Combustion releases long-sequestered geologic carbon directly into the atmosphere as carbon dioxide gas.

Extra Practice (Drought Cascade): Lack of water reduces plant photosynthesis and biomass (producers decline) → Herbivores suffer starvation, water deficit, and population decline → Carnivore population crashes due to prey scarcity.

Exit Ticket Key:

• Prompt A: Bacteria fix unusable gaseous \(N_2\) into biologically available nitrates (\(NO_3^-\)) that plants incorporate into amino acids/proteins.
• Prompt B: Decomposers prevent chemical stagnation; they recycle locked nitrogen into soil and convert organic carbon into \(CO_2\) via decay.

Biology IA Review Packet • Teacher Answer Key Day 1 Key • Page 1 of 4

Teacher Scoring Guide • Day 2 of 4 ANSWER KEY

Day 2: Ecological Hierarchy & 10% Rule

Standards: Biotic/abiotic distinction, food web arrows, trophic energy efficiency.

Packet Pages: 4–6 • Interim Q17–Q26

1-2 Biotic vs Abiotic & Hierarchy Ladder (Packet Page 4)

Classification Keys

Do Now Classification:

• Water Temp: Abiotic

• Green Algae: Biotic

• Dissolved \(O_2\): Abiotic

• Bass Fish: Biotic

Teacher note: Emphasize that dissolved \(O_2\) is a chemical molecule (non-living), despite being required by living fish.

Hierarchy Ladder (Smallest to Largest):

1. Organism: Single individual (One single bass).

2. Population: All members of ONE species (All Lake Michigan bass).

3. Community: ALL interacting living species (Bass + algae + frogs).

4. Ecosystem: Living community + non-living environment (Lake abiotic + biotic).

3 Food Web Analysis & Golden Arrow Rule (Packet Page 5)

IA Standards 22–24

1. Same Trophic Level Analysis (IA Q23):

Exemplar Answer: Both the mouse and the grasshopper are primary consumers (herbivores). They both feed directly on the primary producer (grass), which means they occupy the exact same second trophic level (Tier 2: Primary Consumers) in this ecosystem.

2. Tracing Four-Step Energy Pathway to Hawk:

Grass (Producer) → Grasshopper (Primary) → Sparrow (Secondary) → Hawk (Tertiary/Apex)

Alternate correct pathway: Grass → Mouse → Snake → Hawk (Both demonstrate 4 sequential trophic steps).

4-6 10% Rule Math, Exam Item & Exit Ticket (Packet Page 6)

Calculations & Misconceptions

Pyramid Calculation Math:

Producers: 10,000 kcal (100%)

Primary: 1,000 kcal (10%)

Secondary: 100 kcal (1%)

Tertiary: 10 kcal (0.1%)

Rule: Move decimal one place left for each higher level (\(\times 0.10\)).

IA Exam Item (Q24 Marine Web):

Correct Answer: C. 4

Chain: Kelp (Level 1) → Sea urchin (Level 2) → Sea otter (Level 3) → Killer whale (Level 4).

Common error: Counting arrows instead of organisms, or forgetting kelp is Level 1.

Day 2 Exit Ticket Model Responses:

• Prompt A: \(80,000 \text{ kcal} \times 0.10 = \mathbf{8,000 \text{ kcal}}\) are incorporated into rabbit tissue biomass.
• Prompt B: The remaining 90% (72,000 kcal) is converted and lost as thermal energy (heat) during cellular respiration, muscle movement, maintaining body temperature, and excreted waste.

Biology IA Review Packet • Teacher Answer Key Day 2 Key • Page 2 of 4

Teacher Scoring Guide • Day 3 of 4 ANSWER KEY

Day 3: Symbiosis, Niches & Keystone Species

Standards: Inter-species interactions, competitive exclusion, native vs non-native dynamics.

Packet Pages: 7–9 • Interim Q27–Q35

1-2 Symbiosis Symbols & Case Files (Packet Page 7)

Interaction Scoring

3-4 Niches, Keystone & Invasive Species (Packet Page 8)

IA Standards 31–35

Niches vs Competitive Exclusion:

Niche Partitioning (IA 31): Coexistence achieved by dividing microhabitats/resources (e.g. warblers feeding in distinct vertical zones of spruce trees).

