PRACTICALS EXAM MARK SCHEMES Flashcards
Describe how you could use a plant tissue culture to show totipotency in cotton plant seedlings
- use part of seedling
- in agar
- which contains growth hormones/substances
- aseptic technique
- cover top of container to reduce contamination
- supply light
- leave appropriate time for growth e.g. 1-6 weeks
- look for leaves/roots forming
How can you carry out an investigation into caffeine on the heart rate of Daphnia?
- suspend Daphnia in cotton wool to limit movement
- determine base heart rate in absence of caffeine
- use a range of caffeine solutions (e.g. made with dilutions)
- allow Daphnia to acclimatise for 5 minutes at least in each sample
- use specific method to count heart rate (e.g. dots on a piece of paper)
- repeats/replicates
- control variable e.g. size/age/type of Daphnia or temperature, pH
How can you test permeability of cell membranes in beetroot/other similar vegetables?
- use a sample of at least 5 vegetables with difference between them (e.g. different ages)
- ensure samples have same surface area/mass/source
- ensure relevant variables are controlled (e.g. growing conditions/light intensity)
- measure permeability via use of colorimeter
- replicates/repeats for each group to allow calculation of mean
How can an experiment be carried out to investigate the effect of enzyme concentration on initial rate of reaction?
- use a range of concentrations of an enzyme (at least 5)
- ensure substrate concentration does not become limiting factor
- mix the two together
- measure dependent variable with time (e.g. collection of gas with upturned burette)
- measure initial rate by recording data at specific time intervals
- control variable e.g. pH, temperature
- replicates/repeats at each enzyme concentration
- control used as comparison
How can you compare the tensile strength of plant fibres?
- pieces of fibres same length and width/diameter
- control of environmental variables e.g. temp or humidity
- control of procedural variable e.g. size of masses used
- suspend fibres and add masses until fibre breaks
- repeat and find mean
- if anomalous result found, exclude from mena
- safety procedure
How can an experiment to investigate the antimicrobial properties of plants be set up?
- make extract with plant seeds
- agar plate with bacteria/culture of bacteria grown in nutrient broth
- aseptic technique e.g. bunsen/flaming the loop
- extract placed on paper disc
- control also created (disc with just solvent)
- incubated at temperature between 20 and 3 degrees for 5 days
- look for zone of inhibition and work out circumference
- repeat to calculate mean
Experiment to work out differences in percentage cover (along sand dunes)
- systematic sampling
- quadrats
- method for measuring percentage cover (e.g. counting number of squares covered)
- repeats to make a valid comparison
- statistical test performed e.g. Chi squared
Investigation to measure impacts of light intensity on above ground dry mass of crops
- select field of plants
- sample at suitable time intervals using randomly placed quadrats
- measure light intensity
- harvest, dry and weigh crop
- monitor/record other abiotic factors
How would you set up an investigation to measure the rate of light dependent reaction?
Hill reaction - use of DCPIP to measure light dependent reaction
- isolate chloroplasts: grind leaves into paste, suspend in isolation solution, centrifuge and use different parts of the pellet/liquid
- put into test tubes (control tube = in the dark)
- time taken to decolourise DCPIP measured
- statistical analysis
Investigation for determination of Q10 for an extract of an enzyme
- control of temperature (e.g. by use of water baths)
- provide excess substrate
- control concentration of enzyme
- measure concentration of substrate/product at stated time intervals
- find initial rate
- use of Q10 calculation
Experiment to investigate the effect of temperature on growth of a plant
- use a range of (minimum) 5 temperatures
- different temperatures achieved by using water baths or incubators
- determination of growth over a period of time
- growth assessed by size/mass of plant or length of roots
- control variables = concentration of inorganic ions
- repeats to calculate a mean/average
Experiment to investigate temperature effect on growth rate of monolayer of human cells
- control temperatures via water bath/incubator
- abiotic factors controlled = pH, humidity, CO2 or O2 conc
- provide nutrients for cells
- use aseptic technique to prevent contamination
- culture for stated period of time
- method for measuring growth, e.g. mass/number of cells
Experiment to compare effectiveness of different antibiotics
- prepare agar plates with bacterial cultures
- prepare solutions of antibiotics
- place onto paper discs/prepare mast rings
- control time and temp of incubation
- same conc and volume of antibiotics
- measure area of inhibition
- do one antibiotic per plate, and range of dilutions
- statistical test to determine which is most effective
Procedure for root tip squash to show mitosis
- remove root tip and place in hydrochloric acid to macerate the tissue
- rinse in distilled water and add a few drops of a stain such as acetic orcein
- place on a slide and cover with coverslip
- calculate mitotic index by the number of cells undergoing visible stages of mitosis (chromosomes present)
- safety procedure e.g. safety goggles when handling acid/stain
Experiment to compare already amplified DNA from 2 different samples
Gel electrophoresis
- restriction endonucleases to cut DNA into fragments
- DNA samples loaded onto agarose gel
- electric current passed through/potentially difference applied across gel
- markers added to visualise the bands (fluorescent dye)
- position of bands produced can be compared
