Exploring Flowers under an Educational Microscope
Flowers are perhaps the easiest specimen that students or children can bring to their classroom at school for their microscope lessons. In this microscope activity, we will be using a low power stereo microscope and a high power compound microscope.
To refresh our memories, flowers play a vital role in our ecosystems as they perpetuate their species with the help of insects and other agents. Flowers consists of the brightly colored leaves called the petals. Underneath these petals are small greenish leaves that are the sepals. The petals and sepals are connected on the receptacle which is the tip of the whole floral system.
The petals are collectively known as the corolla. Inside the corolla are the slender cylinder-shaped stalks called the stamen, the filament and the anther which is the enlarged yellow body at the tip. Use a simple magnifying lens, also knows as a simple microscope, to observe the anther and you will see that it has longitudinal slits that opens to release yellow powder. This powder is the pollen and within its small yellow grains are the sperm cells.
The pollen grains are of different shapes and colors depending on the variety of the plant. An activity that teachers can suggest to their students for their microscope lesson relating to botony is to collect various flowers and compare the appearance of its pollen grains under a hand lens or a low power stereoscopic microscope.
If we take a look at the stamens, we will see a rounded base that tapers upward to a cylinder-like stalk ending into a rough area. This is the pistil and the rounded base is the ovary while the stalk is called the style and the rough end is the stigma.
We can examine the ovary by taking one from a withered flower. In this case, the ovary is already well-developed and is good for examining under a scientific microscope. If we open the ovary and take a look at it under a stereo binocular microscope, we will see some small bodies that are round and whitish in color. These are the egg cells which will later develop into seeds.
Let us take an ovule, cut a cross section of it and put it under a high power compound light microscope.
First, let us review the different types of microscopes. The high power compound type of microscope varies from the low power stereoscope. The compound microscope has four or so objectives on a turret that can be rotated. The depth of field is quite small, so not much can be in focus at the same time. The specimens are normally placed on blank microscope slides and topped off with a cover slip. The low power type of microscope known as the stereoscope can see much more all in focus and is simplier for the student or beginning microscopist to use.
Now, back to our experiment. You will see that it has a large egg sac in the innermost part and in it many small cells lie. The largest of these cells is the egg cell that grows into an embryo plant when fertilized. The mass of tissue that surrounds the sac is the nucellus. After being acquainted with the structure of the flower, we will then try to find out how these colourful things operate. Fertilization of the egg cell happens when the pollen is transferred to the pistil of another flower. The pollinating insects that slit from one flower to another and a strong wind are responsible for the transfer.
We will then observe the reproduction process of the flower under the high power compound light microscope. This process starts when the pollen grains fall on the stigma’s surface. The grains start to germinate and send a tube that is slender and thin-walled into the pistil. Near the tip of this tube are the microscopic sperm cells which grow into the style’s tissues. This process can be observed by cutting a very thin section of a newly pollinated pistil and examine it under a high power microscope. You will see that the pollen tubes are descending down the style to the ovary. This process can take place in a matter of a few hours to as long as three days. Some of the flowers also have hollow pistils that allow free passage of the pollen. There are other pistils that have solid tubes that the pollens need to eat their way to the ovary.
When the pollen reaches the ovary, it enters the embryo sac where the egg cell is contained. The pollen discharges the sperm cells and these in turn enter the egg cell. After the fertilization, the cell divides exponentially until it develops into an embryo. While the ovary grows into a fruit, the ovule then develops into a seed. The fruit is the final product of this fertilization process. Once the flower reaches this stage, its function is already accomplished so afterwards it withers.
Examining the flower under the microscope will help us learn more about the wonders of nature. It will also be an easy microscope activity especially to students or children. One thought is for the teacher or parent to take the students on a field nature trip. This hiking trip will be greatly enhanced if the student carries their portable field nature microscope in their backpack. They can easily take it out and begin examining the parts of the flower under this field microscope during their nature hike.