Competitive Exclusion (IA 32): Two species requiring the exact same limiting resource cannot coexist; one outcompetes and displaces the other.

Keystone vs Invasive Contrast:

Keystone (Sea Otter): Native organism with disproportionately large stabilizing effect. Removal triggers trophic cascade and habitat collapse.

Invasive (Non-Native): Introduced organism without natural predators; overconsumes resources and collapses native biodiversity.

5-7 IA Exam Items & Exit Ticket (Packet Page 9)

Exemplars & Reasoning

IA Practice Q1 (33): C. Keystone species

The collapse of kelp and total species count confirms the sea otter's outsized ecological importance.

IA Practice Q2 (35): B. Few natural predators

Unchecked population growth allows invasive species to exhaust resources needed by native species.

Extra Practice (Zebra Mussels): Under competitive exclusion, two organisms cannot occupy identical plankton-filtering niches. Zebra mussels reproduce explosively and deplete the plankton stock before slow-developing larval fish can adapt or switch food sources.

Day 3 Exit Ticket Model Responses:

• Prompt A: In mutualism (+/+), both species gain biological advantages (e.g. clownfish & anemone: protection and nutrient exchange). In commensalism (+/0), one benefits while the host experiences zero impact (e.g. barnacles on whales: transport to feeding zones).
• Prompt B: A keystone species is a beneficial native organism that maintains structural biodiversity; an invasive species is an introduced organism that disrupts ecological balance and harms native populations.

Biology IA Review Packet • Teacher Answer Key Day 3 Key • Page 3 of 4

Teacher Scoring Guide • Day 4 of 4 ANSWER KEY

Day 4: Population Dynamics & CRQ Scoring

Standards: Carrying capacity (K), predator lag, fossil superposition, constructed responses.

Packet Pages: 10–12 • Interim Q36–Q43

1-2 Limiting Factors & Carrying Capacity (Packet Page 10)

Concept Scoring

Do Now Classification:

• Contagious Virus: Dependent

• Major Hurricane: Independent

• Food Competition: Dependent

• Wolf Hunting: Dependent

Rule of thumb: Density-dependent factors intensify as population density increases.

Carrying Capacity (K) & Crash (IA 37–38):

Definition: Maximum population supported sustainably by ecosystem resources.

Overshoot & Crash: Populations exceeding K degrade their resource base faster than regeneration permits; famine and mortality trigger a steep population crash.

3-4 Predator-Prey Oscillations & Fossil Strata (Packet Page 11)

IA Standards 39–40

Why Predator Peaks Lag Behind Prey:

Predator reproduction takes time; female predators must acquire excess nutritional energy from abundant prey before gestating and weaning young. When prey crashes, predators do not starve immediately.

Fossil Strata & Ancestry (IA 39–40):

Law of Superposition: Deepest layer (Layer 4) contains the OLDEST fossils (Fossil Z); surface layer contains the youngest.

Homologous Structures: Similar skeletal morphology in Fossils Y and Z indicates divergence from a shared common ancestor.

5-6 CRQ Scoring Rubrics & Final Audit (Packet Page 12)

Crucial Assessment Scoring

CRQ 41: Food Web Construction (2 pts) Criteria: Correct Flow & Hierarchy

Full Credit (2 pts): Includes 5+ organisms across 3+ trophic levels (e.g. Holly/Grass → Rabbit/Deer → Wolf/Hawk). All arrows point toward the organism consuming the energy. Zero backwards arrows.

CRQ 43: Wolf Removal Cascade (2 pts) Criteria: 2+ Specific Populations

Full Credit (2 pts): (1) Deer and rabbit populations rapidly increase due to loss of apex predator control; (2) Surging herbivore density causes severe overgrazing of holly trees and grasses, leading to habitat loss, soil erosion, and subsequent herd starvation.

Final Review Question Model Response:

"Why does energy flow one way, while matter cycles?" Solar energy constantly enters ecosystems, flows through trophic levels, and is irreversibly lost to space as metabolic heat (Second Law of Thermodynamics), requiring continuous sun input. In contrast, matter (atoms like C, N, H, O) cannot be created or destroyed (Conservation of Mass); decomposers and biogeochemical cycles recycle the exact same atoms endlessly.

Biology IA Review Packet • Teacher Answer Key Day 4 Key • Page 4 of 4