School Science Lessons
Biology experiments
Updated: 2008-04-14
Biology names
9.12.0 Diffusion, osmosis, plasmolysis
9.13.0 Transpiration, conduction of water in the plant
3.55 Brownian movement
9.10.0 Respiration in plants
9.12.0 Diffusion, osmosis, osmotic pressure, semipermeable membrane, plasmolysis
9.163 Diffusion with copper (II) sulfate solution
9.164 Diffusion through a colloidal gel
9.165 Cellophane as a semi-permeable membrane
9.166 Sausage skin as a semi-permeable membrane
9.167 Copper ferrocyanide as a semi-permeable membrane
9.168 Prussian blue as a semi-permeable membrane
9.169 Suction potential and tissue tension in celery
9.170 Osmosis with a carrot
9.171 Osmosis with an egg
9.171.1 Osmosis with honey on bread
9.172 Colloidal nature of egg white
9.173 Osmotic pressure and suction potential in dandelion
9.174 Osmosis with dialysis tubing
9.175 Turgor pressure in a potato
9.176 Plasmolysis in beetroot
9.177 Plasmolysis in onion epidermis
9.178 Plasmolysis in hairs on the stamens of Tradescantia
9.179 Imbibition in seeds and dried fruit, broad bean, pea, bean
9.180 Colloidal solution of starch
9.181 Separate a colloid from a crystalloid by dialysis
9.182 Tests for glucose and starch with "Testape"
3.37 Transpiration
6.1.16 Plasmolysis in Elodea
6.1.17 Plasmolysis in Spirogyra
6.1.18 Imbibition in seeds and dried fruit, broad bean, pea, bean
6.1.19 Colloidal solution of starch
6.1.20 Separate a colloid from a crystalloid by dialysis
6.1.21 Tests for glucose and starch with "Testape"
6.1.22 Plasmolysis in hairs on the stamens of spiderwort, Tradescantia
9.13.0 Transpiration, conduction of water in the plant
9.183 Conduction of water in plants, cut flowers in coloured water
9.184 Water transport in plants, root pressure
9.185 Conduction of water and salts through the stem
9.186 Sites of transpiration
9.187 Distribution of stomates in the leaves
9.188 Control of evaporation by potato skin, apple peel
9.189 Effect of temperature on transpiration
9.190 Transpiration and water transport in plants
9.191 Weigh plants to show transpiration
9.192 Compare rates of transpiration with a potometer
9.193 Transpiration through stomates
9.194 Transpiration into a plastic bag
9.195 Transpiration causes a drop in water level
3.31.3 Tests for water with cobalt (II) chloride
6.2.12 Path of the transpiration stream
6.2.13 Transpiring leaves exert suction
5.31 Leaves lose water
9.10.0 Respiration in plants
3.37 Carbon dioxide and respiration
3.38 Carbon dioxide and fermentation for brewing
4.38 Calorific value of fuel
6.6.1 Respiration, limewater test for carbon dioxide
6.6.1.1 ATP
6.6.2 Flowers in a flask
6.6.3 Measure respiration rate of soaked peas
6.6.4 Tests for respiration of soaked peas with limewater
6.6.5 Plants can respire for a short time by anaerobic respiration
6.6.6 Heat energy is liberated during respiration
6.6.7 Absorption of oxygen during plant respiration
6.6.8 Production of carbon dioxide during plant respiration
6.6.9 Respiratory quotient of Compositae flowers
6.6.10 Respiratory quotient calculation for mung bean seedlings
6.6.11 Measure effect of temperature on respiration of small animals
6.6.12 Test gas collected in a respirometer
6.6.13 Respiratory quotient using an alternative design respirometer
6.6.17 Energy from food
6.6.18 Alcoholic fermentation, yeast, Saccharomyces cerevisiae
6.6.19 Butyric acid fermentation
6.6.20 Respiration apparatus
6.6.22 Food is used in respiration
9.155 Respiration apparatus, test for respiration of soaked peas with limewater
9.156 Heat energy from respiration of peas
9.157 Production of carbon dioxide during plant respiration
9.158 Heat of respiration, bakers' yeast, Saccharomyces cerevisiae
9.159 Rotting banana and rotting grass
9.160 Food used in respiration
9.161 Energy from a peanut
9.162 Alcoholic fermentation, yeast
6.1.0 Diffusion, osmosis, osmotic pressure, semipermeable membrane
See diagram 4.7.02 Measure osmosis
Diffusion occurs when two substances flow into each other until both substances are completely mixed. Osmosis occurs when a semi-permeable membrane separating a water and sugar solution allows only water molecules to diffuse through it and so decrease the concentration of the sugar solution. One mole of a non-electrolyte dissolved in water and made up to 22.4 L of solution causes an osmotic pressure, at 0oC of 760 mm. of mercury (1 atmosphere). The cell membrane inside the cell wall of plant cells allows water to diffuse in when the cell is surrounded by a lower concentration solution. The cell swells with the absorbed water and develops an extra pressure called turgor pressure. If the cell is surrounded by a higher concentration solution, water diffuses out of the cell, and the protoplasm shrinks away from cell wall. This process is called plasmolysis.
6.1.16 Plasmolysis in Elodea
1. Mount a complete leaf in water on a slide and examine cells under the high power. Note the small green granules, chloroplasts, which contain the chlorophyll. Then irrigate the leaf with a strong solution of sugar or salt. The green chloroplasts help one to see plasmolysis taking place more easily. Now place a small sprig of Canadian pond weed (Elodea) in boiling water for a few minutes. This kills the cells. Then mount one leaf and treat it as before. Note that plasmolysis does not occur now. This shows that only living cells possess semi-permeable membranes and are therefore able to absorb water by osmosis.
