Autotroph vs Heterotroph
- Organisms need energy in the form of ATP to survive
- The energy stored in ATP comes from other organic molecules, such as carbohydrates, and is transferred during the process of respiration
- The method by which an organism gains organic molecules to fuel respiration is known as its mode of nutrition
- There are two main modes of nutrition; autotrophy and heterotrophy
Autotrophs
- An autotroph synthesises, or produces, its own organic molecules from simple inorganic substances in its environment
- Photosynthetic organisms use light energy to convert carbon dioxide from the air into organic molecules such as carbohydrates
- Some autotrophs use energy from the oxidation of inorganic compounds instead of light energy
- Autotrophs that use light energy are known as photoautotrophs, while those that use energy from oxidation of chemicals are known as chemoautotrophs
- Because autotrophs make their own organic molecules without relying on other organisms, they are known as producers
- Most green plants are autotrophs, along with algae such as seaweeds, and photosynthetic bacteria such as cyanobacteria
Heterotrophs
- Heterotrophic organisms gain their organic molecules by ingesting the tissues of other organisms
- There are several types of heterotroph, including consumers, detritivores, and saprotrophs
Mixing modes of nutrition
- Some organisms are able to make use of more than one mode of nutrition, such as auto- and heterotrophy
- These organisms are referred to as mixotrophs
- Euglena is a single-celled eukaryotic organism that makes use of both autotrophy and heterotrophy
- Euglena cells can take in bacterial cells by endocytosis, and then digest them using digestive enzymes stored in lysosomes
- Euglena cells also contain a light-sensitive spot that enables them to position themselves so that maximum light reaches their chloroplasts
Euglena is a single-celled eukaryote that makes use of autotrophic and heterotrophic nutrition