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what is plasmolysis?
when the protoplasm of a plant cell begins to shrink away from the cell wall because the water potential and the osmotic potential are equal
outline the procedure to determine the water potential of a plant tissue
transfer a small set volume of each mineral salt solution into a watch glass and leave for 20 mins
remove each section using forceps. mount in a drop of the corresponding solution on a microscope slide and cover with a coverslip
observe 25 cells and record how many are plasmolysed
when can a solution be determined to be isotonic?
when the line of best fit crosses the x axis
what does isotonic mean?
when the water potential of the mineral salt solution is the same as the water potential of the plant tissue, so there is no net movement of water
what is incipient plasmolysis?
where the water potential of the cytoplasm is the same as the solution - the point at which plasmolysis just begins to occur - when 50% of the cells in a tissue are plasmolysed
why are the plant cells left in the mineral salt solution for 20 minutes before observation?
to allow time for osmosis to reach equilibrium
why is aseptic technique important?
creates reliable and repeatable data avoids contamination of the sample from outside substances
what is streak plating?
bacteria are spread out on a nutrient agar plate so that distinct individual colonies can be seen colonies grown on clean agar plates to produce non-contaminated samples of one species of bacteria
how can colonies be identified as a particular species of bacteria?
size, colour, and texture of the colony
disinfectant risk assessment
hazard - disinfectant risk - flammable safety precaution - keep away from naked flame in emergency - put out fire, seek assistance
what parts of aseptic technique are used in cp13?
flame sterilise the inoculating loop before and after use flame sterilise the neck of the bottle the mixed culture is in after opening and before closing open the petri dish lid as little as possible
why should the petri dish lid not be taped the whole way around?
so the conditions are not anoxic and the bacteria on the agar can actually grow
how can the colonies produced in cp13 be identified?
white colonies are likely to be salmonella yellow colonies are likely to be staphylococcus
outline the procedure to isolating a particular species of bacteria
dip a sterile inoculating loop into the mixed culture
make streaks on the agar using the inoculating loop
incubate the agar plate for 24 hours
take a sample of the different colonies and streak them on different agar plates and incubate again for 24 hours
what is aseptic technique?
procedure used to avoid contamination of the sample from outside substances, such as microorganisms
how is aseptic technique used in cp12?
wipe down surfaces with antibacterial before & after use bunsen burner to create sterile zone around workspace flame sterilise wire loop and necks of any bottles keep vessels containing bacteria open for minimum amount of time close all windows and doors
what is chromatography used for?
separate and identify small quantities of different compounds
what are the factors affecting the rate of migration?
solubility mass affinity to the paper
outline the procedure for cp11
draw pencil line 1cm above bottom of paper
cut section of leaf and grind in pestle and mortar with 20 drops of propanone to release pigments
use capillary tube to extract pigment and blot on paper
leave paper in solvent for 10 minutes
take paper out of solvent and draw a pencil line where pigments moved to
calculate Rf value for each spot of pigment
chromatography solvent risk assessment
hazard - chromatography solvent risk - flammable, irritant, harmful to inhale safety precaution - avoid contact with solvent, wear eye protection, keep away from flame in well-ventilated room in emergency - wash skin/eyes using cold water, put out flame, seek medical attention
acetone risk assessment
hazard - acetone risk - flammable, irritant, inhalation can cause dizziness and drowsiness safety precaution - avoid contact, wear eye protection, keep away from naked flame in well ventilated room in emergency - wash skin/eyes with water, seek medical assistance
how can pigments be identified?
comparing the Rf values calculated to known Rf values using same chromatography paper and solvent
why does affinity affect the rate of mobility?
pigments have different affinities to chromatography paper, those with lower affinities will travel further up the paper
why does solubility affect the rate of mobility?
pigments that are more soluble travel further up the paper and end up closer to the top at the solvent front
Rf value formula
distance moved by pigment / distance moved by solvent
outline the procedure for cp10
place a piece of pondweed in a beaker of water
cover one side of the beaker with aluminium foil to block out light
cover the other side of the beaker with a coloured light filter
add half a spatula of sodium hydrogencarbonate to the water to provide carbon dioxide
leave for 5 minutes
place the bench lamp a set distance from the beaker e.g. 30cm
measure the movement of the air bubble up the capillary tube
replace the coloured light filter with another and repeat the experiment
sodium hydrogencarbonate risk assessment
hazard - sodium hydrogencarbonate risk - contact with eyes, inhalation safety precaution - wear goggles, avoid contact with skin in emergency - seek medical attention, flood cuts/eyes with cold water
why does a green filter decrease the volume of gas the most?
