CORE Biology (9221) | Energy transferred in ecosystems

Introduction: Following the Energy Trail!

Welcome to one of the most exciting topics in Biology: how energy moves through life! Think of energy as the fuel that keeps every single organism, from a tiny blade of grass to a massive whale, running. In this chapter, we will track this energy as it flows through the environment. Understanding this is key to understanding how ecosystems stay alive and balanced!

Don't worry if terms like "ecosystem" sound complex—we'll break down the journey of energy step-by-step, focusing on simple concepts and clear definitions. Let’s get started!

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1. The Source of Energy: The Power Station

1.1 The Ultimate Energy Source

In almost every ecosystem on Earth, the energy starts in the same place:

• The ultimate source of energy for most life is the Sun (solar energy).
• This light energy must be captured and turned into chemical energy (food) that living things can use.

1.2 Producers: Making the Food

The organisms responsible for capturing the Sun’s energy are called Producers. They are the foundation of almost every food chain.

What do Producers do?

They use a process called Photosynthesis.

• They take in light energy, carbon dioxide, and water.
• They convert these into glucose (a type of sugar/food) and oxygen.

Analogy: Producers (like plants and algae) are like chefs who use solar power to cook food from scratch.

Key Term:

Producers: Organisms (usually plants or algae) that can make their own food using light energy through photosynthesis.

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2. Following the Flow: Food Chains and Trophic Levels

2.1 Consumers: Eating to Get Energy

Organisms that cannot make their own food must eat other organisms to gain energy. These are called Consumers.

We classify consumers based on what they eat:

• Primary Consumers (Herbivores): They eat producers (plants). Example: Rabbits eating grass.
• Secondary Consumers (Carnivores or Omnivores): They eat primary consumers (herbivores). Example: Foxes eating rabbits.
• Tertiary Consumers (Carnivores): They eat secondary consumers. Example: Eagles eating foxes.

Did you know? Organisms that eat both plants and animals are called Omnivores (like humans or bears).

2.2 Understanding Food Chains

A Food Chain shows the simple path that energy takes from one organism to the next.

Crucial Rule: The arrows in a food chain represent the flow of energy.

The arrow points from the organism being eaten to the organism that eats it.

Example: Grass → Rabbit → Fox

In this chain:

• Energy flows from the Grass (Producer) to the Rabbit (Primary Consumer).
• Energy flows from the Rabbit to the Fox (Secondary Consumer).

COMMON MISTAKE ALERT!

Students often draw the arrow pointing to what is eaten. Remember: The arrow points in the direction of the energy flow! Think: "Energy goes into the mouth."

2.3 Trophic Levels

The feeding position of an organism in a food chain is called its Trophic Level (TL). This helps us categorize them:

TL 1: Producers (e.g., Grass)
TL 2: Primary Consumers (e.g., Rabbit)
TL 3: Secondary Consumers (e.g., Fox)
TL 4: Tertiary Consumers (e.g., Eagle)

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3. Energy Transfer Efficiency: The Loss of Power

3.1 Why Chains Are Short

If every consumer eats another organism, why don't food chains go on forever (TL 10, TL 11, etc.)? The answer is that a huge amount of energy is lost at every step.

When energy is passed from one trophic level to the next, most of it is wasted or used up by the organism itself before it can be transferred.

Energy is lost in several ways:

1. Respiration (Heat Loss): All organisms respire (use energy to live). This releases energy, mainly as heat, into the environment. This heat cannot be used by the next trophic level.
2. Movement and Living Processes: Energy is used for finding food, moving, breathing, etc.
3. Waste/Excretion: Not all parts of an organism are eaten or digested (e.g., bones, fur, faeces). This energy leaves the food chain as waste.

Because energy is constantly being lost, the amount of available energy decreases rapidly as you move up the food chain.

3.2 The 10% Rule (A General Estimate)

Only about 10% of the energy stored in one trophic level is typically transferred to the next trophic level. The other 90% is lost to the environment.

Example: If the grass has 10,000 units of energy, the rabbit that eats it will only gain about 1,000 units (10%). The fox that eats the rabbit will only gain about 100 units (10% of 1,000).

3.3 Representing Energy Loss: Pyramids

To visualize this huge drop in energy, we use Pyramids of Energy or Pyramids of Biomass.

Biomass: This is the total dry mass (the mass of the living material) of all the organisms in a specific area or at a specific trophic level.

Pyramids of Biomass show the reduction in the total mass of organisms at each successive level.

• The producer level (bottom) is always the largest.
• Each level above it gets smaller and smaller, reflecting the massive loss of energy (and therefore, less living matter can be supported).

Think of it like building blocks: You need a massive base (Producers) to support a small top block (Tertiary Consumers).

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4. Recycling Materials: The Clean-Up Crew

4.1 Decomposers: The Essential Recyclers

Unlike energy, which flows through an ecosystem and is eventually lost as heat, materials (or nutrients) must be recycled. This is where Decomposers come in.

Key Term:

Decomposers: Organisms (mainly bacteria and fungi) that break down dead organisms, animal waste, and fallen leaves.

The Importance of Decomposers:

1. They return the materials stored in dead bodies and waste back to the environment (soil and air).
2. They break down complex molecules into simple mineral ions (nutrients).
3. These nutrients are then absorbed by the Producers (plants) to start the whole process over again.

If decomposers stopped working, waste and dead bodies would pile up, and plants would run out of essential nutrients like nitrogen—the entire ecosystem would collapse!