MYP Biology Food Chains and Webs Notes

What Do Food Chains And Food Webs Show?

1. Food chains and food webs describe feeding relationships in an ecosystem.
2. They show who eats whom and how organisms depend on each other for energy and nutrients.
3. The Energy Transfer article explained why energy decreases at higher trophic levels.
4. This article builds on that idea by showing how organisms connect into feeding pathways that influence ecosystem stability.
5. The goal is to understand not just how energy moves, but also species interdependence.

What Is A Food Chain?

1. A food chain is a simple, linear sequence showing how energy and nutrients pass from producers to consumers.
   1. Producer → Herbivore → Carnivore → Apex Predator.
2. Each step in the chain is a trophic level.

What Roles Do Organisms Play In A Food Chain?

1. Producers: plants and algae that make food using photosynthesis.
2. Primary consumers: herbivores that eat producers.
3. Secondary consumers: carnivores or omnivores that eat primary consumers.
4. Tertiary consumers: carnivores that eat secondary consumers.
5. Apex predators: top predators with no natural predators.
6. Detritivores and decomposers: worms, fungi, and bacteria that break down dead material and recycle nutrients.

What Is A Food Web?

1. A food web is a network of interconnected food chains showing all feeding relationships in an ecosystem.
2. Food webs are more realistic because:
   1. Most organisms have multiple food sources.
   2. Many species feed at more than one trophic level.
   3. They reveal how energy and nutrients move through entire communities.
3. Food webs highlight interdependence and show which species strongly influence ecosystem stability.

Why Are Food Webs More Stable Than Food Chains?

1. Food webs provide multiple pathways for energy flow.
2. If one species declines, consumers can often switch to alternatives.
3. Predators relying on several prey species are less likely to starve.
4. This flexibility reduces the risk of population collapse.
5. Food webs absorb disturbances more effectively than single chains.

What Happens When A Species Is Removed?

1. Removing a species disrupts feeding relationships across the ecosystem.
2. This often triggers a trophic cascade that affects multiple populations.
3. Small changes spread widely because food webs are highly interconnected.

What Are Keystone Species And Why Are They Important?

1. Keystone species regulate populations that would otherwise dominate.
2. Losing a keystone species can reorganise or collapse a food web.

How Does Energy Transfer Shape Food Web Structure?

1. Only around 10 percent of energy passes to the next trophic level.This energy loss shapes food web structure:
   1. Fewer organisms exist at higher levels.
   2. Top predators are rare.
   3. Long food chains are inefficient and uncommon.
2. This creates the familiar pyramid pattern of many producers, fewer herbivores, and very few carnivores.

Ecological Pyramids

1. Ecological pyramids visually represent trophic levels.
2. Three types exist:
   1. Pyramid of numbers: counts organisms.
   2. Pyramid of biomass: shows living mass.
   3. Pyramid of energy: always upright because energy decreases each level.
3. Pyramids help students visualise how energy, biomass, or population size decreases at higher trophic levels.

Why Do Food Webs Change Over Time?

1. Food webs adjust as environmental conditions change.
2. Causes include:
   1. Seasonal changes
   2. Migration
   3. Climate change
   4. Species introductions or extinctions
   5. Human impacts such as overfishing or deforestation
3. Changing conditions shift population sizes and trophic relationships.
4. A food web’s ability to adapt determines its resilience.