Unit 2 Review

Evaporation

The process where liquid water from oceans, lakes, and rivers absorbs heat energy and changes into water vapor in the atmosphere.

Transpiration

The process where plants release water vapor into the atmosphere through the tiny pores (stomata) of their leaves. 

Condensation

The cooling of water vapor in the atmosphere, changing it from a gas back into tiny liquid water droplets to form clouds. 

Precipitation

Moisture that falls from the atmosphere back to Earth's surface in the form of rain, snow, sleet, or hail. 

Infiltration

Water entering the top surface layer of soil. 

Percolation

Downward movement of water filtering through deeper soil and rock layers into aquifers.

Aquifer

An underground layer of permeable rock, sand, or sediment that stores groundwater.

Human Impacts on the Water Cycle:

1. Deforestation & Urbanization: Impaves surfaces, reducing infiltration/groundwater recharge while increasing surface runoff. 

2. Overconsumption: Depleting aquifers through over-extraction and inefficient systems. 

3. Pollution: Chemical, waste, and sewage runoff contaminating fresh water sources.

The Carbon Cycle

Photosynthesis Reaction (Equation)

Plants take in atmospheric CO_2 and water with sunlight to produce glucose (C_6H_{12}O_6) and oxygen (O_2).

Equation for The Carbon Cycle

How Carbon Enters the Atmosphe

Respiration (plants/animals/soil), burning fossil fuels (BFF), deforestation/combustion, volcanic eruptions, and ocean release. 

How Carbon Leaves the Atmosphere

Photosynthesis by terrestrial plants/phytoplankton and direct ocean absorption.

Major Carbon Sinks (Traps)

Oceans (stored as dissolved CO_2 or Calcium Carbonate (CaCO_3) in shells/sediments/limestone), sedimentary rocks, and forests/living biomass. 

Ecological Effects of Human Impact on Carbon

Global Climate Change: Excess atmospheric CO_2 from burning fossil fuels traps heat. 

Ocean Acidification: Absorbing excess CO_2 lowers ocean pH, harming marine organisms that build calcium carbonate shells. 

Nitrogen Fixation

Converts unusable N_2 gas into Ammonia (NH_3) or Ammonium (NH_4^+). 

Organisms: Bacteria like Rhizobium (in legume root nodules) and Cyanobacteria (in oceans).

Unique Feature of Nitrogen

Makes up 78% of the atmosphere as N_2 gas, but cannot be directly used by plants or animals until it is "fixed" by bacteria or lightning. 

Nitrification

Soil bacteria convert Ammonium (NH_4^+) into Nitrites (NO_2^-) and then Nitrates (NO_3^-).

Assimilation

Plants absorb Nitrates (NO_3^-) or Ammonium (NH_4^+) from the soil to make biological molecules like proteins and DNA; animals get nitrogen by eating plants.

Ammonification

Decomposers (fungi and bacteria) break down organic waste and dead organisms, returning nitrogen to the soil as Ammonium (NH_4^+). 

Denitrification

Denitrifying bacteria in anaerobic soil/wetlands convert Nitrates (NO_3^-) back into N_2 gas, returning it to the atmosphere.

Human Impacts & Solutions (Nitrogen)

Fertilizer runoff causes Eutrophication / Algae Blooms (depleting dissolved oxygen). Burning fossil fuels releases N_2O/smog components. 

Solution: Planting Riparian Buffers (vegetation borders around water bodies) to absorb runoff and using organic fertilizers. 

Unique Feature of Phosphorus

Does NOT enter the atmosphere (it has no significant gaseous phase). 

Main Reservoir / Sink of Phosphorus

Found in the geosphere within rocks and sediments as Phosphate (PO_4^{3-}). 

How Phosphorus is Released

Weathering (the physical/chemical breakdown of rocks by wind and water) slowly releases phosphate into soil and water.

Human Impact on Phosphorus

Mining phosphate rock and overusing synthetic fertilizers leads to agricultural runoff, resulting in algal blooms and aquatic hypoxia.

Main Reservoir & Forms of Sulfur

Concentrated in the geosphere within coal and rocks. It mainly circulates through soil, water, and ecosystems as Sulfate (SO_4^{2-}). 

