Honors Biology – Unit 2: Matter & Energy in Organisms and Ecosystems

Honors Biology – Unit 2: Matter & Energy in Organisms and Ecosystems

Ecology, Energy Flow, and Cell Energy

I. Ecology and the Biosphere

What Is Ecology?

  • Ecology is the study of interactions among organisms and between organisms and their physical environment.

  • Ecological studies include both biotic (living) and abiotic (nonliving) factors.

The Biosphere

  • The biosphere includes all regions of Earth where life exists.

  • It extends from about 5 miles above Earth’s surface to 7 miles below the ocean surface.

  • Components include:

    • Land

    • Water

    • Atmosphere (air)

II. Ecosystems, Biomes, and Environmental Factors

Ecosystems

  • An ecosystem consists of all living organisms in an area and their nonliving environment.

  • Ecosystems vary in size and include interactions between organisms and their surroundings.

Biotic and Abiotic Factors

  • Biotic factors: Living components of an ecosystem (plants, animals, fungi, bacteria).

  • Abiotic factors: Nonliving components (sunlight, water, air, temperature, rocks).

Biomes

  • A biome is a large geographic region defined by its climate and characteristic plants and animals.

III. Energy Flow in Ecosystems

Autotrophs (Producers)

  • Autotrophs produce their own food by capturing energy.

  • Photosynthetic autotrophs use sunlight to make food.

  • Chemosynthetic autotrophs use chemical energy from inorganic compounds.

Heterotrophs (Consumers)

  • Heterotrophs obtain energy by consuming other organisms.

    • Herbivores eat plants.

    • Carnivores eat animals.

    • Omnivores eat both plants and animals.

    • Decomposers / Detritivores break down organic waste and recycle nutrients.

IV. Food Chains, Food Webs, and Trophic Levels

Food Chains and Food Webs

  • Energy flows in one direction: from the sun (or inorganic chemicals) → producers → consumers.

  • A food chain shows a single pathway of energy transfer.

  • A food web connects multiple food chains within an ecosystem.

Trophic Levels

  • Each step in a food chain is a trophic level:

    1. Producers

    2. Primary consumers

    3. Secondary consumers

    4. Tertiary consumers

Ecological Pyramids

  • Energy Pyramid: Only about 10% of energy is transferred to the next trophic level; the rest is lost as heat.

  • Biomass Pyramid: Shows the total mass of living tissue at each trophic level.

  • Pyramid of Numbers: Shows the number of organisms at each trophic level.

Biomagnification

  • Biomagnification occurs when toxic substances increase in concentration at higher trophic levels.

  • Example: DDT accumulating in top predators.

V. Cycling of Matter

Biogeochemical Cycles

  • Matter is recycled within and between ecosystems.

  • Biogeochemical cycles involve biological, geological, and chemical processes.

Water Cycle

  • Evaporation: Liquid water → water vapor

  • Condensation: Water vapor → liquid

  • Precipitation: Rain, snow, sleet, hail

  • Transpiration: Water released by plants

  • Infiltration: Water soaks into soil

  • Runoff: Water flows over land into bodies of water

Carbon Cycle

  • Carbon moves through ecosystems via:

    • Photosynthesis

    • Cellular respiration

    • Decomposition

    • Fossil fuel combustion

Nitrogen Cycle

  • Nitrogen fixation: Bacteria convert atmospheric N₂ into ammonia or nitrates usable by plants.

  • Nitrification: Ammonium → nitrites → nitrates

  • Denitrification: Nitrates converted back into N₂ gas

  • Nitrogen-fixing bacteria are essential to this cycle.

Phosphorus Cycle

  • Phosphorus cycles through rocks, soil, water, and organisms.

  • Does not have a gaseous phase.

  • Weathering releases phosphates into soil and water.

VI. Community Interactions and Ecosystem Dynamics

Habitat and Niche

  • Habitat: The physical place an organism lives (its address).

  • Niche: The role an organism plays in its ecosystem (its occupation).

Community Interactions

  • Competition: Organisms compete for limited resources.

  • Predation: One organism (predator) captures and eats another (prey).

  • Symbiosis:

    • Mutualism: Both species benefit.

    • Commensalism: One benefits, the other is unaffected.

    • Parasitism: One benefits while harming the host.

Ecological Succession

  • Succession is the gradual change in species composition over time.

  • Primary succession: Occurs where no soil exists (e.g., volcanic rock).

  • Secondary succession: Occurs where soil remains after a disturbance (e.g., wildfire).

VII. Population Ecology

Factors Affecting Population Size

  • Birth rate

  • Death rate

  • Immigration

  • Emigration

Population Growth Patterns

  • Exponential growth: Rapid growth under ideal conditions (J-shaped curve).

  • Logistic growth: Growth slows as resources become limited (S-shaped curve).

Carrying Capacity

  • Carrying capacity (K) is the maximum population size an environment can sustain.

Limits to Growth

  • Density-dependent factors: Competition, disease, predation.

  • Density-independent factors: Weather, natural disasters, human activities.

VIII. ATP and Chemical Energy

ATP Structure and Function

  • ATP (adenosine triphosphate) is the primary energy carrier of cells.

  • Composed of adenine, ribose, and three phosphate groups.

ATP Cycle

  • Energy is released when ATP is converted to ADP through hydrolysis.

  • ATP is regenerated using energy from food.

ATP vs. Glucose

  • Both store energy.

  • Glucose stores long-term energy.

  • ATP provides immediate energy for cellular processes.

IX. Photosynthesis

Overall Equation

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂

Chloroplast Structure

  • Thylakoid: Site of light-dependent reactions

  • Stroma: Site of the Calvin cycle

Light-Dependent Reactions

  • Require light

  • Occur in thylakoid membranes

  • Produce ATP, NADPH, and oxygen

Calvin Cycle

  • Occurs in the stroma

  • Uses CO₂, ATP, and NADPH

  • Produces glucose

Limiting Factors of Photosynthesis

  • Light intensity

  • Carbon dioxide concentration

  • Temperature

X. Cellular Respiration

Aerobic Cellular Respiration

  • Overall equation:
    C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

Stages of Cellular Respiration

  1. Glycolysis: Occurs in cytoplasm; breaks glucose into pyruvate; produces small amount of ATP.

  2. Krebs Cycle: Occurs in mitochondrial matrix; releases CO₂ and transfers energy to carriers.

  3. Electron Transport Chain: Occurs in inner mitochondrial membrane; produces most ATP.

Fermentation

  • Occurs in absence of oxygen

  • Allows glycolysis to continue

  • Types:

    • Lactic acid fermentation

    • Alcoholic fermentation

Efficiency

  • Aerobic respiration produces much more ATP than glycolysis alone.

XI. Relationship Between Photosynthesis and Cellular Respiration

  • Photosynthesis stores energy by making glucose.

  • Cellular respiration releases energy by breaking down glucose.

  • The products of one process are the reactants of the other.

XII. Human Impact and Environmental Issues

  • Biodiversity: Variety of life in an ecosystem

  • Conservation: Protection and wise use of natural resources

  • Deforestation: Removal of forests

  • Invasive species: Non-native species that cause harm

  • Eutrophication: Nutrient runoff causing excessive plant growth and oxygen loss

  • Pollution: Harmful substances added to the environment