Practical Skills Flashcards
SB5k CP - Describe the method you would undertake to investigate the growth of bacteria in relation to antibiotic concentration.
- Using aseptic technique, pour an agar plate, making sure that the bases is covered with a smooth layer of agar * Open a bottle of bacterial culture without putting it down and pass the neck through the flame of a Bunsen burner * Take out a sterile pipette and without putting it down, draw some bacterial culture * Slightly open the lid of the petri dish and add some culture. Then place the pipette in disinfectant * Unwrap a sterile spreader, and open the lid of the petri dish slightly, and spread the culture around in a side to side motion. * Using a permanent marker, section out the bottom of the petri dish into four sections * Label one, the control * Using sterilised forceps dip three paper discs each into a different concentration of antibiotic solution, sterilising between * Place each disc in a section of the dish (not near the edge) * Leave for incubation * Measure clear spaces in each section
B5k CP - What are methods of aseptic techniques?
- Sterilising equipment before use * Lighting a flame nearby * Only opening the Petri dish slightly * Using an autoclave * Cleaning down surfaces before use * Wearing gloves
SB5k CP - Why do we carry out bacterial cultural in aseptic conditions?
To avoid contamination with microorganisms in the air
SB5k CP - How do you measure the radius and the area of a clear space?
The length from the centre of the area where there hasn’t been bacterial growth to the edge of this section, is the radius of the clear space. The area is πr²
SB3c - Describe the lab extraction of a precipitate of peas DNA.
- Thoroughly mash up some peas * Make a solution of salt water and detergent without making it soapy * The detergent will break down the cell surface membranes and membranes around the nucleus * Mix the mash into the solution * Place the beaker containing this mixture in a water bath at 60 degrees for 15 minutes * Pour some of the filtrate into a boiling tube and add two drops of the protease enzyme (to break down proteins) * Tilt the tube slightly and let some ice cold ethanol run down the side of the tube slowly * Leave for a few minutes. DNA is insoluble in ethanol, thus the ethanol will cause the DNA to precipitate
SB1i CP - Describe the method you would use to investigate osmosis through potatoes
- Cut discs of raw potato, blot them dry, and measure their mass. * Put each disc in a sugar (or salt) solution of different concentrations * After 30 minutes, measure the mass of each disc again. * Subtract the initial mass from the final mass of each disc. * Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass. * The highest change in mass means there was the greatest difference between water concentration as osmosis works with the concentration gradient This can work with any semi-permeable membrane.
SB1f- How can we use a calorimeter?
- Burn a known mass of the food under a boiling tube filled with a known volume of water. * Calculate the change in temperature of the water.
SB1f CP - What tests are used to identify main components in food? * Starch * Proteins * Lipids * Sugars
- Starch: Iodine will go from yellow to blue-black * Proteins: Biuret’s solution will go from blue to purple * Lipids: Add ethanol and shake - a white emulsion-fatty layer should form if it is present * Sugars: Benedict’s solution while heating which will turn anywhere from green to yellow to red, indicating how much sugar is present This is a semi-quantitative test. It mostly gives non-measurable values.
SB1b CP - How do you use use a microscope?
- Put a thin sample of tissue (e.g. onion epidermis) onto a microscope slide * Add a few drops of a suitable stain/dye (e.g. iodine), so that the sample can be seen * Place a coverslip on top of the tissue and place the slide onto the microscope stage. * Use the objective lens with the lowest magnification, and focus on the sample. * Increase the magnification and refocus to see different features of the cell. * If you record the image you see, note down the magnification it was taken at Option 2: You microscope you’re doing it right
SB6b CP - Describe a method, using algae balls and hydrogen carbonate indicator, to investigate rates of photosynthesis at differing light intensities.
Add 20 algae balls and the same amount of indicator to as many glass bottles as you need
Compare the colour of the bottle at the start to a key to work out its starting pH (they should all be the same)
Place a tank of water between the light and the first glass to absorb the heat given off by the light
Cover one with foil so it is in the dark and place it next to the one closest to the lamp
Measure out the distances you place all of the bottles
Turn on the light and wait till you see noticable changes in the pH
Once you’ve decided to stop, work out the pH again by comparing to a key
Work out the change in pH/hour to be your rate of reaction
Plot a graph of rate of reaction vs distance from light
SB6d - Describe how you can investigate rates of transpiration
A potometer is used for this. It involves using a plant attached to a rubber stopper connected to a reservoir of water and a capillary tube.
The capillary tube should have at least one bubble in it and should have a scale .
As the plant uses up water it will draw water from the tube moving the air bubble.
The speed of the bubble will allow you to calculate the rate of transpiration
SB6f - Describe Darwin’s experiments with auxin and what can be concluded from the results.
Three intact shoots exposed to light. One covered with a black cap, one with a transparent cap and one normal
The one with the black cap didn’t bend towards the light while the other two did
This shows that auxins are dependent on light to work
One where the tip was removed didn’t bend towards the light.
This showed that auxins are produced in the tip of the shoot
A tip was also placed on a permeable and and impermeable base (removed from the plant)
The one on the permeable base (agar block) bent towards the light but the other didn’t
This shows that auxins need to travel further down in the plant to work
SB8e CP - Describe how you would investigate rates of respiration in small organisms
Set up the test tube with a bung attached to it so that:
A CO2 absorber (e.g soda lime) is at the bottom
Cotton wool is on top
The organism(s) are on this
The blob of coloured liquid is right at the start
The 0cm mark of the ruler is lined up with the liquid
This is called a simple respirometer
You measure how far along the capillary tube the blob moves every so often
Distance moved ÷ time = rate of respiration
Alter the temperature to see how this affects the rate of respiration
This is your independent variable, so ensure you keep everything else the same as they are your control variables
To set up a control experiment for this, you would have the same set-up with no organisms
Describe how Quadrats are used to sample an area.
*Choose an area on the school field where the grass is often cut. Map the area and then lay a numbered grid over the map.
*Use random numbers to determine where to place your first quadrat. You can use a computer generated random number table to do this.
*Count the number of different plant
species within this quadrat (the species richness).
*Return to your starting position and repeat steps two and three a further 14 times using different random numbers.
*Repeat steps one to four for a part of the school field which the grass is infrequently cut.
*Compare your results by calculating a
mean for each location.