How Sulfur Enters the Atmospher

Released as Sulfur Dioxide (SO_2) through volcanic eruptions, sea spray, decomposition, and human activities like burning coal and industrial processes.

Ecological Effect of Excess Sulfur

Industrial emissions of SO_2 combine with atmospheric moisture to produce acid rain (sulfuric acid), damaging forests, soils, and aquatic systems.

First Law of Thermodynamics

Energy cannot be created or destroyed; it can only change forms (Conservation of Energy). 

Second Law of Thermodynamics

During every energy transfer, some useful energy is lost to the environment as low-quality heat, increasing entropy. 

The 10% Rule of Energy Transfer

Only about 10% of usable energy is passed up from one trophic level to the next; 90% is lost as metabolic heat or unusable waste.

GPP

The total rate at which primary producers turn solar energy into chemical energy (glucose) via photosynthesis. 

NPP

The remaining energy stored as plant biomass after subtracting energy used for cellular respiration.

Formula for NPP

NPP = GPP - Respiration

Positive Feedback Loop:

Pushes a system further in the same direction, amplifying change (e.g., Arctic sea ice melting → lower albedo → more heat absorbed → more ice melts).

Negative Feedback Loop:

Counteracts a change to bring a system back to balance/homeostasis (e.g., a thermostat turning an AC unit on/off to maintain set temperature).

Biotic

The living or once-living parts of an ecosystem (e.g., plants, animals, bacteria, fungi).

Abiotic

The non-living physical and chemical components of an ecosystem (e.g., temperature, water, sunlight, soil pH, rock minerals).

Primary Producers (Autotrophs)

Organisms at the base of the food web that make their own chemical energy from inorganic sources through photosynthesis (using sunlight) or chemosynthesis (using chemical energy).

Primary Consumers (Herbivores)

Heterotrophs that feed directly on primary producers to obtain energy (e.g., grasshoppers, zooplankton, cows).

Secondary Consumers

Carnivores or omnivores that eat primary consumers for energy (e.g., frogs, small fish, birds).

Tertiary Consumers

Carnivores that eat secondary consumers (e.g., snakes, tuna).

Apex Predators

Top consumers at the end of a food chain that have no natural predators in their ecosystem (e.g., orcas, hawks, polar bears).

Scavengers

Animals that consume large amounts of carcasses/dead matter left by other predators (e.g., vultures, hyenas).

Detritivores

Organisms that internalize and eat decaying organic bits (detritus) using a mouth (e.g., earthworms, crabs, millipedes).

Decomposers

Microorganisms that break down dead material externally via enzymes and absorb the nutrients, recycling elements to the soil (e.g., bacteria, fungi).

Food Chain

A single, linear pathway showing direct energy transfer from one organism to another.

Food Web

A complex, interconnected network of multiple food chains illustrating all feeding relationships in an ecosystem.

Bioaccumulation

The buildup of a persistent toxin/fat-soluble pollutant within the tissues of a single organism over its lifetime.

Biomagnification

The increase in concentration of toxins at progressively higher trophic levels up the food chain, hitting apex predators hardest.

Fixation

N2 → NH3/NH4+

Nitrification

NH3/NH4+ → NO2- → NO3-

Assimilation

NO5 → Organic Nitrogen (in plant tissues)

Ammonification

Organic Nitrogen → NH3/NH4+

Denitrification

NO3- →N2

Carbon: Key reservoir =, key driver

Main reservoir = sedimentary rock; key driver = weathering/erosion.

Phosphorus: Main reservoir =, key driver

Main reservoir = sedimentary rock; key driver = weathering/erosion.

Sulfur

Released naturally by volcanoes and hydrothermal vents; human source = coal combustion.

Problem: Nutrient pollution happens when excess fertilizer from farms washes into lakes and rivers, causing huge algae blooms that block sunlight. When this algae dies, tiny bacteria eat it up and use up all the oxygen in the water. Without oxygen, fish and other aquatic life suffocate, creating "dead zones."

Solution: People can stop this by planting trees and grass along riverbanks to absorb the runoff before it reaches the water. Farmers can also use less fertilizer, and cities can treat wastewater to filter out these extra nutrients before dumping it back into nature.

Fixation

Nitrification

Assimilation

Ammonification

Denitrification