Required Practical's Flashcards
What is the aim of RP 1? (Enzyme Activity)
Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction.
How can a control be set up in RP 1? (enzyme activity)
Replace the enzyme solution with distilled water
How can the results of RP 1 be used to find the initial rate of reaction? (enzyme activity)
Plot the results on a graph of ‘rate of reaction’ against ‘time’
Draw a tangent at time = 0 to find the initial rate
Outline the practical procedure used to measure the effect of temperature on enzyme activity, using trypsin and milk. (RP 1)
Immerse equal volumes of trypsin and milk stored in different test tubes, in a water bath for 5 mins for the temp to equilibrate
Mix together and start timing, record the time taken for milk to become colourless- hydrolyse, use the control
Test at least 5 temps with 3 repeats
How is the rate of reaction calculated?
RoR = 1/ time
What is the effect of temperature on enzyme activity? RP1
As temperature increases, kinetic energy increases so more ES complexes form. The rate of reaction increases up until optimum
Beyond that, bonds in the enzyme tertiary structure breaks, which changes the shape of the active site. The substrate and enzyme are no longer complementary so RoR decreases
What is the title of RP 2? (mitosis)
Calculating the mitotic index using plant cells
What is the mitotic index? (RP 2)
The ratio of cells undergoing mitosis to the total number of cells in the sample
mitotic index = number of cells with visible chromosomes/ number of cells in the sample
Outline the procedure to prepare a root tip slide ( RP 2)
- Warm 1M HCL to 60 degrees water bath
- cut a root tip using a scalpel and add to the HCL, leave for 5 mins
- Remove from HCL and wash with distilled water
- cut the tip of the root and place on a slide
- add a few drops of the stain to make chromosomes visible.
What is the title of RP 3? (water potential)
Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue.
What is the purpose of calibration curves RP 3? (water potential)
They are used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations
How is a calibration curve used in RP 3? (water potential)
To find the concentration of plant tissue
Plot a calibration curve of percentage change in mass against concentration
Find the X- intercept where the plant tissue is isotonic to the sucrose solution
What occurs to the potato in RP 3 when in hypotonic and hypertonic solutions? (water potential)
Hypotonic- water moves into the plant tissue by osmosis and the potato increases in mass
Hypertonic- water moves out of the plant tissue by osmosis, plant tissue decreases in mass
Why are the potato discs left in solution for 20 mins in RP 3?
To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution
Outline the procedure of RP 3? (water potential)
- Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5cm3 to 5 different test tubes
- cut a potato into equal sized chips and weigh
- Place a chip in each test tube and leave for 20 mins
- take out, dab the excess water and weigh them again
- change percentage change in mass
Why is the percentage change used in RP 3 rather than actual change in mass? (water potential)
Potato chips may not all have the same starting mass
Allows for comparison
Explain the results of RP 3. (water potential)
The potato chips with concentration lower than the sucrose solution loses mass as there is a net movement of water out of the cells
The potato chips with concentrations higher than the sucrose solution gains mass as there is a net movement of water into the cells
Why are the potato chips dabbed in RP 3?
To remove access water to not change any results
What is the aim/ title of RP4? (cell membranes)
Investigation into the effect of a named variable on the permeability of cell-surface membranes.
How is beetroot used in RP4? (cell permeability)
To measure the permeability of cell membranes
The higher the permeability, the more red pigment leaks out into the surrounding solution- then a colourimeter can be used to determine the absorbance
Outline the procedure of RP 4? (membrane permeability)
- cut beetroot into 6 identical cubes with a scalpel
- Place each cube in a different test tube with equal volumes of distilled water
- Place each test tube into water baths ranging from 20-80 degrees. leave for 20 mins
- Filter each solution out into a cuvette and measure absorbance
What is the result of RP 4? (cell permeability)
Increasing temperature increases membrane permeability causing a higher absorbance
What is the title of RP5? (dissection)
Dissection of an animal or plant gas exchange system or mass transport system or of organs within such a system
Name some precautions to be wary of in RP5? (dissection)
- wear disposable apron or lab coat
- Cover cuts
3, cut away from yourself and use forceps to hold tissue when cutting - wear disposable gloves
Give 2 precautions for clearing in RP 5. (dissection)
- Disinfect hands
- Disinfect instruments
- carry sharp instruments by pointing down
- Put organs/ paper towels/ gloves in a seperate bag
Discuss ethical issues of dissection
- morally wrong to kill animals for dissection purposes only
- Animal raised for disection may be in bad conditions
What is the title of RP6? (aseptic technique)
Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth
State aseptic techniques. (RP6)
- wipe down surfaces with antibacterial cleaner before and after experiment
- use a bunsen burner in the work space so convection currents draw microbes away from the culture
- Flame the wire hoop before using to transfer bacteria
- Flame the neck of the bottles before using to prevent bacteria entering the vessel
- keep all vessels with bacteria open for minimum amount of time
- close windows and doors to limit air currents
Why is bacteria incubated at 25degrees? (RP6)
To prevent the growth of pathogens which occurs at higher temperatures
How do you measure effectiveness in RP6? (aseptic technique)
Measure the diameter and calculate the area of the zone of inhibiton
