C4.2: Transfer of Energy and Matter

System

Set of interacting or interdependent components

Open System

Energy or matter can enter or exit

**ecosystems are open systems bc living organisms need energy/matter (chemical resources) from other organisms and abiotic surroundings

Closed System

Energy can enter, but matter cannot

Sunlight as Energy

Sunlight is the initial source of energy for most ecosystems

Cyanobacteria, plants, and algae (producers) convert sunlight to carbon compounds via photosynthesis, then energy is eventually available to other organisms

High Intensity Areas

eg. Sahara Desert, little sunlight energy is harvested bc few producers

Low Intensity Areas

eg. redwood forests, lots of sunlight energy is harvested bc many producers, therefore more energy is available to ecosystem

Exceptions to Sunlight as Energy (2)

1. Light must pass through water to reach producers in aquatic ecosystems (transmission is not 100%)

-depth/presence of living/nonliving matter influences light availability

-deeper ecosystems rely on other sources of energy

2. Some ecosystems develop in darkness, such as caves, streams bring inorganic matter (dead leaves) w/ stored energy

Isolated Caves

Do not receive any external energy inputs, primary producers are archaebacteria

Archaebacteria

Derive energy from methane, sulfides, or other inorganic compounds via chemosynthesis

Autotrophs

-use CO2 or hydrogen carbonate (HCO3-) as a source of carbon along w/ nitrate, phosphate, and other simple inorganic substances

need energy to make their own carbon compounds in 2 endergonic reactions

-carbon fixation (calvin cycle)

-linking monomers to polymers via condensation rxn (anabolic)

Types of Autotrophs (2)

Photoautotrophs and Chemoautotrophs

Photoautotrophs

Plants, eukaryotic algae, cyanobacteria

use sunlight as source of energy for photosynthesis

Chemoautotrophs

Bacteria, archaebacteria

use inorganic chemical reactions as source of energy for chemosynthesis

-sulfur, hydrogen sulfide (H2S), iron, and hydrogen releases energy when oxidized, which is then used for carbon fixation

Iron Sulfide

FeS2, found in low-oxygen environment (sedimentary rocks)

-when exposed to air, FeS2 produces Fe2+, SO42+, and H2SO4 (sulfuric acid)

Iron-Oxidizing Bacteria

Removes electrons from Fe2+ (formed from Iron Sulfide) in oxidation rxn, which becomes Fe3+ (releases energy)

-the electrons (energy) released by Fe2+ oxidation are accepted by electron carriers in plasma membrane of bacteria

some electrons are used to reduce NAD, others are used to generate a proton gradient

*Iron-Oxidizing Bacteria are double-membraned*

Proton Gradient

Used to generate ATP via chemiosmosis, e- are accepted by O2 w/ H+ to produce H2O

Heterotrophs

Obtain carbon via consumption of other organisms, practice assimilation

Assimilation

Digest complex carbon compounds (proteins) into small, soluble ones that can pass through cell membranes

reused to build heterotroph's own, necessary carbon compounds

Internal Digestion

Consumers ingest food and digest internally

-multicellular organisms take food into gut by swallowing, mix w/ digestive enzymes and absorb into cells

-unicellular organisms take food into cell via endocytosis, digest in phagocytic vacuoles and absorb into cytoplasm

External Digestion

Saprotrophs secrete hydrolytic enzymes to digest food externally

Dependence of Autotrophs on Heterotrophs

Autotrophs depend on heterotrophs for CO2, heterotrophs depend on autotrophs for O2

Why?

-before photosynthesis, there was little O2 in atmosphere, appearance of plants caused decrease of CO2 in atmosphere (a limiting factor for photosynthesis)

-appearance of O2 (from plants) allowed for evolution of aerobic respiration in heterotrophs

Global Carbon Flux Estimates

Annually, in terrestrial ecosystems, 120 gigatons of carbon are fixed by photosynthesis and released by respiration

*proves major interaction btwn autotrophs and heterotrophs*

Decomposers

use dead organisms as source of energy

either saprotrophs or detritivores

Saprotrophs

Type of decomposer, secrete digestive enzymes to break down organic matter externally, then absorb products of digestion

-absorb energy from detritus

Detritivores

Ingest and digest matter internally (earthworms/vultures)

