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Autotrophs and Heterotrophs

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Autotrophs synthesise carbon compounds from inorganic sources of carbon and other elements. Heterotrophs obtain carbon compounds from other organisms.

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Key Content

All living organisms can be classified into one of two groups based on how they obtain the carbon compounds they need for energy and growth.

Autotrophs

Autotrophs synthesise carbon compounds from inorganic sources of carbon and other elements. They are also known as producers because they produce their own food. Examples include plants, algae, and photosynthetic bacteria.

Autotrophs form the foundation of food chains and provide energy for all other organisms in the ecosystem. The most common process used by autotrophs is photosynthesis, which uses light energy to convert carbon dioxide and water into glucose.

Heterotrophs

Heterotrophs obtain carbon compounds from other organisms. They are also known as consumers because they obtain their food by consuming other organisms. Heterotrophs cannot make their own food.

Heterotrophs include:

• Herbivores (consume plants)
• Carnivores (consume animals)
• Detritivores (consume dead organic matter)
• Decomposers (break down dead organic matter)

Why This Matters for Energy Flow

This fundamental division determines how energy and matter flow through ecosystems. Energy enters ecosystems through autotrophs (which capture it from sunlight) and then flows to heterotrophs when they consume autotrophs or other heterotrophs.

1. For each organism below, classify it as an autotroph or heterotroph and explain your reasoning:

1. Why is the distinction between autotrophs and heterotrophs important for understanding energy flow in ecosystems?

Human Impacts on Energy Flows and Matter Transfer

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Human activities, such as burning fossil fuels, deforestation, urbanization and agriculture, have impacts on flows of energy and transfers of matter in ecosystems.

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Key Content

Human activities significantly affect how energy flows and matter is transferred through ecosystems. Four major human activities affect these processes:

1. Burning Fossil Fuels

Although burning fossil fuels increases the CO₂ available for photosynthesis, other pollutants and the impacts of climate change actually reduce primary productivity overall. Pollutants damage organisms, warming reduces dissolved oxygen in water, and temperature stress harms many species.

2. Deforestation

Removing forests leads to:

• Loss of ecosystem biomass (the trees themselves store huge amounts of carbon)
• Disruption of food webs (animals lose habitat and food sources)
• Reduced capacity for photosynthesis (fewer plants to capture solar energy)
• Release of stored carbon into the atmosphere

3. Urbanisation

Converting natural land to cities and towns causes:

• Loss of ecosystem biomass (concrete replaces vegetation)
• Disruption of food webs (native species displaced)
• Reduced capacity for photosynthesis (impermeable surfaces cannot support plant growth)
• Increased energy demands that affect ecosystems elsewhere

4. Agriculture

Agricultural expansion leads to:

• Loss of ecosystem biomass (diverse ecosystems replaced with monocultures)
• Disruption of food webs (simplified ecosystems support fewer species)
• Reduced capacity for photosynthesis (crops often have lower productivity than native vegetation)
• Removal of matter from ecosystems when harvests are transported away

Common Thread

All four activities share common impacts: loss of ecosystem biomass, disruption of food webs, reduced photosynthetic capacity, and alteration of the carbon cycle. These activities often overlap and compound each other's effects.

1. For each case study below, analyse how the human activity affects energy flows and matter transfer in the ecosystem.

Case Study 1: The Amazon Rainforest - Deforestation

Background: Between 1988 and 2008, deforestation in the Brazilian Amazon fluctuated between 10,000 and 30,000 km² per year. The primary cause (65-70%) is cattle ranching, followed by small-scale agriculture (20-25%) and logging (2-3%).

An area of tropical rainforest the size of a football pitch is destroyed every four seconds. The Amazon stores approximately 150-200 billion tonnes of carbon in its biomass.

Questions:

1. What happens to the producers (autotrophs) when deforestation occurs?
2. How does this affect energy availability for consumers (heterotrophs) at different trophic levels?
3. What happens to the carbon that was stored in the forest biomass?
4. How might deforestation create a positive feedback loop related to climate change?