2. Note absorption of methylene blue by Elodea. Place a shoot of Elodea in a very dilute solution of methylene blue. Leave for a few hours and note that the Elodea plant becomes deeply coloured by adsorption of the dye.
6.1.17 Plasmolysis in Spirogyra
See diagram 1.1: Spirogyra
1. Put the algae, Spirogyra, in water on a microscope slide. While looking at the cells under the microscope add drops of sodium chloride solution near the algae. The cytoplasm shrinks away from the cell walls and forms a clump. Absorb the salt water with absorbent paper. While looking at the algae cells under the microscope, add drops of water near the algae and absorb excess water with absorbent paper. The cytoplasm swells to occupy most of the space in the cell. When you put salt water near the algae, water diffused out of the cytoplasm causing it to shrink. When you mop up the salt water and put pure water near the algae, water diffused back into the cytoplasm in the cells making it swell.
6.1.18 Imbibition in seeds and dried fruit, broad bean, pea, bean
1. Measure the displacement of dry broad bean or pea seeds with a measuring cylinder partly filled with water. Put the seeds in moist sawdust for two days and then again measure their displacement. Estimate the percentage increase in volume because of the imbibition of water.
2. Put sultanas, grains, dried apricots in pure water and leave them for some time. Then place them into a concentrated solution of sugar or salt. Each gains water and swells when placed in pure water, then shrinks in the concentrated solution.
6.1.19 Colloidal solution of starch
Shake 2 g of starch with a little cold water in a test-tube until it forms a paste. Boil 100 mL of water in a beaker, and while the water is boiling, slowly pour the paste from the test-tube, drop by drop, into it. After cooling, note that this colloidal solution is opaque. Test the solution for starch by adding a few drops of iodine solution.
6.1.20 Separate a colloid from a crystalloid by dialysis
Use of a semi-permeable membrane to separate a colloidal solution from a true solution is called dialysis. A Soxhlet thimble is a filter made usually of cellulose. It looks like a white test-tube. Collodion, cellulose tetranitrate, is made by dissolving nitrocellulose (gun cotton, nitrate movie film) in ether or acetone. It was used in medicine to cover wounds and remove warts. Also, it was used in wet plate photography.
1. Make a dialyser by soaking a Soxhlet thimble in a 5% solution of collodion in glacial acetic acid. Alternatively, you can try making a dialyser by dipping your finger in collodion then waving you finger in the air. Wash the dialyser with tap water. Add sodium chloride solution to a 2% colloidal solution of gelatine to produce a mixture of a colloidal solution and true solution. Put the mixture in the dialyser. Put the dialyser in a beaker of water with the water level with the mixture in the dialyser. After one day test the liquids. Test the liquid in the dialyser with tannic acid that precipitates gelatine out of solution. Test the liquid in the beaker with silver nitrate solution that reacts with sodium chloride to produce a white precipitate of silver chloride. The crystalloid sodium chloride passes through the membrane but the colloid collodion does not. An artificial kidney works in the same way.
2. Repeat the experiment with a colloidal solution of starch. Test the liquid in the dialyser with the iodine test for starch.
6.1.21 Tests for glucose and starch with "Testape"
Prepare two same size pieces of dialysis tubing as follows: Hold the end under water until it is soft. Tie a knot in the end and pull so that the knot is tight. Hold the other end under water until it is soft. To open the tubing, rub the fingers back and forth until it opens. Half fill beaker 1 with glucose solution. Half fill beaker 2 with starch solution. Half fill each piece of dialysis tubing with deionized water and put one in beaker 1 and the other in beaker 2. Cover each beaker with a watch glass, and leave overnight. Pour one finger breadth of the starch solution into a test-tube. Add two drops of iodine solution. The solution becomes blue black. Pour one finger breadth of the glucose into a test-tube. Tear off a small piece of "Testape", and dip it in the glucose solution. A green colour shows glucose. The next day use "Testape" to test the glucose solution in beaker 1 and the liquid in the dialysis tubing. Both test positive. Add drops of iodine to the starch solution in beaker 2 and to the liquid in the tubing. Only the liquid in beaker 2 tested positive. The liquid in the dialysis tubing in beaker b tested negative. Glucose can pass through the wall of dialysis tubing but starch cannot.
6.1.22 Plasmolysis in hairs on the stamens of spiderwort, Tradescantia
See diagram 9.178: Plasmolysis in Tradescantia
(a) Mount a complete leaf in water on a slide and examine cells under the high power. Note the green chloroplasts that help you to see the extent of the cytoplasm. Use absorbent paper to draw concentrated sugar or salt solution across the cell while you are still looking at them with the microscope. The cytoplasm shrinks into the centre of the cell away from the cell wall, taking the chloroplasts with it. Plasmolysis has occurred. (b) Repeat the experiment by drawing pure water across the same waterweed cells. The cytoplasm and chloroplasts spread out through the cell. Plasmolysis has been reversed. (c) Repeat the experiment with waterweed that had been dipped in boiling water for two minutes. Use absorbent paper to draw concentrated sugar or salt solution across the cell while you are still looking at them with the microscope. Plasmolysis does not occur because only living cells possess semi-permeable membranes that control plasmolysis
6.2.12 Path of the transpiration stream
Herbaceous plants lose several hundred times their own weight of water in a day, mostly through stomata on the leaves. Within the mesophyll of the leaf a large wet surface is exposed to enable the adsorption of carbon dioxide for photosynthesis. When the air outside the leaf is drier than the air within, water vapour can diffuse out through the stomates causing more water to evaporate from the leaf cells. Then the suction pressure of the leaf cells rises, draws water from the veins and creating negative hydrostatic pressure in them to draw water up the xylem vessels. The xylem vessels are merely pipes and the water flows passively so water can be made to flow in the reverse direction by sealing the normal basal end, cutting off the apex of the shoot and dipping the cut stem into water.
