Paper 1 Biology Practicals A-level Questions & Answers 100% Answers!!, Exams of Biology

Download Paper 1 Biology Practicals A-level Questions & Answers 100% Answers!! and more Exams Biology in PDF only on Docsity! Paper 1 Biology Practicals A-level Questions & Answers 100% Answers!! 1. Investigation into the effect of a named variable on the rate of an enzyme- controlled reaction a, b, c, f, l 2. Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index d, e, f 3. Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue c, h, j, l 4. Investigation into the effect of a named variable on the permeability of cell-surface membranes a, b, c, j, l 5. Dissection of animal or plant gas exchange or mass transport system or of organ within such a system e, h, j 6. Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth - ANSWER Method In this method the named variable is temperature Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction Any variable can be tested such as: the temperature, pH, concentration of the substrate, and the concentration of the enzyme. - ANSWER1. Make two control samples: ● Take two flat bottomed tubes. ● Add 5cm3 of milk suspension to each tube. ● Add 5cm3 of distilled water to one tube- this control will indicate the absence of enzyme activity. ● Add 5cm3 of hydrochloric acid to the other- this control indicates the colour of a completely hydrolysed sample. 2. Take three test tubes and measure 5cm3 milk into each. Place in water bath at 10°C for 5 minutes to equilibrate. 3. Add 5cm3 trypsin to each test tube simultaneously and start the timer immediately. 4. Record how long it takes for the milk samples to completely hydrolyse and become colourless. 5. Repeat steps 2-3 at temperatures of 20°C, 30°C, 40°C and 50°C. 6. Find the mean time for the milk to be hydrolysed at each temperature and use this to work out the rate of reaction. Conclusion - ANSWERMilk contains a protein called casein which, when broken down, causes the milk to turn colourless. Trypsin is a protease enzyme which hydrolyses the casein protein. ● As the temperature increases from 10°C, kinetic energy increases so more enzyme-substrate complexes form. This means that the rate of reaction increases up to the optimum temperature. ● At temperatures beyond the optimum, bonds in the enzyme tertiary structure break, which changes the shape of the active site. This means that the substrate and enzyme are no longer complementary.. Preparation of stained squashes of cells from plant root tips; set-up and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index - ANSWER1. Heat 1 mol dm-3 HCl at 60°C in a water bath. 2. Cut a small sample of the root tip using a scalpel. 3. Transfer root tip to HCl and incubate for 5 minutes. 4. Remove from HCl and wash sample in cold distilled water and remove the very tip using a scalpel. 5. Place tip on a microscope slide and add a few drops of stain (e.g. toluidine blue O). This makes the chromosomes visible and will therefore show which cells are undergoing mitosis. 6. Lower the cover slip down carefully onto the slide. Make sure there are no air bubbles in the slide which may distort the image, and that the coverslip doesn't slide sideways which could damage the chromosomes. 7. Place under a microscope and set the objective lens on the lowest magnification. 8. Use the coarse adjustment knob to move the lens down to just above the slide. 9. Use the fine adjustment knob to carefully re-adjust the focus until the image is clear (you can use a higher magnification if needed). Investigation into the effect of a named variable on the permeability of cell-surface membranes - ANSWER1. Cut beetroot into 6-10 identical cubes using a scalpel. 2. Wipe/rinse to clean off any pigment released as a result. 3. If investigating temperature: place each of the cubes of beetroot in an equal volume of distilled water (5-15ml). 4. Place each test tube in a water bath at a range of temperatures (30-80°C). 5. If investigating concentration of solvents: create a dilution series of ethanol using distilled water. Ethanol concentrations should range from 0-100% ethanol. 6. Leave the samples for 20 minutes - the pigment will leak out of the beetroot. 7. Set the colorimeter to a blue filter and zero using a cuvette with distilled water. 8. Filter each sample into a cuvette using filter paper. 9. Measure the absorbance for each solution. A higher absorbance indicates higher pigment concentration, and hence a more permeable membrane. Graph and conclusions for Investigation into the effect of a named variable on the permeability of cell-surface membranes - ANSWER● Plot a graph of absorbance against ethanol concentration/temperature. Conclusion Temperature ● As the temperature increases, the permeability of the cell-surface membrane also increases. This is because the proteins in the membrane denature as the heat damages the bonds in their tertiary structure. This creates gaps in the membrane, so it is easier for molecules to pass through it. ● At low temperatures, phospholipids have little energy and are packed closely together to make the membrane rigid. This causes a decrease in permeability and restricts molecules from crossing the membrane. NB: At very low temperatures, ice crystals can form which pierce the cell membrane and increase the permeability. Concentration of ethanol ● Ethanol causes the cell-surface membrane to rupture, releasing the betalain pigment from the cell. Higher concentrations of ethanol will cause more disruption to the membrane and more gaps will form. Thus, as concentration of ethanol increases, the permeability of the cell-surface membrane also increases Dissection of animal or plant gas exchange or mass transport system or of organ within such a system - ANSWERDissecting instruments should be clean and sharp. • Disinfectant and hand washing facilities should be available. To open the heart, start at the aorta and cut around the outside edge of the heart. • Lay the heart flat on a dissection board and label the structures. • Dispose of all items including gloves and paper towels in a special disposal bag. Dissection of animal or plant gas exchange or mass transport system or of organ within such a system - the drawing skills - ANSWERUse a sharp HB pencil ● Make sure drawing is large enough for detail and labels (at least half a page advisable) ● No shading ● Use single and continuous lines (no sketching) ● Label lines should be drawn with a ruler ● Do not cross label lines ● Lines should not have any arrows ● Label all the structures ● Do not use colour ● Include a magnification/scale Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth - ANSWER1. Carry out aseptic techniques in next flashcard. 2. Use a sterile pipette or wire hoop to transfer bacteria from broth (distilled water, bacterial culture, nutrients) to agar plate (petri dish containing agar jelly). 3. Spread bacteria evenly over plate using a sterile plastic spreader. 4. Use sterile forceps to place a multi disc antibiotic ring on the plate. Ring should only be moved by holding the centre, NOT the arms. 5. Lightly tape a lid on, invert and incubate at 25°C for 48 hours. DO NOT tape around the entire dish as this prevents oxygen entering and so promotes the growth of more harmful anaerobic bacteria. 6. Sterilise equipment used to handle bacteria and disinfect work surfaces. After Incubation 7. Measure the diameter of the inhibition zone (clear circle) for each antibiotic. DO NOT remove the lid from the agar plate. 8. Work out the area of the inhibition zone using the formula: Pi*(diameter)/4 Aseptic Techniques - ANSWERAseptic Techniques ● Wipe down surfaces with antibacterial cleaner, both before and after experiment. ● Use a Bunsen burner in the work space so that convection currents draw microbes away from the culture. ● Flame the wire hoop before using it to transfer bacteria. ● Flame the neck of any bottles before using them to prevent any bacteria entering the vessel (air moves out so unwanted organisms don't move in). ● Keep all vessels containing bacteria open for the minimum amount of time. ● Close windows and doors to limit air currents