Planaria Lab Report

Planarians are platyhelminths or flatworms that are characterized to have a primeval type of nervous system. The flatworms commonly inhabit aquatic ecosystems and their bodies show bilaterally symmetrical, wherein the left and right halves are equivalent to each other. The simple nervous system of planarians is mainly composed of a primitive brain that is composed of big structures called ganglia, situated in the anterior region of the body. Running along the length of its body are two nerve cords that are positioned on the ventral side of the flatworm.

Planarians are also equipped with cup-shaped eyes that are employed for visual sensing. These flatworms are also equipped with pits that contain chemoreceptors. Planarians are so simple that it has fascinated scientists in using these as model systems in studying animal behavior and movement (Abbott and Wong, 2008). The term taxis pertains to an action that is triggered by a particular stimulus. When a certain taxis results in the movement of an animal towards to stimulus, then the action is considered positive.

On the other hand, when an animal moves away from the stimulus, the taxis is said to be negative. There are many taxes that are present in the environment and several types of taxes have been identified. Rheotaxis is the action performed by an animal during its exposure to water currents. The response of an animal to a source of light is known as phototaxis, while the reaction to chemicals in the environment is known as chemotaxis. In this laboratory report, the results of experiments performed in testing three different types of movement in planarians are reported.

METHODS AND MATERIALS A. Rheotaxis Materials: Petri plate, water, Pasteur pipette, rubber bulbs, Planaria Methods: A Petri plate was half-filled with water and left for 2 minutes in order to make the water stand still. A planarian was introduced and watched for any movement for 5 minutes. Using a Pasteur pipette with a rubber bulb attached to one end, water currents were introduced to the plate. The planarian was observed for any movements in response to the water current. B. Phototaxis Materials: Petri plate, water, flashlight, Planaria

Methods: A Petri plate was half-filled with water and left for 2 minutes in order to make the water stand still. A planarian was introduced and watched for any movement for 5 minutes. Using a flashlight, one end of the plate was illuminated and the reaction of the planarian was observed for 5 minutes. C. Chemotaxis Materials: Petri plate, water, piece of bread, Planaria Methods: A Petri plate was half-filled with water and left for 2 minutes in order to make the water stand still. A planarian was introduced and watched for any movement for 5 minutes.

A small piece of bread was dropped on one end of the plate and the reaction of the planarian was observed for 5 minutes. RESULTS A. Rheotaxis The planarian was observed to swim in the same direction as the current that was introduced to the water, indicating a positive rheotaxis response. B. Phototaxis The planarian moved towards the area where the light was present, indicating positive phototaxis response. C. Chemotaxis The planarian moved towards to piece of bread that was introduced, indicating a positive chemotaxis response.

Table 1. Taxis responses of planarians to different stimuli Response of planarian Type of taxis Positive taxis Negative taxis Rheotaxis + – Phototaxis + – Chemotaxis + – DISCUSSION The movement of planarians serves as a good indicator for its response to different types of stimuli. The rheotaxis, phototaxis and chemotaxis experiments conducted in this laboratory exercise showed that the planarians gave a positive response to all stimuli, as shown by either its movement with the water current, or its movement towards to stimuli itself.

The movement of the planarians shows its response to any changes in its environment. Since the planarians are commonly located in aquatic habitats, it is common for this animal to encounter water currents in the natural environment. The response of the planaria involving swimming together with the direction of the current indicates that it does not resist any movements in the aquatic environment is lives in and thus can be carried to other parts of the body of water. The introduction of light using a flashlight mimics the presence of sunlight in the planarian’s natural habitat.

The positive phototaxis response of the planaria to the area where the light from the flashlight was concentrated on indicates that planarians would move towards the source of sunlight, which in turns is known to be more beneficial to these organisms because there would be more dissolved oxygen in these areas, as well as phytoplankton. The introduction of a piece of bread to the Petri plate resulted in a positive chemotaxis response from the planarian. This condition mimics the presence of food resources in its natural aquatic habitat.

This positive response shows that planarians will move towards an area where it could find nourishment for itself. These three experiments on planarian movements provides us information on how animals move and behave based on the presence of a particular stimulus. It is very interesting to know the specific responses of the planarians to different types of stimuli. Reference Abbott, S. M. and Wong, G. K. (2008). The conditioning and memory retention of planaria (Dugesia tigrina) for directional preferences. BIOS, 79(4),160–170.a

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