AQA GCSE (9-1) Biology: Organisation of an Ecosystem

Key Takeaways for Organisation of an Ecosystem

1. Levels of Organisation

• Definitions:
  • Population: All organisms of the same species in a habitat (e.g., all daisies in a field).
  • Community: Multiple populations interacting in a habitat (e.g., daisies, bees, and earthworms in a field).
  • Ecosystem: Community + abiotic factors (e.g., a pond ecosystem includes water, fish, plants, and temperature).
• Key Rule: Ecosystems rely on interdependence—organisms depend on each other for survival (e.g., pollinators and plants).

2. Sampling Techniques

Quadrats

• Purpose: Estimate population size or biodiversity.
• Random Sampling:
  • Use random coordinates to avoid bias (e.g., rolling dice to select grid points).
  • Formula for population estimation:
    Total population=(Total areaQuadrat area)×Mean per quadratTotal population=(Quadrat areaTotal area​)×Mean per quadrat
    Example: 10 quadrats (1m² each) average 8.6 daisies → Total daisies in a 5060m² field ≈ 8.6 × 5060 = 43,516.
• Systematic Sampling:
  • Use transects (straight lines) to study distribution changes (e.g., seaweed along a rocky shore).

Key Tips

• Always use random sampling for population estimates.
• Sample size: More quadrats = more reliable results (e.g., 50 quadrats better than 10).
• Avoid bias: Never choose “best-looking” spots!

3. Producers, Consumers & Decomposers

• Producers: Photosynthetic organisms (plants/algae) making glucose:
  CO2+H2O→lightGlucose+O2CO2​+H2​Olight​Glucose+O2​
• Consumers:
  • Herbivores (e.g., rabbits), carnivores (e.g., lions), omnivores (e.g., humans).
  • Only ~10% energy transferred between trophic levels (rest lost as heat/waste).
• Decomposers: Fungi/bacteria breaking down dead matter (recycling nutrients).

4. Carbon Cycle

• Key Processes:
  1. Photosynthesis: Plants absorb CO₂.
  2. Respiration: All organisms release CO₂:
     Glucose+O2→CO2+H2O+EnergyGlucose+O2​→CO2​+H2​O+Energy
  3. Combustion: Burning fossil fuels releases CO₂:
     CH4+2O2→CO2+2H2OCH4​+2O2​→CO2​+2H2​O
  4. Decomposition: Dead matter → CO₂.
• Atmospheric CO₂: 0.04% (rising due to human activity).

5. Water Cycle

• Key Processes:
  • Evaporation (liquid → gas), Transpiration (water loss from plants), Precipitation (rain/snow).
  • Infiltration: Water seeping into soil → groundwater.
  • Subsurface flow: Movement of groundwater to oceans.

6. Decomposition

• Factors Increasing Rate:
  • Warm temperatures, moisture, oxygen, neutral pH.
• Practical Example: Milk decay → pH drops due to lactic acid from bacteria.
• Preservation: Bodies in peat bogs stay intact due to cold, acidic, anaerobic conditions.

7. Environmental Change Impact

• Bioindicators:
  • Lichens: Indicate air quality (e.g., beard lichen = clean air).
  • Mayfly nymphs: Indicate clean water.
• Adaptations:
  • Cacti: Spines reduce transpiration.
  • Camels: Concentrated urine, fat stores for water.
• Global Warming:
  • Species migrate (e.g., mosquitoes spreading to warmer regions).
  • Caused by greenhouse effect (trapped CO₂).

Exam Tips

• Equations: Memorise photosynthesis/respiration formulas with $$ delimiters.
• Sampling: Always justify why random sampling is used (avoid bias).
• Energy Transfer: Highlight ~10% rule in food chains.
• Data Interpretation: For decay experiments, link temperature to enzyme activity.

Common Mistakes:

• Confusing systematic (transects) vs. random sampling.
• Forgetting decomposers in the carbon cycle.
• Misinterpreting bioindicator data (e.g., lichen types).

Revision Mantra: “Producers start the chain, decomposers recycle again!” 🌱♻️

50 GCSE Questions on Organisation of an Ecosystem

Section 1: Levels of Organisation & Sampling

1. Define the term population.
2. Explain why random sampling is preferred over non-random methods.
3. Describe how to use a quadrat to estimate daisy population in a field.
4. What is the purpose of a transect?
5. Calculate the total daisy population if 10 quadrats (0.25m² each) average 8.6 daisies in a 5060m² field.
6. Why might sampling only red squirrels in England give an inaccurate UK population estimate?
7. Name three ways organisms are recorded in a quadrat.
8. What does concordant results mean in ecology?
9. Explain the difference between random and systematic sampling.
10. Why must quadrats be placed at random coordinates?

Section 2: Producers, Consumers & Decomposers

11. Write the word equation for photosynthesis.
12. Why are plants called producers?
13. Give two examples of consumers.
14. Explain why only ~10% of energy is transferred between trophic levels.
15. What role do earthworms play in decomposition?
16. Name a decomposer found in soil.
17. Why are fungi not classified as consumers?
18. Describe how extremophile bacteria obtain energy.
19. What is biomass?
20. Why is algae critical to oxygen production?

