why is an insufficient number of values of independent variables e.g. 10C increase each temp, a limitation?
lack of results between intervals so could miss changes and be less accurate. to improve, include more intermediate ranges.
why is using different species for an experiment a limitation?
difference state may induce random error so to improve, use large sample of same organism, same species, age and size to make results more representative of population
what is the limitation of using a stop watch?
use to a greater agree of resolution e.g. 1.01s to increase accuracy
why is lack of control variables a limitation?
not confident in the effect of changing IV is causing the change in the DV, so ,method is not valid. =
why is choosing a piece of equipment with low resolution a limitation? e.g. measuring cylinder
measurements are made with high uncertainty. Therefore, using volumetric syringe.
how is using a piece of equipment that hasn’t been calibrated correctly a limitation?
introduces systematic error so increases accuracy. Therefore, must check that thermometer reads 0C degrees, and zero on all balances.
what is a good method to prove the IV is directly causing the change in the DV?
having a baseline control for comparison.
random error contributes to uncertainty. How can we reduce random error?
making more measurements and calculating mean.
how to increase accuracy of a practical?
- take more intermediate readings
- take more repeat readings to obtain a more accurate mean
list ways in which to improve confidence in findings
- repeat readings
- identify anomalies and repeat experiment to dilute the effect of anomalies.
- calculate standard deviation (less SD, increased confidence)
- conduct statistical test
how to improve validity of a practical
- look for gaps in method they have not controlled e.g. pH, temp, species, conc., volume etc…
- listing limitations of practical, and suggesting improvements e.g. thermostatically controlled water baths.
what are the 5 aspects of validity?
accuracy
precision
confidence
repeatability
reproducibility
what is the process of dissecting bony fish?
- cut away from operculum
- cut one gill out
- put in water
- stain with dye and view on microscope slide
what is the process of dissecting insects?
view spiracles with a magnifying class
explain the dissection of a stem
- use a scalpel
- stain xylem with methylene blue
- see spiral lignin in microscope
what are the precautions you must consider when investigating transpiration rates with a potometer
- healthy shoot
- set up underwater
- seal joints with vaseline
- syringe to reset apparatus
- cut bottom of stem underwater to prevent air bubbles in xylem
ways to capture animals (biodiversity)
- pit fall trap
- mark recapture
- tree beating
- sweep net
- pooter
why must the leaves be dry in potometer?
to increase water potential gradient
describe stratified sampling
number of samples is proportionate to each area - it ensures areas are not missed, divided strata and sample in each.
what are two methods of systematic sampling
belt and line transects
describe how to produce a cutting of a plant tissue
- cut healthy shoot at an angle
- add hormone auxin
- water soil
- place plastic bag over and spray with water to increase humidity
- remove lower leaved
describe micropropagation (tissue culture)
- cut explant
- sterilise
- add nutrient medium + hormones
- forms a callus = which divides to form clones
why should a glass slide be placed over a beaker investigating chromatography?
to prevent evaporation of the solvent
state the process of thin paper chromatography
- Grind up the leaves using a pestle and mortar.
- Draw a line on the TLC plate with a pencil about 2cm from the bottom.
- place a dot of pigment in the middle of the pencil line.
- allow dot to dry then add another dot over the first, repeat process until you have a concentrated pigment.
- add small amount of solvent 1cm from bottom.
- Place the TLC plate in the beaker, with a glass over to prevent evaporation
- calculate rf
