ECOLOGY QUESTION 1983:			L. PETERSON/AP BIOLOGY

	Describe the trophic levels in a typical ecosystem. Discuss the flow of 
	energy through the ecosystem, the relationship between the different 
	trophic levels, and the factors that limit the number of trophic levels.

STANDARDS:
DESCRIPTION AND SYSTEM RELATIONSHIPS:			Max. = 8 points
Define and/or identify:
__  producers
__  consumers (herbivores - carnivores - omnivores)
__  decomposers
Identification of:
__  autotrophs
__  heterotrophs
Define:
__  trophic level
__ Complex system
Comparisons (Pyramids):
__  organism (numbers)
__  organism (size)
__  organism (biomass)
__  inverted, numbers and/or biomass

__  Material Cycling
__  Description of food chain and/or web

ENERGY FLOW IN THE SYSTEM:					Max. = 6 points
__  source
__  process (photosynthesis)
__  producers support the system
__  energy loss
__  quantification of loss
Use of Energy:
__  heat
__  metabolic
__  building compounds
__  amount of energy contained (comparative)
Relationship of R:
__  Prnet
__  Prgross

LIMITING FACTORS:    (No Max.)
__  Energy (2 points)
__  Change in Prnet
__  Change in Prgross
__  Biomass (materials)
__  Producer numbers
__  Efficiency









	ECOLOGY QUESTION 1985:			L. PETERSON/AP BIOLOGY

	Describe the process of ecological succession from a pioneer community 
	to a climax community. Include in your answer a discussion of species
	 diversity and interactions, accumulation of biomass, and energy flow.

STANDARDS:
DESCRIPTION
__  Definition of Succession
__  Differentiation (Primary/Secondary)
Examples:
__  Pioneer
__  Climax
__  Sere (two or more examples = 2 points)
__  Modification of the environment

SPECIES DIVERSITY
__  Explanation of increase
__  Types of Competition (or Niche)
__  Examples
__  Change in Population Density
__  Description of Food Web
__  R-Strategists -> K-Strategists (2 points)
__  Change in Symbiotic Relationships (increase toward mutualisms)

BIOMASS
__  Production increase and explanation (2 points)
__  Levels of Organizationm (Autotrophs & Heterotrophs)
__  Examples of Producers (etc.)
__  Pyramid or Explanation

ENERGETICS
__  Source (Sun)
__  Utilization - Photosynthesis
__  Explanation of Decrease (entropy -unused) OR  Pyramid + Explanation
__  Climax Stability (Dynamic Equilibrium)
__  P/R toward 1
__  Net Productivity Decrease



















	ECOLOGY QUESTION 1986:			L. PETERSON/AP BIOLOGY

	Describe the biogeochemical cycles of carbon and nitrogen. Trace these
	elements from the point of their release from a decaying animal to their 
	incorporation into a living animal.

STANDARDS:

The question was divided into two sections for grading, with a maximum number of points of 8 per section. For each maximum assigned, there were more points possible 
to allow the student several ways to reach the maximum.

For the CARBON CYCLE, it was possible to earn points for each of the following statements or ideas:
__  Explanation of the role of green plants as producers
__  Mention of herbivores in a way that indicated an understanding of their role 
__  An indication that carnivores obtained C from herbivores
__  Discussion of the role of decomposers in returning C to the atmosphere as CO2
__  Mention of CO2 production via respiration of green plants, herbivores or carnivores
__  Discussion of the C in oil, natural gas, and coal as originating from the remains of 
       organisms
__  Mention of CO2 release to the atmosphere through the burning of fuel or through 
       release of C from limestone.
__  Discussion of the existence of dissolved CO2 in the bodies of water on the earth.
__   An indication that human activity had a significant impact on the carbon cycle.

In the case of the nitrogen cycle, there were 14 possible points from which it was possible for the student to earn the maximum of 8 for that portion of the questions. 
__  An indication that organic molecules were broken down to amino acids after death
__  Discussion of deamination
__  Mention of NH4+ as the product of deamination
__  Indication that ammonium ion can be converted to nitrate (a second point if there is 
       inclusion of the further oxidation to nitrate)
__  Discussion of denitrification
__  Mentioning the role of microbes, industry, or lightning in affecting atmospheric 
       nitrogen.
__  Understanding that when nitrogen gas is fixed, it is converted to the ammonium ion.
__  Indication that nitrate or nitrite or ammonium ions can be taken up by organisms
__  Mention of nitrogen loss to living organisms which results from burning or leaching
__  Indication that plants use absorbed nitrogen to make proteins
__  An understanding of the conversion by animals of plant proteins into animal proteins
__  Indication that on death or in excretion organic nitrogen is released into the 
       environment.
__  Indication of a significant impact of human activity on the nitrogen cycle. 











