Plant Nutrition Experiments PDF

Chapter 6 : Plant nutrition 6.3 FACTORS AFFECTING PHOTOSYNTHESIS Controls Control group: has all the substances that it needs including the substance to be tested For example sometimes the control is a leaf or part of a leaf The control group does not got the variable Experimental group: given ev...

Chapter 6 : Plant nutrition 6.3 FACTORS AFFECTING PHOTOSYNTHESIS Controls Control group: has all the substances that it needs including the substance to be tested For example sometimes the control is a leaf or part of a leaf The control group does not got the variable Experimental group: given everything it needs except for one substance that is to be tested Experimental control: is a set up to test the effect of certain variable Testing leaves for starch  Destarching plants -Means the removal of the stored starch in a plant -The easiest way to do this is to leave the plant in a dark cupboard for at least 24 hours. The plant can’t photosynthesize while they are in the cupboard because there is no light, so they use up their stores of starch. Importance of Destarching : To be sure that any starch can be detected is formed during the experiment, not stored before the experiment  Experimental skills 6.1 Testing a leaf for starch Leaves turn some of the glucose that they make in photosynthesis into starch. If we find starch in a leaf, that tells us if it has been photosynthesising. In this experiment, you will practise working safely, making careful observations and drawing conclusions. You will need: a 250 cm3 beaker Safety a burner, tripod and gauze Alcohol is flammable (burns easily). Do a boiling tube not collect the alcohol until you have some iodine solution, with a dropper turned out your burner. If your alcohol Forceps (or someone else’s) does start to burn, a glass rod put a damp cloth over it immediately some alcohol (methylated spirits) – collect this only when you are ready to use it a fresh green leaf that has been photosynthesising a white tile  Experimental skills 6.1 Method 1. Boil some water in a beaker (Figure 6.17). Take a green leaf from a healthy plant and drop it into the boiling water. This breaks down the cell membranes in the leaf. Leave the leaf in the boiling water for about 30 s. This step is important to a. Denature the enzymes and to prevent any further chemical changes b. Make the cell more permeable to iodine solution by breaking down ( the cell membrane, cell wall and chloroplast membrane) 2. Turn out the flame 3. Put some alcohol into a boiling tube. Stand the tube of alcohol in the hot water - To dissolve the chlorophyll, to be able to observe the change in color after adding iodine solution clearly (water bath is used because alcohol is flammable) Experimental skills 6.1 Method 4. Use the forceps to remove the softened leaf from the hot water. Drop it into the tube of alcohol. Chlorophyll is soluble in alcohol, so it will come out of the leaf. Leave the leaf in the alcohol until all the chlorophyll has come out of the leaf. 5. The leaf will now be brittle (it will break easily). Carefully remove it from the alcohol, and dip it into hot water again to soften it. 6. Spread out the leaf on a white tile and cover it with iodine solution. A blue- black colour shows that the leaf contains starch -If the color remains yellow brown this means that starch is absent -If the color changes to dark blue( blue black) this means that starch is present Experimental skills 6.1/Questions and answers 1) Why did the alcohol become green? The alcohol dissolved the chlorophyll 2) Why was the leaf put into alcohol after being put into boiling water? Boiling broke down the cell membranes, making it possible for chlorophyll to come out of the cells 3) Describe the results of your experiment. What conclusion can you make? The leaf becomes blue-black, indicating that it contains starch 4) Cell membranes are partially permeable. They will not allow starch or iodine molecules to pass through them. Use this information to explain why it was necessary to boil the leaf Boiling breaks down cell membranes. This is necessary because there are membranes around the chloroplasts and around the cell which need to be broken down to allow the iodine to come into contact with the starch, which is inside the chloroplasts inside the leaf cells 5) Suggest why it is a good idea to remove the chlorophyll from the leaf, before adding iodine solution to it to allow any change in colour to be seen more clearly Experimental skills 6.2 Investigating the necessity for chlorophyll for photosynthesis In this investigation, you will use the starch test again. A variegated leaf is one that has some white areas and some green areas (Figure 6.18). You will practise recording your observations with a labelled drawing. Experimental skills 6.2 Investigating the necessity for chlorophyll for photosynthesis You will need - the same apparatus as for Experimental skills 6.1 Testing a leaf for starch - a fresh variegated leaf, taken from a plant that has been photosynthesising Method 1. Make a drawing of your variegated leaf. Do not colour it. Label the parts that are green and the parts that are white 2. Test the leaf for starch, following the procedure described in Experimental skills 6.1 3. Record your results by drawing and labelling the leaf after you have added iodine solution to it. Experimental skills 6.2/Questions and answers Investigating the necessity for chlorophyll for photosynthesis Questions 1. Which parts of the leaf contained starch? the green parts contained starch. 