An energy pyramid provides a means of describing the feeding and energy relationships within a food chain or web. Each step of an energy pyramid shows that some energy is stored in newly made structures of the organism which eats the preceding one. The pyramid also shows that much of the energy is lost when one organism in a food chain eats another. Most of this energy which is lost goes into the environment as heat energy. While a continuous input of energy from sunlight keeps the process going, the height of energy pyramids (and therefore the length of food chains) is limited by this loss of energy.
Material Cycles:
Water Cycle
The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. Some of the water molecules which are used in photosynthesis are returned to the environment. The change of water from the liquid to the gas state is called evaporation, while the water lost to the atmosphere by the activities of plants is referred to as transpiration water loss. This water vapor eventually condenses to form clouds, and is returned to the earth as precipitation. This process is called the water cycle. The processes of cell respiration and excretion also releases some water to the environment as well.
Carbon-Oxygen Cycle
Carbon dioxide molecules are used in the process of photosynthesis to form energy-rich organic sugar compounds. These carbon dioxide molecules are returned to the environment by the process of cell respiration, when the energy from these compounds is eventually released by cells. Some carbon is also returned to the environment by the decomposition of dead organisms.
Oxygen is required by many living things to release the energy in their food in the process of aerobic cellular respiration. Oxygen is released to the environment as a waste product of the process of photosynthesis.
Other compounds, such as nitrogen, are cycled in the environment when organisms synthesize proteins from simpler compounds and then return these nitrogen compounds to the environment when they die and decompose.
Role of Decomposers
The number of organisms any environment can support is the carrying capacity of the environment. Carrying capacity is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of decomposers such as bacteria and fungi.
Vocabulary: abiotic factors, biotic factors, carrying capacity, competition, predator, prey, parasite, host, scavenger, decomposer, autotroph, producer, herbivore, primary consumer, carnivore, secondary consumer, omnivore, heterotroph, food chain, food web, energy pyramid, transpiration