Video Transcript
Leeches, shown in the picture,
attach to the body of another organism and obtain their nutrition by consuming some
of that organism’s blood. What classification of
heterotrophic organisms do they belong to?
Let’s start off by defining some of
the key terms in the question to figure out how to answer it. We’re told that leeches are
heterotrophic organisms, but what does this term actually mean? Heterotrophic organisms obtain
their food by consuming and ingesting other living or once-living organisms. For example, we, humans, are
heterotrophs as we consume animal, plant, and sometimes fungal matter to obtain our
nutrition, all of which are living or once-living organisms. Let’s find out what kind of
heterotroph this leech is by comparing the three main classifications of
heterotrophic organisms in a table. The three different groups of
heterotrophs are parasites, saprophytes, and holozoic organisms.
Let’s look at the characteristics
of how these groups typically obtain their food, starting with parasites. Parasites tend to live inside or on
the surface of the body of another living organism, called the host. And they tend to obtain their
nutrition at the host’s expense, just like how this parasitic vine absorbs nutrients
from its host tree. Saprophytes, on the other hand,
tend to obtain their nutrition from dead or decaying organisms rather than a living
host. Saprophytes like this fungus can do
this by releasing extracellular enzymes out of their body and onto rotting organisms
to break down their large nutrients into smaller food molecules. The smaller molecules are then
absorbed into the saprophyte cells to be used as required.
Holozoic organisms do not tend to
be fussy about whether their host is living or dead. And rather than releasing enzymes
onto their food, they ingest solid, liquid, or gas food particles into their body
first. Once their food has been ingested,
the food particles are digested with enzymes inside the holozoic organism’s body
before the smaller nutrients are absorbed into their cells to be used as
required.
Let’s take a look back at our
question to discover which classification of heterotrophs the leech belongs to. The question tells us that the
leech attaches to the body of another organism. This suggests that the leech might
be a parasite which lives on or in the body of its host. We are also told that the leech
consumes the organism’s blood to obtain its nutrition. This reflects the other key feature
of parasites that they obtain their nutrition at the host’s expense. Losing blood would definitely be
detrimental to the leech’s host’s health, and possibly survival. Therefore, we can conclude that the
leech can be classified as a parasite.