2. Write a brief conclusion for your experiment Chlorophyll is needed for photosynthesis Experimental skills 6.3 Investigating the necessity for light for photosynthesis In this investigation, you will use the starch test to compare the starch content of parts of a leaf that have and have not received light. This is another chance to practise recording results using a labelled drawing, and to write a short conclusion You will need a healthy plant growing in a Safety pot, which has been in a dark Alcohol is flammable (burns cupboard for two days easily). Do not collect the alcohol some black paper, scissors until you have turned out your and paper clips burner. If your alcohol (or (after one day) the same someone else’s) does start to apparatus as for Experimental burn, put a damp cloth over it skills 6.1 Testing a leaf for immediately starch Experimental skills 6.3 Investigating the necessity for light for photosynthesis Method 1. Cut out a shape from the black paper, which you can attach to a leaf. If you like, you can cut your initials into the paper (Figure 6.19) 2. Attach the paper to a leaf on the potted plant. Do not take the leaf off the plant! 3. Put the plant into a place where it gets plenty of light. Leave it until the next day 4. Now remove the leaf from the plant. Remove the black paper from the leaf 5. Test the leaf for starch 6. Record your results by drawing and labelling the leaf after you have added iodine solution to it Experimental skills 6.3/Questions and answers 1. The potted plant was put into a cupboard to make sure it used it up all its starch stores and had no light to be able to make more. This is called destarching. Suggest why this was a necessary part of this experiment. If the plant was not destarched, we would not know whether any starch we found had been made during the experiment or before. 2. Explain why, in this experiment, the leaf had to remain attached to the plant for a day, after you put the black paper onto it. To give the plant time to photosynthesise and make starch 3. Use your results to write a short conclusion to your experiment Light is necessary for photosynthesis Controls o In Experimental skills 6.3, you wanted to find out whether light was needed for photosynthesis. To do this, you needed to be able to compare a part of a leaf that did have light with a part that did not have light The part of the leaf that you did not cover was the control in your experiment. You could compare the part that did not have light with this normal part. If you had covered all the leaf, and found that none of it photosynthesised, you would not be sure that the reason was because it had no light. It could have been because the whole plant was not photosynthesising o In Experimental skills 6.2, you wanted to find out whether chlorophyll was needed for photosynthesis. The white parts of the leaf had no chlorophyll, and you could compare these with the normal, green parts. These green parts were the control in this experiment.  Experimental skills 6.4 Investigating the necessity for carbon dioxide for photosynthesis In this investigation, you will compare the ability of two leaves on the same plant – one with carbon dioxide and one without – to make starch. This is not an easy experiment to set up, so you will probably just use one set of apparatus for the whole class You will need a healthy plant growing in a pot, which has been destarched (see Experimental skills 6.3) Safety: Alcohol is flammable (burns two transparent containers, e.g. conical flasks two rubber bungs to fit the flasks, each with a slit easily). Do not collect the alcohol until in one edge in which a leaf stalk can fit you have turned hout your burner. If petroleum jelly your alcohol (or someone else’s) does a method of supporting the transparent start to burn, put a damp cloth over it containers immediately some potassium hydroxide solution some distilled water (after one day) the same apparatus as for Experimental skills 6.1 Testing a leaf for starch Method 1. Set up the apparatus as shown in Figure 6.20. Note that you will have to find a way of supporting the flasks so that they don’t pull on the leaves – you could use a retort stand and clamps. Once you have that organised, put the liquids into the two flasks. Next, hold one of the leaf stalks carefully, and slot it into one of the rubber bungs. Then gently push the flask over the bung and into its support. Repeat with the other leaf and flask 2. Rub petroleum jelly over the rubber bungs, to try to prevent any air entering or leaving the flask 3. Place the apparatus in a light place and leave it for at least one day Experimental skills 6.4/Questions and answers Investigating the necessity for carbon dioxide for photosynthesis 1. What was the control in this experiment? Either leaf could be said to be the control. One has carbon dioxide and one does not; it is justifiable to say that either one is the experiment, and the other is the control. The essential point is that you need both, in order to compare the results 2. Suggest why distilled water was added to one flask, rather than just leaving it empty This was to control a variable. The only difference between the two flasks is that one has a liquid that absorbs carbon dioxide, and the other has a liquid that does not. Experimental skills 6.4/Questions and answers Investigating the necessity for carbon dioxide for photosynthesis 3. Write a short conclusion for your experiment. Carbon dioxide is necessary for photosynthesis 4. Why was potassium hydroxide put in with one leaf and water with the other? Potassium hydroxide absorbs carbon dioxide. Water does not. Having a liquid in both flasks helps to control a variable. 5. Why was petroleum jelly put around the bungs This prevents carbon dioxide entering the flask from the air.  To show that oxygen is produced in photosynthesis 1. Set up the apparatus shown in the diagram Make sure that the test tube is completely full of water 2. Leave the apparatus near a warm, sunny window for a few days 3. Carefully remove the test tube from the top of the funnel, allowing the water to run out, but not allowing the gas to escape 4. Light a wooden splint, and then blow it out so that it is just glowing. Carefully put it into the gas in the test tube. If it bursts into flame, then the gas is oxygen  Questions and answers) Observation: -Bubbles of a gas evolve in the apparatus which is placed in light (test for this gas using a glowing splint you observe that it relights) Conclusion: Oxygen evolves during photosynthesis Questions 1. Why was this investigation done under water? 2. This investigation has no control. Try to design one Answers 3. to allow oxygen to be collected over water 4. A control could be apparatus identical to the one in the diagram, but with no plant, or design another apparatus but put it in a dark place.  Experimental skills 6.5 Investigating the effect of varying light intensity on the rate of photosynthesis In this experiment, you will use an aquatic plant – that is, one that lives in water. This makes it easy to measure the rate of photosynthesis, because we can see bubbles of oxygen being released into the water. In order to measure a rate, we need to measure how much oxygen is given off in unit time – that You will need is, a definite length of time such as one minute a healthy aquatic plant, which has been in the light Safety and has been Keep water away from the lamp photosynthesising the apparatus shown in Figure 6.21 Before you start Check that you a paperclip know how to use your stopwatch or a lamp timer, and that it is working properly a ruler to measure the distance between the lamp and the plant Experimental skills 6.5 Investigating the effect of varying light intensity on the rate of photosynthesis Method 1. Collect a piece of aquatic plant. Cut off a piece about 7 to 9 cm long. Work out which way up it is. Attach a paperclip to the top of it 2. Set up the apparatus as in the diagram. The paperclip will hold the top of the plant down, so that its cut end floats upwards 3. Place the lamp as close as possible to the beaker. Measure the distance, and record it in a results table like this: Experimental skills 6.5 Investigating the effect of varying light intensity on the rate of photosynthesis Method 4. Start the stopwatch or timer and count the number of bubbles released from the cut end of the stem in one minute. Record this, and then repeat two more times 5. Move the lamp a little bit further from the plant. Measure the new distance, and repeat step 4 6. Repeat step 5 several times, until you have bubble counts for at least five different distances. Do more if you have time 7. Plot your results as a line graph, with distance on the x-axis and mean number of bubbles on the y-axis. Make sure that the two axes are labelled fully, and that you choose suitable scales. Join the points using ruled, straight lines between the points. Experimental skills 6.5/Questions and answers Investigating the effect of varying light intensity