IB MYP Integrated Science- Biology - Interdependency-Study Notes - New Syllabus

Interdependency

🌱 Introduction

All living organisms depend on each other and on their environment for survival.
This network of dependence is called interdependency.
It helps maintain balance, stability, and continuity in ecosystems.

🔗 What is Interdependency

Definition

Interdependency means organisms rely on each other for food, shelter, pollination, seed dispersal, decomposition, and maintaining environmental balance.

It includes:

• Living on living (biotic-biotic interactions)
• Living dependent on nonliving (biotic-abiotic interactions)

🌿 Types of Interdependent Relationships

Mutualism (both benefit)

Both species help each other survive.
Examples: Bees pollinate flowers and get nectar; Rhizobium bacteria fix nitrogen in legume roots; Clownfish and sea anemone protect each other.

Commensalism (one benefits, other unaffected)

One organism gains; the other is not harmed.
Examples: Birds sitting on tree branches; Barnacles on whales; Orchids growing on trees.

Parasitism (one benefits, one harmed)

The parasite benefits while the host is harmed.
Examples: Tapeworm in human intestine; Mistletoe absorbing nutrients from trees; Fleas or ticks on animals.

Predation (one kills and eats the other)

The predator hunts the prey.
Examples: Lion hunting zebra; Snake eating mouse; Owl eating rodent.

Competition (both negatively affected)

Organisms compete for the same resource such as food, water, space, light, or mates.
Examples: Plants competing for sunlight; Tigers competing for territory; Birds competing for nesting sites.

🌍 Interdependence Between Biotic and Abiotic Factors

Organisms also depend on nonliving factors.

• Plants depend on sunlight, water, CO₂, and minerals.
• Fish depend on dissolved oxygen.
• Humans depend on air, water, temperature, and soil.

Changes in abiotic factors affect populations, distribution, and survival.

🔄 Why Interdependency Matters

• Maintains Balance: Keeps population sizes in check and maintains food webs.
• Nutrient Cycling: Decomposers break down dead matter so nutrients return to the soil.
• Supports Biodiversity: Healthy interactions allow species to coexist and evolve.
• Ensures Energy Flow: Each organism depends on another for energy transfer.

🐾 Classic Examples of Interdependency

• Plants and Animals: Plants provide oxygen and food; animals provide CO₂ and pollination.
• Predator Prey Cycles: If prey decreases, predator population falls; if predators decrease, prey overpopulate.
• Decomposers and Producers: Decomposers recycle nutrients; producers rebuild biomass.
• Grassland Example: Grass → Rabbit → Fox.

📊 Summary Table

📦 Quick Recap 
Interdependency is how organisms depend on each other and their environment.
Includes mutualism, commensalism, parasitism, predation, competition.
Essential for ecosystem balance, biodiversity, and nutrient cycling.
Every species affects others directly or indirectly.
Removing one species can disturb the whole system.