Methods For PAGS Flashcards
How to prepare a wet mount?
1) Pipette a small drop of water onto the slide.
2) Then use tweezers to place the specimen on top of the water drop.
3) carefully lower the cover slip on top of the slide using a mounted needle to avoid air bubbles.
4) This step is only if specimen needs to be stained. add a drop of stain next to the edge of the cover slip, put a bit of paper towel next to the opposite side. The stain will get drawn under the slip covering the specimen.
How to use a light microscope?
1) start by clipping the slide onto the stage
2) use the lowest powered objective lens. Use the coarse adjustment knob to bring the stage up to just below the objective lens
3) look down the eyepiece. Use the coarse adjustment knob ti move the stage downwards away from the objective lens until the image is roughly in focus
4) adjust the focus with the fine adjustment knob until you get a clear image.
5) if you need to see th slide with greater magnification, use a higher powered objective lens and refocus
How to use a eyepiece graticule and stage micrometer to measure size of specimen?
1) line up the eyepiece graticule and the stage micrometer.
2) each division on the stage micrometer is 0.1mm long.
3) at the wanted magnification, work out how many divisions on the stage micrometer is equal to how many divisions on the eyepiece graticule eg 1 division on the stage micrometer is 5 divisions on the eyepiece graticule.
4) this means every division on the eyepiece graticule is 0.1/5= 0.02mm.
5) if you look an object under the microscope at the wanted magnification and find it is 20 eyepiece divisions long, you know it measures 0.02 x 20= 0.4mm
How to carry out serial dilutions to produce solutions of different concentrations?
1) line up 5 test tubes in a rack
2) add 10cm3 of the initial glucose solution to the first test tube and 5cm3 of water to the other 4.
3) Then using a Pipette, draw 5cm3 of the solution of the first test tube and add to the distilled water in the second test tube. Mix solution thoroughly using glass rod. This is half as concentrated at initial solution.
4) repeat this process 3 more times. Replace Pipette every time.
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How to determine unknown concentration of glucose using colorimeter?
1) Carry out a serial dilution to work out known concentrations of glucose solutions. carry out Benedict’s test on each solution . Use same volume of Benedict’s solution in each case.
2) remove any precipitate.
3) Calibrate/zero a colorimeter using a blank. Add a red filter.
4) measure the Absorbance of the solution.
5) use results to plot a calibration curve showing Absorbance against glucose concentration.
6) repeat test for unknown solution in the same way and use the calibration curve to find its concentration
How to carry out paper chromatography to identify unknown amino acids?
1) draw pencil line near bottom of chromatography paper. Put concentrated spot of mixture of amino acids.
2) add small volume of prepared solvent, to a beaker and dip the bottom of the paper into it. This should be done in a fume cupboard.
3) as the solvent spreads up the paper, the different amino acids move with it, but seperate.
4) when the solvent has reached almost the top of the paper, take paper out and mark solvent front. Leave out to dry before analysing.
5) before analysing, spray the paper with ninhydrin solution to turn amino acids purple.
6) calculate Rf values and compare to known database.
How to purify DNA using a precipitation reaction?
1) break up the cells using pestle and mortar. This breaks cell walls
2) add detergent to cells and heat in water bath, this breaks cell membranes. Heat in water bath prevents enzymes working properly.
3) put beaker in ice bath to cool. When it’s cooled, filter the mixture.
4) add protease enzymes to mixture, this breaks down histones associated with the DNA.
5) slowly add cold ethanol down the side of the tube. Leave tube for a few minutes. White precipitate should form.
What is one way in which you can monitor enzyme activity?
You can measure how fast the product of a reaction appears. For example with catalase, you can see how quickly oxygen is produced.
1) Mix a solution containing hydrogen peroxide and catalase in a test tube.
2) Seal it using a bung with a delivery tube.
3) Place the end of the delivery tube into an inverted measuring cylinder filled with water.
4) As oxygen is produced, it will displace the water in the measuring cylinder. You can then measure how much oxygen is being produced per minute.
What is another way you can measure rate of enzyme controlled reaction.
You can see how quickly the substrate disappears.
1) Mix a solution containing starch and amylase in a test tube.
2) Place a drop of iodine solution in each well of a spotting tile.
3) At each minute, use a pipette to take a sample from the starch/amylase mixture. Drop this into a well containing iodine solution.
4) The iodine solution will turn blue-black if starch is present. Record the time when the solution no longer changes colour – this is when the reaction is complete. You can then use it to calculate the average rate of reaction (i.e. the rate at which starch is being broken down by amylase) per minute.
How to investigate effect of temperature on permeability of the cell membrane?
1) cut 5 equal sized pieces of beetroot and rinse them to remove any pigment released during cutting.
2) place the 5 pieces in 5 different test tubes, each with 5cm3 of water.
3) place each test tube in a water bath at different temperatures eg 10, 20, 30, 40, 50 degrees, for the same length of time.
4) remove beetroot from test tubes leaving just the liquid.
5) now use colorimeter. The higher the permeability, the more pigment is released so the higher the Absorbance of the liquid.
6) controls: size of beetroot, the area of beetroot pieces are selected from, time they are rinsed.
7) if testing ethanol, each test tube contains different concentrations of ethanol. These can be created with serial dilutions.