chloroplasts don't absorb much green light - they reflect it, giving them their green appearance
when is the greatest volume of gas produced?
when there is no filter, because all wavelengths of light can be absorbed
what does the volume of gas indicate?
assumed to be oxygen - volume of gas produced is directly proportional to the rate of photosynthesis
cp10 control variables
light intensity amount of sodium hydrogencarbonate time allowed for gas collection temperature
what is a respirometer?
a piece of equipment used to measure the rate of respiration
how does a respirometer work?
adding a drop of coloured liquid to the length of tubing. as the organism respires and the volume of oxygen in the tube decreases, the pressure also decreases and the liquid moves down the tube towards the respirometer
outline the procedure for cp9
assemble the respirometer
add 5g of one organism to the boiling tube and replace the bung
place a drop of coloured liquid in the open end of the respirometer and use a syringe to draw the liquid as far back as possible from the respirometer and record the starting position
close the tap and start the stop clock
open the tap after 5 minutes and record the position of the tube
repeat the process with another organism or a control
soda lime risk assessment
hazard - soda lime risk - corrosive safety precaution - wear eye protection, avoid contact with skin in emergency - wash off skin immediately, flood eyes/cuts with cold water
what factors can affect the results of cp9?
change in temperature or atmospheric pressure handling the apparatus may add heat and change the readings
what is used to absorb carbon dioxide in cp9?
soda lime
how do you find the volume of oxygen consumed using a respirometer?
measure the distance moved by the coloured liquid, and use the formula volume = distance x pi x r2
how is the rate of respiration measured using data from a respirometer?
volume of oxygen used / mass / time
cp9 control variables
mass of organism time temperature mass of soda lime apparatus must be air-tight - replace air between each set up
what are the ethical issues surrounding this practical?
the way the locusts are raised and killed is killing a living thing wrong? is it justified in the name of science?
disinfectant risk assessment
hazard - disinfectant risk - flammable safety precaution - keep away from open flames in emergency - put out fire, seek assistance
outline the procedure for dissection in cp6
pin the locus to the dissection board and remove the exoskeleton
identify the internal gas exchange system. flood the specimen with water so the tracheae show silvery-grey
examine the tracheae under a microscope
what is a potometer?
a device used to measure the uptake of water, and therefore the rate of transpiration, in plants
what affects the rate of transpiration?
light intensity, humidity, wind speed, and temperature
lamps risk assessment
hazard - lamp risk - temporary damage to eyes safety precaution - do not look directly at lamp in emergency - wait for afterimage to disappear, seek appropriate assistance if needed
bags risk assessment
hazard - bag risk -tripping safety precaution - keep under desks and away from workspace in emergency - seek appropriate medical assistance, clean spillages
why does light intensity affect rate of transpiration?
affects the rate of photosynthesis, which affects the amount of stomata open
why does temperature affect the rate of transpiration?
increases the rate of diffusion and evaporation from the stomata
why does humidity affect the rate of transpiration?
affects the rate of diffusion and evaporation by decreasing concentration gradient between plant and the atmosphere
why does wind speed affect the rate of reaction?
increases concentration gradient by mechanically removing water from the outside the stomata
betalain
red, water-soluble pigment in beetroots found in vacuole of each cell
how can the permeability of a membrane be changed?
temperature concentration of solvents e.g. ethanol
how can permeability of a beetroot cell membrane be measured?
amount of pigment leaked through the cell membrane into an aqueous solution using a colorimeter
ethanol risk assessment
hazard: ethanol risk: irritant/flammable safety precaution: wear eye protection, keep away from naked flames in emergency: wash eyes and skin with cold water
what is the effect on cell membrane permeability as the temperature increases and why?
permeability increases because proteins in the membrane denature and heat damages the bonds making their tertiary structure. this creates gaps in the membrane, making it easier for molecules to pass through it
why do low temperatures cause a decrease in membrane permeability?
phospholipids have little energy and are packed closely together to make the membrane rigid - decreases permeability and restricts molecules from crossing the membrane
outline the procedure to investigate the effect of temperature on permeability of cell membrane?
