C4.2 Transfers of Energy and Matter

ecosystem

ecological systems composed of all organisms in an area together with their abiotic environment

system

a set of interacting or interdependent components

• open systems - resources (including chemical substances and energy) can enter or exit

• closed systems - energy can enter or exit, chemical resources cannot be removed or replaced

amount of energy reaching Earth’s surface in sunlight and amount harvested by producers varies around the world

• high sunlight intensity, little energy harvested (few producers) vs. low sunlight intensity, more energy harvested by producers

• reduced light penetration in marine and freshwater ecosystems - contain organisms and non-living matter, turbidity (suspended clay/silt, dense phytoplankton populations)

energy in cave systems

• streams entering cave may bring dead or organic matter, providing energy supply

• archaebacteria (producers) gain energy from chemical reactions that have methane, sulfides or any other inorganic compounds such as substrates, energy used to synthesize carbon compounds in chemosynthesis metabolism

• microscopic invertebrates feed on biofilms of chemosynthetic archaebacteria, fed on by other invertebrates

food chain

sequence of organisms where each feeds on the previous one

• producers - absorb sunlight using chlorophyll and photosynthetic pigments, convert light to chemical energy, used to fix energy in carbon compounds

• consumers - obtain energy from carbon compounds in organisms on which they feed

• arrows indicate direction of energy flow

• different from food webs

saprotrophs

type of decomposer, bacteria and fungi

• secrete digestive enzymes into dead organic matter, digest externally, absorb products of digestion, including sugars and amino acids

• break down complex insoluble carbon compounds into simpler soluble ones, gradual breakdown of solid structures, recycling chemical elements

carbon compounds required to fulfill organisms’ nutritional requirements

• amino acids for protein synthesis

• sugars for energy supply, synthesis of polysaccharides

• fatty acids for energy supply and constructing membranes

• organic bases for synthesizing nucleic acids during DNA replication and transcription

• steroids, many other groups of carbon compounds

autotrophs

self-feeding organisms, able to make all carbon compounds themselves

• use CO2 or hydrogen carbonate (HCO3-) as carbon source, nitrate, phosphate, other simple inorganic substances as sources of other elements

• external energy source (light or chemical reactions) needed to carry out anabolic reactions to build carbon compounds from simple inorganic substances

• photoautotrophs or chemoautotrophs

photoautotrophs

• use external light energy

• fusion reactions in the sun generate vast amounts of energy in the form of electromagnetic radiation

• small portion absorbed by photosynthesis in plants, eukaryotic algae, cyanobacteria

chemoautotrophs

• use exothermic inorganic chemical reactions (prokaryotes, bacteria, archaebacteria)

• substrate in reduced state is oxidized, releasing energy which is used to synthesize carbon compounds, producing their own sugar, amino acids, etc.

iron-oxidizing bacteria as an example of a chemoautotroph

*

heterotrophs

organisms who fulfill nutritional requirements by obtaining carbon compounds from other organisms, use products of digestion to build large complex carbon compounds

assimilation

process of absorbing carbon compounds into cells

• molecules must be small and soluble enough to pass across cell membranes, large compounds must be digested before absorption

divisions of heterotrophs based on digestion of food (internal vs. external)

• saprotrophs - grow into/across surface of food, secrete hydrolytic enzymes to digest food externally

• consumers - ingest food

• multicellular consumers - swallow food, mix with enzymes from digestive glands, internal digestion

• unicellular consumers such as paramecium - take food into cells by endocytosis, digested inside phagocytic vacuoles, products of digestion absorbed from vacuoles into cytoplasm

vital activities requiring ATP

• synthesizing large molecules

• pumping molecules or ions by active transport

• moving structures within cells

• maintaining constant body temperature

ATP produced by cellular respiration, carbon compounds oxidized to release energy

trophic levels

grouping of organisms based on how they obtain energy and carbon compounds

construction of energy pyramids

x

reductions in energy availability at each successive stage in food chains due to large energy losses between trophic levels

1. incomplete consumption - energy in dead parts of organisms passes to saprotrophs or detritus feeders rather than organisms in next trophic level, energy lost from food chain

