Planarian Behavior
Planarian Behavior – Biology II Honor
Overview
Work in pairs for this lab. You will directly observe planarian movement. You will then formulate a hypothesis about planarian behavior, and propose an experiment to test this hypothesis. Your experiment should be focused on one of the various types of stimuli listed below. Your experiment must collect both qualitative and quantitative data. Think about how you can increase the sample size of your observations to minimize the effect of confounding variables.
The animal
Hydra oligactis, the animal we are using this week, is a planarian. Planarians are in the phylum Platyhelminthes (which means “flat worm”), which contains about 25,000 species, most of which are in the tapeworm and fluke groups. These are parasitic, living in other organisms where they can cause serious disease such as schistosomiasis (See Sadava, Fig. 31.15, and pp 695-696). Other flat worms are native to salt water, fresh water, or moist soil. Platyhelminthes are the simplest bilaterally symmetric and triploblastic animals (meaning they have all three primary germ layers: endoderm, mesoderm, and ectoderm). Planarians have a single opening, the mouth, found on the ventral surface. It leads to a well-developed, highly branched gastrovascular cavity which is the site of both digestion and circulation of nutrients. There is no separate exit, so undigested food has to leave by the mouth. There is no system within the body to distribute oxygen, this constrains flatworms to be flat, as they must respire by diffusion and no cell can be too far from the outside. Planaria are quite active, moving by contraction of muscle fibers that are oriented in different directions, in a manner similar to how we move our tongues around. The direction of movement is controlled by the nervous system, which consists of an anterior “brain” consisting of large ganglia. Two ventral nerve cords run the length of the body from the ganglia. Between the ventral nerve cords
Overview
Work in pairs for this lab. You will directly observe planarian movement. You will then formulate a hypothesis about planarian behavior, and propose an experiment to test this hypothesis. Your experiment should be focused on one of the various types of stimuli listed below. Your experiment must collect both qualitative and quantitative data. Think about how you can increase the sample size of your observations to minimize the effect of confounding variables.
The animal
Hydra oligactis, the animal we are using this week, is a planarian. Planarians are in the phylum Platyhelminthes (which means “flat worm”), which contains about 25,000 species, most of which are in the tapeworm and fluke groups. These are parasitic, living in other organisms where they can cause serious disease such as schistosomiasis (See Sadava, Fig. 31.15, and pp 695-696). Other flat worms are native to salt water, fresh water, or moist soil. Platyhelminthes are the simplest bilaterally symmetric and triploblastic animals (meaning they have all three primary germ layers: endoderm, mesoderm, and ectoderm). Planarians have a single opening, the mouth, found on the ventral surface. It leads to a well-developed, highly branched gastrovascular cavity which is the site of both digestion and circulation of nutrients. There is no separate exit, so undigested food has to leave by the mouth. There is no system within the body to distribute oxygen, this constrains flatworms to be flat, as they must respire by diffusion and no cell can be too far from the outside. Planaria are quite active, moving by contraction of muscle fibers that are oriented in different directions, in a manner similar to how we move our tongues around. The direction of movement is controlled by the nervous system, which consists of an anterior “brain” consisting of large ganglia. Two ventral nerve cords run the length of the body from the ganglia. Between the ventral nerve cords