1. To show that the leaves are mainly responsible for causing the flow of water, you can remove leaves and compare the rates of water movement. Use two leafy shoots of balsam to study of water conduction in stems. Cut a fresh surface on the lower end of each shoot with a sharp razor blade, keeping the end wet under water as you cut. Leave in water for at least two minutes. Place one shoots in a tube of dye provided and watch continuously until you see colour rise in the vascular bundles in the stem and has reached the leaves. Remove the other shoot from the water, dry the cut end and seal with petroleum jelly. Cut the stem under water near the terminal rosette and leave inverted in water for two minutes. Transfer the shoot to the dye provided and watch continuously until you see colour flow. Note that the direction of flow is the reverse of that previously noted.
2. Stand the cut stems of white flowers and some cut shoots in dilute red ink or eosin dye. Note the stain reaching the petals and leaves. Cut across the stems to see the die in the xylem of the vascular bundles in the veins.
6.2.13 Transpiring leaves exert suction
The use of elemental mercury in experiments is NOT recommended
See diagram 9.192.1 Suction pressure
Make all joints air tight and do not include any air bubbles. The mercury will rise in the narrow glass tube.
6.6.1 Respiration, limewater test for carbon dioxide
See diagram 3.34.1: Limewater test for carbon dioxide
1. Calcium hydroxide is only slightly soluble in water. Prepare the weak alkali calcium hydroxide solution, limewater, by adding solid calcium hydroxide, slaked lime, to demineralized water. Shake vigorously and allow to stand. Calcium hydroxide solid is only slightly soluble in water. When the white solid has settled as a fine white sediment, decant the clear limewater above the sediment. To replenish the limewater, add more demineralized to the sediment in the stock bottle, shake and allow to settle. The settling process may take several days.
2. Pass carbon dioxide through the clear limewater. The solution becomes a milky because of a fine precipitate of calcium carbonate.
Ca(OH)2(aq) + CO2(g) --> Ca(CO3)2(s) + 2HCl(l)
Pass more carbon dioxide through the limewater. The solution becomes clear again because of the formation of soluble calcium hydrogen carbonate.
CaCO3(s) + CO2(g) + H2O(l) --> Ca(HCO3)2(aq)
Pass air through freshly made limewater. After a long time you may see a faint cloudy precipitate.
3. The air contains about 0.4% carbon dioxide. Use a drinking straw to exhale into the limewater. A cloudy precipitate soon forms because you exhaled breath contains about 4% carbon dioxide.
4. Carbon dioxide gas is produced during respiration. Demonstrating respiration in plants is not easy. However you can say that plants breathe out the same gases as humans and then do the limewater test for carbon dioxide. limewater test for carbon dioxide. This demonstration always interests students because it lets them see the effect of the carbon dioxide they breathe out. You need fresh limewater for this demonstration so do your preparation the day before the lesson. Heat calcium carbonate (coral) strongly to change it into quicklime (calcium oxide). Add this to water, shake and stand for a few days until the top of the liquid is clear. To show carbon dioxide gas, breathe down a tube or a straw to make bubbles in the clear liquid. The carbon dioxide gas will turn the clear liquid a white milky colour. Plants (and animals) breathe in oxygen gas from the air to breakdown food into carbon dioxide gas and water. The energy stored in the food is then let out and can be used for growth, movement and to keep the plant (or animals) alive. This process is called respiration. Respiration equation: oxygen gas + simple sugar (food) --> carbon dioxide gas + water + energy. The carbon dioxide gas produced by respiration goes out into the air. Photosynthesis and respiration are reverse processes. Photosynthesis equation: carbon dioxide gas + water + energy --> food + oxygen gas. During photosynthesis energy from the sun is taken in and stored in food. During respiration that energy taken in is let out and used.
6.6.1.1 ATP
1. The RNA nucleotide adenosine monophosphate contains the purine base adenine has one phosphate group, PO4. Adenosine triphosphate, ATP, has three phosphate groups. The terminal third phosphate of ATP can be transferred to other molecules to make them more reactive, the stable glucose molecule can receive a phosphate from ATP, phosphorylation, become glucose-phosphate and be quickly broken down. ATP is made in mitochondria from the oxidation of glucose, cellular respiration when glucose combines with oxygen, oxidation, to form carbon dioxide, water and 38 molecules of ATP. During oxidation, electrons from glucose pass step by step through the cytochrome enzyme system, that contains iron, in the mitochondria.
