The use of a microscope is to provide a magnified view of objects that are being analyzed, which are otherwise too small to be seen by the naked eye. They can be described according to their illumination and lens arrangement. Microscopes are able to use either light or electrons as their illumination source, which are respectively known as light-powered and electron microscopes. Monocular microscopes have a single eyepiece, whereas binocular microscopes possess two eyepieces positioned side by side for simultaneous viewing with both eyes. A simple microscope consists of one single lens system, whereas a compound microscope consists of two main lens systems – an ocular and objective – which are superimposed over each other to provide greater magnification.
In Biology, microscopes can also be described according to some specific purposes such as dissecting microscopes, which are commonly referred to as dissectors and are especially suitable for use while dissecting very small or delicate specimens. Microscopes are usually equipped with a series of interchangeable eyepiece lenses (oculars), each with different individual magnifications. The majority of ocular magnifications are as follows: X4, X5, X6, X7, X8, X10, X12, and X15. On a typical monocular microscope, objective magnifications are as follows: X4 = SCANNING POWER = S.P., X10 = LOW POWER = L.P., and X40 = HIGH POWER = H.P.
To find the overall magnification factor obtained when using any microscope, it is calculated by the following mathematical formula: OCULAR magnification X OBJECTIVE magnification = OVERALL magnification. The condenser lens is situated below the stage and causes light rays to converge onto the specimen situated on the stage, thus illuminating it adequately when magnified by the viewing lens. The amount of light passing through the condenser lens can be varied by opening and closing the iris diaphragm, situated at the bottom of the condenser.
AIM: (i) To become familiar with the features and function of the monocular and stereo microscopes. (ii) To gain firsthand experience in sketching scientific diagrams from prepared slides. EQUIPMENT USED: Monocular microscopes, microscope lamp, lens cleaning tissue, lens-cleaning fluid, and various prepared slides. PROCEDURE: When using a monocular microscope, adjust the condenser lens so that it comes to rest against the bottom of the stage.
Wind it down about 2mm below this level; now it’s in the ideal position. The iris diaphragm should also be readjusted each time a slide is moved from S.P. to L.P. or H.P.
Obtain the first of the prepared slides and examine it under the scanning power. ALWAYS begin with the S.P., then the L.P., and finally the H.P.! NEVER the other way around! Adjust the course-focusing mechanism followed by the fine focus knob; this will ensure maximum clarity. Having adjusted the course focus while operating the scanning power setting, there is no need to use it again with either the L.P. or H.P. magnifications. Use only the FINE FOCUS with these magnifications.
When operating either focusing mechanism, ALWAYS adjust the two wheels TOWARDS yourself, NEVER away from you! This will ensure that the objective moves AWAY from the slide, NOT towards it. Therefore, the objective CANNOT be rammed through the specimen slide!
In scientific sketching, try to keep BOTH eyes open, using one to peer down the microscope, and using the other eye to draw with. In addition, the sketches should ALWAYS include a Title, Magnification factor, Labels (if possible), and be approximately -1 full page in size.
Discussion/Conclusion:
Microscopes have many components, but one component was used at all times and most likely without even noticing you used it. That component sits at the top of the microscope, which you look through and is called the ocular. The ocular is interchangeable with different individual magnifications, including X10, which was used in examining all prepared slides.
Therefore, even if the objective magnification was X4 (S.P.), X10 (L.P.), or X40 (H.P.), the ocular did not change; it was still the same magnification of X10. By using the mathematical formula of Ocular times Objective will equal the overall magnification you were using while examining a slide. These magnifications were: OCULAR X OBJECTIVE = OVERALL MAGNIFICATION FACTOR. X10 X X4 = 40 times = S.P. X10 X X10 = 100 times = L.P. X10 X X40 = 400 times = H.P.
The specimens that are on slides come in many colors and shapes; it depends on what specimen and which stain is used. In this experiment, the prepared slide specimens that were examined were an Ovary and Testes Colon Appendix that were pink, Striated Muscle was a purple-red color, and Grass Root Tip came in three colors: red, light blue, and cream.
Each slide was examined with Scanning power, Low power, and High power. There are tremendous differences between the slides because out of the five slides selected, four are from different parts of an animal, and one is a plant slide. The main difference is between the magnification factors; scanning power (S.P.) is the only one that enables you to view all or most of the specimen section.
Viewing in S.P., the specimen section structure is very cramped with everything very close together (refer to sketches). When changing to low power (L.P.), the specimen section structure is larger, and the section is a lot freer, enabling the viewer to view between the section’s components (refer to sketches).
High power (H.P.) is where the specimen section structures are huge and more unattached compared to those of S.P. and L.P. Therefore, in H.P., the structure can look totally different from S.P. and L.P., and the specimen section seems almost like a completely different slide altogether. By examining the specimen’s sides and the sketches, this was drawn while the slide’s specimen was under the microscope. Through these sketches and titles, enough information was given to seek out and research the suitable reference to complete this report.
