Last Thursday on February 16th, we observed cells undergoing mitosis on onion root tips. This was accomplished by a lengthy process that basically consisted of our instructor giving us "fixed" root tips, which is where cells are actively dividing. They are fixed because mitosis was suspended in the root apical meristem, or the root tip. We took these fixed root tips and put them in a dish labelled "Carnoy Fixative I" for 4 minutes. After 4 minutes, we transferred the root into a dish labelled "Carnoy Fixative II" for an additional 4 minutes. We then cut off about 1 to 2 mm of the root tip and put it on a slide. Once on the slide, we followed typical slide procedure and stained it with TBO. However, when we put the cover slip on the slide, we made sure to press straight down without twisting the cover slip. We then observed the slide under a compound microscope using oil immersion. This is what we saw: -Adalberto Marquez
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Submitted by Tyler Yates In lab we examined various roots from two different dicot plant specimens. Pisum Sitivum (pea), and Vicia faba(bean). Cross sections were prepared and examined under a compound microscope. The picture below on the right is a cross section of Pisum Sativum and an annotated image to the left identifies the structural internal components. Notice the external root hairs stained dark blue surrounding the epidermis. internal to the epidermis is the cortex made up of the larger clear parenchyma cells of the ground tissue. The group of cells in the middle is the stele, or procambium. The procambium includes the vascular tissues as well as the pericycle; surrounded by the endodermis. The pericycle, in dicot roots, gives rise to lateral roots, cork cambium, and portions of vascular cambium. Notice that the pith is absent in dicot roots . In lab on Thursday February 16th we explored root structures of monocot and dicot roots. Our class examined a Corn plant to identify parts of the root. Monocot roots have adventitious roots where lateral roots give rise to fibrous roots. These type of roots do not have a primary root, but instead have many that branch out from the stem. Although the structure of the monocot and dicots are different, they still encompass the same internal anatomy. The image below on the left shows a picture of a Corn plant root through a microscope. The cross-section was stained with TBO and the microscope magnification is at 40x. The image on the right is a drawing of a monocot root with its labeled parts. The third image is another example of a monocot root structure. The epidermis layer of cells is found the outermost edge of the root and is the same for both monocot and dicot roots. In from the epidermis is the exodermis layer of cells (not labeled in on the image). Next is the cortex, which is made up of all the cells between the exodermis and the endodermis. The endodermis is the first, outermost layer of dark cells. The next layer of dark cells in known as the pericycle. The the larger bubble looking circles are the xylem cells. Surrounding the xylem cells are the phloem cells. The pith is the innermost cells from the xylem cells. Lastly, the stele is the area inside the endodermis cells.
By Keira Mitchell By: Chelsea Maddox Just this last week in lab on Thursday, February 16th we took a look at structure of roots and their external features. From what we have learned so far about roots is that they have many functions. One: they anchor the plant to a substrate. Two: absorb water and minerals. Three: they conduct water, mineral, and carbohydrates. Four: roots store the carbohydrates while playing an additional role in asexual reproduction. The external features and structure of roots is very important because they are associated with how they carry out the above functions. Plants have two types of branched root systems. One being a fibrous root system and another being taproot system. Angiosperms have been classified into two major groups known as monocots and dicots. The monocots is associated with a fibrous root system because they are commonly short-lived so they are composed of adventitious, branched roots. So you've probably guessed by now, dicots are associated with the taproot system because the plants strive to live longer. The taproot system has a primary root that develops as a taproot which then gives rise to secondary, adventitious, branched roots. The images I am going to show below are of corn (Zea mays), a monocot with a fibrous, adventitious root system.
Unlike corn (Zea mays), a broad bean plant (Vicia faba) is a dicot with a taproot root system. Even though the root system isn't fibrous, it is still considered to have adventitious, branched roots. Below are some images I took in lab on Thursday, February 16th of the mature broad bean plant. Unfortunately, I am unable to label the close up view of the dicot broad bean with the taproot system because it just looked like mess because the picture I have of the root are bunched together too tight. However, to the left, I have uploaded an image of the broad bean root system labeled for a better understanding of the difference between monocot and dicot root. Numbers 4 and 5 I feel do a great job pointing out which part is what in these figures. One thing I found interesting in class and I was highly encouraged to present within this blog is the unique nitrogen-fixing organs that result from a symbiotic interaction between the plant and nitrogen fixating bacteria known as root nodules. Most legumes result in infection by bacteria of the host-plant root. More information of how the process of infection begins you can gather from recommended reading (Ch. 29, pgs. 693-700 in Raven's Biology of Plants). Assuming the recommended reading was done before lecture on February 9th, you may remember reading about the two different types of root nodules. They can be distinguished by either indeterminate or determinate. Indeterminate root nodules are elongated and cylindrical due to the presence of the meristem. However, the determinate root nodule is presented in spherical form due to the lack of the persistent meristem. The image I will be showing you below is of indeterminate root nodules on the roots of a mature broad bean plant. These nodules on the mature broad bean are common of the legume (Fabaceae) family. "Legumes secrete compounds called flavonoids from their roots, which in turn trigger the secretion of nod factors in the rhizobia. Coming full circle, the nod factors spark a reaction in the legumes, causing the roots to swell and form the nodules you see here. It is within these nodules that rhizobia live in harmony with their host plant."
Read more at http://www.gardenbetty.com/2012/11/a-look-at-legumes-rhizobia-and-root-nodules/#ZV650Ij8EhVTtrGs.99 The coolest part about lab on Thursday was getting to cut open the root nodule on the broad bean plants while examining it under the dissecting microscope. When cut open, the nodule represented a pinkish/red color (pictured below). The nodule having the color inside represents the presence of leghaemoglobin which means the nodule is active and is fixing a lot of nitrogen for the plant. FUN FACT: the redder the nodule, the more ACTIVE it is! |
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