Welcome to another new day for Biology Tips Daily, offering tips and tricks to help you ease into the biology mastery.
Today's topic is another common confusion - Protostomes vs Deuterostomes.
We bet that 99% of all biology students in the history of life don't know or don't remember the difference between protostomes and deuterostomes. We confess that we forget them from time to time, too.
Protostomes are creatures like worms, beetles, and octopi. What could possibly unite such a diverse group of creatures?
What unites them is actually quite memorable...if you are a jargon freak! Technically protostomes are characterized by spiral determinate cleavage, schizocoelous formation of the coelom, and development of the mouth from the blastopore. Got that?
What about deuterostomes? Who are they? You are a deuterostome and so is a sea cucumber.
What could you possibly have in common with a sea cucumber that would make both of you "deuterostomes"?
Technically humans and sea cucumbers are characterized by radial indeterminate cleavage, enterocoelous formation of the coelom, and development of the anus from the blastopore.
Again with the terminology!
All these technical terms refer to events that occur early in development following fertilization. It is quite remarkable that you and a sea cucumber have more similarities in the way that you develop than sea cucumbers and worms. Essentially, what this means is that you are more closely related to a sea cucumber than something more anatomically sophisticated like...a worm.
Actually these events and the terms we use to describe them are more straightforward than you imagine. In fact, they have to do with early patterns of cell division, how cavities are formed very early in development, and the ultimate fate of a certain feature of early development.
Let's begin with the difference between spiral and radial cleavage. They refer to patterns of early cell division, called cleavage, that grow the zygote (the single-celled, fertilized egg) to a solid ball of cells early in development. In spiral cleavage, cells divide at an oblique angle to the polar axis of the zygote. In radial cleavage, cells divide parallel or perpendicular to the polar axis of the zygote. How about determinate and indeterminate? These terms refer to the fate of the early cells. If cleavage is determinate, the developmental fate of cells is made early and irreversibly. In other words, these cells make commitments to become certain kinds of cells very early on during the cleavage stage. Having done this, their fates are set. There is no going back!
By contrast, in indeterminate cleavage, cells maintain their ability to become any kind of cell at a later time during development. These are the so-called stem cells you read so much about as having so much potential for medical interventions.
A coelom is a body cavity so coelom formation refers to the particular way that a body cavity is formed. Schizocoelous and enterocoelous are just two different ways of forming a coelom, by splitting off groups of mesoderm cells or pinching in a group of mesoderm cells.
Finally, the fate of an early feature, the blastopore differs between protostomes and deuterostomes. The blastopore, an opening at one end of the digestive tube, becomes the mouth of protostomes and the anus of deuterostome. The irony is inescapable. Your first recognizable early feature is your anus. Need I comment more?
In any event, to understand the difference between protostomes and deuterostomes, you really only have to remember three things: the patterns of cleavage, how the coelom is formed, and which part of the digestive systems develops first. That's not so much to remember.
You might also want to remember why this is important in the first place. These patterns of early development are evidence of who is related to whom, evolutionarily speaking. Protostomes are more closely related to one another than they are to deuterostomes.
Until then, stay tuned for more biology tips.
Seize the Day!
Dr. Wayne Huang
"The Rapid Learning Coach"
BioTips@RapidLearningCener.com
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