IB MYP 4-5 Biology-Ecosystems- Study Notes - New Syllabus
IB MYP 4-5 Biology-Ecosystems- Study Notes – New syllabus
IB MYP 4-5 Biology-Ecosystems- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Components (producers, consumers, decomposers)
- Energy pyramids (10% rule)
- Case study: Coral reef ecosystem interdependence
Ecosystems
What Is an Ecosystem?
An ecosystem is a biological community of living organisms interacting with each other and with their physical (abiotic) environment.
It includes both:
- Biotic components – living organisms
- Abiotic components – sunlight, water, temperature, soil, etc.
Ecosystems can be large (rainforests, oceans) or small (ponds, soil).
Main Components of an Ecosystem
1. Producers (Autotrophs)
Organisms that produce their own food using sunlight or chemical energy. They form the base of the food chain.
- Most common: Green plants and algae
- Use photosynthesis to convert solar energy into chemical energy (glucose)
- In some deep-sea ecosystems, chemosynthetic bacteria act as producers (using chemical energy from hydrothermal vents)
2. Consumers (Heterotrophs)
Organisms that depend on other organisms for food. They cannot make their own food.
Consumers are classified based on their position in the food chain:
- Primary consumers – Herbivores (e.g., deer, grasshoppers)
- Secondary consumers – Carnivores that eat herbivores (e.g., frogs, small birds)
- Tertiary consumers – Carnivores that eat other carnivores (e.g., snakes, eagles)
- Omnivores – Eat both plants and animals (e.g., humans, bears)
- Top predators – Apex consumers with no natural predators (e.g., lions, sharks)
3. Decomposers (Saprotrophs)
Organisms that break down dead organisms and organic waste into simpler substances.
- Common decomposers: Bacteria and fungi
- Detritivores (e.g., earthworms, dung beetles) assist by physically breaking down dead material
Summary Table
| Component | Role in Ecosystem | Examples |
|---|---|---|
| Producers | Make food using sunlight or chemicals | Green plants, algae, chemosynthetic bacteria |
| Consumers | Eat other organisms for energy | Herbivores, carnivores, omnivores |
| Decomposers | Break down dead material and recycle nutrients | Fungi, bacteria, earthworms |
Energy Pyramids – The 10% Rule
What Is an Energy Pyramid?
An energy pyramid is a diagram that shows the flow of energy through different trophic levels in an ecosystem.
- Each level represents a group of organisms with a similar role in the food chain.
- Producers form the base.
- Followed by primary consumers, secondary consumers, and so on.
- Energy decreases as it moves up the pyramid.
The 10% Rule
Only about 10% of energy at each trophic level is passed to the next level.
- Most energy is lost as heat (respiration)
- Some energy is used for movement and life processes
- Some energy is lost in undigested material
This explains why food chains typically have only 4–5 levels.
Example of a Simple Energy Pyramid
| Trophic Level | Organism Example | Energy (units) |
|---|---|---|
| Tertiary Consumer | Eagle | 10 |
| Secondary Consumer | Snake | 100 |
| Primary Consumer | Grasshopper | 1000 |
| Producer | Grass | 10,000 |
Importance of the 10% Rule
- Explains why top predators are fewer in number
- Helps understand energy limits in ecosystems
- Shows energy transfer inefficiency through food chains
- Encourages understanding of energy-efficient ecosystems
Note:
- Energy pyramids are always upright because energy always decreases as it moves upward
- The 10% rule is an average – actual transfer efficiency may vary
- Understanding energy flow is essential to studying ecosystem dynamics and productivity
Case Study: Coral Reef Ecosystem
Interdependence in a Biodiverse Marine Habitat
Overview of Coral Reefs: Coral reefs are marine ecosystems formed by colonies of coral polyps. They exist in warm, shallow oceans and represent one of the most biologically diverse ecosystems on Earth. Despite occupying less than 1% of the ocean floor, they support about 25% of all marine species.
Key Biotic Components
- Coral Polyps: Tiny animals that form calcium carbonate skeletons and build the reef. They live in colonies and have a mutualistic relationship with algae (zooxanthellae).
- Zooxanthellae (Symbiotic Algae): Photosynthetic algae living inside coral tissues. They provide food to the coral and receive protection and carbon dioxide in return.
- Consumers:
- Herbivores (e.g., parrotfish) graze on algae, preventing overgrowth.
- Carnivores (e.g., reef sharks, groupers) regulate prey populations.
- Omnivores and detritivores contribute to energy flow and nutrient recycling.
- Decomposers: Bacteria and fungi break down organic waste and dead organisms, recycling nutrients within the ecosystem.
Abiotic Factors Influencing Reefs
- Temperature: Optimal range is around 23–29°C. Reefs are sensitive to warming.
- Light: Vital for photosynthesis by zooxanthellae.
- Salinity: Stable salt levels are crucial.
- Water clarity: Cloudy water reduces light penetration.
- pH: Lower pH due to acidification weakens coral skeletons.
Interdependence and Balance:
Coral reefs thrive through close interactions among species and with their environment. Coral and algae are mutually dependent, herbivores prevent algal overgrowth, predators maintain species balance, and decomposers ensure nutrient recycling. Disrupting one part (like overfishing herbivores) can destabilize the entire system.
Threats and Human Impact
- Coral bleaching: Algal loss due to heat stress leads to coral mortality.
- Pollution: Increases turbidity and nutrient overload.
- Ocean acidification: Weakens coral skeletons.
- Overfishing: Eliminates key consumers and disrupts the food web.
- Coastal development: Destroys habitats and alters ecosystem dynamics.
Summary:
Coral reefs are intricate ecosystems where biotic and abiotic interactions are essential for survival. Coral-algae symbiosis drives productivity, and all organisms contribute to ecological balance. These ecosystems are extremely vulnerable to environmental changes and human disturbances.