Coursework: Response to Light in Blowfly Larvae.

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Florence Annan

Candidate number: 5900

Centre number: 48255

U6A

Miller/Williams

Question: Response to Light in Blowfly Larvae.

Null Hypothesis: Blowfly larvae have no response to light. They have no preference ion moving towards a light source or away from a light source. This will be shown at the end of the experiment by there being a 50% even spread in either tray.

Hypothesis: Blowfly larvae have a reaction to light. A larger proportion will move away from the light during the experiment than will move towards it.

Reasoning: Almost all larvae react to the light and attempt to move away from it, as due to their large surface area and their thin epidermis they risk drying out. The larvae have photoreceptor cells. These are specialized cells, which consist of two molecules in a membrane, opsin, and a light sensitive protein, which surrounds the chromophore, which is a pigment that is used to detect colours.  Clusters of these cells allow the maggot to detect only a very basic sense of the direction and intensity of light- enough to distinguish whether they are heading towards an area of light or away from one, but not enough to discriminate an object from its surroundings. Therefore, the larvae will know that they are moving away from an area containing more light and so will try to move in that direction in order to reduce their risk of drying out. They also risk being predated upon if they go into the daylight where they will be more visible to predators. Therefore, they tend to hide in the dark, which tend to be where their food source is located.

Flies lay their larvae on rotting flesh as when the eggs hatch there is a food source readily available. Larvae feed by extracellular digestion (similar to fungi) by excreting enzymes that digest the surrounding flesh of the decaying organism and then reabsorbing the digested flesh through mouth hooks.  Maggots are very particular about only eating rotting flesh and for this reason they are being reintroduced into surgery, as a surgeon cannot distinguish as easily what is healthy and what is decaying tissue and therefore risk removing more tissue than is needed.

As blowfly larvae feed on dead organisms, they spend most of their lives in this stage inside the corpse, where it is dark. Therefore, if it is light they will move towards the dark even more in order to reach their food source. When they have matured, they leave the corpse and search for a protected place to pupate. This is the life cycle of a blowfly:



Preliminary investigation:

I created a box which looked like this:

I collected this data:

I carried out a preliminary investigation to see whether there was a correlation and whether there was any point in carrying this investigation out. From the preliminary investigation I discerned that the maggots had a tendency to move towards the darker end of the box. However the experiment was flawed in terms of the counting methods and the temperature was not controlled. Therefore, during my actual experiments I have taken great steps to ensure that the temperature is controlled and that as many of the other variables are controlled as possible.

The maggots have other factors which will influence the direction they move in which could be misinterpreted as a taxis towards or away from the light. Therefore, these and other variables need to be controlled.

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 This is the equipment needed. It needs to be set up like the diagram shows.

Method:  

Creating the system: two boxes are needed. The refrigerator packs of 24 cans are the best.  Alternatively, you can cut one in half as I did. Then cut a hole in the top of one of the boxes. This has to be wide enough to allow the light in. Your box has to be study enough to support the weight of a bowl of water. Next a “bridge” has to be made. Mine was created out of a long thin piece ...

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