2. incomplete digestion - not all food digested and absorbed, indigestible material egested in feces, energy passed to saprotrophs or detritus feeders

3. cell respiration - substrates oxidized to CO2 and water, releasing energy, waste products which cannot supply energy to next trophic level

• smaller energy flow from each trophic level due to smaller amounts of energy-containing substances

• with each trophic level, more energy per unit of biomass

heat loss to environment in both autotrophs and heterotrophs

• all organisms contain some chemical energy to heat, maintaining constant body temperature or as a side effect of activity

• second law of thermodynamics - energy transfers are never 100% efficient, not all energy from oxidation of carbon compounds in cell respiration transferred to ATP, remainder converted to heat when ATP used in cell activities

• heat lost to abiotic environment, heat passes from hotter to cooler bodies and cannot be recycled

restriction in the number of trophic levelsq

so much energy lost at each step of the food chain, less energy available to each successive trophic level, not enough to support another trophic level

production in ecosystems

accumulation of carbon compounds in biomass, accumulation when living organisms grow and reproduce, vary in different biomes

primary producers

autotrophs, synthesize carbon compounds from simple substances

gross primary production (GPP)

total biomass of carbon compounds made in plants by photosynthesis

net primary production

gross primary production (GPP) minus biomass due to respiration of plant; amount of biomass available to consumers

secondary production

accumulation of carbon compounds in biomass by heterotrophs

• lower per unit area than primary production, loss of biomass with every trophic level due to cellular respiration

pool

reserve of an element, organic or inorganic (ex. CO2 in atmosphere as inorganic pool of carbon)

flux

transfer of the element from one pool to the other: photosynthesis, feeding, respiration

ecosystems as open systems

both matter and energy can enter or exit, carbon enters/exits as carbon dioxide through cell respiration or photosynthesis

• carbon sink - photosynthesis exceeds respiration, net uptake of carbon

• carbon source - respiration exceeds photosynthesis, net release of carbon

decomposition

saprotrophs digest dead organic matter, release carbon as carbon dioxide due to respiration

sequestration

removal of carbon from carbon cycle (ex. peat turns into coal, carbon in coal removed from carbon cycle for millions/hundreds of millions of years)

natural gas and oil as carbon sinks

• formed over past 550 million+ years

• deep burial of partially decomposed organic matter under sediments

• high temperature caused chemical changes, produced oil and natural gas trapped under porous rock

coal as a carbon sink

• formed 325-250 million years ago

• accumulation of wood and other plant matter in swamps, buried under other sediments

peat as a carbon sink

• formed mostly in the last 10,000 years

• incomplete decomposition of dead plant matter due to acidic and anaerobic conditions in waterlogged bogs and swamps

biomass as a carbon sink

• past few thousand years or more recent

• plant biomass derived from photosynthesis, transferred along food chains to animal biomass

combustion

burning in air, carbon sinks transformed into carbon sources as carbon dioxide is produced and released into the atmosphere

• flashpoint - specific ignition temperature which must be reached for combustion to occur

carbon balance

sequestration and photosynthesis vs. combustion and respiration

Mauna Loa Observatory, Hawaii

measures atmospheric carbon dioxide concentrations, results helped plot Keeling curve (Charles Keeling)

Keeling Curve trends

1. annual fluctuations

2. long-term trend - annual increase not completely reversed by December, concentration at end of year is higher; overall increase 1959-onwards due to anthropogenic factors

causes of annual fluctuation in CO2 emission

• CO2 concentrations increase October-May, decrease May-October due to global imbalances in rates of photosynthesis and respiration

• photosynthesis higher overall in northern hemisphere summer, plants over most of earth’s land surface are in main growth season

release of oxygen in photosynthesis

• one oxygen atom removed from each of two water molecules, oxygen atoms linked by double covalent bond using energy derived from light

• catalyzed by oxygen-evolving complex at center of photosystem II, developed in archaebacteria

chemical elements needed by all living organisms

• carbon, hydrogen, oxygen

• nitrogen, phosphorus

• approximately 15 other elements

• inorganic nutrients obtained from abiotic environment

nutrient cycles

recycling of chemical elements needed by organisms in an ecosystem