Unit 1: The Living World: Ecosystems

Explain how the availability of resources influences species interactions.

• In a predator-prey relationship, the predator is an organism that eats another organism (the prey).
• Symbiosis is a close and long-term interaction between two species in an ecosystem. Types of symbiosis include mutualism, commensalism, and parasitism.
• Competition can occur within or between species in an ecosystem where there are limited resources. Resource partitioning—using the resources in different ways, places, or at different times—can reduce the negative impact of competition on survival.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Describe the global distribution and principal environmental aspects of terrestrial biomes.

• A biome contains characteristic communities of plants and animals that result from, and are adapted to, its climate.
• Major terrestrial biomes include taiga, temperate rainforests, temperate seasonal forests, tropical rainforests, shrubland, temperate grassland, savanna, desert, and tundra.
• The global distribution of nonmineral terrestrial natural resources, such as water and trees for lumber, varies because of some combination of climate, geography, latitude and altitude, nutrient availability, and soil.
• The worldwide distribution of biomes is dynamic; the distribution has changed in the past and may again shift as a result of global climate changes.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Describe the global distribution and principal environmental aspects of aquatic biomes.

• Freshwater biomes include streams, rivers, ponds, and lakes. These freshwater biomes are a vital resource for drinking water.
• Marine biomes include oceans, coral reefs, marshland, and estuaries. Algae in marine biomes supply a large portion of the Earth’s oxygen, and also take in carbon dioxide from the atmosphere.
• The global distribution of nonmineral marine natural resources, such as different types of fish, varies because of some combination of salinity, depth, turbidity, nutrient availability, and temperature.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Explain the steps and reservoir interactions in the carbon cycle.

• The carbon cycle is the movement of atoms and molecules containing the element carbon between sources and sinks.
• Some of the reservoirs in which carbon compounds occur in the carbon cycle hold those compounds for long periods of time, while some hold them for relatively short periods of time.
• Carbon cycles between photosynthesis and cellular respiration in living things.
• Plant and animal decomposition have led to the storage of carbon over millions of years. The burning of fossil fuels quickly moves that stored carbon into atmospheric carbon, in the form of carbon dioxide.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Explain the steps and reservoir interactions in the nitrogen cycle.

• The nitrogen cycle is the movement of atoms and molecules containing the element nitrogen between sources and sinks.
• Most of the reservoirs in which nitrogen compounds occur in the nitrogen cycle hold those compounds for relatively short periods of time.
• Nitrogen fixation is the process in which atmospheric nitrogen is converted into a form of nitrogen (primarily ammonia) that is available for uptake by plants and that can be synthesized into plant tissue.
• The atmosphere is the major reservoir of nitrogen.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Explain the steps and reservoir interactions in the phosphorus cycle.

• The phosphorus cycle is the movement of atoms and molecules containing the element phosphorus between sources and sinks.
• The major reservoirs of phosphorus in the phosphorus cycle are rock and sediments that contain phosphorus-bearing minerals.
• There is no atmospheric component in the phosphorus cycle, and the limitations this imposes on the return of phosphorus from the ocean to land make phosphorus naturally scarce in aquatic and many terrestrial ecosystems. In undisturbed ecosystems, phosphorus is the limiting factor in biological systems.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Explain the steps and reservoir interactions in the hydrologic cycle.

• The hydrologic cycle, which is powered by the sun, is the movement of water in its various solid, liquid, and gaseous phases between sources and sinks.
• The oceans are the primary reservoir of water at the Earth’s surface, with ice caps and groundwater acting as much smaller reservoirs.
• Enduring understanding ERT-1: Ecosystems are the result of biotic and abiotic interactions.

Explain how solar energy is acquired and transferred by living organisms.

• Primary productivity is the rate at which solar energy (sunlight) is converted into organic compounds via photosynthesis over a unit of time.
• Gross primary productivity is the total rate of photosynthesis in a given area.
• Net primary productivity is the rate of energy storage by photosynthesizers in a given area, after subtracting the energy lost to respiration.
• Productivity is measured in units of energy per unit area per unit time (e.g., kcal/m²/yr).
• Most red light is absorbed in the upper 1m of water, and blue light only penetrates deeper than 100m in the clearest water. This affects photosynthesis in aquatic ecosystems, whose photosynthesizers have adapted mechanisms to address the lack of visible light.
• Enduring understanding ENG-1: Energy can be converted from one form to another.

Explain how energy flows and matter cycles through trophic levels.

• All ecosystems depend on a continuous inflow of high-quality energy in order to maintain their structure and function of transferring matter between the environment and organisms via biogeochemical cycles.
• Biogeochemical cycles are essential for life and each cycle demonstrates the conservation of matter.
• In terrestrial and near-surface marine communities, energy flows from the sun to producers in the lowest trophic levels and then upward to higher trophic levels.
• Enduring understanding ENG-1: Energy can be converted from one form to another.

Determine how the energy decreases as it flows through ecosystems.

• The 10% rule approximates that in the transfer of energy from one trophic level to the next, only about 10% of the energy is passed on.
• The loss of energy that occurs when energy moves from lower to higher trophic levels can be explained through the laws of thermodynamics.
• Enduring understanding ENG-1: Energy can be converted from one form to another.

Describe food chains and food webs, and their constituent members by trophic level.

• A food web is a model of an interlocking pattern of food chains that depicts the flow of energy and nutrients in two or more food chains.
• Positive and negative feedback loops can each play a role in food webs. When one species is removed from or added to a specific food web, the rest of the food web can be affected.
• Enduring understanding ENG-1: Energy can be converted from one form to another.