ECOSYSTEMS Energy and Matter

Ecosystems- Matter and Energy Ecosystems are all about the cycling of matter and the flow of energy. The Laws of Thermodynamics cannot be ignored. 2 2

Metabolism Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell Arises from interactions between molecules w/in the cell Bioenergetics: How organisms manage their energy resources

Energy Pathways Catabolic pathways: degradative process such as cellular respiration; releases energy which is now available for work Ex. Transport, ciliary beating Anabolic pathways: aka biosynthetic pathways - building process; Consumes energy Ex. protein synthesis, photosynthesis

Thermodynamics – study of E transformations Energy (E)~ capacity to do work (cause change) Kinetic energy~ energy of motion; Heat(thermal energy) – associated with random movement of molecules Potential energy~ stored energy – chemical energy – due to location/structure Closed system vs open system 1st Law: conservation of energy; E transferred/transformed, not created/destroyed 2nd Law: transformations increase entropy (disorder, randomness) All energy is not used, some is released as heat. Living systems increase entropy in their surroundings Combo: quantity of E is constant, quality is not Energy flows in as light and leaves in the form of heat

Free energy (G) Free energy: portion of system’s E that can perform work (at a constant T) ∆G = ∆H - t ∆s Change in free E = enthalpy – (Temp x change in entropy) Enthalpy: total E ∆G = G final state – G initial state Use ∆G to determine if a process will be spontaneous (occur on its own) or nonspontaneous (needs E added to occur)

Exergonic reaction: net release of free E to surroundings – causes a decrease in G; ∆G if negative = spontaneous Endergonic reaction: absorbs free E from surroundings – stores free E; ∆G is positive = nonspontaneous Closed systems reach equilibrium – can do no work A cell at equilibrium is dead Living organisms have a constant interaction w/ environment – this keeps pathways from reaching equilibrium

Energy Coupling & ATP E coupling: use of exergonic process to drive an endergonic one (ATP) Adenosine triphosphate – primary source of all E ATP tail: high negative charge ATP hydrolysis (use of water to break apart molecules) : releases free E Phosphorylation – transfer of a phosphate group to another molecule – transfers E

Another look at METABOLISM Catabolic processes of cellular respiration Bioenergetics – flow of energy through an animal Harvest energy from food they eat – 1st used for cellular resp then biosynthesis Endotherms: bodies warmed by metabolic heat – high energy strategy – birds, mammals Basal Metabolic Rate (BMR): minimal rate powering basic functions of life (endotherms) Ectotherms: bodies warmed by environment – smaller energy cost – fish, amphibians, reptiles Standard Metabolic Rate (SMR): minimal rate powering basic functions of life at a particular temp (ectotherms)

Excess/insufficient G (free energy) G greater than required for SMR/BMR used for growth or energy storage Reproduction – requires much additional G Species try to limit this extra requirement in different ways Seasonal, biennial, reproductive diapause (arrested development of sex cell production/hormone production) May lead to increases in population size G lower than required for SMR/BMR May lead to cell death = loss of mass or possible death to the organism May lead to decreases in population size

Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community As well as all the abiotic factors with which they interact Ecosystems can range from a microcosm, such as an aquarium To a large area such as a lake or forest Regardless of an ecosystem’s size Its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems While matter cycles within them

Ecologists view ecosystems as transformers of energy and processors of matter The laws of physics and chemistry apply to ecosystems Particularly in regard to the flow of energy Energy is conserved But degraded to heat during ecosystem processes Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores) A change in the free energy can lead to a change in other levels

Energy flows through an ecosystem Entering as light and exiting as heat Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow

Primary Production The amount of light energy converted to chemical energy by autotrophs during a given time period Ecosystem Energy Budgets The extent of photosynthetic production sets the spending limit for the energy budget of the entire ecosystem The Global Energy Budget The amount of solar radiation reaching the surface of the Earth Limits the photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms

Primary Production http://www.bigelow.org/foodweb/chemosynthesis.jpg Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide (CO2). It may occur through the process of photosynthesis, using light as a source of energy, or chemosynthesis, using the oxidation or reduction of chemical compounds as a source of energy. Almost all life on earth is directly or indirectly reliant on primary production. “Primary Productivity” refers to the rate at which that production happens. http://www.bigelow.org/foodweb/chemosynthesis.jpg 15 15

