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Autotrophs & Heterotrophs (HL) (DP IB Environmental Systems & Societies (ESS)) : Revision Note

Alistair Marjot

Written by: Alistair Marjot

Reviewed by: Bridgette Barrett

Updated on

Autotrophs & Heterotrophs

What are autotrophs and heterotrophs?

  • All living organisms can be classified into two groups based on how they obtain carbon compounds: autotrophs and heterotrophs

    • Autotrophs synthesise carbon compounds from inorganic sources like carbon dioxide and water

    • Heterotrophs obtain carbon compounds by consuming other organisms (either plants, animals, or decomposing organic matter)

Comparison of autotrophs and heterotrophs. Autotrophs: plants, some bacteria, algae; producers use photosynthesis. Heterotrophs: animals, most bacteria, fungi; consumers.
Autotrophs make their own carbon compounds (e.g. glucose) whereas heterotrophs obtain them from a range of food sources

Types of autotrophs

Photoautotrophs

  • Photoautotrophs use light as their external energy source to produce organic compounds through photosynthesis

    • Examples include: green plants, algae, and some bacteria, like cyanobacteria

  • They convert carbon dioxide and water into glucose and oxygen using light energy

Chemoautotrophs

  • Chemoautotrophs use energy from exothermic inorganic chemical reactions to produce organic compounds through chemosynthesis

    • Examples include: some bacteria and archaea, especially those found in extreme environments, such as hydrothermal vents or deep-sea ecosystems

  • They can oxidise substances like hydrogen sulphide or ammonia to obtain energy

    • For example, bacteria living near hydrothermal vents use sulphur compounds to produce energy in environments without sunlight

  • The giant tube worm (Riftia pachyptila) lives on or near hydrothermal vents deep in the ocean

    • Giant tube worms have a symbiotic relationship with chemosynthetic bacteria living inside them

    • The bacteria use hydrogen sulphide from the vent and oxygen and carbon dioxide from the surrounding water to produce sugars through chemosynthesis

    • The tube worms rely on the bacteria for food because they lack a digestive system

    • This allows them to survive in extreme environments where light and traditional food chains do not exist

  • Chemoautotrophs are the primary producers in these extreme environments

    • This means they create energy-rich compounds like sugars that support other organisms in these food webs

Types of heterotrophs

  • Herbivores: obtain carbon compounds by consuming plants

  • Carnivores: obtain carbon compounds by consuming other animals

  • Omnivores: obtain carbon compounds by consuming both plants and animals

  • Decomposers: obtain carbon compounds by breaking down dead organic material, returning nutrients to the ecosystem

    • Examples include: fungi, bacteria, and earthworms

Examiner Tips and Tricks

Sometimes, understanding the origin of a word can help you to remember the meaning, for example:

Autotroph comes from:

  • 'auto' = 'self'

  • 'trophic' = 'feeding'

Heterotroph comes from:

  • 'hetero' = 'different'

  • 'trophic' = 'feeding'

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Alistair Marjot

Author: Alistair Marjot

Expertise: Biology & Environmental Systems and Societies Content Creator

Alistair graduated from Oxford University with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems & Societies. Alistair has continued to pursue his interests in ecology and environmental science, recently gaining an MSc in Wildlife Biology & Conservation with Edinburgh Napier University.

Bridgette Barrett

Reviewer: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.

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