Ap Environmental Science Unit 1 Review

AP Environmental Science Unit 1 Review: Everything You Need to Know

The first unit of AP Environmental Science lays the crucial groundwork for understanding the interconnectedness of natural systems and the impact of human activities on our planet. This unit focuses on Ecology, which is the study of the interactions between organisms and their environment. Mastering these fundamental ecological principles is essential for success in the AP exam and for developing a comprehensive understanding of environmental issues.

I. Ecological Principles: The Foundation of Environmental Science

Ecology provides the framework for understanding how the environment functions and how human actions affect it. Here's a breakdown of the key ecological concepts:

A. Levels of Organization

Life on Earth is organized into various levels, each building upon the previous one. Understanding this hierarchy is crucial for comprehending the complexity of ecosystems.

• Individual: A single organism, such as a tree, a fish, or a bacterium. Its focus is on survival and reproduction.
• Population: A group of individuals of the same species living in the same area and interacting with each other. Population ecology studies population size, density, distribution, and growth rates.
• Community: All the different populations of species that live in the same area and interact with each other. Community ecology examines the interactions between different species, such as competition, predation, and mutualism.
• Ecosystem: A community of organisms interacting with their physical environment, including non-living components like air, water, and soil. Ecosystem ecology studies the flow of energy and cycling of nutrients within an ecosystem.
• Biome: A large geographic area characterized by specific climate conditions, plant communities, and animal communities. Examples include deserts, forests, grasslands, and aquatic biomes.
• Biosphere: The sum of all ecosystems on Earth, encompassing all living organisms and their interactions with the atmosphere, hydrosphere, and lithosphere.

B. Ecosystem Components

Ecosystems are composed of living (biotic) and non-living (abiotic) components that interact with each other.

1. Biotic Factors: These are the living organisms in an ecosystem, including:

   • Producers (Autotrophs): Organisms that produce their own food through photosynthesis (e.g., plants, algae) or chemosynthesis. They form the base of the food chain.

   • Consumers (Heterotrophs): Organisms that obtain energy by consuming other organisms.

     • Primary Consumers (Herbivores): Eat producers (e.g., deer, grasshoppers).
     • Secondary Consumers (Carnivores/Omnivores): Eat primary consumers (e.g., snakes, birds).
     • Tertiary Consumers (Carnivores): Eat secondary consumers (e.g., hawks, lions).
     • Decomposers (Detritivores): Break down dead organic matter and waste products, returning nutrients to the ecosystem (e.g., fungi, bacteria).

   • Trophic Levels: The position an organism occupies in a food chain or food web. Energy flows from one trophic level to the next, but with significant loss at each transfer (explained in detail below).

2. Abiotic Factors: These are the non-living components of an ecosystem, including:

   • Sunlight: The primary source of energy for most ecosystems.
   • Water: Essential for all life processes.
   • Temperature: Affects metabolic rates and distribution of organisms.
   • Nutrients: Chemical substances that organisms need for growth and survival (e.g., nitrogen, phosphorus, potassium).
   • Soil: Provides support and nutrients for plants.
   • Air (Atmosphere): Provides gases like oxygen and carbon dioxide.
   • Salinity: The concentration of salt in water, crucial in aquatic environments.

C. Energy Flow

Energy flows through ecosystems in a unidirectional manner, starting with the sun and passing through various trophic levels.

1. Photosynthesis: The process by which producers convert sunlight into chemical energy (glucose). This is the foundation of most food chains. The equation for photosynthesis is:

   6CO2 + 6H2O + Sunlight → C6H12O6 + 6O2
   

   Carbon dioxide + Water + Sunlight → Glucose + Oxygen

2. Cellular Respiration: The process by which organisms break down glucose to release energy. All organisms, including producers, perform cellular respiration. The equation for cellular respiration is:

   C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)
   

   Glucose + Oxygen → Carbon dioxide + Water + Energy

3. Food Chains and Food Webs:

   • Food Chain: A linear sequence of organisms through which energy and nutrients pass as one organism eats another.
   • Food Web: A more complex representation of energy flow in an ecosystem, showing interconnected food chains and the multiple feeding relationships among organisms.

