Amongst the seven characteristics of life, including movement, sensitivity, reproduction, growth, excretion and respiration, there is nutrition. This is the need of all organisms to intake a supply of organic nutrients, or in other words, carbon compounds (for example, glucose and amino acids). The form in which these are obtained can be either autotrophic or heterotrophic. If an organism makes its own supply of organic nutrients from carbon dioxide and other substances, this means they carry out an autotrophic type of nutrition; this means they self-feed. Most plants are autotrophic as they produce glucose through photosynthesis, carried out in chloroplasts as shown to the above.
Most animals however are heterotrophic, meaning they feed on others; whether they are herbivores and feed on plants or carnivores and feed on other animals. The video to the right shows a hummingbird, which is heterotrophic obtaining its organic nutrients from the nectar of a plant that is autotrophic.
There are some unicellular organisms that carry out both heterotrophic and autotrophic nutrition, meaning they are mixotrophic. Such is the case of euglena gracilis (below), which carries out photosynthesis in its chloroplasts as well as also feeding on detritus or smaller organisms by endocytosis.
Biologists usually use the Mousseur Cress, or Arabidopsis thaliana (bottom right image) as a model of autotrophic nutrition and other areas of botanical study as it does not live for long, it is quick to grow, and most importantly, it has a relatively small genome consequently making it easier to investigate upon.