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Notes On Lab Practicals

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Published in: Biology
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Biology practicals for A levels

Rissa S / Abu Dhabi

4 years of teaching experience

Qualification: Bachelor of Secondary Education Major in Biology

Teaches: Science

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  1. INTERNATIONAL A LEVEL BIOLOGY Core Practical Student Sheet @Pearson Core Practical 10: Investigate the effects of light intensity, light wavelength, temperature and availability of carbon dioxide on the rate of photosynthesis using a suitable aquatic plant Objectives • To understand how to measure the rate of photosynthesis by measuring oxygen production • To investigate the effect of changing the light intensity, light wavelength, temperature and availability of carbon dioxide on the rate of photosynthesis Safety • Wear eye protection. • Avoid skin contact with the sodium hydrogencarbonate and be careful not to raise or inhale any dust from it. • Do not handle electric sockets, plugs or switches with wet hands. • Wash your hands with soap and water after all practical work is finished. Maths skills • Find arithmetic means. • Understand the terms mean, median and mode. • Understand measures of dispersion, including standard deviation and range. • Plot two variables from experimental or other data. Equipment eye protection piece of pondweed large beaker of water sodium hydrogencarbonate aluminium foil spatula light filters photosynthometer Procedure Planning paperclip bench lamp ruler thermometer stop clock balance (accurate to 0.05 g) weighing boats water baths or beakers of water at different temperatures 1. Before starting this investigation, you should examine the equipment and read all the instructions carefully. If you have time, set up a pilot run. 2. Choose an independent variable from: light intensity, light wavelength, temperature and availability of carbon dioxide. Record your variables in the space below. Independent variable: Dependent variable: O Pearson Education Ltd 2019. Copying permitted for purchasing institution only. This material is not copyright free. Practical activities have been safety checked but not trialled. Users may need to adapt the risk assessment information to loca circumstances. This document may have been altered from the original.
  2. INTERNATIONAL A LEVEL BIOLOGY Core Practical Student Sheet @Pearson 3. There are many other variables that should be controlled, but these have not been accounted for in the instructions. Identify all factors that should be controlled and give details of how they will be controlled. Control variable Part 1: Light intensity How to control the variable 2. 3. 4. 5. 6. 7. 8. 9. . Place a piece of pondweed, approximately 10 cm long, in a large beaker of water. Remove any bubbles by gently running a finger and thumb over the surface of the pondweed under the water. Cover one side of the beaker with aluminium foil, so that light can only enter the beaker from the other side. Add half a spatula of sodium hydrogencarbonate to the water and leave for 5 minutes. Position the bench lamp 10 cm from the beaker. Allow the pondweed to adjust for 5 minutes. Fill the capillary tubing of the photosynthometer with water. Place the funnel end of the tubing in the beaker of water and position the pondweed with the cut end at the top of the funnel opening (as shown in figure A). A paperclip attached to the opposite end of the pondweed can help to weight it in the correct position. As bubbles of oxygen begin to form and pass into the capillary tubing, start the stop clock. After a suitable time, use the syringe to draw any oxygen produced into the capillary tubing. Record the volume of gas produced. Use the syringe to refill the capillary tubing, then begin recording again. Using the same pondweed and apparatus, repeat steps 7 and 8 with the lamp at different distances from the beaker. If you have time, take repeat measurements for each distance. capillary tubing thermometer aluminium foil light source pondweed scale syringe figure A Measuring the rate of photosynthesis by measuring oxygen production O Pearson Education Ltd 2019. Copying permitted for purchasing institution only. This material is not copyright free. Practical activities have been safety checked but not trialled. Users may need to adapt the risk assessment information to loca circumstances. This document may have been altered from the original. 2
  3. INTERNATIONAL A LEVEL BIOLOGY Core Practical Student Sheet Part 2: Light wavelength @Pearson . Place a piece of pondweed, approximately 10 cm long, in a large beaker of water. Remove any bubbles by gently running a finger and thumb over the surface of the pondweed under the water. Cover one side of the beaker with aluminium foil, so that light can only enter the beaker 2. from the other side. Add half a spatula of sodium hydrogencarbonate to the water in the beaker and leave 3. for 5 minutes. Position the bench lamp close to the beaker with a colourless filter between the lamp and 4. the beaker. This will be a white light control. Allow the pondweed to adjust for 5 minutes. Fill the capillary tubing of the photosynthometer with water. 