Write An Essay On Planarians

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Planarians are bilaterally symmetric metazoans of the phylum Platyhelminthes usually found in freshwater streams and ponds. Planarians have the ability to regenerate large regions of missing structures and are useful for the investigation of anterior-posterior (AP) polarity in occurrence with molecular and cellular mechanisms. Regeneration involves integration of newly made self-assembled tissue into older pre-existing tissues (Alvarado 2006). Adult somatic stem cells called neoblasts that are distributed throughout the planarian body (Reddien and Alvarado 2004) allow for the regeneration of individuals from minute fragments. Neoblasts are the only mitotically active cells in planarians (Newmark and Alvarado 2000), and can generate any of the…show more content…
Three replicates of three specimens produced 18 separate fragments. However, only 6 anterior fragments and 7 posterior fragments survived. Pairing is necessary for analysis of the anterior versus posterior ratios to standardize the measurements. The planarians were kept in petri dishes with water that was not changed from the day of the cut to the final measurements a week later, and there was no feeding. Growth was measured using image J and key structures. The key structure looked at for the anterior fragments was the point of the tail indicating that the wound was healed. The key structures looked at for the posterior fragments were ocilli (eyespots), a pharynx and auricles (sensory lobes). The tail will regenerate more quickly on the anterior fragment than the head and the anterior trunk will on the posterior fragment, as fewer neoblasts will be needed to regenerate the tail, and the latter fragment will contain less neoblasts to divide and create the more complex structures of the head and the pharynx. If complexity slows the regeneration rate, then the head and the anterior trunk will grow more slowly than the
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