Biology Experiments Experiment-1 AIM To prepare a temporary mount of a leaf peel to show stomata. MATERIALS REQUIRED Leaf of periwinkle or balsam, slide, coverslip, forceps, needles, cotton cloth, brush, blotting paper, watch glass, blade, dropper, glycerine, safranin and compound microscope. THEORY Stomata (singular: stoma) are tiny pores present on the surface of the leaves. Though they are found on both upper and lower epidermis of leaf but they are more in number on the lower epidermis. Each stoma is bounded by two kidney-shaped guard cells. These guard cells possess a nucleus and a number of chloroplasts. The walls of guard cells are differentially thickened and elastic, i.e. they are thickened on inner side and thinner and more elastic on outer side. The opening and closing of stomata is operated by the change in the turgidity of guard cells. The stomata help in exchange of oxygen, carbon diodide and water vapour between atmosphere and plant. PROCEDURE 1. Take a freshly plucked leaf, and remove the peel from its lower surface by tearing it. 2. Put the leaf peel in a watch glass containing water so that the peel does not dry. 3. To the watch glass containing leaf peel, add 1-2 drops of safranin to stain the peel. 4. With the help of a brush, place the leaf peel in the centre of a clean slide. 5. Put a drop of glycerine on the slide over the peel. 6. Now, with the help of a needle, gently place a coverslip over the peel. 7. Remove the excess glycerine with a blotting paper. 8. Observe the slide, first, under the lower magnification (i.e., 10 X) of a compound microscope and then, under the higher magnification (i.e., 45 X). OBSERVATIONS 1. Epidermis or leaf peel consists of a number of cells which are irregular in outline and are arranged in single layer with no intercellular spaces. 2. Tiny pores called stomata are seen in the epidermal cells. 3. Each stoma consists of two kidney-shaped guard cells. 4. Each guard cell has a nucleus and many chloroplasts. RESULT Minute apertures called stomata are seen in the temporary mount of leaf peel. Each stoma is enclosed by two kidney-shaped guard cells. These guard cells differ from other epidermal cells in having chloroplast. PRECAUTIONS 1. Peel should be taken from freshly plucked leaf. 2. Peel should not be allowed to dry. 3. Leaf peel should not be over stained. 4. The slide should not be dirty. – 5. Use a brush to transfer the leaf peel from watch glass to slide. 6. Peel should be placed in centre of slide. 7. Curling of peel should be avoided while placing it on slide. 8. The epidermal peel should be small in size. 9. Place the coverslip gently to avoid entry of air bubbles. 10. Excess stain and glycerine should be removed with blotting paper. ******************************************************************************* Experiment-2 AIM To show experimentally that carbon dioxide is given out during respiration. MATERIALS REQUIRED Conical flask, U-shaped delivery tube (tube bent twice at right angles), cotton wool or moist blotting paper, water, thread, beaker, test tube, rubber cork with one hole, 20% freshly prepared KOH solution, Vaseline, soaked gram seeds. THEORY Respiration is a biochemical process during which food (glucose) is oxidized to liberate energy. It is a catabolic process. In the experiment, moist gram seeds are taken as they are actively respiring and releasing CO2. The CO2 released is absorbed by KOH . PROCEDURE 1. Take about 25-30 seeds of gram and germinate these seeds by placing them on moist cotton wool or moist blotting paper for 3-4 days. 2. Place the germinated seeds into a conical flask and sprinkle a little water in flask to moist the seeds. 3. Take freshly prepared 20% KOH solution in a test tube and hang it in conical flask with help of thread. 4. Close the mouth of conical flask by placing a rubber cork containing one hole. . 5. Through the hole of rubber cork, insert one end of the U-shaped glass delivery tube in the conical flask and place the other end into a beaker filled with water. 6. Seal all the connections of the experimental set-up with vaseline so as to make it air-tight. 7. Mark the initial level of water in the U-shaped delivery tube. 8. Keep the apparatus undisturbed for 1-2 hours and note the change in level of water in the delivery tube. OBSERVATIONS After sometime, the level of water in U-shaped delivery tube dipped in water of the beaker rises. RESULT Germinated gram seeds in a conical flask release CO, during respiration. The C02 released is absorbed by KOH present in the hanging test tube in conical flask. This creates a vacuum in conical flask which causes upward movement of water in the delivery tube leading to change in level of water in the delivery tube. PRECAUTIONS 1. Germinating seeds should be kept moist. 2. All connections of the set-up should be air-tight. 3. Freshly prepared KOH solution should be used. ****************************************************************************** Experiment-3 AIM To study binary fission in Amoeba, and budding in yeast and hydra with the help of prepared slides. MATERIALS REQUIRED Compound microscope, permanent slides of binary fission in Amoeba and budding in yeast and hydra. OBSERVATIONS (a) Binary Fission in Amoeba This is a type of asexual reproduction in which two daughter cells (or two individuals) are formed from a single parent. Parent cell becomes elongated. Nucleus divides first and then the cytoplasm divides. At the point of fission, constriction appears and deepens to divide the cell into two daughter cells. Parental identity is lost. (b) Budding in Yeast and Hydra In this type of asexual reproduction, a small protuberance or outgrowth arises from the parent body called bud. Nucleus divides to form two daughter nuclei, of which one passes into the bud. The bud now detaches from the parent body and grows independently as a new individual or may remain attached to parent body, forming chain of cells . Parental identity is not lost.eg. Yeast The bud develops in to small hydra and detaches from the parent body and grows independently. Parental identity is not lost. ****************************************************************************** Experiment-4 Aim To identify the different parts of an embryo of a dicot seed. Theory The process of fertilization in plants leads to the formation of fruits which forms the ripened ovary. The seed can be one or many which form the mature ovule. A seed consists of the following parts: Hilum – It is a scar that is located on the seed coat, associated with the stalk of the plant Seed coat – Forms the exterior covering of the plant, supplying with nourishment and protection to the seed inside Endosperm – It is the tissue containing nutrients for the growth of the embryo Embryo – Several divisions of the zygote gives rise to this structure. It consists of the following parts: Radicle Plumule Cotyledons Germination involves the following steps: Seeds swell, plumules develop into shoots From the radicle of the seeds, the roots arise Formation of cotyledons(one in monocots and two in dicots) Material Required Seeds of red kidney bean/gram Forceps Magnifying glass Cloth Petri dish Water Procedure Soak a few seeds overnight Next morning, drain the excess water out Now wrap the seeds in a clean and a moist cloth for a day, allow it to dry Next, carefully peel the seed coat With the help of forceps, dissect the seed so as to get two equal halves Examine with the help of a magnifying glass. Carefully identify and locate different parts of the seed Sketch out the interior of the seed you examined labeling all the parts as shown in the diagram. Diagram Observation The bean seed resembles the shape of a kidney. It has a convex and a concave side A scar known as the hilum is observed on the slightly darker side of the concave side A tiny pore known as the micropyle is located just adjacent to the hilum The seed is enclosed by a seed coat The embryo possesses two distinct and large cotyledons that resemble the shape of a kidney and are white in color Lateral attachment of the cotyledons to the curved embryonal axis is observed Radicle is examined. It is the rod-shaped and lightly protrusive lower end of the embryonal axis that is found placed towards the micropylar end. The upper end of the embryonal axis exhibits the plumule Hypocotyl is observed which is a section of the embryo axis found in between the radicle and adjunct of cotyledon leaves The epicotyl is also observed which is the section of the embryo axis between the adjunct of cotyledon leaves and plumule. Precautions Care needs to be taken while dissecting the seed as it may damage the seed The cloth that is used to wrap the seeds needs to be moist.
