core prac Flashcards
- Investigate the effect of enzyme and substrate concentrations on the initial
rates of reactions
C: Concentration of enzyme / substrate (eg 0%, 10%, 20%, 30%, 40% or 0, 2, 4, 6, 8, 10 discs of potatoes)
O: Same age, type, surface area/mass, source of yeast/potato/liver/enzyme; Substrate or enzyme in excess (whichever is not being changed) so it isn’t a limiting factor.
R: Repeat the experiment 10 times, discard any anomalies and calculate a mean.
M: Measure the volume of gas produced in seconds. RATE - divide the volume by the number of seconds
- Must be initial rate of reaction:
- Either measure gas produced in the first 30 seconds
- Or measure gas produced every 15s for 2 mins, plot a graph and determine the initial gradient (vol/time) to determine the initial rate of reaction
S: Same volume of enzyme or volume of substrate; concentration of substrate or enzyme; pH using a buffer; temperature using a waterbath; delivery tube diameter
- Investigate the antimicrobial properties of plants, including aseptic techniques for the safe handling of bacteria
C: Type of plant material on the assay disc
O: Same species, strain, age and volume of bacteria grown on the agar
R: Repeat 4 times for each plant material, calculate mean, discard anomalies, calculate standard deviation.
M: Area of zone of inhibition (clear zone where bacteria have been killed) using πr².
- Stats test: T-test
S: Concentration of plant material, lawn of bacteria on petri dish, contamination of petri dish by other microbes, same volume of plant material on each disc, same temperature and time of incubation.
- Aseptic Techniques
- flame necks of bottles
- tape lids down but allow air in
- use of ethanol to clean apparatus used
- safe disposal of plates
- wash hands after handling equipment
- keep ethanol away from naked flames as it is flammable
- suitable method for handling molten agar described e.g. wear heat resistant gloves
- incubator set at less than 30 degrees to discourage pathogenic bacteria from growing
- Carry out a study on the ecology of a habitat, such as using quadrats and transects to determine distribution and abundance of organisms, and measuring abiotic factors appropriate to the habitat.
C: Position of the quadrat along the transect. Regular intervals should be used along the transect (e.g. every 2 meters).
R: Repeat many times (at least 10) in each area/for each transect, calculate mean, discard anomalies, times mean amount in one quadrat by the number of quadrats that fit in the total area. Calculate standard deviation
M: Dry mass, percentage cover, length/width, species richness, within quadrat & use as an estimate for the area
Stats test to look for differences – T test for random sampling of 2 areas, Correlation coefficient for transect
S: Time of day, direction of transect, size of quadrat, method of sampling (e.g. kick sampling with the same force, for the same time), measure abiotic factors
Safety: Don’t throw quadrats, sun protection, wear shoes in rivers to protect from infection
- Investigate photosynthesis using isolated chloroplasts (the Hill reaction)
C: Combination of leaf extract, supernatant, isolation medium and DCPIP
O: Same species - spinach (Chloroplast extracted), same part of plant, same age
R: Repeat 4 times at each condition, calculate mean, discard anomalies, calculate standard deviation
M: Time how long it takes to decolourise the DCPIP in each tube
S: Distance from light, time in light, same volume of filtrate, volume of isolation fluid
Safety: DCPIP - skin irritation, serious eye irritation, harmful if swallowed. Don’t handle electrical equipment/bulbs with wet hands
- Results of the Hill reaction
Tube 1 (leaf extract + DCPIP) colour changes until it is the same colour as tube 4 (leaf
extract + distilled water)
> light dependent reaction reduces the DCPIP
Tube 2 (isolation medium + DCPIP) no colour change > DCPIP does not decolourise when exposed to light
Tube 3 (leaf extract + DCPIP in the dark) no colour change > loss of colour in tube 1 is due to the effect of light on the extract
Tube 4 (leaf extract + distilled water) no colour change. > leaf extract does not change colour in the light
Tube 5 (supernatant + DCPIP) no colour change > supernatant does not contain chloroplasts, so no reduction of DCPIP > this proves chloroplasts are needed to release the electron
The results should indicate that the light-dependent reactions of photosynthesis are restricted to the
chloroplasts that have been extracted
- Investigate rate of respiration
C: Either Temperature OR Mass of organisms (temp only up to 40 degrees - ethics of causing harm to an animal), 5 values stated
O: Germinating Seeds of same age (eliminate environmental and genetic effects on the results)
R: repeat 5 times at each temp/mass, calculate mean and s.d, stats test – Spearman’s rank, correlation coefficient
M: Change in volume of oxygen / volume of oxygen taken up - by measuring the distance moved by the liquid in the u tube and multiplying it by the cross-sectional area of the u-tube (πr2). Per unit of time. Per gram (mm^3 s^-1 ^g-1)
S: Either Mass of organisms OR Temperature and then time left to respire, mass of soda lime, equipment used to measure the oxygen uptake, pre-investigatory environment of the organisms, acclimation time
- Investigate habituation to a stimulus
C: the number of stimulations using a damp cotton bud, continue until habituation is shown
O: Same species, age, mass, of snail. Same parents so genetically similar
R: Repeat whole experiment 5 times with different snails, calculate a mean and standard deviation for each stimulation, stats test spearman’s rank
M: Measure time taken to re-extend eye stalk, use a stop watch, measure to 0.01 seconds (precise)
S: Same stimulus, same force, same temperature, same light intensity