-absorb energy from detritus

Detritus

-dead whole organism

-dead part of organisms like fallen leaves

-undigested material egested by animals (feces)

Importance of Decomposers (2)

1. Break down complex, insoluble carbon compounds into soluble ones, gradually soften and disintegrate solid structures (tree trunk)

2. Recycle chemicals back into ecosystem, prevent accumulation of dead organic matter

Recycling of Chemical Elements

All elements used by living organisms as nutrients are recycled, CHNOPS are necessary to synthesize macromolecules (and other elements in trace amounts)

Role of Decomposers

Limited amounts of elements must be recycled

-decomposers break down carbon compounds and release nitrogen (as NH3) back into environment

collectively known as nutrient cycles

Nutrient

elements that an organism needs

Food Chain

Sequence of organisms (2-5), each of which feed on previous one

-begins w/ producers, continues through various levels of consumers

Producers

Absorb sunlight w/ chlorophyll and other pigments, light energy --> chemical energy as carbon compounds

Consumers

Acquire chemical energy through consumption of other organisms

Food Web

Model that summarizes all possible food chains in a community, more complex, but realistic since consumers feed on more than one species and are fed upon by more than one species

-arrows indicate direction of energy flow

-organisms at same trophic level are often shown at same level, but not always possible bc some feed at more than one trophic level

All organisms need energy in the form of ATP to... (4)

-synthesize polymers (DNA, RNA, Proteins)

-pump molecules/ions across membranes during active transport

-move structures (chromosomes or vesicles, or muscle contractions)

-maintain constant body temperature

Cell Respiration

used by both autotrophs and heterotrophs to produce ATP

-oxidation (loses electron) of carbon compounds releases energy, this energy is then used to phosphorylate ADP-->ATP

Trophic Level

position in the food chain, based on how organisms obtain energy/carbon compounds

-tertiary consumers feed on secondary consumers, who feed on primary consumers, who feed on producers

*typically no consumers feed on the last organisms in the chain, who are often apex predators*

*most consumers occupy different trophic levels due to varied diets*

Reduction in Energy Availability (3)

Incomplete Consumption, Incomplete Digestion, Cell Respiration

Incomplete Consumption

Organisms in a trophic level are not consumed entirely, predators don't eat bones/hair, unconsumed energy or dead parts passes to saprotrophs, but they aren't considered part of food chain

Incomplete Digestion

Not all ingested food is digested/absorbed

-some (cellulose) cannot be digested and is egested as feces

-also passed to saprotrophs/detritivores

Cell Respiration as Energy Reduction

Oxidized carbon compounds produce CO2, H2O, and ATP and cannot provide energy to next trophic level

-only those that are assimilated and used for growth (not oxidized) can be transferred in terms of energy

Implications of Energy Loss

Producers are the most abundant in biomass, biomass of each successive trophic level becomes smaller

-approximately 10% of energy passes btwn trophic levels

-higher trophic levels contain less biomass, but higher energy per unit of biomass

Energy Lost as Heat (2)

Light energy-->chemical energy-->heat

Heat is produced in: cell respiration and ATP formation

heat is ultimately lost to abiotic environment and cannot be recycled

-cannot be converted back to chemical energy

-cannot be reused by other organisms

-over time, heat will radiate out to atmosphere and space

Cell Respiration Heat Production

birds/animals increase heat production to maintain constant body temp, also releases heat due to activity

ATP Heat Production

second law of thermodynamics states that energy transformations are never 100% efficient, not all energy from oxidation of carbon compounds produces ATP, some energy is released by heat

Restrictions on Number of Trophic Levels

Most food chains have 4 or less trophic levels due to energy constraints (limited bc energy loss occurs at each stage and not enough to sustain a trophic level after only a few stages)

Organisms in higher trophic levels don't have to eat more to gain enough energy

-at higher trophic levels, there are fewer or smaller organisms, but they contain larger amounts of energy per unit mass

-less biomass, but per unit energy isn't reduced

Energy Pyramids

Show amount of energy gained per year by each trophic level

They are bar charts w/ horizontal bars to represent trophic levels

Energy Period Construction (5)

1. Pyramids should be stepped, not triangular

2. bars should be labeled ("producers" on bottom, then "primary consumers" then etc)