cut beetroot into 6 identical cubes with a scalpel
place each cube in a different test tube with equal volumes of distilled water
place each test tube into water baths ranging from 30oC-80oC. leave for 20 minutes
filter each solution out into a cuvette and measure the absorbance
what is the effect of ethanol concentration on membrane permeability?
increasing ethanol concentration leads to increased membrane permeability, as ethanol causes gaps to form in the membrane
biohazard risk assessment
hazard: biohazard risk: allergies, soil bacteria, contamination safety precaution: wash hands after practical in emergency: seek assistance
what happens as sucrose concentration increases?
mean pollen tube growth also increases up to an optimum. after this point, as sucrose concentration increases, mean pollen tube growth decreases - osmotic effects of increasing concentrations of sucrose
what are the control variables of this practical?
environment - humid chamber volume and content of nutrient salt solution volume of sucrose solution time allowed for growth
outline the procedure to cp4
dilute the stock sucrose solution to several set concentrations
place a moist piece of filter paper into a petri dish to form a humid chamber
put a few drops of sucrose solution and an equal volume of mineral salt medium onto a clean microscope slide
use a mounted needle to rub the anther of the flowers so they shed some pollen onto the microscope slide
place the slides into the petri dish until it is time to observe them
start the stop clock. place the slides under the microscope and use a calibrated eyepiece graticule to measure pollen tube growth
why should a cover slip not be used?
to allow oxygen to reach the pollen and prevent conditions from being anoxic
what is the role of gibberellins during germination?
it is secreted by the embryo, then it diffuses to the aleurone layer of the endosperm to stimulate the production of amylase. amylase hydrolyses starch to maltose
how is the effect of gibberellin concentration on amylase production investigated?
dilute gibberellin to produce several concentrations
cut seeds in half, use only the half with the endosperm
dip in sodium hypochlorite solution and wash with water
place seeds in each gibberellin solution and leave
place seeds in a petri dish and starch agar, and leave for 12-48 hours
pour potassium iodide onto the plates and measure the clear zone
what does the zone of inhibition indicate?
starch has been hydrolysed by amylase
the larger the zone of inhibition, the higher the amylase concentration
why are the seeds placed in sodium hypochlorite solution?
to sterilise the seeds
what is the effect of gibberellin concentration on amylase production?
increasing gibberellin concentration increases the area of the clear zone, indicating an increased production of amylase and more starch hydrolysed
what are some sources of error in cp14?
the existing gibberellin and amylase content of the seeds may be different
control variables of cp14
time allowed to soak in gibberellin
time left on starch agar plate
source/age of seeds
what is the independent variable of cp15?
sampling method - using a frame, point quadrat, quadrat size
how is percentage cover calculated?
use a quadrat with squares
count how many squares the required species is present in
divide this by the total number of squares available
multiply by 100 to convert into a percentage
outline the procedure to cp15
choose an area to take samples from. use two tape measures to create a set of axes off which coordinates can be read
use a random number generator to generate 10 sets of random coordinates
place the quadrat at each of the coordinates, placing the bottom left corner on the coordinate every time. start with the smaller quadrat
record the percentage cover for the chosen species
record the abundance of each species within the quadrat. this is used to work out density
record how many pins touch the chosen species. if it’s a frame quadrat work out how many quadrat intersection points contain the chosen species underneath.
repeat steps 3-6 with the bigger quadrat
outline the procedure to cp16
choose an abiotic factor
choose an area that has a clear light intensity gradient
lay a 20m tape measure on the ground from the area with sunlight to the shaded area
choose a species that changes in abundance along your transect
place a quadrat at the 0m mark
measure light intensity at the 0m mark within the quadrat
record the abundance of your chosen species by counting how many organisms are present. record this in a table
repeat steps 5 and 6 every 2m along the tape measure until you reach the end of the 20m
repeat steps 3-7 by creating another 2 transects between the area with sunlight to the shaded area
how else can you measure abundance?
working out percentage cover
estimate - less accurate
what is the difference between a risk and a hazard?
the hazard describes the potential source of harm, whereas the risk describes the likelihood of the harm occurring
how can the results be used to determine the relationship between the chosen factor and the morphology of a species?
t-test: find out if there is a significant difference between 2 levels of the independent variable
spearman’s rank: find out if there is a correlation between many levels of the independent variable
what is a null hypothesis?
a hypothesis which states there is no significant difference between two variables and that the difference observed is purely due to chance or error
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