4. Ecological Pyramids: Graphical representations of energy, biomass, or number of organisms at each trophic level.

   • Pyramid of Energy: Shows the energy available at each trophic level. Energy decreases as you move up the pyramid due to the 10% rule (see below).
   • Pyramid of Biomass: Shows the total mass of living organisms at each trophic level. Typically decreases as you move up the pyramid.
   • Pyramid of Numbers: Shows the number of organisms at each trophic level. Can be inverted in some ecosystems (e.g., a single tree supporting many insects).

5. The 10% Rule: Only about 10% of the energy stored in one trophic level is converted to biomass in the next trophic level. The remaining 90% is lost as heat during metabolic processes. This energy loss limits the length of food chains and the number of trophic levels in an ecosystem.

D. Nutrient Cycles

Nutrients are essential elements and compounds that organisms need for survival. Unlike energy, which flows through an ecosystem, nutrients are cycled within and between ecosystems. Key nutrient cycles include:

1. Water Cycle (Hydrologic Cycle): The continuous movement of water on, above, and below the surface of the Earth.

   • Evaporation: Liquid water changes into water vapor.
   • Transpiration: Water is released from plants into the atmosphere.
   • Condensation: Water vapor changes into liquid water, forming clouds.
   • Precipitation: Water falls back to Earth as rain, snow, sleet, or hail.
   • Infiltration: Water seeps into the ground and becomes groundwater.
   • Runoff: Water flows over the land surface into rivers, lakes, and oceans.
   • Human Impacts: Deforestation reduces transpiration, urbanization increases runoff, and pollution contaminates water sources.

2. Carbon Cycle: The movement of carbon through the atmosphere, oceans, land, and living organisms.

   • Photosynthesis: Removes carbon dioxide from the atmosphere and converts it into organic compounds.
   • Respiration: Releases carbon dioxide back into the atmosphere.
   • Decomposition: Decomposers break down dead organic matter and release carbon dioxide.
   • Combustion: Burning fossil fuels and biomass releases carbon dioxide.
   • Ocean Exchange: The ocean absorbs and releases carbon dioxide.
   • Human Impacts: Burning fossil fuels, deforestation, and cement production have significantly increased atmospheric carbon dioxide levels, contributing to climate change.

3. Nitrogen Cycle: The movement of nitrogen through the atmosphere, soil, and living organisms. Nitrogen is a key component of proteins and nucleic acids.

   • Nitrogen Fixation: Conversion of atmospheric nitrogen (N2) into ammonia (NH3) by bacteria in the soil or aquatic environments.
   • Nitrification: Conversion of ammonia (NH3) into nitrite (NO2-) and then nitrate (NO3-) by bacteria. Nitrate is the form of nitrogen that plants can readily absorb.
   • Assimilation: Plants absorb nitrate (NO3-) and incorporate it into organic molecules.
   • Ammonification: Decomposers break down dead organic matter and release ammonia (NH3).
   • Denitrification: Conversion of nitrate (NO3-) back into atmospheric nitrogen (N2) by bacteria in anaerobic conditions.
   • Human Impacts: Fertilizer production, burning fossil fuels, and deforestation have altered the nitrogen cycle, leading to water pollution, air pollution, and climate change.

4. Phosphorus Cycle: The movement of phosphorus through rocks, soil, water, and living organisms. Phosphorus is a key component of DNA, RNA, and ATP.

   • Weathering: Rocks release phosphate ions (PO43-) into the soil and water.
   • Absorption: Plants absorb phosphate ions from the soil.
   • Consumption: Animals obtain phosphorus by eating plants or other animals.
   • Decomposition: Decomposers break down dead organic matter and release phosphate ions back into the soil and water.
   • Sedimentation: Phosphate ions can precipitate out of solution and form sediments in aquatic environments.
   • Human Impacts: Mining for phosphate rock for fertilizer production and runoff from agricultural fields have increased phosphorus levels in aquatic ecosystems, leading to eutrophication.

