Planarians move away from the light and are most active in the dark. Second, light and water current can be used demonstrate kinesis change of speed and taxis change of direction.
Planarians are also sensitive to shock. Therefore, planarians can be conditioned with several stimuli and responses. Only after seven days did they regain their stronger preference to slither away from visible light — suggesting that their eyespots and brains were retaking control.
It was not until the 12th day that their sensitivity to such light increased to the point that they reacted more strongly to light at the bluer end of the visible spectrum.
Read more: Bioelectric tweak makes flatworms grow a head instead of a tail. Trending Latest Video Free. Humans can tell colors apart because our eyes have three kinds of light-sensitive pigments, known as opsins. Each one responds to a different wavelength of light—red, blue, and green, respectively.
By comparing and contrasting the responses of these pigments, we can work out what colors we are seeing. But planarians only have one kind of opsin. Their single opsin responds most strongly to blue light, but it also responds weakly to other colors. The worm perceives these differences in terms of brightness, so blue looks brighter than green and green looks brighter than red—and it can then swim to whatever looks darkest.
His student Nishan Shettigar confirmed this through clever experiments where he carefully adjusted the brightness of his differently colored lights. What use, they say, is half an eye? Flat patches of light-sensitive cells gradually morph into planarian-style cups, which eventually gain focusing lenses.
They evolved from performing a few simple tasks perfectly to performing many complex tasks excellently. It has also been found that the various sensory organs that are linked to the central brain via sensory nerves are responsible for the tactile responses exhibited in planarians Cebria, This paper describes the experimental observations of phototaxis, tactile response, and regeneration after decapitation for a Dugesia flatworm.
Based on prior literature, it was hypothesized that the planarian would exhibit negative phototaxis movement away from source of light , tactile sensitivity resulting in movement away from source of touch, and a complete regeneration into two planarians approximately 5 to 6 days after decapitation. A live Dugesia flatworm was obtained from a beaker of stock culture and added to a petri dish with pond water. The stretched length of the flatworm in millimeters was obtained so as to assess the change in length from pre-decapitation to post-decapitation.
Using a pipette tip, the planarian was gently touched on both posterior and anterior ends to assess response behavior. Finally, the petri dish was placed under a light microscope to assess the phototaxis response of the planarian.
After the measurements for length and observations of phototaxis and tactile responses, the planarian was placed in ice for approximately 5 minutes to slow its movement and then decapitated slightly anterior to the mouth. The head and tail regions were placed in separate, labeled petri dishes to confirm, after regeneration, from which region the regenerated planarian was derived. Measurements of the head and tail region were taken immediately taken after decapitation, 30 minutes after decapitation, and 7 days after decapitation.
Between measurements, the labeled petri dishes were incubated at room temperature, and the water in the petri dish was changed every three 3 to 4 days. After the final measurements, each of the regenerated planarians was finally returned to the stock culture. When placed under a light microscope, the planarian attempted to move away from the light source.
This was repeated several times to ensure that the planarian exhibited the same response each time. Because the planarian moved away from the light source, it exhibited negative phototaxis. Additionally, when touched on both its posterior and anterior ends with a pipette tip, the planarian attempted to move away from the tip, exhibiting sensitivity to touch. With regards to regeneration itself, the planarian length before decapitation was 14 millimeters and each individual region grew to 11 millimeters head region and 6 millimeters tail region after 7 days of incubation at room temperature in pond water.
The average rate of growth over 7 days, as extrapolated from linear regression lines, of the head region was double that of the average rate of growth of the tail region. Figure 1: Length of the planarian at various points after decapitation. Note that the original length of the planarian was 14 millimeters.
Regenerating the central nervous system: how easy for planarians! Developmental Genes and Evolution , Farnesi, R. The frontal organ of a triclad flatworm, Dugesia lugubris.
Cell and Tissue Research , Gurley, K. Science , Inoue, T. Zoological Science , Newmark, P. Developmental Biology,
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