Lumbricus Variegatus Oligochaeta Worm Biology Essay

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The purpose of this study was to investigate the effects of both a stimuli and a depressant on the pulse rate of a Lumbricus variegatus, an oligochaeta worm and how either of the chemicals stimulated the worm's sympathetic and parasympathetic nervous system. The oligochaeta worm was placed in a glass capillary tube to limit movement and the initial heart rate was determined to be 21.06 beats per minute while it was under the microscope. The worm was then given the depressant ethanol or the stimulant caffeine and the heart rate was determined to be an average of 31.3 beats per minute after the chemicals were administered. It was observed that pulse rate gradually decreased to an average of 19.8 beats per minute when the worm was given the ethanol depressant. When it was given the ethanol depressant it lowered while the pulse rate gradually increased when it was given the caffeine. It was determined that the worms circulatory system was under the control of both its sympathetic and parasympathetic nervous system and the chemical induced in the worm acted as a stimulant (caffeine) or a depressant (ethanol) and this had an effect on the organism heart rate.


Stimulants are a class of drugs that enhance the brain activity of an organism and central nervous system, speeding up communication between the two and usually increase alertness and physical activity while depressants slow down the activity of the brain and nervous system slowing down the communication between the two (Grattan-Miscio K.E. and Vogel-Sprott M, 2005). Once the substance enters the bloodstream, it is transported throughout the body to various organs and organ systems, including the brain (Stendel R. et al, 2006). To first enter the brain, the substance's molecules must first get through its chemical protection system, which consists mainly of the blood-brain barrier (Badanich K.A. et al, 2011). Tight cell-wall junctions and a layer of cells around the blood vessels keep large or electrically charged molecules from entering the brain of the organism (Howland J. et al,2010). However, small neutral molecules like those in stimulants and depressants easily pass through the blood-brain barrier and enter the brain (Howland J. et al,2010). Once inside the brain, the substance begins to exert their effects organism, such as its heart rate.

Caffeine a stimulant, enters the blood from the stomach and small intestine and begins to stimulate your central nervous system (Hirata H. et al, 2006). The caffeine then stimulates receptors located in cells within the heart and increases heart rate. This in return also speed up the blood flow because of an increase in heart rate, as well as an increase in blood sugar as well as urine production and body temperature (Howland J. et al,2010). When a depressant enters the system, because of its is highly solubility in water, it travels throughout the body just like water does (Stendel R. et al, 2006). When ingested ethanol for example, can pass through cell wall membrane and is distributed throughout the water content of tissues and cells (Howland J. et al,2010). In its circulation through the body, the ethanol eventually reaches the brain and begins to slow the heart rate of the organism (Stendel R. et al, 2006).

On an organism such as an oligochaeta worm, the effects can be almost instantly due to its thin extracellular layer. The organism blood vessels (which as similar in size to the capillaries in vertebrates) and the effects the chemical stressor it has on its heart rate can be used as model for comparisons to other invertebrates and even vertebrates such as humans as well. (Verdonschot Piet et al, 2003)

In this study the effect of a stimulant and depressant on a cardiovascular system of an organism was studied and it was hypothesized that the caffeine stimulant would increase the heart rate of the oligochaeta worm while the heart rate would decrease if the worm was given the ethanol depressant.

Materials and Methods

The Lumbricus variegatus worm was obtained and placed in lukewarm well of water while the depressant and stimuli solutions were being made. The depressant used in this experiment was ethanol (C2H6O) and was prepared to a concentration of 0.01 percent. The stimuli used was caffeine and was also prepared to a solution concentration of 0.01 percent as well. The worm was placed in a medicine dropper and transferred in a glass capillary tube to immobilize the movement of the worm for appropriate observations. It was then placed under a microscope of x40 magnification and its initial heart rate was observed by taking its pulse for thirty seconds and this was converted to pulse per minute. To observe the pulse rate of the worm, the blood vessel of the organism was detected and each pulsation was counted for a thirty second period. The observations were recorded.

