Paper One Required Practicals Flashcards
How is the slide prepared in light microscopes used to observe plant cells?
❶ add a drop of water to the middle of a clean slide.
❷ cut up an onion and separate into layers using tweezers to peel off some epidermal tissue from the bottom of one of the layers.
❸ place tissue into the water on the slide using tweezers.
❹ add a drop of iodine.
❺ place cover slip on top.
↳ try to avoid getting air bubbles as it can obstruct the view of the specimen.
Name the parts of a light microscope.
GO LOOK AT ANSWERS.
How do you use a light microscope to look at your slide?
❶ clip the slide you’ve prepared onto the stage.
❷ select the lowest powered objective lens
↳ the one with lowest magnification.
❸ use the coarse adjustment knob to move the stage up just below the objective lens.
❹ look down the eyepiece and use the coarse adjustment knob to move the stage downwards until the image is roughly in focus.
❺ adjust the focus with the fine adjustment knob until you get a clear image of whats on the slide.
How do you find out the effect of osmosis on plant tissue?
❶ cut ups potato into identical cylinders.
❷ get some beakers with different sugar solutions in them.
↳ one of them be pure water and the other very concentrated sugar solution then the others concentrations in between.
❸ measure the mass of the cylinders then leave a cylinder in each beaker for twenty four hours or so.
❹ take them out and dry them with a paper towel and measure their masses again.
❺ if they increased in mass, the cylinder has drawn in water by osmosis and if the decrease in mass, water has been drawn out.
How to use the benedict’s test to test for sugars?
❶ prepare a food sample and transfer 5 cm³ to a test tube.
❷ prepare a water bath so its set to 75°C.
❸ add benedict’s solution to the test tube using a pipette.
❹ place the test tube in water bath using a test tube holder and leave it for 5 minutes making sure the tube is facing away from you.
❺ if the food sample contains reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick red depending on how much sugar is in the food.
How to use the iodine solution to test for starch?
❶ make a food sample and transfer 5 cm³ of your sample to a test tube.
❷ add a few drops of iodine solution and gently shake to mix contents.
❸ if the sample contains starch, the colour of the solution will change from browny-orange to black or blue-black.
How to use the biuret test to test for proteins?
❶ prepare a sample of your food and transfer 2 cm³ of your sample to a test tube.
❷ add 2 cm³ of biuret solution to the sample and mix the contents of the tube by gently shaking it.
❸ if it contains protein, the solution will turn from blue to purple.
How to use the sudan III test to test for lipids?
❶ prepare a sample of the food you’re testing and transfer 5 cm³ into a test tube.
❷ use a pipette to add 3 drops of sudan III stain solution to the test tube and gently shake the tube.
❸ if the sample contains lipids, the mixture will separate into two layers and the top layer will be red.