E. Ecosystem Services

Ecosystem services are the benefits that humans derive from ecosystems. These services are essential for human well-being and economic prosperity.

• Provisioning Services: Products obtained from ecosystems, such as food, water, timber, and fiber.
• Regulating Services: Benefits obtained from the regulation of ecosystem processes, such as climate regulation, water purification, and pollination.
• Supporting Services: Services necessary for the production of all other ecosystem services, such as nutrient cycling, soil formation, and primary production.
• Cultural Services: Non-material benefits obtained from ecosystems, such as recreation, aesthetic appreciation, and spiritual enrichment.

II. Biodiversity

Biodiversity refers to the variety of life on Earth at all its levels, from genes to ecosystems. It is a critical component of ecosystem health and stability.

A. Levels of Biodiversity

• Genetic Diversity: The variation in genes within a species.
• Species Diversity: The number and abundance of different species in an ecosystem.
• Ecosystem Diversity: The variety of ecosystems in a region or on Earth.

B. Importance of Biodiversity

• Ecosystem Stability: Diverse ecosystems are more resilient to disturbances and changes in environmental conditions.
• Ecosystem Services: Biodiversity supports a wide range of ecosystem services that are essential for human well-being.
• Economic Benefits: Biodiversity provides resources for agriculture, medicine, and tourism.
• Intrinsic Value: Many people believe that biodiversity has intrinsic value, meaning that it is valuable in its own right, regardless of its usefulness to humans.

C. Threats to Biodiversity

• Habitat Loss: The destruction or degradation of habitats due to deforestation, agriculture, urbanization, and other human activities.
• Invasive Species: Non-native species that compete with native species for resources or prey on them.
• Pollution: Contamination of air, water, and soil with harmful substances.
• Climate Change: Changes in temperature, precipitation, and other climate patterns that can alter ecosystems and threaten species.
• Overexploitation: Harvesting species at a rate that is faster than they can reproduce.

III. Population Ecology

Population ecology focuses on the factors that influence the size, density, distribution, and growth of populations.

A. Population Characteristics

• Population Size: The number of individuals in a population.
• Population Density: The number of individuals per unit area or volume.
• Population Distribution: The spatial arrangement of individuals within a population (e.g., clumped, uniform, random).
• Age Structure: The proportion of individuals in different age groups within a population.

B. Population Growth

• Birth Rate: The number of births per unit time in a population.
• Death Rate: The number of deaths per unit time in a population.
• Immigration: The movement of individuals into a population from another area.
• Emigration: The movement of individuals out of a population to another area.
• Growth Rate: The rate at which a population is increasing or decreasing. Calculated as (Birth Rate + Immigration) - (Death Rate + Emigration).
• Exponential Growth: Population growth that occurs when resources are unlimited and the growth rate is constant. Results in a J-shaped curve.
• Logistic Growth: Population growth that occurs when resources are limited and the growth rate slows down as the population approaches its carrying capacity. Results in an S-shaped curve.

C. Limiting Factors

Factors that limit population growth, such as:

• Density-Dependent Factors: Factors that affect population growth more strongly as population density increases (e.g., competition for resources, predation, disease).
• Density-Independent Factors: Factors that affect population growth regardless of population density (e.g., natural disasters, weather conditions).

D. Carrying Capacity

The maximum population size that an environment can sustain given the available resources.

IV. Community Ecology

Community ecology focuses on the interactions between different species within a community.

A. Types of Species Interactions

• Competition: When two or more species require the same limited resource (e.g., food, water, space). Can be intraspecific (within the same species) or interspecific (between different species).
• Predation: When one species (the predator) kills and eats another species (the prey).
• Parasitism: When one species (the parasite) lives in or on another species (the host) and benefits by harming the host.
• Mutualism: When two species interact in a way that benefits both species.
• Commensalism: When one species benefits from an interaction and the other species is neither harmed nor helped.

