Investigating reflex behaviour in an invertebrate organism

Tom Gowing 10A – Biology practical coursework –

Investigating reflex behaviour in an invertebrate organism

The main point of this is to investigate how an invertebrate organism responds to certain stimuli in a controlled environment. A reflex is a response to certain stimuli. The main difference between this and any other movement is that the impulses from the receptor travel straight to the effectors before going to the brain, whereas most impulses go to the brain first, where it can decide what to do. Reflex behaviour is often for safety reasons, for example if you touch a hot stove, it would take longer for the impulse to travel to the brain and then to the effectors than it would for the impulses to travel straight from receptor to effector. This means that it takes less time for the effectors to respond, meaning less damage is done.

Woodlice will be used for this experiment. Woodlice are not actually insects at all, but a form of crustacean, found commonly in gardens, they thrive in dark, damp places. They feed on almost anything, including wood, plant life and decaying objects. Woodlice have a flattened body with seven pairs of legs. Their respiratory organs (gills) are completely enfolded by perforated plates. The species vary in colour from grey to black. They evolved from sea-based life forms as opposed to insects, which evolved from land-based life forms. A woodlice's skin is therefore permeable - it lets water in and out. If they did not live in damp places they would dry out as the water left their bodies through their permeable skin. Woodlice generally lack any cuticle on their exoskeleton and are therefore likely to become dehydrated even quicker.

Oddly enough, woodlice, along with most other crustaceans, have blue blood. This is because the compound haemocyan is found in their blood. Haemocycanin carries oxygen in the same way that haemoglobin does in mammals. Haemocycanin contains a copper atom instead of the iron atom found in haemoglobin. The blood is pale blue when it is carrying oxygen and colourless when it is not carrying oxygen. Woodlice do actually have a sense of smell and are able to detect chemical odours by using sensory receptors on the ends of the large antennae.

Like many arachnids, woodlice have compound eyes, usually made up of about 22 simple eyes (ocelli). These are their receptors for light.

Variables

There are several variables that could be altered to investigate the reflex behaviour in woodlice. The initial stimuli that can affect the woodlice are: -

Light levels (light/dark)

Temperature (hot/cold)

Food sources (decomposing plant life etc.)

Moisture (very dry/very moist)

Along with my partner (Adam Cubbage) we will be adjusting the light level. To test this accurately and fairly, all other variables must remain the constant. There will be two main compartments. One light, and one dark. They will both contain 15ml of water to keep humidity equal in both compartments. In each compartment will be an equal amount of decomposing leaves for a food source. This will all be done at room temperature (about 20°C). All this should keep all variables, except the one being investigated, ...

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Temperature (hot/cold)

Food sources (decomposing plant life etc.)

Moisture (very dry/very moist)

Along with my partner (Adam Cubbage) we will be adjusting the light level. To test this accurately and fairly, all other variables must remain the constant. There will be two main compartments. One light, and one dark. They will both contain 15ml of water to keep humidity equal in both compartments. In each compartment will be an equal amount of decomposing leaves for a food source. This will all be done at room temperature (about 20°C). All this should keep all variables, except the one being investigated, constant, and at conditions to suit the woodlice.

Before the experiments the woodlice were kept in a darkened, damp enclosure with plenty of food, but 5 minutes before the experiments were performed we took them out and left them in a dish. This was done because I think that if the lice are taken from an ideal climate then there will be a reflex reaction no matter where they are put, simply because they have changed environment. If they are left in an isolated dish before the experiment then the test conditions will seam ideal to them, increasing the accuracy of results.

The species of the lice was checked before each experiment to make sure that they were all of the same species to increase accuracy in the results. Two sets of lice were rotated between experiments. The first set would be used for experiment 1, while the second set rested and the second set would be used for experiment 2 while the first set rested. The first set would be used for experiment 3, the second for experiment 4 and so on. This ensured that there is different lice used, giving more conclusive, widespread results, but kept the situation controlled (i.e. there weren’t completely different lice used for every experiment), keeping results fairly accurate.

Apparatus

In terms of containers we were given a choice of a dual compartment container, with two separate areas, joined by a ‘walkway’, or a circular choice chamber, with four completely separated chambers. I have chosen the dual container as the variable I am investigating is just a case of light or dark, and the ‘walkway’ lets the woodlice move between the two containers.

The woodlice we used were found in my partners back garden, under a piece of rotting driftwood.

This is a full list of apparatus I will use to carry out this investigation: -

Dual-dish chamber,

Black polythene bag (to black out one chamber),

Water,

Food source (leaves, or rotting vegetation)

Woodlice,

Wire gauze,

Rubber bands.

