GCSE Biology: Ecology and Ecosystems Study Notes

Ecological Levels and Definitions

• Organism: A living system, such as a plant, animal, or bacterium.

• Population: Organisms of the same species in a given area (e.g., all butterflies in a field).

• Community: All the populations of different species in a given area.

• Ecosystem: The interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

• Biotic Factors: Living components that affect a community, including food availability, new predators, new pathogens, and competition.

• Abiotic Factors: Non-living components affecting organisms, such as light intensity, temperature, moisture levels, soil $pH$, mineral content, wind intensity, $CO_2$ levels for plants, and $O_2$ levels for aquatic animals.

• Interdependence: Within a community, each species depends on others for food, shelter, pollination, and seed dispersal; removing one species can affect the whole community.

• Stable Community: One where all species and environmental factors are in balance so that population sizes remain fairly constant.

Feeding Relationships and Biomass Transfer

• Trophic Levels:

  • Level 1: Producers (plants and algae) that synthesise molecules, usually glucose via photosynthesis.

  • Level 2: Primary consumers (herbivores).

  • Level 3: Secondary consumers (carnivores that eat herbivores).

  • Level 4: Tertiary consumers (carnivores that eat other carnivores) and Apex predators (carnivores with no natural predators).

• Pyramids of Biomass: Constructive representations of the relative amount of biomass at each trophic level, with Level 1 always at the base.

• Energy Efficiency: Calculated using the formula: $\text{Efficiency} = \frac{\text{Energy after transfer}}{\text{Energy before transfer}} \times 100$

• Biomass Losses: Only approximately $10\%$ of biomass from one level is transferred to the next. Losses occur because:

  • Not all ingested material is absorbed; some is egested as faeces.

  • Some material is lost as waste (e.g., $CO_2$ and water in respiration, urea in urine).

  • Large amounts of glucose are used in respiration for movement and maintaining body temperature.

• Incident Energy: Producers like plants and algae transfer about $1\%$ of the incident energy from light for photosynthesis.

Decomposition and Nutrient Cycling

• Decomposers: Bacteria and fungi that break down dead matter by secreting enzymes into the environment for extracellular digestion (saprophytic feeding).

• Detritivores: Animals like earthworms, maggots, and woodlice that break dead organic material into smaller pieces, increasing the surface area for decomposers.

• Essential Factors for Decay:

  • Temperature: Warmth allows for more rapid enzyme-controlled reactions.

  • Moisture: Necessary for chemical reactions to take place.

  • Oxygen: Required for aerobic respiration by decomposing microorganisms.

• The Carbon Cycle: Returns carbon from organisms to the atmosphere as $CO_2$ through respiration and combustion; plants then fix this carbon during photosynthesis.

• Major Components: Know the main components of the carbon cycle, which include:

  • The atmosphere (carbon dioxide)

  • Oceans (dissolved carbon and carbonates)

  • Terrestrial ecosystems (plants and soil carbon)

  • Fossil fuels (coal, oil, gas)

• Processes Involved: Understand the various processes that drive the carbon cycle:

  • Photosynthesis: Plants absorb carbon dioxide from the atmosphere and convert it into organic matter.

  • Respiration: Both plants and animals release carbon dioxide back into the atmosphere.

  • Decomposition: Microorganisms break down dead matter, returning carbon to the soil and atmosphere.

  • Combustion: Burning fossil fuels releases carbon dioxide and carbon into the atmosphere.

  • Oceanic Absorption: Oceans absorb carbon dioxide from the atmosphere, which can lead to ocean acidification.

• Human Impact: Be aware of how human activities, such as burning fossil fuels and deforestation, are altering the carbon cycle and contributing to climate change.

• Key Terms: Familiarize yourself with terms related to the carbon cycle, such as carbon sequestration, greenhouse gases, and carbon footprint.

• Carbon Sequestration: The process of capturing and storing atmospheric CO2 to mitigate climate change.

• Greenhouse Gases: Gases that trap heat in the atmosphere, including carbon dioxide, methane, and nitrous oxide.

• Carbon Footprint: The total amount of greenhouse gases, particularly CO2, that are emitted directly or indirectly by an individual, organization, or product.

• Greenhouse Gases: Gases that trap heat in the atmosphere, including CO2, methane, and nitrous oxide.

• Carbon Footprint: The total amount of greenhouse gases emitted directly or indirectly by an individual, organization, event, or product.

• The Water Cycle: Provides fresh water for land organisms through evaporation, transpiration, condensation, and precipitation.

Adaptations and Extremophiles

• Structural Adaptations: Physical characteristics (e.g., white fur for camouflage, thick blubber for insulation, or the large ears of a Fennec fox).

• Behavioural Adaptations: Actions or responses (e.g., migration, huddling for warmth, or being active only early/late in the day to avoid heat).

• Functional Adaptations: Changes in internal biological processes (e.g., producing highly concentrated urine to save water or secreting poison).

• Extremophiles: Organisms adapted to survive and reproduce in extreme conditions, such as high temperature, high pressure, or high salt concentration (e.g., bacteria in deep-sea vents).

• Surface Area to Volume Ratio ($SA:Vol$):

  • Large $SA:Vol$: Beneficial in hot climates to lose heat (e.g., large ears).

  • Small $SA:Vol$: Beneficial in cold climates to conserve heat (e.g., Arctic fox).

Required Practical: Temperature and Milk Decay

• Investigation: Measuring the effect of temperature on the rate of decay of fresh milk using $pH$ change.

• Process: Lipase enzymes break down lipids in milk into glycerol and fatty acids, which lowers the $pH$ of the solution.

• Indicator: Cresol red is used; it remains purple/red at alkaline or neutral $pH$ and turns yellow as the milk becomes acidic.

• Results: As temperature increases toward the optimum (approx. $40\,^{\circ}C$), the rate of decay increases; beyond this, enzymes denature and the rate decreases.

Questions & Discussion

• Question: Why does the number of invertebrate animals increase if many small fish die from disease?

• Response: Because fewer invertebrates are being eaten by the small fish.

• Question: How does a vacuum flask improve a decay investigation?

• Response: It reduces the loss of thermal energy, ensuring the temperature readings more accurately reflect the heat released by respiring microorganisms.

• Question: Why did the concentration of carbon dioxide in a sealed flask of decaying grass eventually level off?

• Response: This occurs when the grass has fully decomposed or there is a lack of oxygen for further aerobic respiration by microorganisms.

• Question: What is the benefit of adding sodium carbonate to the milk in the decay practical?

• Response: It makes the solution alkaline so that the Cresol red indicator starts as purple, providing a clear starting point for the colour change to yellow.

To understand the carbon cycle effectively, you should be familiar with the following key aspects:

In-depth knowledge might vary based on the course requirements, but understanding these components, processes, and the human impact on the carbon cycle is fundamental.