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Question Video: Identifying a Class of Heterotrophic Nutrition Biology

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?

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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.

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