Autotrophs and Heterotrophs

Edexcel A-level BiologyPhotosynthesisLesson 1 of 20

All organisms need organic molecules, both as a source of energy and as building materials. They differ in how they obtain them.

Autotrophs make their own complex organic molecules, such as glucose, from simple inorganic molecules (carbon dioxide and water), using an external energy source. They are the producers in food chains.
• Photoautotrophs use light energy, by photosynthesis. Examples are green plants, algae and cyanobacteria.
• Chemoautotrophs use energy released by chemical reactions, such as the oxidation of ammonium ions or iron compounds. Examples are the nitrifying bacteria of the nitrogen cycle and bacteria around deep-sea vents.

More in Photosynthesis

• The Process of Photosynthesis
• Chloroplasts
• Chlorophyll
• Absorption Spectrum Chlorophyll
• Chromatography
• Photosystems
• The Light-Dependent Reactions
• Cyclic Photophosphorylation

All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics