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Learning Evolution under the Microscope

We will be observing a variety of insects for this science microscope activity. This is because we will be touching on the subject of evolution and how this process of change can be witnessed with these certain insects. For this science experiment, the students or children will be using a low power stereo dissecting microscope.

Evolution is the change that happens in an organism’s inherited traits from one generation to another. One of the main causes of this change of traits is what we call the process of natural selection. The inherited traits from the older generation change in order to be more helpful for the survival or reproduction of the organism. The organisms with these advantageous traits are then more likely to pass on these traits to their offspring and so on. Therefore, the harmful or useless traits disappear little by little in the later generations. Natural selection happens mostly due to the environment and the factors that the organism belongs in and has to adapt with.

We can see this natural selection by observing various insects under the low power stereo microscope. The first insect that we need to obtain is a water beetle called a Hydrophilus. It can be found in fresh water bodies like ponds. If we take one of these and examine its shape under the stereoscope, you will notice that it looks like a boat with its legs as its oars. Evolution is at work here when you see the smooth and elliptical features of the beetle that allows it to move freely in an aquatic environment with less resistance.

Let us look at one of the legs of this beetle under the stereo dissecting microscope. You will see that the legs are covered with microscopic hairs that aid in propelling the beetle when moving through the water. When stroking through the surface of the water, these hairs cut the water and push the insect forward. On the other hand, when the legs draw forward from the stroke, the hairs fall back with the water.

Through the beetle that we observed under the low power stereo microscope, we learn that the insects’ legs become modified over time in order to adapt to its environment and serve more purposes. Another example of this is the house fly’s leg. You will wonder how a fly manages to walk on the ceiling upside-down without falling. We will learn the answer to this by obtaining a fly and observe its legs under our dissecting microscope. If you look at the end part of the leg, you will see a pair of claws with a pad in between. Let us focus our microscope on this pad and you will see that it has microscopic pores. Through these microscopic pores, a sticky and transparent fluid passes through. This sticky fluid is emitted by glandular hairs that are contained inside the pads. It allows the fly to walk on smooth surfaces and even upside down.

Aside from the legs, the insects’ antennae have also undergone change to be able to adapt to the challenges of its surrounding environment. For this part we will look at the antennae of the mosquito that are highly developed organs of hearing (especially that of a male’s). If you compare a male mosquito’s antennae with that of a female’s under a stereo binocular microscope, you will see that the male’s antennae has more segments and is hairier. This is because the male mosquito’s antenna has more developed olfactory nerves because they use the antenna’s sense of smell to seek out the opposite sex.

Finally, we will observe an insect’s mouth parts under the stereo microscope. This is perhaps the most developed organ of the insect, the mandible being the most primitive one and from which other types have developed. The grasshopper is perhaps the best specimen to be examined under the stereo dissecting microscope for this observation.

If we look at a grasshopper’s head under the low power stereoscopic microscope, we will see that there seems to be an upper lip at the lower end of the head. This is the labrum which is quite stiff if you try to poke it with a needle. The labrum is the front covering of the mandible and it also functions to pull the food back to these organs. Let us then look at the mandible under the stereoscope. You will see that they are broad, solid, short and an edge that is suitable for biting. These jaws move sideways as opposed to our up and down movement. Also, the maxillae can be found behind these mandibles.

Looking at the parts of the grasshopper’s mouth under the low power stereo dissecting microscope, you will see that the maxilla is divided into three lobes. The inner lobe has microscopic spines, the middle lobe has spatula-shaped ends and the outer lobe has a five-jointed feeler that is called as the maxillary palpus. These maxillae function as food holders and arrangers to be grinded by the jaws. The floor of the mouth called labrum carries the food to the maxilla and mandible. Within the labrum, you will see a fleshy organ with the use of the low power binocular microscope. This is the tongue or the hypopharynx.

Now that we are aware of what the most common mouth part of the insect looks like with the help of a grasshopper under the low power stereo dissecting microscope, we will next look at how these mouth parts evolve to fit other insects’ needs. For example, butterflies and mosquitoes do not need biting parts because they suck their food. The maxilla and mandible, therefore, have developed over time to suit their needs.

In order to see this development, let us capture a butterfly and examine its mouth parts under the stereo binocular microscope. You will see that its maxilla and mandible are elongated. The maxillae have grooved inner sides and form a straw-like appearance.

To further see the development of the mandible, we will also obtain a female mosquito and examine its mouth parts under a low power stereo binocular microscope. You will see that its maxilla and mandible have turned into piercing organs that are delicate and linear. The labrum or the lower lip has turned into a sucking tube. The hypopharynx has also developed into a linear tube that conducts saliva while the labrum encloses on the other mouth parts that are not in use.

Finally, we will look at the honey bee and examine the development of its mandibles under the binocular dissecting microscope. You will find that the honey bee’s mandibles have developed into instruments for cutting while the rest of the mouth parts have formed into a sucking apparatus. Other than for cutting, the honey bee’s mandibles are also used for shaping the wax that is used for building their homes.

By experimenting on these various insects under the low power stereo binocular microscope, we get to have first-hand knowledge about evolution. Organisms change over time to adapt to its environment by improving some of its parts and removing what is not needed. College biology students, especially those specializing in entomology, can perform this experiment as an introductory course on the whole subject of evolution. High school students can perform this science activity as well with the use of their low power stereo dissecting microscopes.

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