1. ECOSYSTEMS Energy and Matter

2. 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

3. 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

4. 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

5. 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

6. 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)

7. 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

8. 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

9. 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)

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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. 15 15

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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 26 26

27. 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

28. 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

29. 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

30. Nutrient Cycling 30