OVARY Cortex
The cortex of the ovary is covered by a modified mesothelium, the germinal epithelium. Deep to this simple cuboidal to simple squamous epithelium is the tunica albuginea, the fibrous connective tissue capsule of the ovary. The remainder of the ovarian connective tissue is more cellular and is referred to as the stroma. The cortex houses the ovarian follicles in various stages of development.
Primordial Follicles
Primordial follicles consist of a primary oocyte surrounded by a single layer of flattened follicular (granulosa) cells.
Primary Follicular (A)
Unilaminar Primary Follicles consist of a primary oocyte surrounded by a single layer of cuboidal follicular cells.
Primary Follicular (B)
Multilaminar Primary Follicles consist of a primary oocyte surrounded by several layers of follicular cells. The zona pellucida is visible. The theca interna is beginning to organize.
Secondary (Vesicular) Follicle
The secondary follicle is distinguished from the primary multilaminar follicles by its larger size, by a well-established theca interna and theca externa, especially by the presence of follicular fluid in small cavities formed from intercellular space of the follicular cells. These fluid-filled cavities are known as Call Exner bodies.
Graafian (Mature) Follicles
The Graafian follicle is very large, the Call Exner bodies have coalesced into a single space, and the antrum is filled with follicular fluid. The wall of the antrum is referred to as the membrane granulosa, and the region of the oocyte and the follicular cells jutting into the antrum is the cumulus oophorus. The single layer of follicular cells immediately surrounding the oocyte is the corona radiata. Long apical processes of these cells extend into the zona pellucida. The theca interna and theca externa are well-developed; the former displays numerous cells and capillaries, whereas the latter is less cellular and more fibrous.
Atretic Follicles (A)
Atretic follicles are in the state of degeneration. They are characterized in later stages by the presence of fibroblasts in the follicle and a degenerated oocyte.
Medulla (B): The medulla of the ovary is composed of a relatively loose fibroblastic connective tissue that houses an extensive vascular supply, including spiral arteries and convoluted veins. Corpus Luteum (C): Subsequent to the extrusion of the secondary oocyte with its attendant follicular cells, the remnant of the Graafian follicle becomes partly filled with blood and is known as the corpus hemorrhagicum. Cells of the membrane granulosa are transformed into large granulosa lutein cells. Moreover, the cells of the theca interna also increase in size to become theca lutein cells, although they remain smaller than the granulosa lutein cells.
Corpus Albicans (D): The corpus albicans is a corpus luteum that is in the process of involution and hyalinization. It becomes fibrotic, with few fibroblasts among the intercellular materials. Eventually, the corpus albicans will become scar tissue on the ovarian surface.
TESTES Capsule: The fibromuscular connective tissue capsule of the testes is known as the tunica albuginea, whose inner vascular layer is the tunica vasculosa. The capsule is thickened at the mediastinum testis, from which septa emanate subdividing the testis into approximately 250 incomplete lobuli testis, each containing one to four seminiferous tubules embedded in a connective tissue stroma.
Seminiferous Tubules: Each highly convoluted seminiferous tubule is composed of a fibromuscular tunica propria, which is separated from the seminiferous epithelium by a basal membrane.
Seminiferous Epithelium: The seminiferous epithelium is composed of sustentacular Sertoli cells and a stratified layer of developing male gametes. Sertoli cells establish a blood-testis barrier by forming occluding junctions with each other, thus subdividing the seminiferous tubule into adluminal and basal compartments. The basal compartments house spermatogonia A (both light and dark), spermatogonia B, and the basal aspects of Sertoli cells. The adluminal compartment contains the apical portions of Sertoli cells, primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa.
Tunica Propria: The tunica propria consists of loose collagenous connective tissue, fibroblasts, and myoid cells.
Stroma: The loose, vascular, connective tissue stroma surrounding the seminiferous tubules houses small clusters of large, vacuolated-appearing endocrine cells in the interstitial cells (of Leydig).
COLON, APPENDIX: Mucosa: The mucosa presents no specialized folds. It is thicker than that of the small intestine.
Epithelium (A): The simple columnar epithelium has goblet cells and columnar cells.
Lamina Propria (B): The crypts of Lieberkühn of the lamina propria are longer than those of the small intestine. They are composed of numerous goblet cells, a few APUD cells, and stem cells.
Lymphatic nodules are frequently present. Muscularis Mucosae (C): The muscularis mucosae consists of inner circular and outer longitudinal smooth muscle layers. Submucosa: The submucosa resembles that of the jejunum or ileum. Muscularis Externa: The muscularis externa is composed of inner circular and outer longitudinal smooth muscle layers. The outer longitudinal muscle is modified into teniae coli, three flat ribbons of longitudinally arranged smooth muscle.
