What is characteristic of heterotrophic organisms?

Heterotrophic organisms are characterized by their inability to produce their own food through photosynthesis or chemosynthesis. Instead, they rely on organic substances for their energy and nutritional needs. This characteristic is particularly applicable to animals, which typically do not have a cell wall, distinguishing them from other life forms like plants and fungi.

The choice indicating that they lack a cell wall and mostly include animals correctly highlights that animals, which are the major group of heterotrophs, do not have a rigid cell wall. This structural feature allows for mobility and flexibility, traits that are crucial for obtaining food directly from their environment.

In contrast, other options do not accurately represent heterotrophic organisms. Those that obtain energy from inorganic substances are more correctly classified as autotrophs (like plants). Additionally, organisms that contain chloroplasts for photosynthesis are also autotrophs, as they can produce their own food, and fungi and many bacteria, while often heterotrophic, do not primarily define the category as a whole. Thus, the distinction made in the correct answer about the lack of cell walls and association with animals reinforces the specific biological characteristics of heterotrophs.