5. Place the funnel end of the tubing in the beaker of water and position the pondweed 6. with the cut end at the top of the funnel opening (as shown in figure A). A paperclip attached to the opposite end of the pondweed can help to weight it in the correct position. As bubbles of oxygen begin to form and pass into the capillary tubing, start the stop 7. clock. After a suitable time, use the syringe to draw any oxygen produced into the capillary tubing. Record the volume of gas produced. Replace the filter with a filter of a different colour and leave for 5 minutes. 8. Use the syringe to refill the capillary tubing, then begin recording again. 9. 10. Using the same pondweed and apparatus, repeat steps 7—9 with a range of different coloured filters. If you have time, take repeat measurements for each filter. Part 3: Temperature . Set up five water baths at your chosen temperatures. 2. Place a piece of pondweed, approximately 10 cm long, in a large beaker of water. Remove any bubbles by gently running a finger and thumb over the surface of the pondweed under the water. Add half a spatula of sodium hydrogencarbonate to the water in the beaker and leave 3. for 5 minutes in the first water bath. 4. Position the bench lamp 15 cm from the beaker. Allow the pondweed to adjust for 2 minutes. Fill the capillary tubing of the photosynthometer with water. 5. Place the funnel end of the tubing in the beaker of water and position the pondweed 6. with the cut end at the top of the funnel opening (as shown in figure A). A paperclip attached to the opposite end of the pondweed can help to weight it in the correct position. As bubbles of oxygen begin to form and pass into the capillary tubing, start the stop 7. clock. After a suitable time, use the syringe to draw any oxygen produced into the capillary tubing. Record the volume of gas produced. Use the syringe to refill the capillary tubing, then begin recording again. 8. Using the same pondweed and apparatus, repeat steps 7 and 8 at the other 9. temperatures. If you have time, take repeat measurements for each temperature. Part 4: Availability of carbon dioxide 1. Place a piece of pondweed, approximately 10 cm long, in a large beaker containing 400 cmg of water. Remove any bubbles by gently running a finger and thumb over the surface of the pondweed under the water. O Pearson Education Ltd 2019. Copying permitted for purchasing institution only. This material is not copyright free. Practical activities have been safety checked but not trialled. Users may need to adapt the risk assessment information to loca circumstances. This document may have been altered from the original. 3
  4. INTERNATIONAL A LEVEL BIOLOGY Core Practical Student Sheet @Pearson 2. 3. 4. 5. 6. 7. 8. Add 0.5 g of sodium hydrogencarbonate to the water and leave for 5 minutes. Position the bench lamp 10 cm from the beaker. Allow the pondweed to adjust for 5 minutes. Fill the capillary tubing of the photosynthometer with water. Place the funnel end of the tubing in the beaker of water and position the pondweed with the cut end at the top of the funnel opening (as shown in figure A). A paperclip attached to the opposite end of the pondweed can help to weight it in the correct position. As bubbles of oxygen begin to form and pass into the capillary tubing, start the stop clock. After a suitable time, use the syringe to draw any oxygen produced into the capillary tubing. Record the volume of gas produced. Use the syringe to refill the capillary tubing, then begin recording again. Repeat steps 1—7 to test a range of different masses of sodium hydrogencarbonate. If you have time, take repeat measurements for each mass. Analysis of results 1. Convert your results to a rate in mms min-I and add these values to your results table. 2. Calculate the mean results for each value tested. Add these values to your results table. 3. Plot a graph to show the mean rate of photosynthesis for each value. Indicate the spread of data using the range or standard deviation. 4. Write a conclusion to discuss your results. Learning tips • Terrestrial plants require carbon dioxide as the carbon source for photosynthesis. For aquatic plants, this can be supplied by hydrogencarbonate ions in water. It is unlikely that you will be able to carry out investigations into all four of the limiting factors. However, you should be aware of the methods used. Questions . Describe the assumptions made about the gas bubbles to enable the calculation of the rate of photosynthesis. Evaluate the validity of these assumptions. 2. Suggest one way in which the investigation could be improved to make the results 3. more reliable. This investigation measured the production of oxygen in a given time to indicate the 4. rate of photosynthesis. Suggest two other measurements that could have been used. Exam-style question 1. Hydrogencarbonate indicator solution changes colour when carbon dioxide is present at varying concentrations in water. Under normal atmospheric conditions, the indicator is orange/red. When levels of carbon dioxide are high, the indicator is yellow. When carbon dioxide is depleted, the indicator is purple. Design a laboratory experiment in which hydrogencarbonate indicator is used to investigate the effects of different wavelengths of light on the rate of photosynthesis in pondweed. O Pearson Education Ltd 2019. Copying permitted for purchasing institution only. This material is not copyright free. Practical activities have been safety checked but not trialled. Users may need to adapt the risk assessment information to loca circumstances. This document may have been altered from the original. (5) 4

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