Unit 1 Ecological niche Tap / Space to flip
Unit 1 The role and resource use of an organism in its community — habitat, diet, activity time, predators, etc.
Unit 1 · 6–8% of exam
The Living World: Ecosystems
Ecosystem structure, energy flow, food webs, biogeochemical cycles, primary productivity. Detailed cycles are on the priority deep dive.
Must-know content
- Biotic vs. abiotic factors — biotic = living (plants, animals, microbes); abiotic = nonliving (sunlight, temperature, water, soil pH).
- Energy flow: producers → primary consumers → secondary → tertiary → decomposers. Energy decreases at each step.
- 10% rule — only ~10% of energy is transferred to the next trophic level; the rest is lost as heat or used in respiration.
- Food chains and food webs; trophic pyramids show energy, biomass, or numbers per level.
- Major terrestrial biomes: tundra, taiga (boreal forest), temperate forest, tropical rainforest, desert, grassland, chaparral. Defined by climate (temperature & precipitation).
- Aquatic biomes: freshwater (lakes, rivers, wetlands), estuaries, marine, coral reefs.
- Primary productivity: GPP = total energy fixed by producers; NPP = GPP − respiration. NPP is the energy available to consumers.
- Symbioses: mutualism (+/+), commensalism (+/0), parasitism (+/-), competition (-/-), predation (+/-).
Example questions
MCQ In a food chain producing 10,000 kcal at the producer level, approximately how much energy is available to a secondary consumer? (A) 10,000 kcal (B) 1,000 kcal (C) 100 kcal (D) 10 kcal
Answer: C. Apply the 10% rule twice: 10,000 → 1,000 (primary consumer) → 100 (secondary consumer).
FRQ Describe ONE difference in NPP between a tropical rainforest and a tundra and explain the reason.
Answer: Tropical rainforest has much higher NPP (~2,200 g/m²/yr) than tundra (~140 g/m²/yr). The rainforest has higher temperature, more sunlight, more rainfall, and a longer growing season, allowing more photosynthesis and biomass production per unit area. Tundra is cold, has limited sunlight in winter, frozen ground, and a short growing season.
MCQ Which best describes a mutualistic relationship? (A) Mosquito feeding on a human (B) Mycorrhizal fungi exchanging nutrients with plant roots (C) Barnacles attached to a whale (D) Two birds competing for the same nesting site
Answer: B. Mycorrhizae provide phosphorus to roots; roots provide sugars to fungi. Both benefit (+/+).
Drill flashcards
Unit 1 Trophic level Tap / Space to flip
Unit 1 Position in a food chain. Producers → primary → secondary → tertiary consumers. Energy decreases at each step.
Unit 1 10% rule Tap / Space to flip
Unit 1 Only ~10% of energy is transferred to the next trophic level; the rest is lost as heat or used in respiration.
Unit 1 GPP vs. NPP Tap / Space to flip
Unit 1 Gross Primary Productivity = total energy fixed by producers. Net = GPP minus producer respiration. NPP is the energy available to consumers.
Unit 1 Food web Tap / Space to flip
Unit 1 Network of interconnected food chains. More realistic than a single chain because most consumers eat multiple species.
Unit 1 Decomposers Tap / Space to flip
Unit 1 Bacteria and fungi that break down dead organic matter, returning nutrients (esp. C, N, P) to the soil and atmosphere.
Unit 1 Mutualism Tap / Space to flip
Unit 1 Symbiosis where both species benefit (+/+), e.g., mycorrhizae and plant roots; bees and flowering plants.
Unit 1 Commensalism Tap / Space to flip
Unit 1 Symbiosis where one species benefits, the other is unaffected (+/0), e.g., barnacles on a whale.