Video Transcript
Which classification of heterotrophic organisms do humans, cats, and rabbits belong
to? (A) Parasites, (B) saprophytes, or (C) holozoic.
Let’s start by defining what a heterotrophic organism is before we explore the
different types to work out the correct answer to this question. A heterotrophic organism, sometimes simply referred to as a heterotroph, is an
organism that must obtain its nutrition by consuming other organisms or the organic
matter from a once-living organism. Humans, cats, and rabbits are all examples of heterotrophic organisms. Everything that we eat, whether it is fungal matter like a mushroom a human might
eat, animal matter like a fish that a cat might enjoy for its dinner, or plant
matter like a carrot nibbled upon by a rabbit, was once a living organism.
Now, let’s take a look at the different classifications of heterotrophs to work out
which specific group humans, cats, and rabbits belong to. One group of heterotrophs are parasites, which live in or on a host organism and
obtain their nutrition by feeding on their host. Parasites tend to obtain their nutrition at their host’s expense, and they are often
associated with disease. For example, leeches obtain their nutrition by feeding on another organism’s blood,
which would definitely be detrimental to the health of the living host.
While domestic pets like cats and rabbits might get their nutrition by relying on a
human owner, these organisms are not parasites as they are not usually harmful to
their human’s health. Furthermore, they do not live inside or on the body of another living organism to
obtain nutrition by feeding on it.
Let’s look at another type of heterotrophic organisms: saprophytes. The prefix sapro- means rotting, while -phyte means feeding. So, saprophytes feed off dead or rotting tissues to obtain their nutrition. Most fungi and some bacteria are examples of saprophytes. For instance, fungi usually feed by releasing extracellular enzymes out of their
cells to digest organisms that are often dead and decaying and then absorbing the
smaller molecules that the organic matter is broken down into. Humans, cats, and rabbits all have enzymes that help them to digest their food. But these enzymes are found within their bodies. They are not released out of their bodies and then to their external environment.
Furthermore, while we do tend to only eat dead organisms, it would not be a good idea
to feed on rotting food as this would be likely to introduce dangerous pathogens
into our bodies, which could make us really ill.
Let’s take a look at the final group of heterotrophs: holozoic heterotrophs. Holozoic organisms are those that obtain nutrition by ingesting and internally
digesting solid, liquid, or gaseous food particles within their bodies. Humans, cats, and rabbits all ingest food into our complex digestive systems, found
within our bodies. There, enzymes are released from certain cells into our digestive tract, where they
can break down large nutrients in food into smaller molecules that can be absorbed
and transported to our body cells for all sorts of useful functions. This means that we have found the correct answer to this question. The classification of heterotrophic organisms that humans, cats, and rabbits belong
to is (C) holozoic.