Primary Production made by Primary Producers Gross primary productivity is the total amount of energy that producers convert to chemical energy in organic molecules per unit of time. Then the plant must use some energy to supports its own processes with cellular respiration such as growth, opening and closing it’s stomata, etc. What is left over in that same amount of time is net primary productivity which is the energy available to be used by another organism. The organisms responsible for primary production are known as primary producers or autotrophs. Primary production is distinguished as either net or gross. Net primary productivity accounts for losses to processes such as cellular respiration. Gross Primary productivity does not account for other process that the primary producer may need to utilize energy for themselves. If any of your students have a part time job, remind them of the difference between their “gross” pay vs. Their “net” pay! 16 16

Primary Production Different ecosystems vary considerably in their net primary production And in their contribution to the total NPP on Earth It is important to examine all three graphs above and understand why differences occur in the net primary productivity in various biomes, but most importantly between aquatic biomes and terrestrial biomes. About 70 percent of the planet is covered in ocean, and the average depth of the ocean is several thousand feet (about 1,000 meters). Ninety-eight percent of the water on the planet is in the oceans, and therefore is unusable for drinking because of the salt. The oceans also have thus also large surface area (graph a, 65%). Primary producers in the ocean account for a high percentage of net primary productivity (graph c), but when equalized over the surface area, their average net primary productivity is quite low (graph b). Which biome is the most productive per unit of volume/area? Alga beds and reefs Which accounts for most of the Earth’s O2 production? Open ocean followed by tropical rain forest. 17 17

Secondary Production The secondary production of an ecosystem = the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time The production efficiency of an organism = the fraction of energy stored in food that is not used for respiration

Trophic efficiency The percentage of production transferred from one trophic level to the next Usually about 10% 10% Rule This loss of energy with each transfer in a food chain can be represented by a pyramid of net production Figure 54.11 Tertiary consumers Secondary Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

Trophic Level Human Population Ask students to compare vegetarian diets to carnivorous diets. Meat eaters require more energy transformations and every transformation involves the loss of energy as heat. 20 20

One important ecological consequence of low trophic efficiencies Can be represented in a biomass pyramid Most biomass pyramids Show a sharp decrease at successively higher trophic levels Certain aquatic ecosystems Have inverted biomass pyramids

Pyramid of Numbers This graphic represents the number of organisms in a field of bluegrass in Michigan. It takes over 5 million primary producers to support 3 tertiary consumers. 22 22

The First Law of Thermodynamics states that energy cannot be created or destroyed, only change form. The Second Law of Thermodynamics states that in each transformation some energy is transformed to heat that increases molecular motion, thus increases entropy. The diagram above is showing that at every transformation, heat is flowing out of the system. This is in agreement with The First Law of Thermodynamics. Some of the of the energy is being transformed by the organisms for their life processes, some is available when they are consumed by the next level, and some is given off as heat. 23

Energy Transformation This illustrates the concept explained on the previous slide. 200 J (biomass eaten by catepillar)  100 J (feces) + 33 J (growth) + 67 J (cellular respiration) 200 Joules = 200 Joules 24 24

Biogeochemical Cycle Remember – Energy flows through; matter cycles within Law of Conservation of Matter – matter is not created or destroyed; it is simply reorganized This slide shows the interaction between geologic processes, abiotic factors and organisms. Matter cycles through the earth in various ways: water cycle, phosphorous cycle, carbon cycle, sulfur cycle, nitrogen cycle. These cycles along with the sun’s energy provide the base resources for producers that transform them into useable energy for other organisms. 25 25

Nitrogen Cycle Global cycle Bacteria are crucial for this cycle to funciton Really important! Note the critical and non-replaceable role of bacteria. This link will allow you to relate the story of Biosphere II and its failure due to lack of bacteria for N cycle. Ask students to explain why this is a global cycle http://www.trevorland.com/words/biosphere-2-a-successful-failure/index.html 26 26

Water Cycle Global cycle Global cycle – In the cycle, water exists in three states; vapor, liquid, and ice. The Sun is the driving force in the cycle. The amount of water on Earth stays fairly constant, but its distribution among the three states may vary. Climate changes could change the distribution of water in the water cycle. 27 27

Carbon Cycle Global cycle Really important! Global cycle – why? Ask students seemingly simple questions such as: How do animals obtain their carbon molecules? Why do animals have to consume organic carbon compounds? Many students err by focusing only on the flow of gases (CO2 and O2) and forgetting the movement of carbon in its many other forms. 28 28

Phosphorus Cycle NOT a global cycle Not a global cycle – why not? Because Phosphorus cannot exist in the gaseous phase and thus it can only cycle in its liquid or solid state and does not ever enter the atmosphere. 29 29

Nutrient Cycling 30