Experiment 3: Cell Structure I OBJECTIVES:
i.
To learn how to prepare specimens for staining an d view under the light microscope.
ii.
To identify the unique and standard structures of plant, animal, yeast and unicellular organisms under the light microscope.
iii.
To identify and use different stains for the different types of organelles.
RESULT:
DISCUSSION: I. EPIDERMAL CELLS OF PLANTS
The function of epidermal cells in plants is to prevent water loss and as a barrier to fungi and other invaders from the outside environment. That is why epidermal cells are closely packed and it contains little intercellular space. In order to prevent water loss, many plants have a waxy cuticle layer deposited on top of the epidermal cells. Stomata (a series of openings) facilitate gas exchange between the inner parts of leaves, stems, and fruits. Stomata allows gas exchange, but it also contributes to water loss. Guard cells are bean-shaped cells covering the stomata opening. They regulate exchange of water vapor, oxygen and carbon dioxide through the stoma. In this experiment, the epidermis from the upper surface of the Rheo discolour leaf is removed and observed under the light microscope. From the microscopic slide, the cytoplasm, nucleus and epidermal cell which is the cell wall can be observed. Eosin was used to stain the epidermal cells. Eosinophilic, is a term that is used to describe the structures that stain readily with eosin. Eosin is used to facilitate the better viewing of the plant tissue under light microscope. The nucleus and cytoplasm is stained red because both of them are eosinophilic. The intensity of red colour in cytoplasm is less as compared to the nucleus. This is because density of the nucleus is much higher than cytoplasm. The epidermis on the lower side of the Rheo discoloured leaf was also removed and observed under the microscope. Abundance of stomata are found in the bottom epidermis compared to the top epidermis. The presence of stomata allows better gaseous exchange of oxygen and carbon dioxide. Spongy mesophyll cells are arranged loosely to create large air space to allow the air pass through. Stomata act as the gateway that allows the air to flow in and out of the cells. Plastids associate the chloroplast to carry out the photosynthesis in the plants. The amount (concentration) of the plastids corresponds to the orientation of the leaf surface to the sunlight. Photosynthesis mainly occurs on the surface of the leave as it is the side
which receives the highest intensity of the sunlight. In contrast, on the lower side of the leave, which photosynthesis does not take place. However, we are unable to view plastids in the epidermal cell in our microscopic slides. II. CELL WALL AND MIDDLE LAMELLA
The leaves of pine trees are called needles. Though their shape is different from the leaves of most angiosperms, they contain more or less the same tissue types. Pines often live in harsh conditions: hot, dry summers and freezing winters. They are good at withstanding environmental stress. The needles have a low surface area-to-volume ratio which helps to reduce damage to the plant. Same as other plant cells structure; it has vascular bundle, transfusion tissue, and resin ducts. Stomata are unique in pine needle that helps pine trees thrive in dry environments.
The pine needle microscopic slide were unable to be prepared as the tissue is too thick to be cut. Therefore, an apoplast reference diagram is obtained from an online source as reference to view the cell wall and middle lamella.
III. YEAST CELLS (SACCHAROMYCES)
Saccharomyces which grows naturally on the surface of fruits is a genus in the kingdom of fungi that includes many species of yeast. Their characteristics include inability to use nitrate and the ability to ferment various carbohydrates. Yeast is a unicellular, flat, smooth, moist, glistening and tannish cream saprophytic fungus. After being stained by iodine solution and observed under high power of magnification, yeast cells appeared to be in yellowish-brown colour bounded by 2 layers of membrane which are cell wall and plasma membrane. On the other hand, lactophenol stains the yeast cells blue-ish. The presence of chitin in the cell wall of yeast cells will stain the cell wall blue. Yeast cells reproduce by budding. It is a form of asexual reproduction. Yeast cell resembles a plant cell in the sense that they have cell wall. It also resembles animal cell
because it has centrioles. Yeast cell is neither animal nor plant cell because yeast cell have both characteristics of a plant and animal cell. IV. BLOOD CELLS
Blood is a type of connectivity tissue and divided into a few components which are plasma (55% of blood) and formed elements also known as the hematocrit. The hematocrit is made up of red blood cells (Erythrocytes), white blood cells (Leukocytes) and platelets (Thrombocytes). Our body consist a great number of red blood cells (Erythrocytes). Blood cell can be produced by haematopoiesis and normally found in blood. Blood has a lifetime of about 120 days. White blood cells are cells of the immune system involved in defending the body against foreign materials and infectious disease. A mammal red blood cell does not contain any nucleus. Therefore it is biconcave when viewed under microscope. Red blood cells mainly carry oxygen throughout the body tissue and recovering carbon dioxide to produce as waste. The white blood cells (leukocytes) in a lesser number compared to red blood cell in our body. They are the cells of the immune system which are responsible in defending the body against various diseases and foreign materials from the