Chapter 3: What Are They and How Do They Work?

What Is Ecology?

Cells Are the Basic Units of Life

• Cells: Smallest unit in both structure and function.
• Cell Theory: All living things are composed of cells
• Eukaryotic Cell: A type of cell that is surrounded by a membrane, nucleus, and other parts.
• Prokaryotic Cell: A type of cell surrounded by a membrane, but no distinct internal parts or nucleus.

Species Make Up the Encyclopedia of Life

• Species: Individuals that can mate and produce offspring

Ecologists Study Connections in Nature

• Ecology: Study of how organisms interact with their abiotic and biotic environments
• Population: Group of individuals that have the same species that all live in the same place
• Genetic Diversity: Reason why people are different from one another
• Habitat: Where individuals live
• Community or Biological Community: Population of different species living in a particular place and potentially interacting
• Ecosystem: Where communities of different species interact with each other.
• Biosphere: Large regions with distinct climates and certain species adapted to them.

What Keeps Us and Other Organisms Alive?

The Earth’s Life Support System Has Four Major Components"

• Atmosphere: Thin layer of gases that surrounds the earth’s surface
• Troposphere: Lower part of the atmosphere, contains nitrogen, weather, and greenhouse gases
• Greenhouse Gases: They trap heat and are in the troposphere.
• Stratosphere: Second layer of the atmosphere that has the ozone layer
• Geosphere: Consists of the core, the mantle, and the crust

Life Exists on Land and in Water

• Biomes: Large regions with distinct climates and certain species adapt to them
• Hydrosphere: All of the water on or near the earth’s surface
• Aquatic life zones: Biomes in water can be freshwater or marine

Three Factors Sustain Life on Earth

1. The flow of energy from the sun to living organisms through food webs.
2. Cycling of nutrients through the biosphere.
3. Gravity helps hold the atmosphere and allows the movement of chemicals.

Ecosystems Have Living and Nonliving Components

• Abiotic: Nonliving components
• Biotic: Living components
• Range of Tolerance: The range of conditions that populations can survive in, individuals may have different ranges than the population

Several Abiotic Factors Can Limit Population Growth

• Limiting Factors: Abiotic components that reduce population growth.
• Abiotic Limiting Factors: Temperature, sunlight, nutrient availability, precipitation, etc.

Producers and Consumers Are the Living Components of Ecosystems

• Trophic Level: The feeding level of organisms in an ecosystem
• Producers/Autotrophs: Organisms that make their own food
• Photosynthesis: Chemical process that converts energy from the sun into food for plants
• Chemosynthesis: Chemical process that a few producers use to convert compounds from their environment into nutrients, without sunlight.
• Primary Consumers (Herbivores): Herbivores, eat producers.
• Secondary Consumers (Carnivores): Carnivores, eat herbivores
• Third or Higher-Level Consumers: Carnivores, eat other carnivores
• Omnivores: Eat both plants and animals
• Decomposers: Consumers that release nutrients from the dead bodies of plants and animals and return them to the soil.
• Aerobic Respiration: The release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen
• Anaerobic Respiration or Fermentation: The release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen

What Happens to Energy in an Ecosystem?

Energy Flows through Ecosystems in Food Chains and Food Webs

• Food Chain: A sequence of organisms that serve as energy for the next
• Food Web: Interconnected food chains
• Explain why in a Pyramid of Energy flow, 90% of the energy is lost at each level. What are the consequences of this?
  • Because of the 2nd law of thermodynamics, energy is lost between each transfer in the food chain. There can't be more than 4 or 5 levels… there are more insects than tigers in the rainforest.. they need to eat a larger quantity of the lower level on the food chain for energy

Usable Energy Decreases with Each Link in a Food Chain or Web

• Biomass: Weight of organic matter in an organism
• Ecological Efficiency: Percentage of usable chemical energy that is transferred from one level to the next

Some Ecosystems Produce Plant Matter Faster Than Others Do

• Gross primary productivity (GPP): Rate at which an ecosystem’s producers convert solar energy to chemical energy
• Net primary productivity (NPP): Rate at which producers produce and store chemical energy minus the right that they use for life process.
• Only ~2% of sunlight is harnessed for photosynthesis
• Standing crop biomass—primary producer biomass total
  • Tropical rain forest = high gross & net productivity • open ocean = high gross productivity, but low net productivity

What Happens to Matter in an Ecosystem?

Nutrients Cycle in the Biosphere

• Biogeochemical Cycles aka Nutrient cycles

Water Cycles through the Biosphere

• Hydrologic Cycle or Water Cycle: Collects, purifies, and distributes the earth’s fixed supply of water.
  • Evaporation, Precipitation, Transpiration; the natural renewal of water quality, necessary for photosynthesis and life, dissolves nutrient compounds and transports nutrients within and between ecosystems, sculpts the earth's surface
• Transpiration: water evaporates from the surface of plants

Carbon Cycles through the Biosphere and Depends on Photosynthesis and Respiration

• Carbon Cycle: How carbon circulates through the biosphere. It is based on CO2 gas and involves photosynthesis, respiration, fossil fuels, etc.
  • Movement of carbon in different chemical forms from the environment to organisms and then back to the environment in the form of respiration and transpiration. Plant and animal matter trapped under the earth turns to carbon when we burn CO2 we release carbon into the atmosphere and increase the temperature

Nitrogen Cycles through the Biosphere: Bacteria in Action

• Nitrogen Cycle: Repeating the cycle of processes during which nitrogen moves through both living and non-living things
  • Electrical activity, volcanic activity, animal waste, and remains return to the soil, decomposition turns nitrogen to ammonia, and (bacteria) create nitrates which are reabsorbed by plants and algae. Humans disrupt this cycle by the use of fertilizers, burning of auto and jet fuels, and destruction of forests. The result is acid rain, excess algae growth, and destruction of the ozone layer
• Nitrogen Fixation: Specialized bacteria in soil and algae in water combine nitrogen gas with hydrogen to make ammonia
• Denitrification: Converting nitrate to nitrogen gas
• Acid Deposition (acid rain): Rain that has been made acidic by certain pollutants in the air

Phosphorus Cycles through the Biosphere

• Phosphorus Cycle: Cycling of phosphorus through the earth's crust, living organisms, and water.
  • Phosphate salts dissolved in water, water returns to the soil, producers absorb phosphate, and consumers eat them.. fertilizers sewage, and mining wastes create too much phosphate which results in excessive algae. Removing scarce phosphate ions from land areas where they are needed by plants and feeding them in excessive amounts to producers in aquatic systems, causes these producer populations to explode.

Sulfur Cycles through the Biosphere

• Sulfur Cycle: How sulfur circulates through the biosphere. It involves SO4 2- salts in deep ocean sediments, rock, H2S from bogs, swamps, etc., SO2 from volcanoes, and H2SO4 from the atmosphere to land.
  • Sulfur found in rocks, runs off to the ocean, evaporates as dimethyl sulfide, and turns into sulfur dioxide in the atmosphere (affects climate and cloud cover) returns to the earth in rain as sulfuric acid.. humans increase sulfur by smelting, and burning coal, refining fossil fuel and mining metals, too much sulfur disrupts the climate and causes acid rain

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