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Investigating the effects of different lead chloride concentrations on the growth of cress seedlings

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Introduction

A-Level Biology Coursework: Investigating the effects of different lead chloride concentrations on the growth of cress seedlings Ying-Jun Ng Candidate number: 2135 Aim To investigate the effect of different lead chloride concentrations on the growth of cress seedlings Background Information Lead (Pb) is the heaviest non-radioactive metal with an atomic number of 82 and atomic weight of 207. Lead is a soft, malleable but dense, ductile heavy metal with poor electrical conductivity. It is highly resistant to corrosion, and because of this property, it is often used to contain a variety of corrosive liquids. Lead is commonly used in building construction, paints, batteries, plumbing, ammunition and fusible alloys. Metallic lead does occur in nature, but it is rare. Lead is usually found in ore with zinc, silver and copper, and is extracted together with these metals. Apart from how it is found naturally, lead is released into the environment by mining and smelting before it makes its way into the air, soil, and water. Lead can also remain in the environment as dust and as compounds in soil or water. Soils near roads and smelting facilities have higher levels of lead than soils in other areas because of their exposure to lead dust, which accumulates over time. Plants exposed to lead can absorb the metal dust through their leaves. Plants can also take up minimal amounts of lead from the soil. In large amounts lead is potentially life threatening and dangerous to humans and plants alike. For humans, over exposure to lead can cause many symptoms and lead to illnesses. Lead poisoning is a medical condition caused by high levels of lead in the blood. Lead can enter the body by over exposure through inhalation, ingestion and contact. The symptoms of lead poisoning include nausea, abdominal pain, insomnia, metallic taste in the mouth, lethargy and in extreme cases seizures, comas, and even death. ...read more.

Middle

For the grid distribution method seeds will be placed on the cotton face pad in a specific way using a 5x5 grid. In this preliminary experiment a cotton face pad will be used as the medium since it proved to be the most effective medium to grow cress seeds on. Equipment list for Preliminary experiment II 3 x plastic Petri plate 3 x Cotton face pad 5x5 Grid 6 inch ruler 25 cm3 cylinder Chinagraph pencil Cress seeds- 120 seeds Distilled water Freezer bags Rubber bands Tweezers Method 1. Remove the Petri dish lids 2. Measure out 15ml of distilled water using the measuring cylinder and pour the water into each Petri dish. 3. Place a cotton face pad in each Petri dish 4. Count 40 cress seeds and sprinkle randomly onto a Petri dish. 5. Count 40 cress seeds and pour the seeds into a pile in the centre of the Petri dish 6. Count 40 cress seeds and place them accordingly using the 5x5 grid. (20 seeds will take up a 5x4 grid therefore two seeds should be placed in each small square of the grid) 7. Open a freezer bag and check there are no holes in the bag. Flick it capturing as much air as possible in the bag 8. Quickly place a Petri dish inside the bag and hold the bag closed 9. Use a rubber band to secure the bag closed. Make sure the rubber band is tight and that the bag is as full of air as possible 10. Repeat steps 7-9 another two times for the other two Petri dishes 11. Leave all three bags for a week then measure the stem length of each cress seedling and record the results 12. Work out the averages of the results to see which distribution method is best to use (Results of preliminary experiment II are displayed in the appendix-Table B) ...read more.

Conclusion

Dilution factor 15 1 = Volume of stock solution 4 15 Therefore * 1 x 15 = Volume of stock solution Dilution factor 1 x 15 = 3.75= Volume of PbCl2 solution to use 4 * Volume of water needed = 15 - 3.75 = 11.25 cm3 (2dp) E: Table to show the dilution factor of PbCl2 for the Final experiment PbCl2 concentration (mol dm-3) Volume of PbCl2 solution to use (cm3) Volume of distilled water to use (cm3) 0.0150 11.54 3.46 0.0120 9.38 5.62 0.0090 6.76 8.24 0.0060 4.50 10.50 0.0030 2.25 12.75 0.0000 0.00 15.00 Working out dilution factor for each concentration Using 0.0150 mol dm-3 as an example * Dilution factor = Concentration of stock solution Concentration of dilute solution wanted Dilution factor = 0.0200 = 1.3 (1dp) 0.0150 * 1 = Volume of stock solution Dilution factor Volume of dilute solution wanted 1 = Volume of stock solution 1.3 Volume of dilute solution wanted * 1 = Volume of stock solution Dilution factor 15 1 = Volume of stock solution 1.3 15 Therefore * 1 x 15 = Volume of stock solution Dilution factor 1 x 15 = 11.54 cm3 (2dp) = Volume of PbCl2 solution to use 1.3 * Volume of water needed = 15 - 11.54 = 3.46 cm3 (2dp) F: Table to show the biomass of cress seedlings grown with different concentrations of lead chloride for the final experiment Biomass (mg) Cress seed 0.0150 mol dm-3 PbCl2 0.0120 mol dm-3 PbCl2 0.0090 mol dm-3 PbCl2 0.0060 mol dm-3 PbCl2 0.0030 mol dm-3 PbCl2 0.0000 mol dm-3 PbCl2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 (Table continued on next page) Biomass (mg) Cress seed 0.0150 mol dm-3 PbCl2 0.0120 mol dm-3 PbCl2 0.0090 mol dm-3 PbCl2 0.0060 mol dm-3 PbCl2 0.0030 mol dm-3 PbCl2 0. ...read more.

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