Required Practicals Flashcards
(13 cards)
Describe a technique used to investigate the effect of temperature on an enzyme controlled reaction. What reactions and used and what controls are used?
Use the reaction between milk suspension (that contains casein) and trypsin (which is a protease enzyme that breaks down casein and gives a colourless solution)
- create two controls: add 5cm3 of milk suspension and 5 cm3 of distilled water to one test tube. This control shows the absence of enzyme activity. Add 5cm3 of milk suspension and 5cm3 of hcl to another test tube, this will show a fully hydrolysed control
- create three test tubes with 5cm3 milk suspension in. Heat in a water bath at 10* then add 5cm3 of trypsin.
- start stopwatch and record the time taken for solution to become colourless. Calc mean time and rate fo reaction (1/t)
- repeat with temperatures of 20, 30, 40 and 50
- plot a graph with temperature agains rate of reaction
Describe a method for calculating the mitotic index. What type of plants can be used for this?
Use the tips of roots in plants, as these are meristem cells that are totipotent and can differentiate.
- heat 1 moldm3 of hcl in a water bath
- use a scalpel to cut a sample of root tip, place it in the hcl and incubate fro 5 mins. This will allow the plant cells to soften
- wash with distilled water and the dry, remove any excess liquid
- place into a microscope slide, and stain with iodine. Gently lower the cover slip and remove any air bubbles
- place onto an optical microscope, set the objective lens to the lowest magnification
- use the coarse and fine adjustment knobs to make the sample clear, then increase the magnification
- calculate the mitotic index by using number of cells with visible chromosomes/ total number of cells
Describe an experiment for investigating the water potential of potatoes
- carry out a serial dilution of sucrose solution, using distilled water.
- create 6 test tubes with 5cm3 of sucrose solutions (0.0,0.2,0.4,0.6,0.8 and 1.0 M sucrose)
- use a cork borer to cut out 6 equally sized potato chips, use a paper towel to dry then to remove any excess water
- weigh each potato chip and place into the different sucrose solutions
- leave for twenty minutes each, then dry and realign each chip. Calculate the percentage change in mass (so they can all be compared)
- plot a graph with percentage change in mass against sucrose conc. where the line of best fit crosses the axis is where the solution would have the same water potential as the potatoes. This can be used to find out the water potential of the potatoes
State four common aseptic techniques
- use antibacterial spray to disinfect the surfaces before and after the experiment
- flame the neck of any bottles using a Bunsen burner, to prevent any unwanted microorganisms from entering (as air will be travelling out the bottle so bacteria cannot enter)
- use a Bunsen burner to flame a metal wire hoop, to sterilise
- keep vessels with bacteria in them open fro a minimum amount of time
Describe an experiment to measure the effect of antibiotics on bacterial growth
Carry out aseptic techniques on all equipment being used
Use a sterilised pipette and wire hoop to transfer bacteria from a broth onto an agar plate, spread evenly using sterilises plastic spreader
Soak four paper disks of equal sizes in different solutions of antibiotics for equal amounts of time, use sterilised tweezers to place them on the agar plate
Gently purr the lid on, invert and incubate at 25* for 48 hours
Without removing the lid measure the area of the inhibition zones for each antibiotic
Why are incubated agar plates kept at 25*?
As if they were kept at 37* (temp of human body) it wold promot the growth of pathogens that can be harmful to humans
What are aseptic techniques and why are they needed?
They a techniques that prevent cotamination of the substances being investigated with unwanted bacteria.
This allows reliable and repeatable results to be obtained
How can you carry out a chromatography experiment?
Dissolve the samples being used in the minimum amount of solvent
Draw the baseline on the chromatography paper, approx 1cm above the bottom. Use a capillary tube to spot the sample onto the baseline. Dry
Place the chromatography paper in
What is the role of dehydrogenase enzyme in plant cells?
Important for the light dependent reaction in photosynthesis
It catalyses the reaction when electrons are accepted by NADP
What is DCPIP?
A redox indicator dye, that changes colour from blue to colourless when reduced
Describe an experiment to investigate the effect of light intensity on dehydrogenase activity in chloroplast
Grind the plant sample using a mortar and pestle, add to a chilled, isotonic solution
Centrifuge at high speeds to obtain a pellet of chloroplast
Set a colorimeter to the red filter, then set to zero using a cuvette with distilled water and chloroplast solution
Place a test tube with chloroplast solution 30cm away from a light source, then add DCPIP. Immediately measure the absorbace of a sample of the solution. Take more readings of samples every 2 minutes for ten minutes
Repeat the experiment, placing the test tubes at increasing distances from the light source to change the light intensity
State two examples of redox indicators
DCPIP- blue to colourless when reduces
Methylene- blue to colourless when reduced
Describe a method for investigating the effect of temperature on the rate of respiration in single celled organisms
Using yeast cells- as they are single celled organisms that aerobically and anaerobically respire
Heat 5cm3 of a buffered yeast and glucose solution in a water bath at 35 degrees
Add methylene to the solution, start the stop watch and shake for ten seconds
Record the time taken for the solution to go from blue to colourless, as this indicates the methylene has been reduced due to glycolysis (occurs in both aerobic and anaerobic respiration)
Calculate the rate of respiration (1/t) and repeat from different temperatures
Plot a graph with temperature against rate