3. depicts loss of energy as one moves up trophic levels

4. units for energy is kilojoules per square meter per year (kj m^-2 yr^-1)

5. If suitable scale used, length of each bar can be proportional to amt of energy represented

Primary Production

Accumulation of carbon compounds in biomass by autotrophs

-biomes vary in their capacity to accumulate biomass

-biomass increases when organisms grow/reproduce

Gross Primary Production

Total biomass of carbon compounds made by autotrophs

units: grams of carbon per square meter per year (g C m^-2 yr^-1)

*autotrophs are primary producers bc synthesize their own carbon compounds*

Net Primary Production

gross primary production MINUS biomass lost during cell respiration (biomass available to consumers)

units: grams of carbon per square meter per year (g C m^-2 yr^-1)

Secondary Production

Accumulation of carbon compounds in biomass by heterotrophs

-ingested carbon compounds are assimilated as proteins, nucleic acids, and other macromolecules, cell respiration then converts them to CO2, H2O, which decreases biomass

*secondary production is always less than primary production*

why crop production is higher per area than meat production

Carbon Cycle

The organic circulation of carbon from the atmosphere into organisms and back again

Pool

reserve of an element

-both organic (ex biomass of producers) or inorganic (ex. CO2 in atmosphere)

Flux

Transfer of element from one pool to another

Types: photosynthesis, feeding, respiration

Photosynthesis

absorption of CO2 from air or water and conversion to carbon compounds

Feeding

Gaining carbon compounds by consumption of other organisms

Respiration

release of CO2 by cell respiration

Carbon Sink

When amount photosynthesis is greater than amount respiration, causing more carbon (in form of CO2 typically) to be taken into the ecosystem

*net uptake of carbon*

Carbon Source

When amount photosynthesis is less than amount respiration, causing more carbon (in form of CO2 typically) to be released from the ecosystem than is taken in

*net release of carbon*

Decomposers and Peat

Decomposers digest dead organic matter/release CO2 in cell respiration

-certain environmental conditions (acidic or anaerobic like swamps) inhibit decomposition and cause peat formation

Peat

accumulation of partially decayed plant matter, during certain periods, peat is transformed into coal, which removes carbon from the carbon cycle

formed from incomplete decomposition of dead plant matter due to acidic and anaerobic conditions (10,000 yrs)

Sequestration

The removal of carbon from the carbon cycle, ex when peat is transformed into coal

Fires

release CO2 by combustion of carbon compounds in living and dead organic matter

Types of Carbon Sinks (4)

1. Natural Gas/oil

2. Coal

3. Peat

4. Biomass

Natural Gas/Oil

formed from deeply buried decomposed organic matter trapped under sediment (500 Million yrs or more), high temps initiate chemical change

Coal

formed from accumulated wood and other plant matter in swamps, buried under sediment (250-325 million years)

Biomass

Accumulated from wood in trees and other recent plant material from photosynthesis (few thousand yrs)

Combustion

When materials burn and release CO2 into atmosphere, requires a flash point to occur spontaneously in nature

rarely occurs but sometimes through volcanic activity or lightning strikes after dry periods

Flash Point

specific initiation temp for combustion to occur

greater than 500 C for oil/natural gas and 400 C for wood

Human Impact on Carbon Emissions

combustion of coal/oil has risen sharply since Industrial Revolution, rapidly introducing carbon into atmosphere and shifting global carbon balance

ex. in 2020, nearly 250 megatonnes of CO2 were emitted from wildfires, while 3,400 megatonnes were emitted by human activity

Keeling Curve

measures of atmospheric [CO2] at Mauna Loa Observatory in Hawaii, begin in 1959 by Charles Keeling

Keeling Curve Trends (2)

Annual fluctuations and long-term increase

Annual Fluctuations

[CO2] increases between october and may (winter) and decreases btwn may and october (summer) when plants are in their growth season (and are therefore using more CO2 in photosynthesis)

Long Term Trend

In a given year, the increase in [CO2] is not completely reversed by the decrease, meaning that there is an overall increase in [CO2] through the years

-due to burning of fossil fuels and other anthropogenic factors like deforestation

Anthropogenic

Human-induced changes on the natural environment