The Bio Brief

What is a Food Chain?

A food chain is a sequence of organisms in which one organism eats another to obtain energy. Each organism occupies a specific level, called a trophic level.

Trophic Levels in a Food Chain

Each step in a food chain is called a trophic level.

Flow Chart: Trophic Levels

Sun

 ↓

Producers (1st trophic level)

 ↓

Herbivores / Primary Consumers (2nd level)

 ↓

Small Carnivores / Secondary Consumers (3rd level)

 ↓

Large Carnivores / Tertiary Consumers (4th level)

Explanation of Trophic Levels

1. Producers (Autotrophs)
   • Green plants and algae
   • Make their own food using sunlight (photosynthesis)
   • Capture solar energy and convert it into food energy
2. Primary Consumers (Herbivores)
   • Eat plants
   • Example: deer, cow, goat
3. Secondary Consumers (Small Carnivores)
   • Eat herbivores
   • Example: frog, lizard
4. Tertiary Consumers (Large Carnivores)
   • Eat smaller carnivores
   • Example: snake, eagle, lion

Flow of Energy in a Food Chain

• Food provides energy to organisms
• Energy flows from one trophic level to the next
• Energy flow is one-way (unidirectional)

Sun → Plants → Animals → Decomposers

Energy Loss in a Food Chain (10% Law)

• Plants capture only about 1% of sunlight energy
• When one organism eats another:
  • Most energy is lost as heat
  • Some energy is used for movement, digestion, growth
• Only 10% of energy is passed to the next trophic level

Example

Plants (100 units of energy)

 ↓

Herbivores (10 units)

 ↓

Carnivores (1 unit)

 ↓

Top Carnivores (0.1 unit)

 Because energy decreases at each level, food chains are usually short (3–4 levels).

Why Are Producers More in Number?

• Maximum energy is available at the producer level
• Energy decreases at higher levels
• Therefore:
  • More producers
  • Fewer herbivores
  • Very few carnivores

What is a Food Web?

In nature, organisms do not depend on only one food source.

A food web is a network of interconnected food chains.

Grass → Deer → Lion

   ↓        ↑

 Insect → Frog → Snake

 Food webs make ecosystems more stable.

Important Features of Energy Flow

1. Energy flow is one-directional
2. Energy does not return to the previous trophic level
3. Energy decreases at each level

Biological Magnification

What is Biological Magnification?

The gradual increase in the concentration of harmful chemicals at higher trophic levels of a food chain is called biological magnification.

How Does It Happen?

• Pesticides and chemicals are used in farming
• They enter soil and water
• Plants absorb them
• Animals eat the plants
• Chemicals accumulate because they are non-degradable

Water/Soil

 ↓

Plants

 ↓

Herbivores

 ↓

Carnivores

 ↓

Humans (maximum concentration)

Why Are Humans Most Affected?

• Humans are at the top trophic level
• Highest amount of harmful chemicals get stored in our bodies
• Washing food cannot always remove these chemicals

Key Points to Remember

• Food chain shows who eats whom
• Each step is a trophic level
• Only 10% energy is transferred to the next level
• Food chains are short
• Food web is a group of food chains
• Biological magnification increases toxins in higher levels