environment. White blood cells are divided into 2 groups which are granulocytes and agranulocytes. There are 3 types of granulocytes which are neutrophils, eosinophils and basophil. Neutrophils are the most common type of white blood cells found in the blood. They are very active and responsible in engulfing bacteria, virus particle, fungi or protozoa. Eosinophils comprise of only about 3 % of the leukocytes. They are responsible in controlling allergic reaction and also defending the body against parasites. Basophil comprises of only less than 1% of the leukocytes. They are also smaller in shape compared to the granulocytes. They produce granules containing histamine and heparin to promote inflammation and blood flow to damaged tissues. Agranulocytes consist of lymphocytes and monocytes. Lymphocytes have large nucleus. They are about 25% to 35% in the white blood cell population. Lymphocytes consist of T cells and B cells. T cells attack tumor cells while the B cells produces antibody to attack foreign cells and protein. Monocytes comprises
about 2-8% of the white blood cells and they are larger than red blood cells. They are responsible in engulfing bacteria. Platelets (thrombocytes) are responsible for blood clotting to prevent excessive blood loss from the body. Platelets are irregular in shape. Besides that, they do not have nucleus. Platelets are fragmented cells from megakaryocytes. Platelets have a lifespan of 5 - 9 days. V. SPIROGYRA
Spirogyra is named for the helical or spiral arrangement of the chloroplasts that is diagnostic of the genus. It is a genus of filamentous green algae of the order Zygnematales. Spirogyra is commonly found in freshwater areas. There are more than 400 species of spirogyra in the world. Spirogyra is unbranched with cells connected end to end in long male reproductive system filaments. The cell wall has two layers. The outer wall is composed of pectin that dissolves in water to make the filament slimy to touch while the inner wall is made up of cellulose. The cytoplasm forms a thin lining between the cell wall and the large vacuole it surrounds. Chloroplasts are embedded in the peripheral cytoplasm. The chloroplasts are ribbon shaped, serrated or scalloped, and spirally arranged, resulting in the prominent and characteristic green spiral on each filament. Each of the chloroplast contains several pyrenoids. Pyrenoids are the centers for the production of starch. It appears as small round bodies under the microscope. From the microscopic slides, cell wall, chloroplast, mucilage, cytoplasm, cell membrane and the pyrenoids can be identified. The spirogyra was viewed under 1000x magnification. Under this magnification, all of the organelles can be seen easily. The nucleus of spirogyra contain DNA that store genetic information. The cell wall of the spirogyra protect the underneath plasma membrane, maintain the cell shape, and withstand the high pressure formed. Pyrenoids were the centers of carbon dioxide fixation within the chloroplasts. Pyrenoids are not membrane-bound, but specialized areas
of
the
plastid
that
contain
high
levels
of
ribulose-1,5-bisphosphate
carboxylase/oxygenase. Mucilage is a thick, gluey substance produced by nearly all
plants and some microorganisms. In spirogyra, mucilage plays a role in the storage of water and food, seed germination, and thickening membrane. The cell walls of the spirogyra contain mucilage. The whole filament is covered by a thin, sticky layer of mucilage that act as glue. It glues the filaments together forming a huge spirogyra mass. Moreover, the mucilage acts as protective layer for spirogyra from desiccation during low tides when the water suppl y is low. VI. FLAGELLUM
Euglena is a unicellular organism under the kingdom prototista. It is commonly found in fresh water. Euglena is one of a unicellular cell that is autotropic and phototropic. It can feed on other smaller organisms via phagocyctosis or even make its own food. Euglena has its own chloroplast, it can carry out photosynthesis depending on the conditions of the environment.
Euglena has a long whippy tail called flagellum.
Flagellum is an organelle with one end projecting out of the cell while another end connected to the cell. Flagellum is made up of microtubule. Flagella help in cell locomotion. Euglena moves around by sweeping the flagellum side by side. When viewed under the microscope, the flagellum of the euglena could not be seen. Magnification of 1000X was used to observe the cell. However, the flagellum of the euglena cell could not be seen. CONCLUSION:
The basic structure a cell contains plasma membrane, cytoplasm and nucleus. Plant cells have chloroplast and some unicellular organisms like euglena has flagella. Rheo discoloured leaf has many stomata at the bottom of the leaves. Red blood cells are unique cells without a nucleus. They are biconcave in shape. Various stains are used to stain cells to view specific organelles under the light microscope. Eosin is used to stain the cytoplasm, collagen and muscle fibers. Iodine is used to stain starch. Chloroplast is pigmented naturally.
References: 1. Biology online [Online]. Available at: http://www.biology-online.org/dictionary/Fimbria [Accessed: 5 February 2013] 2. Wikipedia [Online]. Available at: http://en.wikipedia.org/wiki/Saccharomyces [Accessed: 5 February 2013] 3. http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookplantanat.html 4. http://www.nature.com/scitable/topicpage/the-origin-of-plastids-14125758 5. http://www.k-state.edu/wgrc/Protocols/Cytogenetics/acetocarmine.html 6. http://en.wikipedia.org/wiki/Spirogyra - Wikipedia, the free encyclopedia
