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The effect of inhibitors on the germination and growth of cress seeds

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The effect of inhibitors on the germination and growth of cress seeds Introduction Germination process Before seeds can mature into plants, they need to germinate. When the seed's internal and external conditions are favourable (specific for different seed species), their natural dormancy period brakes and germination begins. The limiting factors for germination are: Temperature (within a specific range limit) Light (Some seeds e.g. lettuce require differing wavelengths of light to germinate; others require specific intensities) Oxygen Water (An adequate supply) When given the right conditions, imbibition occurs as seeds take in water through the testa via osmosis and they enlarge in size. Water dissolves the hormone gibbellerinic acid in the cotyledon which diffuses across the aleurone layer and activates the gene coding for amylase. Amylase is then synthesised by the aleurone layer and diffuses into the endosperm and hydrolyses the starch store present which produces maltose. This is then hydrolysed to glucose which diffuses into the embryo and used in aerobic respiration. When the seed is fully turgid, the testa ruptures and splits allowing oxygen to penetrate the seed for respiration to occur. When seeds begin to respire and utilise glucose, they begin to lose mass until leaves are developed and photosynthesis occurs; they then increase in mass. ...read more.


Weighing dish Thermostatically controlled oven Glass dish Large conical flask Large metal spoon Dessiccator Method * Scoop pulp from half of tomatoes, sieve to discard seeds and place in clean processor. Discard remaining flesh. * Measure 250 ml of propanone and add to pulp. Process for 3 minutes. Pour mixture into glass dish and cover to prevent evaporation. * Repeat above procedure for remaining tomatoes and add mixture to glass dish. Mix thoroughly with large spoon. * Filter the mixture using the funnel lined with filter paper and pour extracts into the conical flask. * Label 1 syringe 'water' and 1 syringe 'extract' to avoid successive contamination of extracts and control. * Label 6 tests tubes in holder : 1) Control 2) 20% 3) 40% 4) 60% 5) 80% 6) 100% * Using the 'water' syringe, add 10 ml distilled water to tube 1. Using the 'extract' syringe add 2 ml of extract tube 2, 4 ml of extract to tube 3, 6 ml of extract to tube 4, 8 ml of extract to tube 5 and 10 ml of extract to tube 6. Seal the tubes. * Line each petri dish with cotton wool of equal amounts and depth. ...read more.


Mass loss of 15 seeds (g) % mass loss or gain of 15 seeds 3 4 5 6 7 8 9 Plot a graph of % mass loss or gain (y-axis) against days for each extract. By calculating the gradient of each graph you can discover the rate of change of mass (g day -�). Comparing each rate from each graph you will be able to see which concentration of inhibitor had the most inhibitory effect on growth. The smallest rate should correspond with the 100% concentration. Using day 2 and 3 percentage germination data calculate mean % germination and plot a graph of extract (x-axis) against mean % germination (y-axis). From this you should be able to see a negative correlation between the variables. This will tell you there is a direct inhibitory effect on germination by the extracts. Graphs could also be drawn to display rate of germination. Extract Mean % germination Control (0%) 20% 40% 60% 80% 100% Risk assessment and safety Propanone is an irritant to eyes skin and lungs and is highly flammable. * Extracts should be produced and used in the fume cupboard/ if unavailable wear a mouth mask. * Extracts should be kept away from flames and dishes and bottles covered * Wipe away spillages with paper towels * Wear safety goggles and gloves * Handle the scalpel and blade carefully ?? ?? ?? ?? ...read more.

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