2. DNA (deoxyribonucleic acid), RNA (ribonucleic acid): 1. messenger RNA, M-RNA 2. transfer RNA, T-RNA 3. ribosomal RNA.
During protein synthesis M-RNA molecules are made from sections of DNA in the nucleus, by transcription, then travel to ribosomes. T-RNA molecules attach to amino acids in the cytoplasm and bring them to ribosomes where they join with base triplets, codons, along the M-RNA strand, translation. A complementary base triplet on each T-RNA, anticodon, joins with the codon of M-RNA, the anticodon AUG joins with the codon UA3. Different T-RNA molecules carry different amino acids, depending on their anticodons. With 64 codons (4 X 4 X 4) and 20 different amino acids in human protein, the same codons of M-RNA can stand for the same amino acid, codons UUA, UUG, CUU, CUC, CUA and CUG stand for the amino acid leucine. As each amino acid is linked to the growing polypeptide, a molecule of water is released until an enzyme, antibody or structural protein forms in animals or plants.
3. Respiratory activity of organisms
See diagram 9.2: Respiration
The respiratory activity of organisms can be shown with an apparatus that moves air over leaves, insects or a small animal and bubbles it through a weak solution of limewater, Ca(OH)2. The system must be isolated from atmospheric carbon dioxide. Set up the apparatus as shown in the diagram but leave the third bottle empty. Run the apparatus by siphoning the large container, a carboy, until it is empty. Note the results. Replace the solutions in all bottles, and this time put loosely packed leaves or an animal into the third bottle. Compare the results of the first run, the control, with the second run. limewater turns from clear to cloudy in the presence of carbon dioxide. This can be shown by blowing through a drinking straw into a container of clear limewater. Plant leaves produce oxygen and carbon dioxide in the light and produce carbon dioxide in the dark.
Do of the experiments suggested in 6.6.1 in the light and in a dark room, and compare the results.
6.6.2 Flowers in a flask
See diagram 6.6.1
Do NOT use elemental mercury for school experiments!
Collect living flowers and push them down into a flask. Invert the flask over mercury, so that the mouth of the flask is below the surface. Use a bent tube to introduce strong caustic potash solution to the surface of the mercury inside the neck of the flask. After a few hours, the mercury will rise inside the flask because of the respiratory activity of the flowers. During the process, oxygen is absorbed from the enclosed atmosphere of the flask, and an almost equal volume of carbon dioxide is given off. The reduced volume of gases in the flask is owing to the absorption of carbon dioxide by the caustic potash.
6.6.3 Measure respiration rate of soaked peas
See diagram 6.6.2
Do NOT use elemental mercury for school experiments!
Mark the level of the mercury in the tube at hourly intervals.
6.6.4 Tests for respiration of soaked peas with limewater
See diagram 6.6.3 | See diagram 9.156
Draw air slowly through the apparatus with a filter pump. The air current bubbles through limewater before passing the soaked peas. That limewater remains clear. The air current bubbles through limewater after passing the soaked peas. That limewater becomes milky.
6.6.5 Plants can respire for a short time by anaerobic respiration
See diagram 6.6.5
Do NOT use elemental mercury for school experiments!
Fill a test-tube with mercury and, sealing the end with the finger, invert it over a dish of mercury, with the mouth of the tube below the surface. Then, by means of the fingers, insert some soaked peas, one at a time into the mouth of the tube. These peas will rise to the top of the tube. Support the tube in this position by means of a clamp. After 24 hours, the peas will have given off a gas which has forced the mercury some distance down the tube. Show this gas to be carbon dioxide by allowing a strong caustic potash solution to rise into the test-tube from a bent tube inserted at the mouth. The potash, now in contact with the carbon dioxide, absorbs it, and the mercury rises again in the tube.
6.6.6 Heat energy is liberated during respiration
See diagram 6.6.6 | See diagram 9.157
Prepare two thermos flasks fitted with one-hole stoppers for the insertion of thermometers. Put dry pea seeds and water to the first thermos flask. Boil the same number of seeds and put them and water in the second thermos flask. Adjust the thermometers in both thermos flasks so that the bulb of each thermometer touches the peas. Note the rising temperature in the first thermos flask. Actively respiring plants generate heat. Note the steady temperature in the second thermos flask until the activity of micro-organisms causes a sharp rise in temperature. Examine the contents of the two thermos flasks.
6.6.7 Absorption of oxygen during plant respiration
See diagram 4.9.10
Plants take oxygen in and give carbon dioxide out during respiration. Green plants also take in carbon dioxide and give out oxygen during photosynthesis. Plant respiration can only be noted when there is no photosynthetic activity so this experiment uses plants or parts of plants which have no chlorophyll necessary for photosynthesis, mushrooms or flowers of Compositae. Use the burning time of a candle in an enclosed known volume of air to prove the presence of oxygen. Smear the bottom edge of a 5 litre polystyrene bell jar with glycerine to provide a good seal, and is then put on a glass plate. Put a lighted candle in the bell jar using the candle holder. Close the neck of the bell jar immediately with the rubber stopper of the candle holder. Record the burning time of the candle. The candle burns for 90 to 120 seconds enclosed in the bell jar.
6.6.8 Production of carbon dioxide during plant respiration
See diagram 4.9.11 | See diagram 9.157
1. Plant respiration can only be observed only where no photosynthetic activity occurs, so use plants that have no chlorophyll necessary for photosynthesis, e.g. mushrooms or the white flowers of the Compositae family, daisies, with the green leaflets of the calyx removed to prevent photosynthesis. Use the burning time of a candle in an enclosed known volume of air to prove the presence of oxygen. Smear the bottom edge of a big jar with petroleum jelly then put it on a glass plate. Open the neck of the jar then put a lighted candle down the neck onto the glass plate. Close the neck of the jar immediately. Record the burning time of the candle. Put mushrooms or white flowers in the jar. Close the neck of the jar. After two hours put the lighted candle into the jar. Record the burning time of the candle. The candle burn a shorter time because plants extract oxygen from the air during respiration.
