Learning Objectives

After studying this topic, you should be able to:

• Define Food Chain and Food Web.

• Classify the different types of food chains.

• Explain Trophic Levels.

• Understand Lindeman's 10% Law.

• Differentiate between Food Chain and Food Web.

• Explain the role of food webs in ecosystem stability.

Food Chain

Definition

A Food Chain is a linear sequence that shows the transfer of food, energy, and nutrients from one organism to another through feeding relationships. It represents the process of "eating and being eaten."

Characteristics

• Linear pathway.

• Energy flow is unidirectional.

• Represents one feeding pathway.

• Begins with producers.

• Ends with top consumers.

Example

Grass → Grasshopper → Frog → Snake → Eagle

Limitations of Food Chain

• Shows only one feeding pathway.

• Does not indicate the number of organisms.

• Does not show alternative food sources.

• Cannot explain ecosystem stability.

Types of Food Chains

There are three major types of food chains.

1. Grazing Food Chain (GFC)

Definition

A food chain that starts with green plants (producers), which capture solar energy through photosynthesis.

Sequence

Green Plants
      ↓
Herbivores
      ↓
Carnivores
      ↓
Top Carnivores

Example

Phytoplankton → Zooplankton → Small Fish → Large Fish

Importance

• Major energy pathway in aquatic ecosystems.

• Energy originates from sunlight.

2. Detritus Food Chain (DFC)

Definition

A food chain that begins with dead organic matter (detritus).

Sequence

Dead Organic Matter
        ↓
Detritivores
        ↓
Decomposers
        ↓
Consumers

Examples of Detritus

• Fallen leaves

• Dead plants

• Animal remains

• Organic waste

Importance

• Major energy pathway in terrestrial ecosystems.

• Recycles nutrients back into the environment.

3. Parasitic Food Chain

Definition

A food chain in which energy flows from a host organism to one or more parasites.

Characteristics

• Parasites depend on living hosts.

• Host is generally not killed immediately.

• May involve hyperparasites (parasites on parasites).

Example

Tree → Bird → Lice → Bacteria

Trophic Levels

Definition

A trophic level is the feeding position occupied by an organism in a food chain.

Trophic Levels

Energy Flow

Energy always flows in one direction:

Sun
 ↓
Producers
 ↓
Primary Consumers
 ↓
Secondary Consumers
 ↓
Tertiary Consumers
 ↓
Top Consumers

Characteristics

• Unidirectional.

• Decreases at every trophic level.

• Lost mainly as heat during metabolism.

Lindeman's 10% Law

Definition

According to Raymond Lindeman's 10% Law, only about 10% of the energy available at one trophic level is transferred to the next trophic level.

The remaining 90% is lost through:

• Respiration

• Movement

• Growth

• Heat

Example

Conclusion

Because of continuous energy loss:

• Food chains usually contain 4–5 trophic levels only.

Food Web

Definition

A Food Web is a network of interconnected food chains showing multiple feeding relationships within an ecosystem.

Characteristics

• Complex network.

• Multiple feeding pathways.

• Organisms have more than one food source.

• Increases ecosystem stability.

Importance of Food Web

• Provides alternative food sources.

• Maintains ecological balance.

• Prevents ecosystem collapse.

• Enhances biodiversity.

• Increases ecosystem stability.

Golden Rule of Stability

The more complex the food web, the more stable the ecosystem.

If one species disappears, predators can switch to other food sources.

Simple Food Web

          Grass
        ↙   ↓   ↘
Rabbit Grasshopper Mouse
   ↓        ↓       ↓
 Snake     Frog    Snake
     \      |      /
        Eagle

Comparison Tables

Food Chain vs Food Web

Grazing Food Chain vs Detritus Food Chain

Important Definitions

Food Chain

Linear pathway showing energy transfer through feeding relationships.

Food Web

Interconnected network of food chains.

Trophic Level

Feeding position of an organism.

Detritus

Dead and decaying organic matter.

Lindeman's 10% Law

Only 10% of energy is transferred from one trophic level to the next.

Frequently Confused Concepts

Food Chain vs Food Web

Grazing Food Chain vs Detritus Food Chain

Energy Flow vs Nutrient Cycling

Examination Focus (High Probability MCQs)

Frequently Asked Topics

• Definition of Food Chain.

• Definition of Food Web.

• Types of Food Chains.

• Trophic Levels.

• Lindeman's 10% Law.

• Difference between Food Chain and Food Web.

• Grazing Food Chain vs Detritus Food Chain.

• Ecosystem stability.

• Energy flow in ecosystems.

Common Mistakes

❌ Food chain shows the number of organisms.

✔ Food chain shows only the sequence of energy flow.

❌ Grazing Food Chain is dominant everywhere.

✔ Aquatic ecosystems → Grazing Food Chain

✔ Terrestrial ecosystems → Detritus Food Chain

❌ Energy is recycled.

✔ Energy flows in one direction.

❌ Food web is less stable.

✔ Food web is more stable than a food chain.

Memory Tricks

Types of Food Chains

GDP

• G → Grazing Food Chain

• D → Detritus Food Chain

• P → Parasitic Food Chain

Ecosystem Dominance

Go Aquatic, Do Terrestrial

• G → Grazing → Aquatic

• D → Detritus → Terrestrial

Energy Transfer

"10 Moves Forward, 90 Lost"

Only 10% of energy reaches the next trophic level.

Quick Revision

One-Line Revision

• Food Chain → Linear sequence of feeding relationships.

• Food Web → Interconnected network of food chains.

• Trophic Level → Feeding position of an organism.

• Lindeman's 10% Law → Only 10% of energy is transferred to the next trophic level.

• Grazing Food Chain → Major energy pathway in aquatic ecosystems.

• Detritus Food Chain → Major energy pathway in terrestrial ecosystems.

• Complex Food Web → Greater ecosystem stability.