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Seed Germination

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Daniel Thomson-Smith Seed Germination Coursework-Skill P Aim-To investigate the effects of heavy metals on the growth of cress seedlings. Background Information Heavy Metals A heavy metal is an element, which has an atomic number higher than 20. The metals have a metallic appearance at room temperature, but the metals are toxic in low concentrations, which are relevant to the investigation of the effects on seed growth. Irrespective of metal density, if the metal is toxic then it is known as a heavy metal. Heavy metals are natural components of the earths crust and trace elements of heavy metals are needed to maintain the metabolism of the human body. Some examples needed are copper, selenium and zinc. Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation is the increase in concentration of a chemical in a biological organism in a period of time, compared to the chemical's concentration in the environment. Compounds accumulate in living organisms any time they are taken up and stored faster than they are broken down (metabolized) or excreted. Examples of Heavy Metals Examples of heavy metals include: Mercury (Hg) Cadmium (Cd) Arsenic (As) Chromium (Cr) Thallium (Tl) and Lead (Pb) As lead is a common metal found in the environment, I have used this heavy metal for the investigation. Lead accumulates in soil organisms, as heavy metal compounds such as lead chloride can dissolve in rain water and are absorbed into the plant through active transport. Lead is a bluish-white metal. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity. It is very resistant to corrosion but tarnishes upon exposure to air. Native lead is rare in nature. Currently lead is usually found in ore with zinc, silver and copper and it is extracted together, with these metals. The majority of lead concentrations in the environment are from human activities, with the combustion of leaded petrol releasing lead salts into the atmosphere. ...read more.


The coleoptiles and radicles should also be shorter than the control tests. Chelate proteins used in the active transport (see background for active transport) of nutrients into the seed are denatured by lead nitrate, as lead has an affinity for sulphur. The lead binds to the covalent sulphur-sulphur interactions which are broken which denatures the chelate protein. If the chelate protein can not bind with essential nutrients, then active transport will stop. If the chelate proteins are denatured, then the seed will not be able to take up magnesium which is essential for the production of chlorophyll. Magnesium is the central metal ion bonded to the porthyrin ring. If magnesium is not obtained by the seed, then chlorophyll is not produced which is used in the light dependent stage of photosynthesis. The light-dependent stage of photosynthesis uses light absorbed by chlorophyll pigments to provide ATP and NADPH which is needed for the reduction of carbon dioxide to carbohydrate in the light independent stage. Chlorophyll a has two forms of peak absorption p700 and p680, with chlorophyll b and carotenoids used in accessory pigments. If magnesium is not present than the plant cannot capture light energy from across the spectrum, which means ATP + NADPH synthesis stops. Photophosphorylation of ADP to ATP is either carried out by cyclic or non-cyclic photophosphorylation. Non-cyclic photophosphorylation involves the use of both photosystem I and II, where light energy takes electrons to a higher state of energy. Electrons are absorbed by electron carriers which are where ATPsynthase converts ADP and inorganic phosphate to ATP. Electrons end up at photosystem I which are used to reduce NADP to NADPH for the light independent reaction. Electrons are replaced at photosystem II by photolysis. Cyclic photophosphorylation does not need NADP, so NADP is not reduced in this process, but ATP is still synthesised. 'Z-Scheme'/Non-Cyclic Photophosphorylation If photosynthesis does not take place because chlorophyll production is inhibited by the lack of magnesium, then ATP and NADPH are not available for use in the light dependent reactions in the Calvin-Benson cycle. ...read more.


Less than 10 seeds mean that there would be more light, water, space and nutrients which would also affect the reliability of results. Temperature All Petri dishes kept in the same laboratory. Germination is enzyme dependent. If the temperature is closer to the optimum temperature then germination will be faster. If temperature is cooler or further from the optimum then germination occurs slowly. High temperatures denature enzymes which stops germination. Light Intensity Same place in the laboratory If light intensity is lowered, there is reduced production of ATP and NADPH which means less glucose is made in the independent reaction. If light intensity is higher then more ATP and NADPH is produced increasing growth as there is more glucose. Volume of Solution Same volume of 3cm3 obtained using a 5cm3 syringe. A larger volume would result in a larger difference on negative growth, with less volume resulting in more growth available in lead nitrate solution. Time cress seedlings were left in solutions All seedlings were left in solutions for 1 week. If the time is longer than a week then seed growth would be seen to have a more negative impact. Less than a week and the full effect of lead nitrate may not be seen. Health and Safety Procedure Risk Precaution Making 1.000M solution of lead nitrate and serial dilutions Lead nitrate in large amounts can damage fertility * Goggles-prevents splashes to eyes. * Gloves-prevents contact between lead and skin * Warning tape-to warn others lead nitrate can be dangerous. * Spillage Kit-allows any spillages to be cleaned safely. * Wash benches-prevents anybody coming into contact with the lead. Using glassware breakages * Handle glass carefully. * In the instance of breakages, double wrap in newspaper and dispose of in a glass bin. * If skin is cut use a sterile wipe and cover with a plaster. Sterile wipes clean away bacteria, chemicals and impurities. The plaster reduces the risk of contamination. Results Concentration of lead nitrate (molar) Number of seeds germinated Average length of coleoptile (mm) Average length of radicle (mm) 0.100 0.075 0.050 0.025 0.010 0. ...read more.

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