The worm was then given the caffeine stimulant by putting one drop of the solution into the capillary tube . A time of two minutes was given before the pulse rate was taken to allow for absorption of the solution by the worm. After the two minutes, the pulse rate of the worm was taken for a period of thirty seconds and was converted to pulse per minute and then recorded.

Another worm was taken and transferred into a capillary tube and its initial heart rate was observed and recorded under a microscope though the same procedure of the first worm. It was then given a drop of the ethanol depressant solution and a time of two minutes was also waited to allow for absorption of the chemical. The pulsation rate was observed for a period of thirty seconds and was converted to pulse per minute and recorded.

Results and Discussion

As shown in figure one and two below, when the stressors were given to the worms, they did have an effect on their heart rate. The chemical stressor caffeine (Figure 1) did induce an increase in the pulse rate of Lumbriculus worm (t20 = 4.22, p < 0.005). Similarly the ethanol depressant had a huge impact on the worms heart rate as well by decreasing it (t20 = -2.52, p < 0.005) as shown in figure 2 below.


Figure 2

The worms heart rate decreased when it had absorbed the ethanol and increased when it had absorbed the caffeine. Caffeine mimics some of the effects of adrenaline in the heart. It increases the amount of cyclic AMP (cAMP) ,a second messenger , in the sinoatrial node of the heart (Badanich K.A. et al, 2011). The cAMP levels increase and this increases the electrical activity of the sinoatrial node, making the heart 'beat' faster. (Hirata H. et al, 2006). Like adrenaline and it can affect the main pumping chambers such as ventricles leading to an increase in the rate of contraction and relaxation of each heart beat (Grattan-Miscio K.E. and Vogel-Sprott M, 2005). This means that as well as beating faster, the heart's individual beats are associated with an increased volume of blood ejected into the circulation per unit time (Howland J. et al,2010). This is called cardiac output and even two or three cups of strong coffee or tea containing enough caffeine can cause an increase in human heart rate of 5-20 beats/min(Hirata H. et al, 2006).

Similarly  ethanol slows down heart rate. It depresses the parasympathetic nervous system by acting as what is known as a non selective central nervous depressant (Howland J. et al,2010).The amounts of ethanol necessary to achieve this effect in humans would be sufficient also to depress the respiratory centres of the brain and greats amounts of the depressor can even result in death (Stendel R. et al, 2006).

The effect of ethanol on the cardiovascular system of an organism is undeniably a visible one. The chemical stressor does indeed decrease or increase the heart of the organism that ingests the chemical. The worms, in this experiment , pulsation decreased at a very slow rate due to the properties of ethanol and caffeine stimulated the heart by increasing the beats per minute drastically. The affects of the stressors can be seen not only in animals but in humans as well. The circulatory system works in conjunction with the central nervous system and whatever is ingested in the body is taken to the brain through the blood vessels (Grattan-Miscio K.E. and Vogel-Sprott M, 2005). The effects of chemical stressors can be seen in a variety ways such as the lethal effects it has in drugs and the less lethal effects such those in energy drinks and coffee (Howland J. et al , 2010).

The hypothesis was correct, the stressor caffeine did increase the worms heart rate and the ethanol did decrease it similarly. The results were similar to those in other studies. This experiment can be improved by taking more accurate results of the heart rates by counting the pulsations more accurately. Also a way the experiment can be modified is to gradually increase the concentration of both the ethanol and the caffeine and determining in that context the effect the ethanol and caffeine has on the central nervous and cardiovascular systems. That way the effects can be seen linearly and questions such as would the increase in concentration of the stressor have an linear effect on the heart rate of the organism or not can be asked , as well as would it plateau at a certain level can be thought about. By observing the effects the stressors on the organism from a mathematical perspective, its effects can be seen could be better understood on its affects on humans.