IB MYP 4-5 Biology-Energy Transfer & Cycles- Study Notes - New Syllabus
IB MYP 4-5 Biology-Energy Transfer & Cycles- Study Notes – New syllabus
IB MYP 4-5 Biology-Energy Transfer & Cycles- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Food webs vs. chains
- Carbon cycle (photosynthesis/respiration/combustion)
- Nitrogen cycle (role of bacteria)
Energy Transfer and Cycles
Food Chains vs. Food Webs
Introduction:
All living organisms require energy for their biological processes. In ecosystems, this energy flows from the sun through producers and into various consumers. Understanding this flow is key to grasping how ecosystems function and is best visualized using food chains and food webs.
Food Chain
Definition: A food chain is a straight-line sequence that shows how energy and nutrients pass from one organism to the next.
Basic Structure:
- Producer: Plants or algae that make food via photosynthesis
- Primary consumer: Herbivores that eat producers
- Secondary consumer: Carnivores that eat herbivores
- Tertiary consumer: Predators that eat secondary consumers
- Decomposers: Break down dead organisms and recycle nutrients
Example: Grass → Grasshopper → Frog → Snake → Eagle
Key Feature: Food chains are simple and linear but do not reflect the full complexity of real ecosystems. Arrows indicate energy flow.
Food Web
Definition: A food web is a network of interconnected food chains within an ecosystem, showing multiple feeding relationships.
Key Features:
- Illustrates complex interactions between species
- Organisms can occupy multiple trophic levels
- Shows how energy flows through various interconnected pathways
Example: A rabbit may be eaten by both a fox and a hawk; a hawk may also eat a snake that feeds on a mouse. These interlinkages form a food web.
Food Chain vs. Food Web – Comparison Table
| Feature | Food Chain | Food Web |
|---|---|---|
| Structure | Linear | Network-like, branched |
| Complexity | Simple | Complex |
| Realism | Idealized | More realistic |
| Energy Flow | One pathway | Multiple pathways |
| Impact of Changes | Limited view | Reveals wide-reaching effects |
Summary:
Food chains offer a simplified look at energy transfer in ecosystems, while food webs give a detailed and realistic picture of organism interactions. Both help in understanding how energy and matter flow, and how ecological balance is maintained.
Carbon Cycle
Processes: Photosynthesis, Respiration, Combustion
Introduction:
The carbon cycle is a fundamental Earth system that describes how carbon atoms move through living organisms, the atmosphere, oceans, and the Earth’s crust. Carbon is essential for life because it forms the backbone of organic molecules like carbohydrates, proteins, and DNA.
Key Reservoirs of Carbon
- Atmosphere: as carbon dioxide (CO₂)
- Biosphere: in living organisms
- Hydrosphere: dissolved in oceans as carbonates
- Geosphere: in rocks, fossil fuels, and soil
Main Processes in the Carbon Cycle
1. Photosynthesis
- Carried out by plants, algae, and cyanobacteria
- Uses CO₂ from the atmosphere and sunlight to make glucose
- Converts inorganic carbon into organic compounds
- Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
- Effect: Removes CO₂ from the atmosphere and stores energy in plant biomass
2. Respiration
- Occurs in plants, animals, fungi, and microbes
- Releases energy by breaking down glucose
- Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
- Effect: Returns CO₂ to the atmosphere
3. Combustion
- The burning of fossil fuels and organic matter
- Releases CO₂ and heat
- Examples: Factory emissions, car exhaust, forest fires
- Effect: Increases atmospheric CO₂ and contributes to climate change
4. Decomposition
- Done by bacteria and fungi
- Releases CO₂ (aerobic) or methane (anaerobic) back into atmosphere or soil
5. Fossilization and Sedimentation
- Dead organisms may become fossil fuels
- Marine organisms contribute to rock formation
Carbon Cycle Flow Summary:
CO₂ enters plants via photosynthesis → carbon moves through the food chain → CO₂ released through respiration and decomposition → fossil fuels combusted return CO₂ quickly to the atmosphere.
Importance of the Carbon Cycle
- Maintains climate balance
- Supports essential life processes
- Regulates atmospheric CO₂ levels
- Disruptions contribute to global warming
Nitrogen Cycle
Focus: Role of Bacteria
Introduction:
Nitrogen is essential for life. It’s a major component of proteins, DNA, RNA, and ATP. Although 78% of the atmosphere is nitrogen gas (N₂), most organisms cannot use it in that form. The nitrogen cycle describes how nitrogen moves through the atmosphere, soil, and living organisms, with bacteria playing a key role in its transformation.
Key Stages of the Nitrogen Cycle
1. Nitrogen Fixation
- Goal: Convert N₂ gas to Ammonia (NH₃) or Ammonium (NH₄⁺)
- Done by:
- Nitrogen-fixing bacteria (e.g., Rhizobium) in legume root nodules
- Free-living soil bacteria (e.g., Azotobacter)
- Lightning and industrial processes also fix nitrogen
- Why important: Makes nitrogen available to ecosystems in a usable form
2. Nitrification
- Goal: Convert ammonia into nitrates (NO₃⁻)
- Steps:
- Nitrosomonas converts NH₄⁺ to Nitrite (NO₂⁻)
- Nitrobacter converts NO₂⁻ to Nitrate (NO₃⁻)
- Why important: Nitrates are the primary nitrogen source for plants
3. Assimilation
- Plants absorb NO₃⁻ and use it to build amino acids, proteins, and nucleic acids
- Herbivores eat plants → nitrogen moves through the food chain
- Carnivores eat herbivores → nitrogen continues cycling
4. Ammonification (Decay)
- Goal: Convert organic nitrogen in dead organisms and waste to ammonia (NH₃)
- Done by: Decomposer bacteria and fungi
- Result: NH₄⁺ returns to soil
5. Denitrification
- Goal: Convert NO₃⁻ back into N₂ gas
- Done by: Denitrifying bacteria (e.g., Pseudomonas) in anaerobic conditions
- Result: Nitrogen returns to the atmosphere
Summary Table:
| Process | Type of Bacteria | Function |
|---|---|---|
| Nitrogen Fixation | Rhizobium, Azotobacter | Convert N₂ → NH₃ or NH₄⁺ |
| Nitrification | Nitrosomonas, Nitrobacter | NH₄⁺ → NO₂⁻ → NO₃⁻ |
| Ammonification | Decomposer bacteria and fungi | Organic nitrogen → NH₄⁺ |
| Denitrification | Pseudomonas | NO₃⁻ → N₂ gas |
Why Is the Nitrogen Cycle Important?
It supplies usable nitrogen to living things, supports global food chains, and maintains ecosystem balance. Human disruption through excessive fertilizer use and pollution can disturb this cycle and lead to environmental problems like eutrophication.