on the rate of photosynthesis Questions and answers 1. Explain why an aquatic plant was used in this experiment The plant releases oxygen as bubbles, which we can see and count 2. Light intensity decreases as the distance of the lamp from the beaker increases. Write a conclusion to summarise what your results show about the effect of light intensity on the rate of photosynthesis As light intensity increases, the rate of photosynthesis increases. Experimental skills 6.5/Questions and answers Investigating the effect of varying light intensity on the rate of photosynthesis Questions and answers 3. Lamps produce heat as well as light. Explain why you would be unable to draw a conclusion about light intensity, if you did not use a heat shield The heat shield prevents temperature becoming an uncontrolled variable 4. It is possible to collect the gas given off by the plant and measure its volume. Suggest why this would be an improvement on the method you have used here The bubbles released may not all be the same size. It is also not easy to count them reliably. Measuring volume will give a more reliable indication of the quantity of oxygen released Features of your graph The axes are both fully labelled, including units The scales on both axes go up in even steps The scales use at least half of the graph paper The points are plotted as small, neat crosses in exactly the right place The lines between the points are drawn with a ruler, and exactly meet the centres of the crosses. Experimental skills 6.6 Investigating the effect of carbon dioxide concentration or temperature on the rate of photosynthesis In this experiment, you will use a similar method to Experimental skills 6.5. This time, however, your independent variable will be either carbon dioxide concentration or temperature. You are going to plan your own experiment. You will need the apparatus used in Experimental skills 6.5 if you are going to investigate the effect of carbon dioxide concentration: sodium hydrogencarbonate and a spatula if you are going to investigate the effect of temperature: electronic water-baths, or access to ice and hot water, and a thermometer. Experimental skills 6.6 Investigating the effect of carbon dioxide concentration or temperature on the rate of photosynthesis Method 1) Decide which variable you will investigate – carbon dioxide concentration or temperature. If possible, make sure that different groups in your class investigate different variables 2) Think about how you will vary your chosen variable. You can vary carbon dioxide concentration by adding different masses of sodium hydrogencarbonate to the water that the plant is in. You can vary temperature by standing the beaker in a water-bath at different temperatures, or by adding ice and hot water to the water around the plant You should aim to have at least five values of your independent variable Experimental skills 6.6 Investigating the effect of carbon dioxide concentration or temperature on the rate of photosynthesis Method 3) Think about other variables that you should try to keep constant, and how you will do this 4) Write out your plan. You could structure it like this: o Independent variable and how you will vary it oValues of the independent variable you will use oVariables that you will keep constant, and how you will do this oThe variable that you will measure, and how you will do this oPossible safety risks, and how you will minimise them oAn outline results chart, ready to complete as you work Experimental skills 6.6 Investigating the effect of carbon dioxide concentration or temperature on the rate of photosynthesis Method 5) If possible, exchange your plan with another person in your class who is investigating the other variable. Give them feedback on their plan. Use their feedback to you to make improvements to your own plan 6) When you are ready, carry out your experiment and record your results Experimental skills 6.6/Questions and answers 1. Plot a line graph to display your results Look for these features on the line graph: independent variable (temperature or mass of sodium hydrogencarbonate added) on the x-axis/dependent variable (number of bubbles per minute) on the y-axis/good scales on both axes, going up in sensible and regular intervals, and using at least half of the grid provided/points plotted accurately, as neat crosses/lines drawn with a ruler between points 2. Write a short conclusion 3. You probably encountered some difficulties or problems as you did your experiment. What were they, and how did you overcome them? 4. If you could start again, and had lots of time available, what improvements would you make to your experiment? 2, 3 and 4 These answers will depend on the learner’s results, and their experience in carrying out their planned investigation.  