What is the procedure for testing the effect of caffeine on Daphnia heart rate?
- Prepare 5 caffeine concentrations and a control solution.
- Pipette pond water and 3 drops of distilled water into a cavity slide and add a Daphnia.
- Count heartbeats under a microscope for 15 seconds and multiply by 4 for bpm.
- Repeat with 5 other Daphnia for mean calculation and repeat at 5 different caffeine solutions.
What factors must be controlled when experimenting with Daphnia?
- Age
- Species
- Size
- Gender
- Temperature of solution
- pH
- Volume of solution
- Acclimatisation time
Why is it considered unethical to use animals like Daphnia in experiments?
- Possibility of death
- Cannot give consent
- Unethical to use animals in experiments
Why are daphnia a suitable organism to use?
- Daphnia are transparent so heart can be observed without dissection
- Daphnia are invertebrates, underdeveloped nervous system so may not feel pain
- Daphnia are cheap/ easily produced
What is the procedure for determining the vitamin C concentration using DCPIP?
- Extract juice/vitamin C solution and titrate into DCPIP solution.
- Swirl flask until color change blue to colourless occurs, record volume used.
- Repeat 5 times for mean calculation.
What safety precautions should be taken when using DCPIP?
Wear safety goggles and avoid skin contact.
What is the procedure for measuring cell membrane permeability using beetroot?
- Cut equal-sized beetroot cylinders and soak in distilled water overnight.
- Place in boiling tubes with distilled water at different temperatures for 30 minutes.
- Measure absorbance with a colorimeter.
How does temperature affect membrane permeability according to the beetroot experiment?
As temperature increases, membrane permeability increases due to phospholipids gaining kinetic energy and proteins denaturing.
What is the procedure for testing the effect of enzyme concentration on reaction rate?
- Set up a water bath for constant temperature.
- Mix casein with trypsin and time how long for casein to turn transparent.
- Repeat for different concentrations of trypsin.
What is the relationship between enzyme concentration and reaction rate?
As enzyme concentration increases, the initial rate of reaction increases until substrate concentration becomes limiting.
Describe procedure for investigating mitosis in root tip
- Cut off 5mm of plant (garlic) root tip (meristem – site of mitosis)
- Place in 1M HCl to soften plant tissue and break down middle lamella and then wash off with water
- Transfer to a microscope slide and macerate the sample using mounted needle to obtain a single layer of cells so that light can pass through and squash with coverslip
- Stain sample with Toluidine blue which binds to DNA so that chromosomes are visible so the stages of mitosis can be seen
- Observe cells under a microscope at x400 magnification
- Calculate mitotic index by doing: number of cells with visible chromosomes/ total number of cells in field of view
What are the risks associated with observing mitosis in plant root tips?
- Cuts from scalpel
- Skin/eye damage from HCl and stains
- Breaking coverslip
What is the procedure for measuring tensile strength of plant fibers?
- Use plant fibers of the same species and dimensions.
- Attach fiber to clamp stand and add weights until it breaks.
- Calculate tensile strength by dividing force by cross sectional area of plant.
What is the procedure for investigating plant mineral ions?
- Half fill 5 beakers with perilite granules to ensure no minerals are already present
- Add same volume, 40 cm3 of mineral ion solution to each of the 3 beakers (e.g. 1 = mineral solution with no nitrate, 2 = mineral solution with no magnesium, 3 = with no calcium)
- Add 40 cm3 of water to beaker 4 (negative control) + 40 cm3 of mineral solution containing all ions to beaker 5 (positive control)
- Place a seedling of same species/ age of plant into perilite using forceps and cover beaker with cling-film to allow light and temperature to reach seedling and place under light bank
- Measure initial height/ mass/ number of leaves/ colour or plant each day for 2 weeks
- Add the same volume of the correct solution to each tube on a regular basis to ensure that there is sufficient water for photosynthesis and access to mineral ions
- Repeat the experiment 5 times for each solution to find and remove anomalies and calculate a mean
What is the procedure for testing antibacterial properties of plant extracts?
- Prepare sterile agar plates and spread bacteria.
- Soak paper discs in plant extract and place on agar.
- Measure zones of inhibition after incubation.
What is the procedure for investigating photosynthesis using isolated chloroplasts?
- Grind leaf in isolation medium and filter.
- Centrifuge to separate chloroplasts.
- Add DCPIP solution and record time taken to decolourise.
What does DCPIP represent in the photosynthesis experiment?
DCPIP takes the place of NADP and is reduced in light-dependent reactions, going colorless when reduced.
What are the two types of ecological investigations?
Systematic and Random.
What is a systematic investigation?
Samples are taken at fixed intervals, usually along a line using transects.
When is a random investigation used?
To measure the distribution of an organism in an area that is fairly uniform and very large.
How do you identify the sampling area?
Use a tape measure to place a quadrat every 4m along the transect or use a random number table to generate random coordinates.
What should you do to count organisms in a quadrat?
Count the number of organisms or calculate % cover at set time intervals.
How many repeats should be used in ecological investigations?
At least 10 repeats/quadrats/multiple transects.
What is a common method for recording data?
In a tally chart, table, or graph.