Section 3: Carbon Cycle

21. Name four key processes in the carbon cycle.
22. Write the balanced equation for respiration.
23. How does combustion contribute to atmospheric CO₂?
24. What percentage of atmospheric CO₂ is currently present?
25. Explain how carbon in dead plants re-enters the atmosphere.
26. Convert the combustion of methane into a chemical equation.
27. Why is decomposition essential in the carbon cycle?
28. What happens to carbon in fossil fuels during combustion?
29. How do decomposers like bacteria recycle carbon?
30. Why is the carbon cycle described as a closed loop?

Section 4: Water Cycle

31. Define precipitation.
32. What percentage of Earth’s water is freshwater?
33. Describe infiltration.
34. Explain the role of transpiration in the water cycle.
35. Name three states of water in the cycle.
36. How does subsurface flow differ from runoff?
37. What is an aquifer?
38. Why is most precipitation over oceans?
39. How do plants contribute to atmospheric water vapour?
40. What human activities disrupt the water cycle?

Section 5: Decomposition & Environmental Impact

41. List three conditions that speed up decomposition.
42. Why does milk pH drop during decay?
43. How does temperature affect decay rates?
44. Explain why Tollund Man was preserved in peat bogs.
45. What is silage, and why do farmers use it?
46. Why is manure added to fields?
47. Name two bioindicators for water quality.
48. How are cacti adapted to desert life?
49. Describe how global warming affects species migration.
50. Why are lichens used as air pollution indicators?

Detailed Answers

1. Population: All organisms of the same species in a habitat (e.g., all daisies in a field).
2. Random sampling avoids bias, ensuring every part of the habitat has an equal chance of being sampled.
3. Method:
   • Use random coordinates to place quadrats.
   • Calculate mean per quadrat.
   • Total population = (Total area ÷ Quadrat area) × Mean per quadrat.
4. Transect: A line for systematic sampling to study distribution changes (e.g., seaweed on a shore).
5. Calculation:
   50600.25×8.6=43,516 daisies0.255060​×8.6=43,516 daisies
6. Sampling bias: 85% of UK red squirrels live in Scotland; sampling only England underestimates populations.
7. Recording methods: Count individuals, count species, estimate percentage cover.
8. Concordant results: Repeatable results that are similar, increasing reliability.
9. Random: Unbiased placement; Systematic: Regular intervals (e.g., along a transect).
10. Avoid bias: Prevents selecting areas with more/less organisms.
11. Photosynthesis:
    Carbon dioxide+Water→lightGlucose+OxygenCarbon dioxide+Waterlight​Glucose+Oxygen
12. Producers synthesise glucose from inorganic compounds (CO₂, H₂O).
13. Consumers: Herbivores (rabbits), carnivores (lions).
14. Energy loss: Through respiration, heat, undigested waste (e.g., faeces).
15. Earthworms: Break down organic matter, aerate soil.
16. Decomposer: Bacteria/fungi (e.g., Bacillus).
17. Fungi secrete enzymes externally; they don’t ingest food like animals.
18. Extremophiles: Use chemicals (e.g., sulfur) from hydrothermal vents for chemosynthesis.
19. Biomass: Organic material from living/recently dead organisms.
20. Algae: Produce ~70% of Earth’s oxygen via photosynthesis.
21. Carbon cycle processes: Photosynthesis, respiration, combustion, decomposition.
22. Respiration:
    Glucose+O2→CO2+H2O+EnergyGlucose+O2​→CO2​+H2​O+Energy
23. Combustion: Burning fossil fuels releases stored carbon as CO₂.
24. CO₂ percentage: 0.04% (rising due to human activity).
25. Decomposition: Microbes respire, releasing CO₂ from dead matter.
26. Methane combustion:
    CH4+2O2→CO2+2H2OCH4​+2O2​→CO2​+2H2​O
27. Recycling: Decomposers return carbon to the atmosphere/soil.
28. Fossil fuels: Stored carbon → CO₂ when burned.
29. Bacteria: Break down organic matter, releasing CO₂ via respiration.
30. Closed loop: Carbon is reused, not created/destroyed.
31. Precipitation: Rain, snow, hail.
32. Freshwater: ~2.5% (most in glaciers/ice caps).
33. Infiltration: Water seeping into soil → groundwater.
34. Transpiration: Plants release water vapour from leaves.
35. States: Solid (ice), liquid (oceans), gas (vapour).
36. Subsurface flow: Underground movement; Runoff: Surface movement.
37. Aquifer: Permeable rock storing groundwater (e.g., Peak District).
38. Oceans cover 71% of Earth’s surface, receiving most precipitation.
39. Plants: Absorb water via roots → release vapour through stomata.
40. Disruption: Deforestation, urbanisation, pollution.
41. Decay conditions: Warmth, moisture, oxygen.
42. Milk pH drop: Bacteria produce lactic acid from lactose.
43. Temperature: Higher temps → faster enzyme activity → quicker decay.
44. Tollund Man: Preserved by cold, acidic, anaerobic peat bog conditions.
45. Silage: Partially decomposed grass fed to livestock; retains nutrients.
46. Manure: Adds nitrogen/minerals for plant growth.
47. Bioindicators: Mayfly nymph (clean water), rat-tailed maggot (polluted).
48. Cacti: Spines reduce transpiration; thick stems store water.
49. Migration: Species move to cooler regions (e.g., mosquitoes spreading north).
50. Lichens: Sensitive to sulfur dioxide; die in polluted air.

Tip: For equations, memorise formats using delimiters(e.g.,delimiters(e.g., \text{CO}_2 $$). Highlight key terms like transect and bioindicator in answers! 🌍