Identification of Trophic Level
Classifying species as autotrophs, consumers, detritivores, or saprotrophs
- A species can be classified as an autotroph, consumer, detritivore, or saprotroph on the basis of its mode of nutrition
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, with few exceptions
- Some unusual plants are parasitic, gaining their nutrients from the roots of host plants, or via networks of fungi in the soil
Heterotrophs
- Heterotrophic organisms gain their organic molecules from other organisms
- There are several types of heterotroph, including consumers, detritivores, and saprotrophs
Consumers
- Consumers gain their organic molecules by ingesting the tissues of other living or recently dead organisms
- The consumers that eat plants are known as herbivores, and are the primary consumers in a food chain
- The consumers that eat other animals are carnivores, and those that eat the primary consumers are secondary consumers
- Carnivores that eat secondary consumers are tertiary consumers
Detritivores
- Detritivores gain organic molecules by ingesting the tissues of dead organisms or ingesting animal waste
- Detritivores digest their food inside their bodies
- Examples of detritivores include earthworms, woodlice and dung beetles
Saprotrophs
- Saprotrophs also gain their organic molecules from dead matter, but they digest their food externally
- Saprotrophic organisms secrete enzymes onto dead matter, and these enzymes break down the food before nutrients are absorbed
- Saprotrophs include fungi and bacteria
Classifying Species as Autotrophs, Consumers, Detritivores, or Saprotroph Table
Examiner Tip
The two main modes of nutrition are autotrophism and heterotrophism, and within those modes are different types e.g. a heterotroph can be a consumer, a detritivore, or a saprotroph depending on its food source and its method of digestion