Cockroaches and Hemolymph Concentration in the Body Essay Example for Free

Cockroaches and Hemolymph Concentration in the Body Essay This lab was conducted to determine the concentration of hemolymph in the body of a cockroach. It was done by making serial dilutions to make a standard graph by injecting a dye into a cockroach and determining the concentration at different times with the use of a spectrophotometer to find the optical density which is measured in absorbance. Results showed that the concentration was not within the pre-experiment research range. Introduction: Cockroaches as well as all other insects have an open circulatory system. Unlike humans who have a closed circulatory system with arteries and veins, insects do not have any arteries or veins. They have a body of internal fluids and they use diffusion to transfer nutrients and oxygen across their bodies. This process of diffusion is only made possible because of their small bodies. In practical terms, cockroaches are cheaper than vertebrates, and since they are neither furry nor cuddly their use does not anger the animal-rights enthusiasts. In terms of economics and public health, we need to know everything we can about insects because of their enormous impact on humans as crop pests, carriers of disease, pollinators, etc. But they also have a fascination in their own right. For instance, they represent the only other major group of animals that, with the higher vertebrates, have successfully conquered the terrestrial habitat. Insects and mammals have a vastly different evolutionary heritage: evolution has had to work with very different basic body plans to produce two highly successful terrestrial organism (Smith 119-139). Insects regulate their hemolymph volume by a variety of mechanisms including hormonal and metabolic factors. In an aquatic environment, insects must continuously excrete water to compensate for water uptake, whereas in a hot, dry terrestrial environment the insect must conserve water – in both these instances, the volume of the hemolymph is regulated to prevent excessive water gain or loss. In any given insect species, the volume of the hemolymph at any particular time during the life cycle will tend to be fairly constant. However, stressing the insect, for example by exposure to very high temperatures or by starvation, will result in changes in the hemolymph volume. The Internal fluid in the insect’s body is termed Hemolymph it contains both blood and other fluids. The hemolymph is used to transfer nutrients, ions, and waste to different organs in the body. It also is used to defend against microorganisms that might attack the insect’s body. The Hemocoel houses the hemolymph where all the organs are located. My hypothesis was that the hemolymph in the insect’s body was about 20-40% of the body mass. Materials and Methods: In order to find the cockroachs hemolymph volume, a small quantity of concentrated dye was injected which helped one to find how much the dye was diluted. A spectrophotometer was used to find the dye concentration needed in the cockroach. A spectrophotometer worked because dyes and other chemicals absorb light of characteristic wavelengths, and the amount of absorption depended on the concentration of the chemical. Knowing the original concentration and the final concentration it was to calculate what volume (the hemolymph volume) would have been necessary to dilute the dye that much. A range of volumes was chosen extending from below to above the probable values for hemolymph volume; you can produce a standard curve for optical density of solution on which you can read hemolymph volume directly. One advantage of this was that any errors in the procedure with the cockroach were likely to be similar to those for determining the standard curve, and they therefore canceled each other out. We started off by making serial solutions to make a standard curve for dye concentrations. We put 100, 200, 300 and 400 ul of a Ringer solution mixed with 10 ul of dye. We then put 5 ul of the first tubes into tubes that had 2500 ul of Ringer solution using a pippete. We then measured the optical density (Absorbance) of our serial dilutions with a spectrophotometer at 522 nm. Then we graphed the data, we made it linear by doing 1/OD to get an equation for the line. The next thing we did is we anesthetized our cockroaches with CO2 and we weighed our cockroaches. We then injected 10 ul of dye into the abdomen of the insect. We waited until the dye was mixed in the hemolymph evenly then we took samples at different points in time at 5, 15 and 20 min in time. We injected next to the armpit of the leg and used cold capillaries to obtain our samples. We then used the spectrophotometer to measure the OD of the samples mixed with 2500 ul of ringer solution at the different time periods. We then plotted the data and obtained the  equation. Then we plugged the reciprocal of y intercept to the equation and found the x value which equals the volume. This is a graph illustration of time(seconds) Versus optical density Discussion: After the lab was done, my original hypothesis was rejected. I predicted that the cockroach would have 20-40% hemolymph concentration. This turned out to be incorrect. Our cockroach had a percentage of approximately 15%. The result is not far from the 20% range I predicted nevertheless, not specifically accurate at all. According to my prior research, an average hemolypmh is around 25 percent and makes up about 20% of the body weigh of the cockroach. According to this research, my hypothesis was correct about the concentration of hemolyph (Czpla 171-181) There is always some variation within experiments so; something that was done during the experiment possibly could have gone wrong. The variation could have been due to the lack of following the specific time or variables. It was most likely due to a human error, which my group possible overlooked. There could have been mishandling of the specialized equipment such as the pipette or the spectrometer. It is really easy to mishandle the pipet and can result in the wrong amounts of water used for the experiment. This could affect the optical density and result in excess data. Some of the equipment was old and not always properly and fully functional. In a good preparation, the three data points for optical density (OD) will lie approximately on an exponentially declining curve (dye excretion rate may be a function of dye concentration). The extrapolation back to zero time should therefore follow this curve. Often, however, the first point will be noticeably high or low compared to the trend of the later points. This is probably due to poor mixing, either because of poor circulation, or poor injection where the dye sometimes appears to be trapped close to the point of injection. In this case, the best that can be done is to extrapolate from the later points, which, since there are only two points, will have to be a linear extrapolation. My results were in an exponentially declining curve so,I can not relate any error due to the mixing. A factor, which should be discussed because it could’ve provided some potential errors, is the removal of hemolymph from the cockroach during the 30-minute sampling period. This could have reduced the hemolymph volume. The error becomes progressively larger as the 5  µl samples are removed. If mixing is incomplete, the OD may apparently increase. Another possible source of error is the distribution of the dye, that is, how long does it take for the dye to be distributed uniformly throughout the hemolymph? This could have been a potential error, it is something I remember happening during the experiment though I did not realize the implications of it at the time. As time goes by, the Optical Density in the samples taken goes down in value. That shows that the dye within the body of the cockroach is getting transferred outside of the body of the insect. The Hemolymph concentration in this cockroach is . 2/1. 3= 15% that is not within the range of the concentration that should be which is within the range of 20-40%. There might have been an error in the spectrophotometer or maybe the dye didn’t spread well enough within the body, which would ruin our results. The sex of the cockroach might also play a role on the concentration of Hemolymph. For the future, if I were to carry out the same experiment I would stick to my prediction but would be more careful in carrying out the experiment. I would make sure I carried out the experiment exactly right.