How to investigate breathing using spirometer?
1) a spirometer has an oxygen-filled chamber with a moveable lid.
2) the person breathes through a tube connected to the oxygen chamber.
3) as the person breathes in and out, the lid of the chamber moves up and down.
4) these movements can be recorded by a pen attached to the lid of the chamber, this writes on the rotating drum, creating a spirometer trace. Or can be hooked up to motion sensor which displays data on data logger,
5) soda lime in the tube absorbs carbon dioxide.
How to dissect fish gills?
1) wear lab cost and gloves
2) place fish in a dissection tray or cutting board
3) push back the operculum and use scissors to carefully remove the gills. Cut each gill arch through the bone at the top and bottom
4) should be able to see the gill filaments
How to dissect the gas exchange system of insects?
1) fix the insect to the dissecting board. You can put dissecting pins thrift it’s legs to hold it in place.
2) to examine tracheae, cut and remove a piece of exoskeleton from along the length of the insect’s abdomen.
3) use a syringe to fill the abdomen with saline solution. You should be able to see network of thin silvery-grey tubes. These are tracheae. Silver due to being filled with air.
4) can examine under light microscope using wet mount slide. You should see rings of chitin inn the walls of the tracheae, they are there for support.
How to dissect plant stems?
1) use a scalpel to cut a cross section of the stem (transverse or longtitudinal). Cut sections as thinly as possible
2) use tweezers to gently place the cut sections in water until you have to use them. This stops them from drying out.
3) transfer each section to a dish containing a stain eg toluidine blue O. This should stain lignin in xylem walls blue-green.
4) rinse the sections in water and mount each one onto a slide and view under light microscope.
How to investigate transpiration rate using Potometer?
1) cut shoot underwater to prevent air entering the xylem. Cut it at a slant to increase surface ares available for water uptake.
2) check that the apparatus is watertight and air tight, to avoid unwanted air bubbles.
3) dry the leaves and allow time for the shoot to acclimatise and then shut the tap.
4) remove capillary tube from beaker of water until one bubble of air forms and place tube back into beaker.
5) record the starting position of the bubble
6) start a stopwatch and record the distance moved by the bubble per unit time. Movement of bubble is rate of transpiration.
7) control temperature, humidity, light, wind.
How to examine blood smears
1) red blood cells- no nucleus. Will be majority of image
2) neutrophil- multi-lobed nucleus. Cytoplasm is grainy
3) lymphocyte - nucleus takes up most of cell. Cytoplasm not grainy
4) monocyte - kidney bean shaped nucleus. Cytoplasm not grainy
How to sample an area to measure biodiversity?
1) choose an area to sample,
2) count of the number of individuals of each species
3) repeat this process, take as many samples as possible.
4) can take samples using random or non-random sampling.
Examination of stained pancreatic tissue?
Cluster of cells is called islets of Langerhans.
If special stain has been used , small purple cells are Beta cells and pink cells are alpha cells.
If Large vessel is present, this is pancreatic duct
Examination of stained liver/hepatic tissue
1) large white circular shape is central vein
2) white gaps around central vein are sinuosoids
3) cells present in image are hepatocytes and red dots are nuclei
Examination of cortex of kidney
The cortex contain the glomerulus, which is a bundle of capillaries
The white area around the glomerulus is the bowman’s capsule
The circular areas around it are the PCTs and DCTs. They are surrounded by squamous epithelial cells
Examination of the medulla of the kidney
This is where the loops of henle are. This is shown by the white strips
The loops of henle are surrounded by capillaries
How to tell the difference between the different types of muscle?
1) skeletal/voluntary muscle - striated (striped), many nuclei, long muscle fibres
2) smooth/involuntary muscle - no striated appearance, each muscle fibre has one nucleus. Spindle shaped
3) cardiac muscle - some cross striations, muscle fibres are shaped like cylinders and are branched, each fibre has one nucleus, muscle fibres are connected by intercalated discs
Practical investigation into phototropism
1) take 9 wheat shoots. They should be planted in individual pots in the same type of soil. Should be roughly equal in height.
2) cover the tips of 3 shoots with a foil cap. Leave 3 shoots without foil. Wrap the base of the final 3 shoots with foil, leaving the tip exposed.
3) Set up the shoots in front of a light source and leave them for two days. The shoots should all be the same distance from the light source and experience the same intensity. All other variables like temperature, exposure to moisture etc should be controlled.
4) by the end of the two days, the shoots with the tips exposed, grow towards the light source, whereas the ones with the tip covered by the foil cap should have grown straight up. Record the amount of growth and direction of growth in mm.
Practical investigation into geotropism
1) line 3 Petri dishes with moist cotton wool. Use same volume of water and same cotton wool in each dish.
2) space out 10 cress seeds on the surface of the cotton wool in each dish
3) tape a lid onto each dish and wrap each one in foil (prevents light affecting results)
4) choose an area where you can leave the dishes and should be of stable temperature eg cupboard
5) prop one dish upright (90 degrees), one on a slope (45 degrees), place last dish flat.
5) leave for 4 days. Then look at shoot and root growth.
6) shoots grow away from gravity and roots grow towards gravity no matter the angle
7) to get quantitative results, measure the amount of growth of shoots and roots and the angle of growth
