BIOLOGY PRACTICALS GRADE 10 PRACTICAL 1 Aim To experimentally demonstrate that carbon dioxide is released during the process of respiration. Theory The process of respiration is biochemically carried out wherein food, glucose to be precise, is oxidized and energy is released. In this experiment, gram seeds (moistened) are used. The purpose of using these seeds is that they release carbon dioxide and are respiring actively. The released carbon dioxide is consumed by the solution of KOH. Material Required 1. Soaked gram seeds 2. U-shaped delivery tube 3. Conical flask 4. Blotting paper (moist) /cotton wool 5. Thread 6. Water 7. Beaker 8. Test tube 9. Rubber cork with a single hole 10. Freshly prepared KOH solution (20%) 11. Vaseline Procedure 1. Germinate close to 25 seeds. This can be done by wrapping them in moist blotting paper or cotton wool for around 3 to 4 days. 2. Set up the germinated or sprouted seeds in the conical flask. Spray some water into the flask to dampen the seeds. 3. With the help of a thread, suspend the conical flask containing the test tube having a freshly prepared 20% KOH solution. 4. Use the rubber cork to seal the opening of the conical flask. 5. One edge of the U-shaped glass delivery tube present in the conical flask should be inserted through the hole in the rubber cork. The other edge should be placed into a beaker that is saturated with water. 6. All attachments of the set-up should be sealed. This can be done using vaseline to create an air-tight environment. 7. The initial water level present in the U-shaped delivery tube needs to be marked. 8. Leave the experimental set-up uninterrupted for 1 to 2 hours. Observe the fluctuations in the water level in the tube. Observation Careful observation after a certain period of time reveals that the water level in the U-shaped delivery tube has risen in the beaker. Conclusions The rise in level water indicates that carbon dioxide is released as a result of germinating gram seeds during the process of respiration in the conical flask. The carbon dioxide that is released in the process is absorbed or consumed by the KOH solution that is suspended in the test tube in the conical flask, creating a vacuum or a void in the flask resulting in the upward water movement in the tube. Hence, the water level in the tube changes. Precautions The seeds that are to be germinated need to be moistened Air-tight environment for all the connections in the experimental set-up The KOH solution that is used needs to be freshly prepared Care needs to be taken to ensure that one end of the delivery tube is placed in the conical flask. The other edge is submerged in the water of the beaker 5. The tube that contains the KOH solution needs to be suspended carefully 1. 2. 3. 4. PRACTICAL 2 Aim To prepare a temporary mount of a leaf peel in order to show the stomata of a leaf Principle Plants are the primary producers. They carry out physiological processes such as photosynthesis and respiration which requires a gas exchange between the tissues of plants and the atmosphere. This process is carried out through tiny openings located in leaves, known as stomata. 1. 2. 3. 4. 5. 6. Describe the structure of stomata. Stomata are small elliptical openings on leaves that contain chloroplasts. They are girdled by two-kidney shaped cells known as guard cells on either side of the stomata. The guard cells possess a thick inner wall and a thin outer covering which control the closing and opening of the pores of stomata. Discuss the closing and opening of the stomata. Turgidity of the guard cells causes the stomata to open while the flaccid nature of the guard cells causes the stomata to close. Material Required A potted plant of Bryophyllum or Tradescantia Needles Forceps Watch glass Dropper Glass slides 7. A brush 8. Coverslips 9. Blotting paper 10. Safranin 11. Compound microscope 12. Glycerine Procedure 1. Pick a healthy leaf from the potted plant 2. Fold the leaf to gently pull the peel apart to separate a peeled section from the lower surface of the leaf. Use the forceps to perform this step. Allow the peel to remain in a watch glass holding water for some time. 3. In the watch glass, stain the sample by adding some drops of safranin through a dropper. 4. Take the peel out after 2-3 minutes. Set it on a clear glass slide 5. Add a drop of glycerin on the peel. Put a clear coverslip over it gently using a needle. 6. Excess glycerin and stain can be removed using blotting paper 7. Examine the slide first under a low-power and then under a high-power magnification of a compound microscope. 1. 2. 3. 4. 5. 1. 2. 3. 4. 5. 6. 7. Observation Visible epidermal cells. The cells in their outline are irregular with no intercellular spaces Small openings, stomata are scattered through the epidermal cells Guard cells are observed which have chloroplasts and nucleus Guard cells are observed having a thin outer covering and a thick inner boundary(concave) Guard cells control the closing and opening of the stomata. Conclusions Epidermal cells are found containing stomata on the lower surfaces of the leaf. Precautions Avoid folding the leaf too much. The peel should be snipped to a proper size The peel should always be placed at the centre of the slide and the slides should be held from the sides. The peel should neither be overstrained nor under strained A brush should be used to handle the peel, otherwise would damage cells. Glycerin should be used in order to prevent drying of the peel Coverslip needs to be placed in such a way that air bubbles are avoided Blotting paper can be used to remove excess stain PRACTICAL 3 Aim To study about (a) Binary Fission in amoeba and (b) Budding in yeast with the help of prepared slides Principle Budding and binary fission are types of asexual reproduction observed in lower organisms such as bacteria, unicellular protozoans and some other entities. In this type of reproduction, the parent cell divides or is split into two daughter cells through mitosis wherein each daughter cell develops into an adult. Amitosis is the division of the nucleus. It is a kind of asexual reproduction wherein a new organism develops from a bud or an outgrowth due to the process of cell division at a particular site. Material Required 1. Compound microscope 2. Permanent slides of budding in yeast and binary fission in amoeba Procedure 1. Place the slide under a compound microscope 2. Focus the slide, first under low power and later under high power of the compound microscope 3. Various stages of budding and binary fission can be carefully examined 1. 2. 3. 4. Observation (a) Binary fission in Amoeba Initially, the pseudopodia are retrieved. The body of amoeba is coiled and becomes round Amitosis is observed, the division of the nucleus takes places which are followed by splitting of cytoplasm At the point of fission in the body of the amoeba, a constriction starts to develop. The constriction or furrow turns deeper resulting in the formation of two daughter cells (b) Budding in yeast 1. Tiny outgrowth is observed on the parent cell 2. Division of the nucleus is observed which is later seen in the bud 3. Repetitive budding leads to the formation of a chain of cells Conclusions The prepared slides display asexual reproduction. One individual is involved to produce a new offspring of its own kind. Precautions 1. Slides need to be aligned and focused accurately 2. Sketch out your observation that is observed under a microscope 3. The slides first need to be examined under a low-power magnification of the compound microscope and then under high-power magnification.