	ECOLOGY QUESTION 1989:			L. PETERSON/AP BIOLOGY

	Using an example for each, discuss the following ecological concepts.
		a)  Succession
		b)  Energy flow between trophic levels
		c)  Limiting factors
		d)  Carrying capacity

STANDARDS:
a) SUCCESSION:						Max. = 3 points
__  Definition:   demonstrate process of change in communities through time
__  		   modification of environment/transition of species composition
__  Examples:    generalized - lake -> marsh -> meadow -> forest
		   specific - lichen -> moss -> herbs -> shrubs -> forest
__  Primary   - no life/soil -> pioneer organisms/soil development
__  Secondary - disturbance -> climax/stable community
 
b) ENERGY FLOW BETWEEN TROPHIC LEVELS:	Max. = 3 points
__  Examples:   grass -> locust -> mouse -> snake
	              grass -> herbivore -> carnivore -> detritivore
	 	  producer -> 10 consumer -> 20 consumer -> 30 consumer
		  food chain/web - elaboration of trophic levels
__  Producers (autotrophs) start energy flow
__  Consumers (heterotrophs) acquire energy from primary producers
__  Productivity - measure of rate at which energy is converted 
		   from radiant to biomass and kinetic energy of action or PG - R = PN	
__  Efficiency - 10% rule/90% energy loss or pyramid of energy

c) LIMITING FACTORS:					Max. = 3 points
__  Definition:  any factor operating to restrict population growth
Examples:
__  biotic -  population density, competition, predation
__  abiotic - moisture, temperature, weather/climate, wind, sunlight, soil,
	          topography, geographic location, nutrients
__  density-dependent - change birth/death rate as density changes
__  density-independent - change birth/death rate regardless of density

d) CARRYING CAPACITY:					Max. = 3 points
__  Definition:  number of individuals of a population (species) sustainable by an 
       environment (as long as the environment remains the same)
__  Examples:  predator/prey; rabbits in Australia; deer on Kaibab; human population; 
__  Limiting factor(s) determine carrying capacity (competition, waste, predation)
__  Population grows -> rate slows -> stabilize (N decreases)
       or
__  Population falls -> growth resumes -> stabilizes (N decreases)
       or
__  dN/dt = rN (K-N/K) with explanation or graph with explanation
__  K/r strategies related to carrying capacity 










	ECOLOGY QUESTION 1993:				L. PETERSON/AP BIOLOGY

	Living organisms play an important role in the recycling of many elements 
	within an ecosystem. Discuss how various types of organisms and their
	biochemical reactions contribute to the recycling or either carbon or
	nitrogen in an ecosystem. Include in your answer one way in which human
	activity has an impact on the nutrient cycle you have chosen.

	This question required students to integrate material typically presented at
	widely separated times in their course wor, namely ecology, biochemistry,
	and organismal diversity. Conceptual understanding was extremely important;
	simple recall of words or phrases did not earn points. Students were required
	to choose one cycle, and to trace the pathway(s) of the chosen element through 
	appropriate organisms and metabolic sequences to return to the starting
	material. Description of the carbon cycle involves trophic structure (energy
	transfer) of the ecosystem, and depends heavily on processes of autotrophy 
	(usually photosynthesis) and heterotrophy (usually aerobic respiration).
	The nitrogen cycle is somewhat more complex; and bacteria play key roles.
	Nitrogen compounds play important structural roles in all organisms but are
	less important in energy transfer. Finally, students described an impact of 
	human technology and related this impact ot the chosen cycle.

					NUTRIENT CYCLING
				            (8 POINTS MAXIMUM)
__  OVERVIEW - Why is recycling necessary?
				        SPECIFIC CYCLE CHOICE
			(GRADE FIRST CYCLE SPECIFICALLY MENTIONED)

	     CARBON					       NITROGEN
__  Demonstrates closed C cycle		__  Demonstrates closed N cycle
__  Carbon sources/pools, locations		__  Nitrogen sources/pools (availability)
__  Basic process of carbon fixation		__  N2 conversion (N2 -> "usable" form)
       (CO2 -> sugar, biomass or organic form)
__   Elaboration of autotrophy			__  Elaboration of fixation
__   Role of respiration (organic C -> CO2)  	__  Nitrification (see addendum)
__  Elaboration of respiration			__  Denitrification (see addendum)
__  Uniqueness of autotrophy			__  Uniqueness of bacteria to processes
        (universality of respiration)			__  Plant assimilation of N compounds:
						         inorganic -> organic
__  Storage forms/products 			__  Storage forms/products 
__  Food chain sequence			__  Food chain sequence
__  Role of decomposer			__  Role of decomposer
__  Unusual cases: (see addendum)		__  Unusual cases: (see addendum)
	methanogenesis				deamination
	photorespiration				ammonification
	chemosynthesis				re-reduction (reductases)
							Urea <-> Uric Acid









			HUMAN IMPACT ON CHOSEN CYCLE
				(3 POINTS MAXIMUM)

__  Identify single human technological impact on cycle
__  Explanation of impact/consequence
__  Additional details 

				   Nutrient Cycling
				        ADDENDUM
The intent of this addendum is to clarify details of the scoring standards by providing
additional technical information, names of organisms, enzymes, etc. which may be
mentioned by students. It does NOT replace the standards which should be referred to
for distribution of points, maximum points for certain areas, etc.

