Core Practical 6 Investigate Plant Water Relations Edexcel

Core Practical 6 Investigate Plant Water Relations Edexcel Core Practical 6 Investigating Plant Water Relations Edexcel Plants are essential to life on Earth providing us with food oxygen and a variety of other resources Their survival depends heavily on their ability to absorb and transport water a process known as water relations This practical investigates the influence of different environmental factors on plant water relations using a variety of techniques to measure key parameters Aim The aim of this practical is to investigate the influence of environmental factors on plant water relations by measuring Water potential The tendency of water to move from one area to another driven by differences in free energy Transpiration rate The rate at which water is lost from a plant through evaporation from leaves Leaf water content The amount of water present in the leaves of a plant Materials Plants Two or more plants of the same species eg spinach celery or even leafy vegetables from the supermarket Beakers Several beakers of different sizes Distilled water For creating solutions and rinsing Sucrose To create solutions of different water potentials Scissors For cutting plant material Weighing scale To measure plant mass Stopwatch To measure time intervals Ruler To measure leaf area Potted plants optional For observing transpiration Syringe To inject solutions Potometer To measure transpiration rate optional Microscope and slides To observe leaf cells optional 2 Procedure Part 1 Investigating Water Potential 1 Prepare solutions Prepare solutions of different sucrose concentrations eg 0 1 2 3 using distilled water These solutions will represent different water potentials with lower concentrations having a higher water potential 2 Cut leaf discs Using a cork borer cut several identical leaf discs from each plant Make sure to remove the midrib for consistent results 3 Weigh leaf discs Weigh the leaf discs individually and record their initial weight 4 Immerse leaf discs Place the leaf discs in the prepared sucrose solutions ensuring each concentration has a separate beaker 5 Incubate Allow the leaf discs to incubate in the solutions for a set period eg 30 minutes 6 Remove and blot After incubation remove the leaf discs from the solutions blot them dry gently with paper towels and weigh them again 7 Calculate water potential Calculate the change in weight final weight initial weight for each leaf disc This change represents the amount of water absorbed or lost due to osmosis Plot the change in weight against the sucrose concentration to observe the relationship between water potential and water movement Part 2 Investigating Transpiration Rate Method 1 Using a Potometer 1 Set up a potometer Connect a potometer to a plant and ensure the air bubble is positioned correctly 2 Measure baseline rate Allow the plant to acclimate to the potometer for a few minutes and record the initial position of the air bubble 3 Measure transpiration rate Observe the movement of the air bubble over a set time interval eg 10 minutes Record the distance travelled by the bubble and calculate the transpiration rate by dividing the distance by the time 4 Vary environmental conditions Repeat the experiment under different environmental conditions such as light intensity temperature and wind speed Observe the effect of these variables on the transpiration rate Method 2 Using Potted Plants 1 Select potted plants Choose two identical plants of the same species 2 Control conditions Keep one plant as a control under normal room conditions 3 3 Vary conditions Place the other plant under a specific environmental condition such as a fan for increased wind speed or a light source for increased light intensity 4 Measure water loss Measure the water loss from each plant over a set time interval eg 24 hours by recording the amount of water added to maintain the soil moisture 5 Calculate transpiration rate Calculate the transpiration rate for each plant by dividing the water loss by the time interval Part 3 Investigating Leaf Water Content 1 Select leaves Collect several leaves from the same plant ensuring they are similar in size and appearance 2 Weigh leaves Weigh the leaves individually and record their initial weight 3 Dry leaves Place the leaves in a drying oven at a low temperature eg 70C until they are completely dry usually 24 hours 4 Weigh dried leaves Once dry weigh the leaves again and record their final weight 5 Calculate leaf water content Calculate the leaf water content by subtracting the final weight from the initial weight and dividing the result by the initial weight This will give the percentage of water present in the leaves Analysis Water Potential Analyze the data from Part 1 to determine the relationship between sucrose concentration and water movement Plot the change in weight against the sucrose concentration and interpret the results Transpiration Rate Compare the transpiration rates measured under different environmental conditions Part 2 Discuss the influence of each variable on transpiration and explain the underlying mechanisms Leaf Water Content Analyze the leaf water content data Part 3 and discuss the potential factors that could influence the percentage of water present in the leaves Discussion Discuss the importance of water relations for plant survival and growth Explain the mechanisms underlying water potential transpiration and leaf water content Relate the results of the experiment to realworld scenarios and discuss the implications for plant survival in different environments Evaluate the reliability of the data and suggest any potential sources of error Suggest further investigations that could be carried out to expand on the findings of this practical 4 Conclusion This practical provides a comprehensive understanding of plant water relations by investigating the influence of various environmental factors on key parameters The results demonstrate the intricate mechanisms that plants employ to absorb transport and utilize water highlighting their remarkable adaptation to their surroundings Safety Considerations Wear appropriate safety goggles when handling sharp objects like scissors or cork borers Avoid touching or consuming the solutions used in the experiment Dispose of the solutions and plant material appropriately after the experiment Further Information Water potential The water potential of a solution is influenced by factors like solute concentration pressure and gravitational forces Transpiration Transpiration is driven by the difference in water potential between the inside of the plant and the surrounding air Leaf water content Leaf water content varies depending on the plant species environmental conditions and the physiological state of the plant This practical provides a valuable foundation for understanding the crucial role of water relations in plant physiology By investigating these processes students can gain a deeper appreciation for the interconnectedness of life and the vital importance of water for plant survival