2. Repeat the experiment by pumping air from the jar through limewater. Continue pumping until the limewater becomes milky to indicate the presence of carbon dioxide.
6.6.9 Respiratory quotient of Compositae flowers
See diagram 4.9.12
The ratio of the quantity of carbon dioxide given out during respiration to the quantity of oxygen taken in CO2 : O2, is called the respiratory quotient. If sugars are consumed in respiration, 6 moles of carbon dioxide and 6 moles of water are produced by the complete combustion of one mole of glucose by 6 moles of oxygen.
C6H12O6 + 6O2 ---> 6CO2 + 6H2O
The carbon dioxide given out and the oxygen taken in are in the ratio 1.1, the respiratory quotient = 1. If during respiration substances low in oxygen are consumed, oil, more oxygen must be used for the complete combustion to carbon dioxide and water. So the respiratory quotient is less than 1. If substances rich in oxygen are consumed, organic acids, the respiratory ratio rises above 1.
1. Attach a double burette clamp to a Bunsen burner stand and clamp a respiration vessel to each side. Fill both two thirds filled with small flowers of Compositae with the green leaflets of the calyx removed to prevent photosynthesis. In one respiration vessel is placed a specimen tube containing 6 pellets of potassium hydroxide. Smear the ground glass stoppers with glycerine to provide a good seal and insert in the respiration vessels. Half fill two 100 mL beakers with deionized water and place them under the two respiration vessels. Adjust the latter such that their capillary ends are immersed to a depth of 2 cm in the water. Attach a scale to each capillary. Warm both respiration vessels by placing a hand around them so that a few air bubbles escape from the capillaries. On cooling, the deionized water rises into the region of the scale. After 15 minutes record the level of the water in the two capillaries. Repeat this every quarter of an hour. The meniscus in the capillary of the respiration vessel containing potassium hydroxide rises uniformly. The reduction in volume indicates the uptake of oxygen owing to the respiration of the flowers. Only a small rise in the water level is noted in the other respiration vessel so the amount of CO2 given out must be almost as much as the oxygen taken in. The respiratory ratio of the flowers is thus 1. In general this applies for all higher plants. It clearly indicates that sugar is the predominant substance consumed in the respiration process.
6.6.10 Respiratory quotient calculation for mung bean seedlings:
See diagram 9.72.1a: Mung bean
Mung bean seedlings 1. with foliage leaves developed 2. with radicle just emerged
A 0.72 cm3 per hour 3.24 cm3 per hour
B 0. 06 cm3 per hour 1.20 cm3 per hour
A - B 0.66 cm3 per hour 2. 04 cm3 per hour
RQ =, A -B, / A 0.92 0.63
6.6.11 Measure effect of temperature on respiration of small animals
Use a U-tube to connect the syringe to the pipette and put the apparatus in a water bath. At each new temperature wait 10 minutes before taking readings. Do not use temperatures which cause discomfort to small animals. See graph 4.9.12.2.1 of respiration rates of ten worms measured at 20oC, 25oC, 30oC and 35o3.
6.6.12 Test gas collected in a respirometer
1. Invert the apparatus so that the collected gas is near the open end of the syringe. Push the plunger to introduce a column of gas into the pipette.
2. Seal the end of the gas column with the solution in the syringe to trap a column of 0.8 cm3 gas inside the pipette. Fix the apparatus in a vertical position.
3. Record the volume of gas in the pipette, V1.
4. Expel most of the solution at the lower end of the gas column. Draw in some 2 M sodium hydroxide solution. Keep the tip of the pipette in the sodium hydroxide solution and move the gas column up and down to assist the absorption of carbon dioxide.
5. Record the volume of the gas column every five minutes until the reading, V2, becomes steady. V2 measures the volume of the gas column without carbon dioxide.% carbon dioxide =, V 1 - V2, / V1 X 100
Example result for pond selaginella:
Initial volume of gas column, v = 0.75 cm3
Volume of gas column after absorbing carbon dioxide, v2, = 0.74 cm2
% of carbon dioxide = V1 - V2 X 100 = 1.33%
6. The % oxygen in the gas collected in the syringe can be estimated using alkaline pyrogallol solution. However, this chemical is too dangerous for use in school science experiments.
6.6.13 Respiratory quotient using an alternative design respirometer
Make sure that the joints are airtight, e.g. between the rubber stopper and the boiling tube. If the rubber stopper loses its elasticity after a long period of storage, ve an airtight condition is difficult. The respirometer is sensitive to volume changes owing to slight fluctuations in air temperature so errors in measurement may arise if you do not set up a control for comparison. When measuring the rate of photosynthesis by collecting the oxygen evolved from a pond weed, Figure I c, errors may occur if the gas bubbles generated from the cut ends of the aquatic stem are released at an erratic rate or in variable size, or when the gas bubbles are trapped on the leaf surface or wall of the apparatus. These errors make counting the number of gas bubbles evolved or measuring the volume of gas collected a less than reliable method for assessing the rate of photosynthesis.
6.6.14 Heat of respiration, yeast, Saccharomyces cerevisiae
See diagram 9.157.13 | See diagram 9.157.12 | See diagram 9.204: Yeast cell forming bud
Heat 450 mL 10% sucrose solution to 35oC then add 25 g of baker's yeast, Saccharomyces cerevisiae. Stir the suspension then pour it into a thermos flask. Fit a 2-hole stopper with a thermometer inserted through one hole. As a control, heat 450 mL 10% sucrose solution to 35oC then pour the solution into an identical thermos flask. Fit a 2-hole stopper with a thermometer inserted through one hole. Record the temperatures every 15 minutes. The temperature in the thermos flask containing the sugar solution and yeast rises but the temperature in the control decreases. Energy is liberated during respiration. Part of it is given off to the outside as heat.
