EXERCISE # 1 PLANT CYTOLOGY INTRODUCTION:
Plant cells, like animal cells are complex structures with membrane-bound organelles and a true nucleus. These organelles serve as the control center, powerhouse of the cell, packaging and transport system, communication system and waste-removal system. This exercise tackles the basic structures of the plant cell that will be very significant for the understanding of the plant function. OBJECTIVES:
At the end end of this this activity, activity, the students should be be able to: to: a. relate the different organelles of the cell with its functions b. understand the effect of different stains on the cell structure c. differentiate various types of plastids MATERIALS
Apparatus!lasswares Apparatus!lasswares "icroscope eakers with dropper lides and cover slips calpel!blade • • • •
#eagents!chemicals $istilled water %& ethanol ' ( )*l aturated solution of (a*l +odine • • • •
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METHODOLOGY
pecimen!amples Twig "oss Rhoeo discolor Tomato!red Tomato!red pepper potato • •
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*ell wall . "ake free-hand sections of a twig using sharp ra/or blade. 0. 1bserve in wet mount with water first and then mount in one drop of %& 23t1)4 plus one drop of '( )*l. 5. #epeat with bean stem to decide which kinds of tissues and cells have walls containing lignin in plants. 6. +llustrate *ell "embrane . "ake a wet mount of a "nium 2moss4 7leaf8 and observe the cells in distilled water. 0. A saturated solution of (a*l is available for a second mount or to add to the first one. The distilled water will obviously be hypotonic, the salt solution will be hypertonic. 5. +llustrate *hloroplasts . "ake another wet mount of the "nium 2moss4 7leaf8. 0. Add a drop of iodine stain to the mount. A positive reaction with the presence of of starch is production of blue-black speck. 5. Take note of the number of chloroplasts per cell. 9acuole . 1btain Rhoeo discolor leaves. 0. Peel the upper and lower epidermis. The upper epidermis of the leaf is essentially transparent but the lower epidermis is uite purple. 5. "ake a wet mount of the upper and lower epidermal layers peeled from this leaf and compare them. 6. ;ocate the purple pigment. %. $raw the structures. (ucleus . *ontinue the observation of the upper and lower epidermis. 0. ind another member of the plastid family in association with the nucleus. *hromoplasts . "ake free hand sections of red pepper or tomato and make a wet mount. 0. $raw the structures. 3laioplasts . "ake wet mount out of potato to reveal elaoiplasts. 0. $raw the structures. Amyloplasts . "ake wet mount out of potato. 0. $raw the structures.
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RESULTS and DISCUSSION •
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*ell ?all *ell wall is the outermost layer of the plant cell. +t is a rigid structure which gives support, protection and shape to the cell. +t consists of three layers @ primary cell wall, secondary cell wall and tertiary cell wall. The wet mount of twig with ethanol plus hydrochloric acid 2>ig. 4 showed the rigid structure of the cell wall. %& 23t1)4 with '( )*l is a stain for lignin, a hard substance in which the cellulose fibers become embedded. +t gives wood many if its distinctive properties. Therefore, the twig has walls containing lignin. 1f all polymers, lignin is the only one that is not composed of carbohydrate monomers. +nstead, its primary component is coniferyl alcohol.
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*ell "embrane *ell or plasma membrane is another part of the boundary of the cell that confines the contents of the cell to an internal compartment. +t regulates the flow of materials into and out of the cell with its semi-permeability. +t is made up of phospholipid bilayers with integral and peripheral proteins. ince plant cells have a cell wall, the membrane is not visible unless it is pulled away from the wall slightly. 3ven then, the membrane will not be seen, only its effects in containing the cytoplasm. The first mount is with distilled water 2>ig. 64 which is hypotonic. ?hen a plant cell is placed in a hypotonic solution, it takes up water by osmosis and starts to swell, but the cell wall prevents it from bursting. The plant cell is said to have become turgid8. The pressure inside the cell rises until this internal pressure is eual to the pressure outside. This liuid or hydrostatic pressure called the turgor pressure prevents further net intake of water. Turgidity is very important to plants as it helps in the maintenance of rigidity and stability of plant tissue. ?hen a plant cell is placed in a hypertonic solution, like salt solution, the water from inside the cellBs cytoplasm diffuses out and the plant cell is said to have become flaccid. 2>ig. 54 it will be noticed that the cytoplasm has shrunk and pulled away from the cell wall .This phenomenon is called plasmolysis. The process is reversed as soon as the cells are transferred into a hypotonic solution 2deplasmolysis4. *hloroplasts Among the several types of plastids, chloroplasts are the most common. These have a photosynthetic function: converting light energy to chemical energy. *hloroplasts contain en/ymes necessary for photosynthesis and also the green pigment called chlorophyll, a molecule with the vital role of absorbing light energy. The mount added with iodine produced a blue-black speck in the micrograph. 2>ig. 04 This indicates a positive reaction with the presence of starch. Approximately chloroplasts are found in each cell. 9acuole The upper and lower epidermis of Rhoeo discolor is compared and it is seen that the upper 2>ig. %4 is essentially transparent while the lower 2>ig. C4 is uite purple. toma is visible in the lower epidermis along with its guard cells. Along with these, a purple pigment called anthocyanin is also seen. This water-soluble pigment is stored in the vacuole of Rhoeo discolor , giving it its characteristic color. 9acuole 2>ig. D4 is a membrane-bounded sac filled with a liuid that contains a variety of materials in addition to water like dissolved salts, ions, pigments and waste products. +t is most common in plant cells and cells of certain protists. (ucleus ?ith some ad=ustments, the nucleus became visible in the cell of Rhoeo discolor. 2>ig. E4 (ucleus houses the $(A and serves as the control center of the cell. Proplastids Proplastids 2>ig. '4 are the colorless precursors where the other plastids have developed. These have the ability to divide and differentiate to various types of plastids. *ells that lack chloroplasts can still obtain chemical energy by the aid of the other members of the plastid family since they can change from one type to another, depending of the needs of the plant cell. *hromoplasts
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+n the wet-mount of tomato 2>ig.F4, there are colored pigments seen and these are the chromoplasts. They synthesi/e food materials by photosynthesis. Tomatoes and red pepper turn red on ripening due to the formation of the red pigment called lycopin replacing the chlorophyll. 3laioplasts The wet mount of potato 2>ig. 4 showed non-pigmented plastids called elaioplasts, a type of leucoplast that is speciali/ed in storing lipids and housing body oil deposits as rounded plastoglobuli. Amyloplasts Another type of leucoplast is found in the free-hand section of potato 2>ig. 04. These are speciali/ed for the storage of starch and found mostly on tubers, rice, and wheat.
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REFERENCES •
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#eece, Gane . et. al. *ampbell iology ' th ed. Pearson 3ducation, +nc. 5F ansome t., an >rancisco, *A '6. 0F erg, ;inda #. +ntroduction to otany Philippine 3dition. *engage ;earning Asia Pte ;td. Pasig *ity, Philippines CF%. 0F6
