Matter Energy and Ecosystems
Chapter 2
After this lecture, you will be able to
 Describe the nature of environmental systems
 Explain and apply the fundamentals of environmental chemistry
 Describe the molecular building blocks of organisms
 Differentiate among the types of energy and explain the basis of energy flow
 Distinguish photosynthesis and respiration and summarize their importance to
living organisms
 Define ecosystem and evaluate how living and non-living interact
 Assess ecosystem services and how they benefit our lives
 Describe how carbon, phosphorus, nitrogen, and water cycle through the
environment
Negative feedback loop
 In a negative feedback loop, the output resulting from a system moving in one
direction acts as an input that moves the system in the other direction
 Input and output neutralize one another
 Stabilizes the system
 Most systems in nature involve negative feedback loops
Positive feedback loop
 A positive feedback loop drives it further toward an extreme rather than
stabilizing it
 Runaway cycles of positive feedback are rare in nature but are common in
natural systems altered by humans
Vanishing Oysters of the Chesapeake Bay
Chesapeake Bay was the world’s largest oyster fishery
Overharvesting, pollution, and habitat destruction ruined it
The economy lost $4 billion from 1980 to 2010
Strict pollution standards and oyster restoration efforts give reason for hope
Oyster fishery
The Chesapeake Bay
Sources of nitrogen and phosphorus
Eutrophication in aquatic systems
Global hypoxic dead zones
Why do energy and chemistry matter?
“Every organism is a chemical factory that captures matter and energy from its
environment and transforms them into structures and processes that make life
possible.”
Matter
 Matter is all material in the universe that has mass and occupies space
 It can be solid, liquid, or gas
 Law of conservation of matter
 Matter can be transformed from one type of substance into others but it
cannot be destroyed or created
 Because the amount of matter stays constant…
o It is recycled in nutrient cycles and ecosystems
o Pollution and waste don’t go “away”
Elements
 An element is a fundamental type of matter
 A chemical substance with a given set of properties
 Nutrients are elements needed in large amounts by organisms
 Examples: carbon, nitrogen, calcium
Molecules and compounds
 Molecules are combinations of two or more atoms
 Chemical formula: indicates the type and number of atoms in the molecule
(oxygen gas: O2)
 A compound is a molecule composed of atoms of two or more different
elements
o Water: two hydrogen atoms bonded to one oxygen atom: H2O
Carbon dioxide: one carbon atom with two oxygen atoms: CO2
o
Hydrogen ions determine acidity
 Water can split into H+ and OH–
 The pH scale quantifies the acidity or basicity of solutions
 Acidic solutions: pH < 7
 Contain more H+
 Basic solutions: pH > 7
 Contain more OH–
 Neutral solutions: pH: 7
 A pH of 6 contains 10 times as many H+ as a pH of 7
Matter is composed of compounds
 Living things depend on organic compounds
 Organic compounds consist of carbon atoms bonded together
 They may include other elements such as nitrogen, oxygen, sulfur, and
phosphorus
 Carbon can be linked in elaborate chains, rings, other structures
 Inorganic compounds lack the carbon–carbon bond
Hydrocarbons
 Hydrocarbons are organic compounds that contain only carbon and hydrogen
 The simplest hydrocarbon is methane (natural gas)
 Fossil fuels consist of hydrocarbons
 Crude oil contains hundreds of types of hydrocarbons
Organic compounds
 Material making up biomolecules and macromolecules
 Formed by rings and chains of carbon
 Four major categories:
 Lipids
 Carbohydrates
 Proteins
 Nucleic Acids
Cells compartmentalize macromolecules
 All living things are composed of cells, which are the most basic unit of
organismal organization
 Cells vary in size, shape, and function
 They are classified according to their structure
Cells
 Cells are surrounded by lipid membrane controlling flow of materials in and
out of cell
 Enzymes are proteins that serve as molecular catalysts, regulating chemical
reactions
 Most chemical reactions require an initial input of energy, or energy of
activation, to get started
 Enzymes, rather than heat, are used in cells to catalyze chemical reactions
Energy
Energy is the ability to do work
Kinetic - Energy in moving objects
Potential - Stored energy
Chemical - Stored in food or fossil fuels