6.6.15 Rotting banana and rotting grass
1. Squeeze very ripe fruit into a watery mash, banana. Put the mash in a small bottle then fill the bottle with water. Attach a balloon to the mouth of the bottle. Put the bottle and balloon in a warm place. Measure the size of the balloon at the same time each day. The balloon inflates because of the carbon dioxide gas produced by the action of bacteria on the sugars in the rotting fruit.
2. Sterilize rotting grass by boiling in water. Prepare sterile agar containing beef broth in test-tubes sealed with cotton wool. Remove the cotton wool and pour into 3 sterilized Petri dishes A and 2. After pouring immediately replace the dish lids. When the agar is set use sterilized forceps to rub the sterilized rotten grass over the agar in dish A, the control. Replace the lid, and seal with adhesive tape. Rub rotting grass over the agar in dish B and seal with adhesive tape. Leave the dishes upside down and undisturbed in a warm dark place for 4 days. Examine the dishes each day for bacteria and fungi growing in small colonies like dots. The bacterial colonies are usually shiny and smooth. The fungal colonies are usually fuzzy or furry. Note whether bacterial or fungal colonies appeared first and whether they appeared in dish A or B.
6.6.16 Food used in respiration
See diagram 9.113.2d : Bean seed germination
Put absorbent paper in two aluminium foil trays and add 50 g of wheat grains. To one dish add water shaken with thymol to prevent mould growth. Put the trays under jars raised to admit air. Put both trays in the dark. When the yellow seedlings are more than 5 cm long, dry both dishes in an oven until the weight is constant. Record the results as the weight of 1. dry seeds 2. dry seeds after heating 3. germinated seeds after heating.
6.6.17 Energy from food
Use equal weights of dried food, bread, puffed rice, nuts. Put 20 mL of water in a test-tube attached to a stand. Push the blunt end a needle into a cork then stick the sharp end into the food sample. Record the temperature of the water in the test-tube. Set alight the food with a Bunsen burner then immediately hold the burning food under the test-tube for two minutes. Record the temperature. Repeat the experiment with different kinds of foods. Which foods leased the most energy when burning? In a science laboratory a "bomb calorimeter" is used to burn food sample and calculate the energy stored in the food sample from the increase in temperature of water around the bomb calorimeter.
6.6.18 Alcoholic fermentation, yeast, Saccharomyces cerevisiae
See diagram 9.156.1: Yeast experiment | See diagram 9.204: Yeast | See diagram 4.209.3: Triple scale wine hydrometer
Many organisms can breakdown organic substances without atmospheric oxygen, anaerobic degradation. The process is called fermentation. The amount of energy produced is less than in an aerobic reaction since further substances of varying energy content are formed. Instead of atmospheric oxygen the intermediate products of the decomposition are used here as hydrogen acceptors. Because the decomposition results from the splitting of molecules, the fermentation can also be defined as a dissimulation. Fission respiration, the most familiar example, is alcoholic fermentation.
In the Bible is caution against putting new wine into old wine-skin containers which would be burst by the gases released by further fermentation: "Neither do men put new wine into old bottles [wine-skins]; else the bottles break, and the wine runneth out, and the botttles perish [are spoilt]" Matthew, ix, 17.
1. Half fill a test-tube with water, add a piece of yeast the size of a pea, and stir the mixture to produce a uniform suspension of the yeast cells. Three quarters fill two test-tubes with 10%t sucrose solution, and fill a third test-tube with the same amount of water. Add 10 drops of water to one of the test-tubes containing sucrose solution, and add 10 drops of the yeast suspension to the other two test-tubes. The contents of each of the test-tubes are poured into fermentation tubes, taking care that the upright limbs of the tubes are completely filled with liquid and contain no air bubbles. During the next few days a gas collects in the upright limb of the fermentation tube containing sugar and yeast suspension. No gas collects in the two control tubes, containing sucrose and water, or water and yeast suspension.
2. Insert two pellets of potassium hydroxide in the fermentation tube in which gas was produced. The gas soon disappears, indicating the presence of carbon dioxide. Pour the contents of this fermentation tube into a flat glass dish and note the distinct smell of alcohol. Yeasts ferment sugar to produce alcohol and carbon dioxide.
3. Half fill a test-tube with water, add a piece of yeast the size of a pea, and stir the mixture to produce a uniform suspension of the yeast cells. Three quarters fill two test-tubes with 10% sucrose solution, and fill a third test-tube with the same amount of water. Add 10 drops of water to one of the test-tubes containing sucrose solution, and add 10 drops of the yeast suspension to the other two test-tubes. The contents of each of the test-tubes are poured into fermentation tubes, taking care that the upright limbs of the tubes are completely filled with liquid and contain no air bubbles In the course of the next few days a gas collects in the upright limb of the fermentation tube containing sugar and yeast suspension. This does not happen in the control tubes, containing sucrose and water, or water and yeast suspension. If 1 - 2 pellets of potassium hydroxide are inserted in the fermentation tube in which gas was produced, the gas disappears within a few minutes, indicating the presence of carbon dioxide. On pouring out the contents of this fermentation tube into a flat glass dish the smell of alcohol is very distinct. Yeasts ferment sugar to give alcohol and carbon dioxide.
