UNIT ONE NOTES

The Living World: Ecosystems

UNIT 1 THE LIVING WORLD: ECOSYSTEMS

• Introduction to Ecosystems
• Terrestrial Biomes
• Aquatic Biomes
• Carbon Cycle
• Nitrogen Cycle
• Phosphorus Cycle
• Water Cycle
• Primary Productivity
• Trophic Levels
• Energy Flow and the 10% Rule
• Food Chains and Food Webs

1.1 INTRODUCTION TO ECOSYSTEMS

• Definition of an Ecosystem: An ecosystem is a community of living organisms in conjunction with the non-living components of their environment, interacting as a system.
• Components of Ecosystems: Ecosystems result from interactions between BIOTIC (living) and ABIOTIC (non-living) components.

1.1 INTRODUCTION TO ECOSYSTEMS - Species Interactions

• Competition:
    - Definition: Two organisms fighting for the same niche or resources within an ecosystem.
    - Types:
      - Interspecific Competition: Competition between different species.
      - Intraspecific Competition: Competition within the same species.
    - Solution: Resource partitioning
      - Definition: When species utilize limiting resources in different ways, places, or times to reduce competition.

• Predation:
    - Definition: One organism kills and consumes another organism.

• Symbiosis:
    - Definition: A relationship between two organisms.

• Types of Symbiotic Relationships:
    - Mutualism:
      - Definition: A relationship where both organisms benefit.
      - Examples: Pollination, corals and zooxanthellae, clownfish and sea anemone.

  - Commensalism:
    - Definition: One species benefits, while the other is neither harmed nor helped.
    - Examples:
      - Owls nesting in hollows of trees.
      - Hermit crabs using discarded snail shells.

  - Parasitism:
    - Definition: One organism obtains resources from another without killing it.
    - Examples: Ticks/fleas on mammals, intestinal tapeworms, mosquitoes biting warm-blooded animals.

1.2 TERRESTRIAL BIOMES

• Definition of Biomes: Biomes are large areas characterized by certain climate conditions and types of ecosystems, determined by precipitation and temperature.
• Climate Influence: Hot, humid regions exhibit greater primary productivity and greater biodiversity than cold or dry regions.

1.2 TERRESTRIAL BIOMES - Types

Specific Questions Related to Biomes

• Soil Quality in Tropical Rainforests (TRF): Nutrients are largely locked within the plants, leading to poor soil quality.
• Terms for Grasslands: Various terms like savanna, steppe, prairie, pampas, and veldt exist due to ecological and regional differences.

1.3 AQUATIC BIOMES

• Types of Aquatic Biomes:
    - Freshwater: Streams, ponds, lakes
    - Marine: Intertidal zones, estuaries, rivers, coral reefs, marshes, wetlands (woody and non-woody), open ocean.

Abiotic Conditions in Aquatic vs. Terrestrial Biomes

• Aquatic Conditions: Depth, light, temperature, velocity (currents), salinity, oxygen
• Terrestrial Conditions: Nutrients (nitrates, phosphates), suspended matter (silt), bottom substrate (muddy, sandy, rocky), annual average precipitation and temperature, latitude and altitude, soil type, topography, wind speed.

Wetlands Analysis

• Wetlands (Swamps, Marshes): Areas that cycle between wet and dry conditions, known for the highest net primary productivity.
• Ecosystem Services Provided by Wetlands:
    - Filtering water
    - Providing habitats
    - Buffering extreme precipitation events

Biodiversity in Aquatic Biomes

• Coral Reefs: Known as the TRFs of the ocean, they represent the most marine biodiversity.
• Most Productive Biomes: Swamps, marshes, and tropical rainforests; least productive include open oceans and deserts.

1.4 CARBON CYCLE

• Key Elements in the Cycle: Carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

Carbon in Different Reservoirs

• Atmosphere:
    - Major gases: $CO_2$, $CH_4$
    - Emitted through respiration, combustion, decomposition.

• Ocean:
    - Contains dissolved $CO_2$ and marine life produces calcium carbonate ($CaCO_3$) in shells.

Historical Carbon Levels

• Graph of Atmospheric Carbon Dioxide: Trends from historical levels to present concentration, focusing on measurements recorded at Mauna Loa, Hawaii.

Ocean Acidification

• Carbon Cycle Imbalance:
    - Seawater absorbs atmospheric $CO_2$, leading to the formation of carbonic acid ($H_2CO_3$)
      - Reaction:
         ext{CO}_2 + H_2O
  ightarrow H_2CO_3
  ightarrow H^+ + HCO_3^-
• Consequences: Decreased pH and carbonate ion availability affecting calcifying organisms like corals.