CARBON CYCLE

Elaboration of photosynthesis:
  Calvin Cycle biochemistry: complete correct equation
  (RuBP + CO2 -> 2 PGA  or 6 RuBP + 6CO2 + 18 ATP + 12 NADPH2 ->
    6 RuBP + hexose + 18 ADP + 12 NADP, etc.) or mention of enzymes involved
   (ribulose bisphosphate carboxylase/oxygenase or rubisco is most likely) or
   mention that these reactions occur in chloroplasts, in stroma, etc.
   mention of distinction between C3 vs C4-CAM pathways or groups of plants.
   mention of seasonal fluctuations.
Elaboration of respiration:
   mention of specific steps in respiration where CO2 is released:
   pyruvate -> acetyl-CoA + CO2, Krebs cycle reactions, etc.
   fermentation reactions: pyruvate + NADH -> EtOH + CO2, etc.
Storage forms/products: standing trees, peat, coal, oil, natural gas, bones, shells, coral,
   chalk, limestone of biogenic origin, etc.
Unusual or special cases:
   methanogenesis: CO2 + 4 H2 -> CH4 + 2 H2O only bacteria actually do this, but 
   students are more likely to describe the environment in which the bacteria grow,
   such as ruminants (belching cows), swamps (waterlogged, anaerobic soils), etc.
Photorespiration: in C3 palnts if CO2/O2 ratio is low, RuBP + O2 -> PGA + P-glycolate
   P-glycolyate -> glyoxylate,  glyoxylate + NH2 -> glycine, glycine + NAD -> 
   CO2 + serine + NH3 + NADH
Chemosynthesis: incorporation of CO2 using an energy source other than light
   (H2, highly reduced organic compounds, etc.)

IMPACT ON CARBON CYCLE:
Burning fossil fuels -> raises CO2 levels
	may produce greenhouse effect, may stimulate autotrophs
Clearing/burning forests -> raises CO2 levels or removes autotrophs
	may produce greenhouse effect, may increase CO2 dissolved in oceans, etc.
Acid rain -> dissolves limestone, releases CO2 or kills autotrophs
	may contribute to greenhouse effect, increase CO2 content of oceans, etc.
Intensive agriculture/desert irrigation -> increase in autotrophs
	removes CO2 from sources, ties up carbon in storage forms
 






				   Nutrient Cycling
				        ADDENDUM

 NITROGEN CYCLE

Elaboration of N2 fixation ("conversion")
   Equation: N2 + 6 H+ + 6e-  -> 2 NH3
   Enzyme complex: nitrogenase or N2ase (strictly anaerobic)
   Specific organisms: Rhizobium, Azotobacter, Klebsiella, Clostridium,
    Nostoc, Anabaena, Gloeotheca, Trichodesmium, etc.
   Distinction between free-living and symbiotic nitrogen-fixing organisms.
   Association of bacteria with plants, legumes, nodulations, leghemoglobin, etc.

Nitrification: in bacteria, NH4+  + 2 O2 -> NO2- + 2 H2O,
			       NO2- + O2 -> NO3-
	this is done by Nitrosomonas, Nitrobacter, etc.
Denitrification: in bacteria, NO3- -> NO2- -> N2O -> N2
	this is true anaerobic respiration; the nitrogen compound acts as an
	alternative electron acceptor, replacing O2. Pseudomonas can do this,
	also Paracoccus, Bacillus, Thiobacillus, etc. Typically occurs in
	water-logged soils depleted of O2.
Unusual or special cases:
    Ammonification: usually by bacteria/fungi
   	proteins -> amino acids,   amino acids -> NH3
   Re-reduction: many organisms can use NO3 or NO2 but must convert these
   back to NH3 first. This is done by a pair of enzymes, namely nitrate reductase
   and nitrite reductase.
   Some organisms excrete urea and/or uric acid.
   Insectivorous plants (Pitcher Plants, Venus Flytrap, etc.) obtain nitrogenous
   compounds by digesting animals.

IMPACT ON NITROGEN CYCLE:
Burning fossil fuels -> releases NOx
	contributes to acid rain
Burning/clearing forest -> increases leaching of N compounds from soil
	decrease in fertility, increased NO3 in runoff water, etc.
Use of N fertilizers -> kills nitrogen fixers, other soil microbes or ->
increased NO3 in runoff water.
	decrease in fertility, possible health effects, eutrophication, 
	algal blooms, possible O2 depletion, etc.
Pesticides -> kill N2 fixers.
	decrease in fertility
Genetic Engineering of N2ase -> higher plants can fix their own N2?