These are responsible for the formation of haustra coli (sacculation). Auerbach’s plexus occupies its position between the two layers. Serosa (A): The colon possesses both serosa and adventitia. The serosa presents small, fat-filled pouches, the appendices epiploicae.
Appendix (B): The lumen of the appendix is usually stellate-shaped, and it may be obliterated. The simple columnar epithelium covers a lamina propria rich in lymphatic nodules and some crypts of Lieberkühn. The muscularis mucosae, submucosa, and muscularis externa conform to the general plan of the digestive tract. It is covered by serosa.
Anal Canal (C): The anal canal presents longitudinal folds, anal columns, that become jointed at the orifice of the anus to form anal valves and intervening anal sinuses. The epithelium changes from the simple columnar of the rectum to simple cuboidal at the anal valves to epidermis at the orifice of the anus. Circumanal glands, hair follicles, and sebaceous glands are present here. The submucosa is rich in vascular supply, while the muscularis externa forms the internal anal sphincter muscle. An adventitia connects the anus to the surrounding structures.
STRIATED MUSCLES
Longitudinal Section (A): Connective tissue elements are clearly identifiable because of the presence of the nuclei that are considerably smaller than those of cardiac muscle cells. The connective tissue is rich in vascular components, especially capillaries. The endomysium is present but indistinct.
Longitudinal Section (B): Cardiac muscle cells form long, branching, and anastomosing muscle fibers. Bluntly oval nuclei are large, centrally located within the cell, and appearing somewhat vesicular. A and I bands are present but are not as clearly defined as in skeletal muscle. Intercalated discs, marking the boundaries of contiguous cardiac muscle cells, may be indistinct unless special staining techniques are used. Purkinje fibers are occasionally evident.
ROOT TIP: As root tissues differentiate behind the growing tip, they form a pattern of cylinders (tubes) within the cylinders. Each cylinder is composed of tissue that has a specific role to play for the plant.
Epidermis: The outermost cylinder is only cell in thickness and is called the epidermis. This encloses and protects the underlying tissues. Some epidermis cells differentiate into hair cells. These stick out into surrounding soil spaces and absorb water and selected mineral ions.
Cortex Parenchyma: A very thick cylinder is found just under the epidermis. This is called the cortex or cortex parenchyma. Parenchyma cells store excess nutrients, usually in the form of starch.
These cells are loosely packed so that the spaces between them can direct water and mineral ions coming from root hairs and cortex spaces and direct them into the central vascular core. Another thin cylinder, the pericycle, is found under the endodermis. Pericycle cells can function like meristem and mitotically produce secondary or branch roots. The pericycle also constitutes the outer boundary of the vascular core, a structure that contains the internal, liquid transport highways of the plant in the form of highly specialized tube-like or conducting tissues.
The vascular cylinder is comprised of tissues that transport nutrients. Water and mineral ions taken in by root hairs and concentrated into the core by the endodermis are transported up into the plant shoot by xylem tubes. Sugar-rich fluid, sucrose, made in the leaves as glucose is transported by phloem sieve tubes into the root core, where it is distributed to root cells for energy production or storage as starch in the cortex parenchyma.
Xylem and phloem tissues are excellent examples of how cell structure dictates function. Xylem cells (A) have to die before they can serve the transport needs of the plant. Dead xylem cells leave behind a thick, hollow, tubular wall, which joins end to end with other xylem walls to form a microscopic but strong and fixable tube, which extends from root to leaf. Xylem walls have slit-like openings or pits, which provide for the sideways transfer of water and mineral ions into surrounding tissue. Close examination of these walls shows that their thickness is due to cellulose and a cement-like substance called lignin. Lignin creates the wood in woody plants. Some walls are reinforced with internal rings or spirals. These rings of lignin help to support the plant. Xylem tubes are sometimes called vessels, i.e., composed of vessel cells or elements. Primitive plants such as pines and firs have tracheid xylem with thinner walls and tapered ends.
Phloem (B) is made up of two basic cell types, both of which are living when they serve the transport needs of the plant. The larger cell type is a sieve tube member; the small is a companion cell. The sieve tube member, though living, does not have a nucleus and therefore does not control its own metabolism. What needs it has are apparently provided for by the tiny companion cell that is attached to the sieve tube member. Sieve tube members are much smaller and have thinner walls than xylem, but like xylem, they join end to end to form sieve tubes that extend leaves to roots. These take their name from the tiny, sieve-like pores in their walls and the larger pores called sieve plates that separate one member from another. Pores provide for the horizontal and vertical movement of the sugar-rich sap that slowly moves down from the leaves, supplying energy and elements to all plant tissues. Large parenchymal cells called pith may also be associated with the vascular cylinder phloem.
