Food chain Study Guide

📖 Core Concepts Food Chain: Linear sequence that moves energy from an autotrophic producer (e.g., grass) to a top consumer (apex predator, detritivore, or decomposer). Food Web: Network of intersecting food chains; shows all possible energy pathways among organisms. Trophic Level: Position in the chain where an organism obtains its energy (producer → primary consumer → secondary consumer → … → apex). Primary Producer (Autotroph): Makes organic matter from inorganic sources via photosynthesis or chemosynthesis. Consumer (Heterotroph): Eats other organisms; subdivided into primary, secondary, tertiary, etc. Apex Predator: Highest trophic level; has no natural predators in that chain. Detritivore / Decomposer: Break down dead material, returning nutrients to the environment. Keystone Species: Species whose impact on the food chain is disproportionately large relative to its abundance. Ecological Pyramid: Visual of decreasing energy, biomass, or number of organisms with each higher trophic level. --- 📌 Must Remember Energy Transfer Efficiency: Only 10 % of energy passes to the next trophic level; 90 % lost as heat, respiration, waste. Maximum Trophic Levels: Because of the 10 % rule, most realistic food chains have ≤ 5 levels. Human Diet Rule: Eating lower‑trophic‑level foods (plants) yields more energy per mass than eating higher‑trophic‑level meat. Keystone Effect: Removing a keystone species can cause cascading extinctions throughout the chain. Biomagnification: Contaminants become more concentrated as they move up trophic levels (ecotoxicology focus). --- 🔄 Key Processes Energy Capture by Producers Sunlight → photosynthesis or inorganic chemicals → chemosynthesis → organic compounds. Transfer to Primary Consumers Herbivores eat producers; only 10 % of producer energy stored as biomass. Secondary & Higher Consumers Carnivores eat herbivores; repeat 10 % transfer each step. Decomposition Dead matter → detritivores → decomposers → nutrients released back to soil/water → available for producers again. Biomagnification (Ecotoxicology) Contaminant ingested by producer → persists through each consumer → concentration ↑ with each trophic jump. --- 🔍 Key Comparisons Food Chain vs. Food Web Chain: Single, linear path. Web: Multiple, interconnected paths; more realistic for complex ecosystems. Primary Producer vs. Lithotroph Producer (Phototroph): Uses sunlight. Lithotroph: Uses inorganic chemicals (e.g., H₂S, CH₄) – a subset of producers. Detritivore vs. Decomposer Detritivore: Eats dead organic matter whole (e.g., earthworms). Decomposer: Chemically breaks down matter (e.g., fungi, bacteria). --- ⚠️ Common Misunderstandings “All food chains have the same length.” Length varies; energy loss limits most to ≤ 5 levels. “Apex predators are always the strongest species.” Apex status is about trophic position, not physical strength. “Energy loss is only due to waste.” Most loss is metabolic heat (respiration), not just uneaten material. “Food webs are just a collection of food chains.” Webs show interdependence; removing one link can affect many pathways. --- 🧠 Mental Models / Intuition “10 % Ladder”: Visualize each trophic jump as a step that only lets 1/10 of the previous step’s energy climb higher. The higher you go, the thinner the rung. “Pyramid of Influence”: The broad base (producers) supports everything above; shrink the base → whole pyramid collapses. “Keystone as a Keystone Arch”: Remove the central stone, the arch (food chain) falls even if the outer stones remain. --- 🚩 Exceptions & Edge Cases Aquatic Food Chains: Some marine systems can sustain 6–7 trophic levels due to higher primary production efficiency. Chemosynthetic Primary Production: In deep‑sea vents, energy originates from chemicals, not sunlight—still counts as a producer but may support different trophic structures. Human Cultural Practices: Fishing or agriculture can artificially shorten trophic pathways (e.g., farmed fish fed plant protein). --- 📍 When to Use Which Choose “Food Chain” when the question asks for a single, linear energy route (e.g., “list the flow from grass to hawk”). Choose “Food Web” for multiple interacting pathways or when assessing stability, keystone impacts, or indirect effects. Apply the 10 % rule to estimate energy available at higher trophic levels or to calculate why a particular consumer cannot be sustained. Use “Ecological Pyramid” when comparing energy, biomass, or organism number across levels. --- 👀 Patterns to Recognize Energy‑Loss Pattern: Every time a trophic level is mentioned, expect a 90 % loss → check if the implied number of levels is realistic. Keystone Indicator: Species that influence many others (e.g., sea otters controlling sea urchin populations) → look for cascade effects. Biomagnification Clue: Presence of persistent pollutants (e.g., DDT, mercury) paired with higher‑trophic‑level organisms. --- 🗂️ Exam Traps Distractor: “100 % energy transfer” – Wrong; violates thermodynamic laws. Trap: “Apex predator = strongest animal” – Apex is about trophic position, not size or strength. Misleading Choice: “Food webs have a single start and end point.” – False; webs are networked with many sources and sinks. Near‑miss: “All food chains have exactly five trophic levels.” – Overgeneralization; many have fewer, some (rare) have more. Confusing “Detritivore” with “Decomposer” – They differ in method of breaking down organic matter; answer choices often mix them up.