Diagrams

Method

First I added equal amounts of water to each side (15ml each), then a wire gauze was placed over the now water filled dishes. Equal amounts of food sources were then placed on each side of the gauze. Five woodlice were then placed on each side of the container and the lid was quickly put on and held in place with a rubber band in the middle. This was then timed for five minutes to see where the ten woodlice gather. This will be done eight times, each taking five minutes. The woodlice were constantly monitored and checked for anomalies. I will note down the amount of woodlice in each compartment every minute and record the results in a table.

A preliminary control experiment was set up identically to the ones above, but with the black bag on top of both sections section. The results from this will be recorded in a separate table.

Predictions

I predict that in the control experiment that the woodlice should stay roughly where they were put as they have their own source of food, and are kept in a moist, dark climate.

I predict that after five minutes in the main investigation, that the majority of the woodlice (about 7 in 10), will move into the darkened area. If any woodlice remain then its because there is a prime source of food.

Results table for preliminary control experiment

Results of preliminary experiment

On the whole the woodlice stayed where they were put. A few problems with the method became obvious though. The first was that it was not just a simple case of just putting the woodlice in the choice chamber. When you put one in on one side, it crawled out the other, and because one side was open while I was inserting the woodlice they all tried to go over to the other side, leaving few bugs in one side and a lot in the other. We eventually got around this by using two separate containers to sore the woodlice in, five in each one, then using these to literally pour the woodlice into each half.

After the preliminary results I still stick to my predictions that after five minutes in the main investigation, the majority of the woodlice (about 7 in 10), will move into the darkened area. If any woodlice remain then its because there is a prime source of food.

I produced graphs of these results (see next two pages), after looking at these we decided that they could show the results more clearly than they do, so I changed the way I did the results for the actual investigation.

Results table for full investigation

I obtained my results as per my plan, with the exception of the way the woodlice were inserted into the choice chamber (see results of preliminary experiment)

Analysis

All these graphs show that there is generally always above 7 woodlice in the dark side, and usually no more than 3 in the light side. There is a slightly anomalous result in experiment 7 in the third and fourth minute where one woodlouse actually goes from the dark side into he light side, but this could be because there was not room for it to gain access to the food source on the dark side, so it would go over to the next one.

The tables and graphs show that woodlice do have a reflex reaction to light, and prefer to live in a darker climate. In experiment 4 all the woodlice had moved to the dark side within the first minute, giving a perfect experiment with 10 woodlice on the dark side and none on the light.

The compound eye (receptor) senses the bright light in the light side and sends impulses to the leg muscles and then to the brain, causing the woodlouse to move, hopefully finding a darker area.

These results all support my original predictions, showing that woodlice do in fact show reflex behaviour.

I worked out a set of average results for each of the 5 minutes. This was calculated by adding all the figures for each minute together and dividing by 8 (the number of experiments).

e.g.

Light experiment 1st Minute = 2+2+2+0+2+3+1+2 = 1.75

8 Average number of lice on light side

1st minute – 1.750

2nd minute – 1.250

3rd minute – 0.875

4th minute – 0.625

5th minute – 0.250

Average number of lice on dark side

1st minute – 8.250

2nd minute – 8.625

3rd minute – 9.125

4th minute – 9.375

5th minute – 9.750

Evaluation

I think my results were very reliable. The only anomalous result was that found in experiment 7 in the third and fourth minutes when 1 woodlouse went back from the light side to the dark side, but this was no fault of mine, nor did it have anything to do with the procedure of the investigation. This could be because there were a lot of other woodlice on the food source in the dark area and therefore not enough room for it to gain access to the food source on the dark side, so it would go over to the light one in search of food. From this I think that they also have a reflex action to do with the need for food. It would be interesting to do a follow up experiment to investigate this.

The preliminary experiments showed that the way the graphs were presented needed adjusting to make them clearer to read and easier to understand. I think this was done successfully.

The only real problem that cropped up in performing these experiments was the method of getting the woodlice into the test chambers, but this was all about technique, and soon became easier. The easiest way to do it is the method I wrote after performing the preliminary experiments (see preliminary test results section).

This experiment was perfectly suitable for investigating the reflex behaviour of woodlice, and no animals were harmed in the process of this experiment.

The evidence produced by this investigation is enough to support my original predictions, and to provide a firm conclusion that woodlice do show reflex behaviour to light levels.

I could also do further investigations on the effect of food sources, dampness and temperature.

Combinations of experiments could also be preformed. For example testing two variables at once. This would tell us which reflexes are strongest, and therefore which conditions woodlice rely on most and are most necessary for their survival.

Investigating reflex behaviour in an invertebrate organism

Tom Gowing 10A – Biology practical coursework –