6.6.19 Butyric acid fermentation
See diagram 4.9.15
The soil contains micro-organisms, among which are spores and vegetative rods of Bacillus amylobacter. This bacillus is able to breakdown the middle lamella of plant cells forming, among other things, butyric acid CH3-CH2-CH2-COOH. From this breakdown it obtains the energy necessary for the maintaining of its metabolic processes. Butyric acid fermentation is of practical importance in flax and hemp production since it loosens the bundles of fibres from the structural matter of the stalks. Bacillus amylobacter is the most important butyric acid producer in the soil. The following experiment shows its activity A cut is made in a medium size potato which is infected by rubbing soil into it. It is well covered with water, contained in a 600 mL beaker, and left to stand at room temperature After 5 days a vigorous fermentation process can be seen to be taking place. Bubbles of gas rise from the cut made in the potato. It smells of butyric acid. The spores and vegetative rods of Bacillus amylobacter present in the garden or arable soil can develop and propagate under the above experimental conditions. The bacillus breaks down the middle lamella of the potato cells, wet rot, thus forming butyric acid. Bacillus amylobacter is anaerobic, dislikes oxygen, so potatoes must be covered with water to keep them away from atmospheric oxygen.
6.6.20 Respiration apparatus
See diagram 9.155
The respiratory activity of organisms can be shown with an apparatus that moves air over leaves, insects or a small animal and bubbles it through a weak solution of limewater, Ca(OH)2. The system must be isolated from atmospheric carbon dioxide. Set up the apparatus as shown in the diagram but leave the third bottle empty. Run the apparatus by siphoning the large container, a carboy, until it is empty. Note the results. Replace the solutions in all bottles, and this time put loosely packed leaves or an animal into the third bottle. Compare the results of the first run, the control, with the second run. limewater turns from clear to cloudy in the presence of carbon dioxide. This can be shown by blowing through a drinking straw into a container of clear limewater. Plant leaves produce oxygen and carbon dioxide in the light and produce carbon dioxide in the dark.
6.6.21 Energy from a peanut
1. Put 20 mL of water in a test-tube. Weigh a peanut (about 1 gram). Push the blunt end of a needle into a cork then stick the sharp end into the peanut. Record the temperature of the water in the test-tube. Set alight the peanut with a Bunsen burner then immediately hold it under the test-tube. Record the temperature of the water in the test-tube. Weigh the burnt remains of the peanut. Heat in calories = weight of water X specific heat of water X rise in temperature of the water. One calorie = 4.186 joules, J. Nutrition information often uses the kilocalorie, food Calorie = 1000 calories. Most students get values of about 12 kJ per gram but nutrition information on food labels usually quote peanuts at about 25 kJ per gram and peanut butter at about 27 kJ per gram. Repeat the experiment with cashew, marshmallow and popcorn.
2. Repeat the experiment with breakfast cereal. Compare the result of your experiment with the information on the packet. This information is more accurate than your experiment because in a science laboratory, a "bomb calorimeter" is used to burn food samples and calculate the energy stored from the increase in temperature of water around the bomb calorimeter. No heat is lost or unaccounted for during this procedure so you may find that the calorific value on the packet may be three times the result of your experiment!
6.6.22 Food is used in respiration
Put absorbent paper in two identical aluminium trays each and add 50 g of wheat seeds to each tray. To one tray add water that has been shaken with thymol or chloroform to prevent mould growth. Place the trays under a cover raised to admit air. Place both trays in a dark cupboard. When the yellow seedlings are several centimetres high, dry both trays in an oven until the weight is constant. Record your results as the weight of 1. dry seeds 50 g 2. dry seeds after heating 3. germinated seeds after heating.
9.155 Respiration apparatus, test for respiration of soaked peas with limewater
See diagram 9.155: Respiration apparatus
The respiratory activity of organisms can be shown with an apparatus that moves air over leaves, insects or a small animal and bubbles it through a weak solution of limewater, Ca(OH)2. The system must be isolated from atmospheric carbon dioxide. Set up the apparatus as shown in the diagram but leave the fourth container empty. Note the results. Replace the solutions in all bottles. Put peas in the fourth container. Draw air slowly through the apparatus with a filter pump. When the air current bubbles through limewater before passing the soaked peas the limewater remains clear. When the air current bubbles through limewater after passing the soaked peas the limewater becomes milky. As limewater turns from clear to cloudy in the presence of carbon dioxide, the peas must have been respiring.
9.156 Heat energy from respiration of peas
See diagram 9.156: Respiration of peas
Prepare two thermos flasks fitted with one-hole stoppers for the insertion of thermometers. Put dry pea seeds and water to the first thermos flask. Boil the same number of seeds and put them and water in the second thermos flask. Adjust the thermometers in both thermos flasks so that the bulb of each thermometer touches the peas. Note the rising temperature in the first thermos flask. Actively respiring plants generate heat. Note the steady temperature in the second thermos flask until the activity of micro-organisms causes a sharp rise in temperature. Examine the contents of the two thermos flasks.