Changing potential into kinetic energy
Releases energy
Produces motion, action, or heat
Potential vs. kinetic energy
Potential energy stored in our food becomes kinetic energy when we exercise and
releases carbon dioxide, water, and heat as by-products
Thermodynamics
First Law of Thermodynamics - Energy is neither created nor destroyed
Second Law of Thermodynamics - With each successive energy transfer, less
energy is available to perform work
…or energy transfer is not 100% efficient
…or entropy increases
Energy
Living organisms require a constant input of energy, since they are ordered
Energy must be supplied from an external source to keep biological processes
running
The sun’s energy powers living systems
Energy that powers Earth’s ecological systems comes mainly from the sun
Using solar radiation to produce food
Autotrophs (producers) are organisms that use the sun’s energy to produce their
own food
Plants, algae, cyanobacteria
Photosynthesis is the process of turning the sun’s light energy into high-quality
chemical energy
Sunlight converts carbon dioxide and water into sugars
Moving to lower entropy
Photosynthesis produces food
Chloroplasts are organelles where photosynthesis occurs
Contain chlorophyll, a light-absorbing pigment
In other words, water and carbon dioxide in the presence of sunlight yields glucose
(sugar) and oxygen
Glucose serves as primary fuel for all metabolic processes in plant cells
Cellular respiration releases energy
 It occurs in all living things (plants, animals, etc.)
 Respiration occurs in the mitochondria
 Organisms use chemical energy created by photosynthesis
 Heterotrophs are organisms that gain energy by feeding on others
 Animals, fungi, microbes

Cellular respiration splits carbon and hydrogen atoms from the sugar
molecule and recombine them with oxygen to create carbon dioxide and
water
Species to ecosystems
 A species is a “type” of organism
 A population is all members of a species living in a given area at the same
time
 A community consists of all of the populations of organisms living and
interacting in a particular area
 An ecosystem is the biological community and its physical environment
Species
Populations
Community
Ecosystem
Ecosystems
 An ecosystem is all organisms and nonliving entities occurring and interacting
in a particular area
 Biological entities are tightly intertwined with the chemical and physical
aspects of their environment
 For example, in the Chesapeake Bay estuary:
 Organisms are affected by water, sediment, and nutrients from the water and
land
 The chemical composition of the water is affected by organism
photosynthesis, respiration, and decomposition
Energy is converted to biomass
 Primary production is the conversion of solar energy to chemical energy in
sugars by autotrophs during photosynthesis
 Gross primary production (GPP) is total amount of chemical energy produced
by autotrophs
 Most energy is used to power their own metabolism
 Net primary production (NPP) is energy remaining after respiration
 Equals gross primary production – cellular respiration
 It is used to generate biomass (leaves, stems, roots)
 Available for heterotrophs
Primary productivity of ecosystems
Net primary productivity
Ecosystems provide vital services
 All life on Earth depends on healthy, functioning ecosystems
 Ecosystem services are essential services provided by healthy, normally
functioning ecosystems
 When human activities damage ecosystems, we must devote resources to
supply these services ourselves
 Example: if we kill off insect predators, farmers must use synthetic pesticides
that harm people and wildlife
 One of the most important ecosystem services:
 Nutrients cycle through the environment in intricate ways
Ecological processes provide services
Nutrients circulate through ecosystems
 Nutrients move through the environment in complex ways
 Matter is continually circulated in an ecosystem
 Nutrient (biogeochemical) cycle is the movement of nutrients through
ecosystems
 Pool (reservoir) is a location where nutrients remain for varying amounts of
time (residence time)
 Source is a reservoir that releases more materials than it accepts
 Sink is a reservoir that accepts more than it releases
 Flux is the rate at which materials move between reservoirs
 Humans affect nutrient cycling
Human activities affect nutrient cycling
Altering fluxes, residence times, and amounts of nutrients in reservoirs
The water cycle affects all other cycles
