unit 5 practicals questions Flashcards
outline the procedure to investigate the digestion of starch agar using germination seeds
- cut seeds in half
- place seeds on starch agar on a petri dish, and leave for 12-48 hours at 25°ac
- set up the control
- pour iodine onto the plates and measure the area of the clear zone
what does the zone of inhibition indicate?
- the clear zone indicates that starch has been hydrolysed by amylase (hence stained by iodine)
- the larger the zone of inhibition, the higher the amylase concentration / greater the amylase activity
state 3 factors that may affect the rate of amylase activity
- age of seed
- gibberellin content
- temperature / pH
how is the control set up in this practical?
- heat half of the seeds in a water bath above 80°C to denature the enzymes present
- then cooled
why is the control set up?
to show that the difference in the size of the clear zone is due to the presence of enzymes in the seed
what are some controlled variables of this practical?
- time left on starch agar plate
- source/age of seeds
- type/species of seed
- volume/concentration of agar used
- germination time
- temperature
- pH
- water availability
introduction to practical:
- the endosperm of a seed is the food source which surrounds the embryo
- it consists primarily of starch as well as proteins and oils
- during germination, starch in the endosperm is hydrolysed to maltose by amylase
the digestion of starch by germinating seeds can be investigated using starch agar plates
hazards, risks, precautions for practical?
- iodine - irritation to eyes and skin - wear safety goggles and gloves
- broken glass - cuts - keep glassware away from edge of desk
- scalpel - cuts - direction of cut away from the body
- boiling water - scalding - handle boiling water with care; use tongs to transfer boiling tubes; wear safety goggles
- water bath - electric shock - ensure hands are dry before plugging in/unplugging water bath
- seeds are maintained at 20°C to reduce the risk of growing potentially harmful contaminants
list some abiotic factors
- light intensity
- temperature
- humidity
- wind speed
- water supply
- day length
- nutrient supply
- rainfall
list some biotic factors
- competition for resources
- predation
- disease
how is % cover calculated?
- use a quadrat with squares
- count how many squares the required species is present in
- only count a square is more than half of the square is covered
outline the procedure of random sampling:
- choose an area to take samples. use a random number generator to generate 10 sets of random coordinates
- use two tape measures to create a set of axes off which coordinates can be read
- place the quadrat at each of the coordinates, placing the bottom left corner on the coordinate every time
- record the percentage cover for the chosen species
- at each coordinate, a measure of the independent variable should be taken
how can the results be used to determine the relationship between the chosen factor and the percentage cover?
- use a statistical test
- e.g Pearson’s linear correlation, Spearman’s rank
state simpson’s index of biodiversity
D = 1- [(n/N)2]
what is species diversity?
the number of difference species in a community and the relative abundance of each population
what is the advantage of random sampling?
- prevents selective sampling from causing bias
outline the procedure of using a transect for systematic sampling:
- use a measurement tape to make a transect over the area you wish to sample
- place quadrats at given intervals along the tape measure (e.g. every 5 metres). the bottom left hand corner of each quadrat should be touching the relevant meter mark, and the left hand edge runs along the tape measure
- identify the different species in each quadrat using a key and count the number of each present
- calculate the percentage cover
which type of graph is used to represent the distribution of a species along a transect?
- a kite diagram
state a hazard and safety precaution involved in the practical of dissection of flowers
- flowers may cause an allergic reaction
- avoid using species of plants that can cause allergic reactions
what is the epidermis of an anther?
- the thin outermost layer of tissue surrounding the anther
what is the pollen sac of an anther?
- a circular structure containing developing pollen grains
where is the vascular tissue found in an anther?
in a bundle at the centre of the anther
what is the stomium of an anther?
the area between 2 pollen sacs
where is the tapetum found in an anther?
it is the layer of tissue surrounding each pollen sac
how can the actual size of the anther be found?
- calibrate the eyepiece graticule with a stage micrometer
- measure the length of the anther using the eyepiece graticule with a
area of a circle formula?
πr^2
r=mm
risk assessment for experiments (involving chi^2 test)
- biohazard - contamination - cover any cuts; wash hands
how is a control set up in a practical measuring enzyme activity?
- replace the enzyme solution with distilled water or boiled enzyme solution
what is the effect of enzyme concentration on enzyme activity?