Experimental skills 6.7 Investigating the effect of light and darkness on gas exchange in an aquatic plant In this investigation, you will use a liquid called hydrogencarbonate indicator to look for changes in carbon dioxide concentration in the water around an aquatic plant. You will make careful observations of colour changes, and then use your results and your own knowledge to try to explain them You will need Note four very clean large test-tubes Hydrogencarbonate indicator (boiling tubes) and airtight bungs changes colour according to how to fit them much carbon dioxide there is. The some hydrogencarbonate indicator colours are: solution two pieces of aquatic plant some black paper and sticky tape a rack or beaker to stand the tubes in. Experimental skills 6.7 Investigating the effect of light and darkness on gas exchange in an aquatic plant Method 1) Pour hydrogencarbonate indicator into each of the four tubes, to the same depth in each one. About a third full works well. Record the colour of the indicator in each tube 2) Place a piece of aquatic plant in the indicator in two tubes. Try to use similar sizes of plant in each 3) Use black paper to wrap around one of the tubes with a plant in it, and one without. Make sure the tubes are completely covered (Figure 6.22) 4) Stand all four tubes in the light and leave them for at least one hour – preferably longer. 5) When the indicator has changed colour in at least one of the tubes without a covering, remove the black paper from the two Experimental skills 6.7/Questions and answers Investigating the effect of light and darkness on gas exchange in an aquatic plant Questions and answers 1) Use the information about the colour of hydrogencarbonate indicator to compare the concentration of carbon dioxide in the four tubes Learners should obtain these results: tube in the dark with no plant: orange-red, a little carbon dioxide tube in the dark with a plant: yellow, a lot of carbon dioxide tube in the light with no plant: orange- red, a little carbon dioxide tube in the light with a plant: purple, no carbon dioxide Experimental skills 6.7/Questions and answers Investigating the effect of light and darkness on gas exchange in an aquatic plant Questions and answers 2) Plants, like all living organisms, respire. They do this all the time. Respiration uses oxygen and produces carbon dioxide. In bright light, plants photosynthesise as well as respiring. They photosynthesise faster than they respire. Use this information to explain your results tube in the dark with no plant: There was nothing to alter the concentration of carbon dioxide in the liquid, so it remained the same colour that it started. tube in the dark with a plant: The plant respired, releasing carbon dioxide. tube in the light with no plant; There was nothing to alter the concentration of carbon dioxide in the liquid, so it remained the same colour that it started. tube in the light with a plant: The plant photosynthesised at a Limiting factors If a plant is given plenty of sunlight, carbon dioxide and water, the limit on the rate at which it can photosynthesise is its own ability to absorb these materials and make them react. However, quite often plants do not have unlimited supplies of these materials, and so their rate of photosynthesis is not as high as it might be. A factor that is in short supply, and that therefore limits how quickly the plant can photosynthesise, is called a limiting factor. Light intensity In the dark: a plant cannot photosynthesise at all In dim light: it can photosynthesise slowly As light intensity increases the rate of photosynthesis increases, until the plant is photosynthesising as fast as it can. At this point, even if the light becomes brighter, the plant cannot photosynthesise any faster Light intensity Between A and B, light is a limiting factor. The low light intensity is preventing the plant from photosynthesising any faster. The plant is limited in how fast it can photosynthesise because it does not have enough light. You can tell that this is so because the rising line on the graph shows that as the light intensity increases, the rate of photosynthesis increases Between B and C, however, light is not a limiting factor. You can see this because, even when the light intensity increases, the rate of photosynthesis stays the same. The graph shows that increasing the light intensity beyond B does not Carbon dioxide Carbon dioxide can also be a limiting factor The more carbon dioxide a plant is given, the faster it can photosynthesise. But once the carbon dioxide concentration reaches a certain level, there is no further increase in the rate of photosynthesis. Temperature  The chemical reactions of photosynthesis can only take place slowly at low temperatures, so a plant can photosynthesise faster on a warm day than on a cold one  Some of the reactions involved in photosynthesis are catalysed by enzymes, and therefore