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Factors that affect the growth in duckweed.

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Emma Phipps Factors that affect the growth in duckweed. PLANNING SECTION Introduction For healthy growth plants need several substances. Three important mineral ions that can only be obtained from the soil through their roots are nitrates, phosphates and potassium. Nitrates are essential for making amino acids and for the 'synthesis' of proteins. Phosphates are essential as they have an important role in reactions involved in photosynthesis and respiration. Potassium is also important as it helps the enzymes involved in photosynthesis and respiration to work. The three main minerals are needed in fairly large amounts, but other elements are required in much smaller amounts. Iron and magnesium are the most important as they are needed to make chlorophyll. Without photosynthesis, along with minerals, plant growth wouldn't take place. Photosynthesis produces glucose for 'food' and takes place in the leaves of all green plants. Glucose is combined with nitrates (collected from the soil) to make amino acids, which are then made into proteins. Protein amino acid contains carbon, hydrogen, oxygen and nitrogen. Along with potassium, phosphorus and sulphur make up the important substances that travel through the roots and up the stem. Photosynthesis needs carbon dioxide, water, light and chlorophyll to continue the process. Without iron and magnesium chlorophyll couldn't be made and therefore the plant would die. Diffusion takes place in the leaves, through the stomata. The membranes allow substances in and out as particles from an area of high concentration move to an area of low concentration. ...read more.


I predict that less than 10 drops of Baby Bio will not have much effect on the duckweed, and more than 10 drops will cause the duckweed to die. I took some of this information from my CGP revision books, SAP's website and SAM Learning. Apparatus * 18 petri dishes * Baby Bio * 500cm3 Distilled water * 2 Pipettes * 1 Beaker * Duckweed - Lemma minor Method * Take the duckweed from the water, dry it out using paper towels and weigh it on a small piece of paper towel - make sure the bit of paper is weighed first * Put 500cm3 of distilled water into a beaker and add the amount of drops needed, starting with 4 drops and going up to 20 drops * Stir it and then put 10cm3 of the solution in each petri dish for the 3 tests for each concentration of Baby Bio * Do this for each concentration, making sure each dish is labelled * For the next 3 weeks weigh the duckweed in each dish, making sure it is dried out before * Keep a record of the results Fair Testing To try and keep this test as fair as possible I am going to keep the amount of water in the petri dishes the same. Also I am going to weigh the duckweed at the same time each week. The mass of the duckweed will vary in each petri dish, as it deemed quite hard to get the mass to be the same each time. ...read more.


This is because: * We didn't look at the duckweed at regular intervals * We didn't sieve the duckweed properly * We patted the duckweed dry - it squashes them + they die above 320C * We had errors transferring the duckweed to the balance * We weighed duckweed on wet filter paper * The water evaporated, which increased osmosis To improve the experiment we need to: * Find a better method of weighing * Use a fresh concentration of solution so that it will be constant * Use filter paper to sieve duckweed * Use forceps to transfer duckweed to dry filter paper on the balance, and then back to the petri dish We could do the same experiment but instead of weighing, we could count the number of leaves. Or we could use squared paper to find the surface area by taking a sample of 10 or 20 - this would give a good range. Another way is to harvest 100 duckweeds, dry them in the oven, and then weigh the dry mass of the dead duckweed. We would weigh different samples from the same conditions every week. However, by taking more out, the duckweed left behind have less competition for nutrients. So we could put 100 duckweeds in 6 petri dishes with the same concentration and would prove to be more accurate over a period of 6 weeks. The fertiliser increases the growth up to a point. We could put the duckweed at the bottom of a graduating tube, fill it up with water, and measure the amount of oxygen each week. ...read more.

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