- as the concentration of enzyme increases, successful collisions to form ES complexes increase, so the rate of reaction increases to an optimum
- beyond the optimum, the rate plateaus as substrate concentration becomes limiting
dependent variable of germinated maize seed on starch agar experiment:
- presence / absence / size / diameter of (clear area / halo)
with reference to your graph, discuss the consistency of your readings [2]
- relevant comment on (length of range bar(s) or absence of range bars)
- comment on variation in (repeats/readings/reliability of mean)
suggest three sources of inaccuracy in this investigation and an improvement for each:
- temperature MAY VARY = use a thermostatically controlled water bath
- colour change is subjective = use a colorimeter
- enzyme extract may settle out/change in concentration = stir before use/use enzyme of known concentration
- different quantity of solution/enzyme on paper discs = soak disc for same length of time
- pH wasnt controlled = use a pH buffer
- paper discs are not uniform area = use paper discs which are identical
- accuracy of measuring cylinder/syringe (only measures to…)/ low resolution = use (graduated pipette / measuring cylinder/ syringe) with higher resolution
- inconsistent measurement of the clear zone (e.g people measuring the diameter differently) = use ruler consistently and have the same person take all measurements / use computer to measure so human error minimised
- uneven distribution of seeds on agar plate = place seeds evenly on agar plate, ensuring are spaced evenly and dont overlap
- germinating seeds may not be at the same stage of development = use seeds of same age
- temperature, light, humidity can affect rate of germination and enzyme activity = keep constant
- digestion rate too slow so hard to measure accurately = longer incubation time for seeds to ensure maximum starch digestion
- variability is size and type of seed = use seeds from same plant/species/size
- uneven distribution of agar could lead to areas with more or less starch available for digestion, affecting size of clear area = ensure agar evenly distributed
- placements of quadrats not random/representative
- quadrat too small/too big
- hard to identify species/error when counting
- time of day/year - different species might boom at different times / activity increases during day etc
- not enough quadrats or too few
- scale of study too small/too big
suggest how the experiment could be modified to investigate the effect of pH on the enzyme
- repeat at (different/named/range of) pH values using BUFFERS
- keeping (all other factors the same/2 relevant named factors)
comment on the reliability of your means and suggest how it could be improved [2]
- correct comment on their results
- (only repeated once/only 2 results for each concentration/large variation between repeats + repeat more times to improve reliability
- use 3 seeds per plate
explain why you calculated percentage change in mass rather than comparing actual changes in mass [1]
- different masses at start + so actual change in mass not comparable / measure change irrespective of initial mass
what information do the range bars provide [1]
- provide information of the (reliability/repeatability/consistency) of the readings / enables you to assess confidence in the (mean/trend)
from your results draw a conclusion that links the independent and dependent variables for this investigation [1]
- the conclusion must refer to the IV and DV
-e.g IV = length of germination
-e.g DV = time taken for iodine to not change colour - conclusion must match their results
- if results are (inconsistent/no obvious patters) the candidate needs to state this
the enzyme extracts were prepared using the same mass of germinating seeds. explain why this provides more accurate results than using the same number of seeds to prepare each extract [3]
- seeds can be different (sizes/masses/volume)
- and so each seed may contain (more/less/different) concentrations of (amylase/enzyme)
- (need to use the same mass of tissue to produce each extract) so that the activity of enzyme can be stated per gram of seed / results are comparable
- (know that change in time for iodine to not change colour) is due to changing (conc of amylase / length of germination / number of days)
identifying the end-point/colour change is said to be subjective. explain what this means and how it could have affected the reproducibility of the experiment [2]
- (subjective means) depends on your interpretation of the (colour / endpoint) varies between people
- less reproducible / cannot replicate / introduces inaccuracies into the data / lead to differences in the times
in instructions, record times in seconds to the nearest 10 seconds.
explain why the times you recorded cannot be used to calculate an accurate value for amylase activity in this investigation [1]
- times only recorded to the nearest 10 seconds
- using your knowledge of germination, explain why amylase activity decreases once seedlings produce leaves [1]
- photosynthesis (can take place / provide source of glucose) / plant can make its own carbohydrate (so less amylase needed to break down starch stores)
a suitable control experiment would be to repeat the experiment using boiled and cooled ____. explain why this would be a suitable control experiment [1]
- enzymes responsible would be denatured
suggest the results you would expect from the control experiment [1]
state one way of improving the accuracy of the data collected [1]
- measure to 0.1mm rather than nearest mm / smaller divisions on ruler
how could this investigation be made more valid [3]
- have a larger sample of leaves
- repeat investigation (using different e.g seed)
- ensure seeds all same age
explain why the seeds were taken from a single parent plant and were grown under the same conditions, other than light intensity [2]
- so that the only difference between the measurements would be due to the light intensity / prevent results being affected by other factors
- to minimise genetic variation between plants
why were measurements taken from seeds of the same age?
- same comparable stages of development/growth/germination / same size
an experiment shows that the size of the clear zone formed around the seeds increases as the temperature rises from 10°C to 30°C, but decreases at temperature above 30°C. suggest an explanation for these results
- at low temperatures, enzyme activity is slow because the enzymes have less kinetic energy, leading to slower starch digestion
- as the temperature increases to 30°C, the enzyme reach their optimum temperature, resulting in faster starch digestion and a larger clear zone.
- at temperatures above 30°C, the enzymes may denature, causing a decrease in the rate of starch digestion and a smaller clear zone
why is it important to keep the age of seeds the same?
- different age of seeds have different mass and different stage of germination, and therefore different conc of amylase
- same age of seed ensures that the enzyme levels are constant
describe how you would design an experiment to investigate the effect of light on the digestion of starch by germinating seeds on agar plates
- control group: place seeds under constant light conditions
- experimental : place seeds in varying light intensities
- keep every other factor constant
in an experiment investigating the digestion of starch by germinating seeds, explain how you would ensure that the starch agar plates are prepared consistently across all trials
- consistent concentration of starch = measure the starch and agar in precise amounts using accurate measuring instruments
- uniform agar distribution = pour the agar mixture into the petri dishes in a uniform manner and ensure even distribution of the solution to prevent inconsistencies in the agar thickness
- control temperature during solidification = allow agar to solidify at room temperature in a controlled environment to avoid any variation in consistency due to different temperatures
- sterilisation = ensure all equipment sterilised to prevent contamination, which could affect consistency of the results
what is the independent variable for the experiment?
- live or dead seeds
- concentration of enzyme?
what is the dependent variable?
- diameter of halo around seed
observations:
- on the plate with boiled seeds, the agar stains uniformly blue-black
- boiling denatured the seeds’ enzymes and no starch was digested
- in the plates with the live seeds, some area of the agar stain blue-black, but there is no staining immediately below the seeds, indicating that the starch there was digested.
- surrounding each seed is a halo lacking stain showing the extent to which amylase had diffused out of the seeds and digested the starch
why put seeds in disinfectant/clean benches with disinfectant / use aseptic technique?
- to kill any microorganisms that might be on the surface of the seed
- on benches
- to not contaminate with microorganisms
examples of aseptic technique:
- dont open lid of petri dish fully
- keep under flame
- flame forcepts
FLOOD petri dishes with iodine