temperature affects the rate of photosynthesis in the same way as any enzyme-catalysed reaction Stomata  Carbon dioxide diffuses into the leaf through the stomata -If the stomata are closed, photosynthesis cannot take place because the plant lacks one of its raw materials Stomata often close if the weather is very hot and sunny, to prevent too much water being lost. This means that on a really hot or bright day photosynthesis may slow down Two limiting factors at once Figure 6.25 shows how light intensity affects the rate of photosynthesis, at two different carbon dioxide concentrations First, look at the curve labelled A  As light intensity increases, up to a value of 25 a.u. (arbitrary units), the rate of photosynthesis increases. light intensity is a limiting factor over this range  But if light intensity increases above 25 a.u, there is no change in the rate of photosynthesis. So light intensity is not a limiting factor; it is not lack of light that is stopping the plant from photosynthesising faster. Two limiting factors at once Figure 6.25 shows how light intensity affects the rate of photosynthesis, at two different carbon dioxide concentrations But the graph does show a way of helping the plant to photosynthesise faster, at these high light intensities. We can give it more carbon dioxide  Curve B shows the results for a plant that was given a higher concentration of carbon dioxide. Clearly, it is photosynthesising faster than the one with a low concentration. So, for curve A at high light intensities, carbon dioxide is a limiting factor. Glass house (Green house) Glass House is a building made of glass or transparent plastic above a fertile soil in which plants can grow Importance of using glass house? 1. In the glass house, crops of summer can be cultivated in winter 2. In the glass house, crops of hot region can be cultivated in cold regions 3. In the green house different conditions can be adjusted for optimum rate photosynthesis Glass house (Green house) Growers can pump carbon dioxide into glasshouses to increase carbon dioxide concentration, they can burn butane or natural gas which provides carbon dioxide Glass house (Green house) Glass house can be provided with optimum light intensity 1. If the light intensity is insufficient, artificial light can be added ( in case of using artificial light a reflector is used to reduce the loss of light energy by converging light directly on the plant) 2. If the light intensity is more than the optimum, a blind is used to reduce the light intensity that may harm certain types of plants. ( a blind is a non transparent material) Glass house( Green house) Light reflectors A blind Glass house (Green house) Glass house can be provided with optimum temperature 1. If the temperature becomes above the optimum, certain windows are opened to get rid of the excess heat( the windows in this case are called ventilators) 2. If the temperature is lower than the optimum, a heater is used to attain the optimum temperature Water: Many glass house have automatic watering systems using sprinkles and humidifiers which ensure plants always get enough water Questions and answers Look at Figure 6.24. Between which values of carbon dioxide concentration is carbon dioxide a limiting factor? Explain how you can tell Between 0% and about 0.12%, because over this range the rate of photosynthesis increases as the carbon dioxide concentration increases. Past paper question Students set up the apparatus shown in fig 3.1 to investigate the effect of carbon dioxide concentration on the rate of photosynthesis of a pond plant. The students used five similar pieces of pond water and five different concentrations of sodium hydrogen carbonate solution, which provides the carbon dioxide The students count the number of bubbles produced by the pond water over a period five minutes Explain how the students made sure that the results were due only to the change in Carbon dioxide concentration. Past paper question Answer 1. Keep the temperature same(constant) 2. Water bath and thermometer 3. Keep the light intensity constant/the same 4. Bench lamp + fixed distance Also u can answer 5- same volume of water /Same volume of sodium hydrogen carbonate 6- same length of time 7- same type of pond water 8-same age of plant 9-same number of leaves Group work Refer to the previous slides to create a chart that summarizes all the experiments performed to investigate : 1 Testing a leaf for starch 2. Investigating the necessity for chlorophyll for photosynthesis 3. Investigating the necessity for light for photosynthesis 4. Investigating the effect of carbon dioxide concentration or temperature on the rate of photosynthesis 5. Investigating the effect of varying light intensity on the rate of photosynthesis 6. Investigating the effect of light and darkness on gas exchange in an aquatic plant