 Water is essential for biochemical reactions and is involved in nearly every
environmental system and cycle
 Hydrologic cycle is the flow of liquid, gaseous, and solid water through the
environment
 Less than 1% is available as fresh water
 Evaporation is the conversion of liquid to gaseous water
 Transpiration is the release of water vapor by plants
 Precipitation is when rain or snow returns water to Earth’s surface
 Runoff is when water flows into streams, lakes, rivers, oceans
Transpiration
Water is also stored underground
 Infiltration is when water soaks down through rock and soil to recharge
aquifers
 Aquifers are underground reservoirs of rock and soil that hold groundwater
 Water table is the uppermost level of groundwater held in an aquifer
 Water in aquifers may be ancient (thousands of years old)
Hydrologic cycle
 Most water is stored in the oceans
 Solar energy continually evaporates water stored in the oceans and land, and
distributes water vapor around the globe
 Condenses over land surfaces, supporting all terrestrial systems
 Responsible for cell metabolism, nutrient flow in ecosystems, and global
distribution of heat and energy
The hydrologic cycle
Human impacts on the hydrologic cycle
 Humans have affected almost every flux, reservoir, and residence time in the
water cycle
 Damming rivers slows water movement and increases evaporation
 Removal of vegetation increases runoff and erosion while decreasing
infiltration and transpiration
 Overdrawing surface and groundwater for agriculture, industry, and domestic
uses lowers water tables
 Emitting air pollutants that dissolve in water changes the nature of
precipitation and decreases cleansing effect
Carbon cycle
 Carbon is a structural component of organic molecules and provides
metabolic energy
 Begins with intake of CO2 during photosynthesis. Carbon atoms are
incorporated into glucose and then:
 Remain in plant material until death, eaten, respired, excreted
 Decomposition returns carbon to the sediment, the largest reservoir of carbon
 Fossil fuels are carbon sink
 Oceans are second largest reservoir of carbon
The carbon cycle
Humans affect the carbon cycle
 Burning fossil fuels moves carbon from the ground to the air
 Since mid-1700s, people have added over 275 billion tons of carbon dioxide
to the atmosphere
 Cutting forests and burning fields moves carbon from organisms to the air
 Less carbon dioxide is removed by photosynthesis
 Today’s atmospheric carbon dioxide reservoir is the largest in the past
800,000 years
 The driving force behind climate change
The nitrogen cycle involves bacteria
 Nitrogen is contained in proteins, DNA, and RNA
 Nitrogen makes up 78% of the atmosphere
 Nitrogen is inert gas and cannot be used by organisms
 It needs lightning, bacteria, or human intervention to become biologically
active and available to organisms
Nitrogen must become biologically available
 Nitrogen-fixing soil bacteria or lightning “fixes” nitrogen gas into ammonium
 Nitrogen-fixing bacteria live in legumes (e.g., soybeans)
 Bacteria then convert ammonium ions first into nitrite ions then into nitrate
ions through process of nitrification
 Plants can take up these ions
 Nitrite and nitrate also come from pollution
 Animals obtain nitrogen by eating plants or other animals
 Denitrifying bacteria convert nitrates in soil or water to gaseous nitrogen,
releasing it back into the atmosphere
The nitrogen cycle
 Humans greatly affect the nitrogen cycle
 Historically, nitrogen fixation was a bottleneck; it limited the flux of nitrogen
from air into water-soluble forms
 Industrial fixation fixes nitrogen on a massive scale
 Overwhelming nature’s denitrification abilities
 Excess nitrogen leads to hypoxia in coastal areas
 Burning forests and fossil fuels leads to acid precipitation, adds greenhouse
gases, and creates photochemical smog
The phosphorus cycle
 Phosphorus is a key component of cell membranes, DNA, RNA and ATP
 No significant atmospheric component
 Most phosphorus is in rocks
 Weathering releases phosphorus into water
 Allowing it to be taken up by plants
 With naturally low environmental concentrations, phosphorus is a limiting
factor for plant growth
The phosphorus cycle
 Humans affect the phosphorus cycle
 Fertilizer from lawns and farmlands
 Increases phosphorus in soil
 Its runoff into water increases phytoplankton blooms and hypoxia
 Wastewater containing detergents releases phosphorus to waterways