9.157 Production of carbon dioxide during plant respiration
See diagram 9.157: Production of carbon dioxide during plant respiration
1. Plant respiration can only be observed where no photosynthetic activity occurs. So use fungi or parts of plants that have no chlorophyll necessary for photosynthesis, e.g. mushrooms or the white flowers of the Compositae family, e.g. daisy. Remove the green leaflets of the calyx to prevent photosynthesis. Use the burning time of a candle in an enclosed known volume of air to prove the presence of oxygen. Smear the bottom edge of a big jar with petroleum jelly then put it on a glass plate. Open the neck of the jar then put a lighted candle down the neck on to the glass plate. Be careful! Melting wax from a burning candle can cause severe skin burns so use safety glasses and insulated heat-proof gloves. Close the neck of the jar immediately. Record the burning time of the candle. Put mushrooms or white flowers in the jar. Close the neck of the jar. Two hours later, put the lighted candle into the jar. Record the burning time of the candle. The candle burns a shorter time because plants extract oxygen from the air during respiration.
2. Repeat the experiment by pumping air from the jar through limewater. Continue pumping until the limewater becomes milky to show the presence of carbon dioxide.
9.158 Heat of respiration, bakers' yeast, Saccharomyces cerevisiae
Heat 450 mL 10% sucrose solution to 35oC then add 25 g of bakers' yeast, Saccharomyces cerevisiae. Stir the suspension then pour it into a thermos flask. Fit a 2-hole stopper with a thermometer inserted through one hole. As a control, heat 450 mL 10% sucrose solution to 35oC then pour the solution into an identical thermos flask. Fit a 2-hole stopper with a thermometer inserted through one hole. Record the temperatures every 15 minutes. The temperature in the thermos flask containing the sugar solution and yeast rises but the temperature in the control decreases.
9.159 Rotting banana and rotting grass
1. Squeeze very ripe fruit into a watery mash, banana. Put the mash in a small bottle then fill the bottle with water. Attach a balloon to the mouth of the bottle. Put the bottle and balloon in a warm place. Measure the size of the balloon at the same time each day. The balloon inflates because of the carbon dioxide gas produced by the action of bacteria on the sugars in the rotting fruit.
2. Sterilize rotting grass by boiling in water. Prepare sterile agar containing beef broth in test-tubes sealed with cotton wool. Remove the cotton wool and pour into 2 sterilized dishes, Dish 1 and Dish 2. After pouring the agar immediately replace the dish lids. When the agar is set, use sterilized forceps to rub the sterilized rotten grass over the agar in Dish 1, the control. Replace the lid, and seal with adhesive tape. Rub rotting grass over the agar in Dish 2 and seal with adhesive tape. Leave the dishes upside down and undisturbed in a warm dark place for 4 days. Examine the dishes each day for bacteria and fungi growing in small colonies like dots. The bacterial colonies are usually shiny and smooth. The fungal colonies are usually fuzzy or furry. Note whether bacterial or fungal colonies appeared first and whether they appeared in Dish 1 or Dish 2.
9.160 Food used in respiration
Put absorbent paper in two aluminium foil trays and add 50 g of wheat grains. To one dish add water shaken with thymol to prevent mould growth. Put the trays under jars raised to admit air. Put both trays in the dark. When the yellow seedlings are more than 5 cm long, dry both dishes in an oven until the weight is constant. Record the results as the weight of (a) dry seeds (b) dry seeds after heating (c) germinated seeds after heating.
9.161 Energy from a peanut
1. Put 20 mL of water in a test-tube. Weigh a peanut (about 1 gram). Push the blunt end of a needle into a cork then stick the sharp end into the peanut. Record the temperature of the water in the test-tube. Set alight the peanut with a Bunsen burner then immediately hold it under the test-tube. Record the temperature of the water in the test-tube. Weigh the burnt remains of the peanut. Heat in calories = weight of water multiplied by the specific heat of water multiplied by the rise in temperature of the water. One calorie = 4.186 joules, J. Nutrition information often uses the kilocalorie, food Calorie = 1000 calories. Most school experimenters get values of about 12 kJ per gram but nutrition information on food labels usually quote peanuts at 25 kJ per gram and peanut butter at 27 kJ per gram. Repeat the experiment with cashew, marshmallow and popcorn.
2. Repeat the experiment with breakfast cereal. Compare the result of the experiment with the information on the packet. The packet information is more accurate than this experiment because in a science laboratory, a "bomb calorimeter" is used to burn food samples and calculate the energy stored from the increase in temperature of water around the bomb calorimeter. No heat is lost or unaccounted for during this procedure so may find that the calorific value on the packet may be three times the result of this experiment.
9.162 Alcoholic fermentation
Do not allow students to handle or use pellets of sodium hydroxide.
1. Half fill a test-tube with water, add a piece of yeast the size of a pea, and stir the mixture to produce a uniform suspension of the yeast cells. Three quarters fill two test-tubes with 10%t sucrose solution, and fill a third test-tube with the same amount of water. Add 10 drops of water to one test-tube containing sucrose solution. Add 10 drops of the yeast suspension to the other two test-tubes. Pour the contents of each test-tube into fermentation tubes. Take care that the upright limbs of the fermentation tubes are completely filled with liquid and contain no air bubbles. During the next few days a gas collects in the upright limb of the fermentation tube containing sugar and yeast suspension. No gas collects in the two control tubes, containing sucrose and water or water and yeast suspension.
2. Insert two pellets of potassium hydroxide in the fermentation tube in which gas was produced. Be careful! Pellets of sodium hydroxide as it can cause severe skin burns so use safety goggles and nitrile heat-proof gloves. The gas soon disappears, showing the presence of carbon dioxide. Pour the contents of this fermentation tube into a flat glass dish and note the distinct smell of alcohol. Yeasts ferment sugar to produce alcohol and carbon dioxide.