Autotrophs & Heterotrophs (HL) (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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)
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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