Photosynthesis and Respiration

• Photosynthesis:
    - Main mechanism of carbon fixation:
       ext{CO}2 + H_2O ightarrow C_6H{12}O_6 + O_2
• Aerobic Respiration:
    - Recapturing carbon:
       C_6H_{12}O_6 + O_2
  ightarrow ext{CO}_2 + H_2O

Residence Time for Carbon

• Average Residence Times:
    - Atmosphere: 3 years (as $CO_2$ gas)
    - Soils: 25–30 years (in carbonate sediments and rocks)
    - Oceans: 1500 years
    - Prehistoric flora and fauna: spanning millions of years.

Carbon Sources and Sinks

• Carbon Sources:
    - Combustion of fossil fuels
    - Deforestation
• Carbon Sinks:
    - Long-term: Oceans
    - Short-term: Plants
    - Ancient plants and animals (fossils).

1.5 NITROGEN CYCLE

• Importance of Nitrogen: Major component of amino acids and nucleic acids; essential for producers to grow. Fertilizers often contain nitrogen.

Nitrogen Cycle Overview

• Major Reservoir: Atmospheric nitrogen ($N_2$), which is mainly fixed by bacteria into usable forms like ammonia ($NH_3$) and nitrate ($NO_3^-$).
• Key Processes:
    - Fixation: $N_2$ is converted to $NH_3$ by lightning or microbes.
    - Ammonification: Conversion of $NH_3$ to ammonium ($NH_4^+$) by bacteria.
    - Nitrification: $NH_4^+$ is converted to $NO_3^-$.
    - Assimilation: Plants uptake $NO_3^-$ to form proteins.
    - Denitrification: Conversion of $NO_3^-$ back to $N_2$ by soil bacteria.

Human Impacts on the Nitrogen Cycle

• Fossil Fuels: Release of nitrogen oxides ($NO_x$) as pollutants.
• Runoff from Fertilizers: Leads to eutrophication, where excess nutrients cause algal blooms and subsequent decline in dissolved oxygen (DO), endangering aquatic life, including fish.

1.6 PHOSPHORUS CYCLE

• Overview: The phosphorus cycle is a slow cycle without an atmospheric phase. Major stores include rocks and marine sediments.
• Human Impacts: Use of fertilizers leads to excess phosphates in water bodies, causing eutrophication similar to nitrogen runoff.
• Limiting Factor: In ecology, phosphorus often limits growth, as does nitrogen less frequently.

1.7 WATER CYCLE

• Key Processes:
    - Transpiration: Water loss from plants (leaf ‘sweat’).
    - Percolation: Water moving into the earth after rain.
    - Driver of the Cycle: The Sun.

Water Cycle Processes

• Precipitation: In the form of rain, sleet, hail, or snow.
• Infiltration: Movement of water into the soil.

1.8 PRIMARY PRODUCTIVITY

• Definition: The rate at which solar energy is converted into organic compounds by photosynthesis over time.

Types of Productivity

• Gross Primary Productivity (GPP): Total rate of photosynthesis in a given area.
• Net Primary Productivity (NPP): Rate of energy storage by photosynthesizers after subtracting energy lost to respiration:
  $ext{NPP} = ext{GPP} - ext{Cellular Respiration}$

Factors Affecting NPP

• Influenced by environmental conditions such as sunlight, temperature, water availability, and nutrients.

1.9 TROPHIC LEVELS

• Trophic Hierarchy:
    1. Producers: Autotrophs that produce their own food.
    2. Consumers: Heterotrophs categorized as herbivores, carnivores, or omnivores.
    3. Recyclers: Scavengers, decomposers, and detritivores that break down organic material.

1.10 ENERGY FLOW AND THE 10% RULE

• Energy Transfer: Only 10% of energy from one trophic level is available for the next; 90% is used by the current trophic level or lost as heat.

Important Energy Calculations

• Daily energy requirements for an average adult human: 2000 kcal/day. Yearly total: 730,000 kcal.
• For chicken consumption:
    - A serving has 120 kcal; for a year: 6083 servings or ~229 chickens consumed.
    - For corn: 12,166 ears required for direct human consumption of necessary kcal.
    - Additional calculations on chicken feed requirements and potential human food distribution based on corn consumption.

1.11 FOOD CHAINS AND FOOD WEBS

• Marine Food Web Example: Include various organisms such as blue whales, crabs, seals, fish, squid, and more.
    - Identify primary producers, consumers, and explain energy flow.
• Key Concepts: Arrows indicate energy transfer direction, with primary producers at the base and apex predators at the top of the chain.