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Biology 20 Key Concepts

Jun 17, 2025

Overview

This lecture reviews key concepts in Biology 20, including ecological organization, energy flow, cycles in nature, major organ systems, and biological processes relevant for the final exam.

Ecology & Biological Organization

  • The biosphere includes all areas on Earth inhabited by life (air, water, land).
  • Producers (autotrophs) make their own food; consumers (heterotrophs) eat others; decomposers break down dead matter.
  • A niche is a species' role; a habitat is where it lives; its range is its geographic area.
  • Biome: a large ecological area defined by climate and dominant flora.
  • Ecosystems consist of communities and their abiotic (non-living) environment.
  • Homeostasis maintains internal stability via feedback systems.
  • The three domains: Archaea, Bacteria, Eukarya.

Hierarchy of Life & Taxonomy

  • Organization: atoms β†’ molecules β†’ organelles β†’ cells β†’ tissues β†’ organs β†’ organ systems β†’ organism β†’ population β†’ community β†’ ecosystem β†’ biosphere.
  • Taxonomic hierarchy: Domain β†’ Kingdom β†’ Phylum β†’ Class β†’ Order β†’ Family β†’ Genus β†’ Species.
  • Classical Kingdoms: Monera, Protista, Fungi, Plantae, Animalia.

Energy Flow & Cycles

  • Energy decreases by ~90% at each trophic level; limits food chains to 5 or fewer levels.
  • Food chain: direct energy flow; food web: interconnected chains.
  • Pyramid of energy: shows energy transfer; pyramid of biomass: shows organism mass at each level.
  • Photosynthesis: plants convert COβ‚‚ and sunlight to glucose; chemosynthesis: bacteria use chemical energy.
  • Biomagnification: toxins increase in organisms higher up the food chain.

Major Nutrient Cycles

  • Nitrogen cycle: nitrogen fixed by bacteria or lightning, assimilated by plants, returned by decomposition or denitrification.
  • Water: unique because of surface tension, cohesion, adhesion, and capillary action.

Evolution & Adaptation

  • Evolution: change in populations' inherited traits over time.
  • Lamarck's theory: traits acquired by use/disuse are inherited.
  • Darwin's theory: natural selection, descent with modification; populations evolve, not individuals.

Human Biology: Systems & Functions

Digestive System

  • Digestion starts in the mouth (amylase), continues in stomach (HCl, pepsin), and completes in the small intestine (enzymes from pancreas, liver, gallbladder).
  • Accessory organs: pancreas (digestive enzymes, neutralizes acid), liver (produces bile, detoxifies), gallbladder (stores bile).
  • Large intestine absorbs water, forms feces, and houses bacteria.

Circulatory System

  • Blood flow: body β†’ vena cava β†’ right heart β†’ lungs β†’ left heart β†’ aorta β†’ body.
  • Blood: plasma (fluid), red cells (Oβ‚‚ transport), white cells (immunity), platelets (clotting).
  • Antibodies recognize antigens for immune defense.
  • ABO and Rh blood group systems determine compatibility.

Urinary System

  • Kidneys filter blood through nephrons: filtration, reabsorption, secretion.
  • Aldosterone increases Na⁺ reabsorption, regulating blood pressure by blood volume.

Respiratory System

  • Air travels: nose β†’ trachea β†’ bronchi β†’ bronchioles β†’ alveoli.
  • Gas exchange in alveoli via diffusion; Oβ‚‚ carried mainly by hemoglobin.
  • Breathing regulated by medulla (brain) and chemoreceptors sensing COβ‚‚/Oβ‚‚.

Muscular System

  • Three muscle types: smooth, cardiac, skeletal.
  • Skeletal muscles work in pairs; contraction via sliding filament model (actin, myosin, ATP, Ca²⁺).
  • ATP powers muscles; requires energy from respiration.

Chemical & Cellular Processes

  • Fermentation produces 2 ATP/glucose; aerobic respiration yields 36 ATP/glucose.
  • Enzymes speed reactions, affected by temperature and pH.
  • Dehydration synthesis: joins molecules, releases water; hydrolysis: splits molecules, uses water.
  • Lipids: glycerol + 3 fatty acids; proteins: amino acids linked by peptide bonds.

Other Key Topics

  • Biomagnification increases toxins up food chains.
  • Physical barriers (like skin) defend against pathogens.
  • Sexual vs asexual reproduction: pros and cons for each.

Key Terms & Definitions

  • Biosphere β€” all life-supporting regions of Earth.
  • Producer/Autotroph β€” organism that produces its own food.
  • Consumer/Heterotroph β€” organism that eats other organisms.
  • Decomposer β€” breaks down dead organic matter.
  • Niche β€” ecological role of an organism.
  • Biome β€” large ecological area with characteristic climate and species.
  • Biomagnification β€” increase in toxin concentration up the food chain.
  • Photosynthesis β€” conversion of solar energy to chemical energy by plants.
  • Fermentation β€” anaerobic breakdown of glucose to ATP.
  • Homeostasis β€” stable internal conditions.
  • Enzyme β€” protein catalyst for biochemical reactions.

Action Items / Next Steps

  • Review diagrams for energy pyramids, digestive, circulatory, urinary, respiratory, and muscular systems.
  • Memorize key definitions and processes (nitrogen cycle, photosynthesis, respiration).
  • Practice identifying organ structures and their functions.
  • Study the effects of temperature/pH on enzyme activity.
  • Prepare for questions on reproduction, biomagnification, and major organ systems.