B. Ecological Succession

The process of change in the species structure of an ecological community over time.

• Primary Succession: Succession that occurs in a previously uninhabited environment, such as bare rock after a volcanic eruption.
• Secondary Succession: Succession that occurs in an environment that has been disturbed but still has soil, such as after a forest fire or agricultural abandonment.
• Pioneer Species: The first species to colonize a new or disturbed environment.
• Climax Community: The final, stable community that develops in an ecosystem.

V. Biomes

Biomes are large geographic areas characterized by distinct climate conditions, plant communities, and animal communities.

A. Terrestrial Biomes

• Tundra: Cold, treeless biome with low-growing vegetation and permafrost (permanently frozen soil).
• Boreal Forest (Taiga): Cold, coniferous forest with long, cold winters and short, mild summers.
• Temperate Rainforest: Moderate temperatures and high precipitation, dominated by coniferous trees.
• Temperate Deciduous Forest: Moderate temperatures and precipitation, dominated by deciduous trees that lose their leaves in the fall.
• Grassland: Dominated by grasses and herbaceous plants, with low to moderate precipitation.
• Desert: Hot and dry biome with sparse vegetation.
• Tropical Rainforest: Hot and humid biome with high precipitation and a wide variety of plant and animal species.

B. Aquatic Biomes

• Freshwater Biomes: Lakes, rivers, streams, and wetlands.
• Marine Biomes: Oceans, coral reefs, and estuaries (where freshwater rivers meet the ocean).
  • Intertidal Zone: The area of the shoreline that is covered and uncovered by the tides.
  • Neritic Zone: The shallow water area over the continental shelf.
  • Oceanic Zone: The open ocean beyond the continental shelf.
  • Benthic Zone: The ocean floor.

VI. Human Impacts on Ecosystems

Human activities have significant impacts on ecosystems, often leading to environmental degradation.

• Deforestation: Clearing forests for agriculture, urbanization, and logging.
• Pollution: Contamination of air, water, and soil with harmful substances.
• Climate Change: Changes in temperature, precipitation, and other climate patterns due to increased greenhouse gas emissions.
• Habitat Loss: The destruction or degradation of habitats due to human activities.
• Overexploitation: Harvesting species at a rate that is faster than they can reproduce.
• Invasive Species: Introduction of non-native species that can disrupt ecosystems.

VII. Frequently Asked Questions (FAQs)

• Q: What is the difference between a food chain and a food web?

  • A: A food chain is a linear sequence of organisms through which energy and nutrients pass, while a food web is a more complex representation of energy flow in an ecosystem, showing interconnected food chains and the multiple feeding relationships among organisms.

• Q: What is the 10% rule and why is it important?

  • A: The 10% rule states that only about 10% of the energy stored in one trophic level is converted to biomass in the next trophic level. The remaining 90% is lost as heat. This energy loss limits the length of food chains and the number of trophic levels in an ecosystem.

• Q: What are the major threats to biodiversity?

  • A: The major threats to biodiversity include habitat loss, invasive species, pollution, climate change, and overexploitation.

• Q: What is the difference between primary and secondary succession?

  • A: Primary succession occurs in a previously uninhabited environment, such as bare rock, while secondary succession occurs in an environment that has been disturbed but still has soil.

• Q: How do human activities impact ecosystems?

  • A: Human activities can impact ecosystems through deforestation, pollution, climate change, habitat loss, overexploitation, and the introduction of invasive species.

VIII. Conclusion

Understanding the concepts covered in AP Environmental Science Unit 1 is crucial for building a strong foundation in environmental science. By grasping the principles of ecology, biodiversity, population dynamics, community interactions, biomes, and human impacts on ecosystems, you will be well-prepared to tackle more complex environmental issues and to contribute to a more sustainable future. Remember to review the key terms and concepts, practice applying them to real-world scenarios, and stay curious about the natural world around you. Good luck with your AP Environmental Science studies!