Core Pracs Flashcards
How to approach ‘Devise an experiment’ Q?
IDCORSS
Dependent variable (equipment, measurements, how to calculate it)
Independent variable (list range of concs/temp tested, at least 5, equipment)
Controls/control variables (eg water as it’s 0 moldm-3, state what you’re controlling, how and why)
Organism (mass, age, species, length)
Repeats (at least 3 times, calculate a mean) (identify and remove anomalies)
Stats test (chi squared/graph-state what you’re plotting/standard deviation as bars on graphs, overlap=no significance)(simpson’s index)(t-test)
Safety (risk assessment, precautions, ethical considerations)
How to investigate trypsin conc affecting the initial rate of reaction? (CP1)
Dilute trypsin with distilled water making 0.2%, 0.4%, 0.6%, 0.8%
distilled water is control
add 2cm3 milk suspension to each conc and test for colorimeter absorbance at 15 second intervals
As conc of trypsin increases….
rate of reaction increases as number of enzyme-substrate complexes forming increases
why does rate plateau after a few minutes in enzyme substrate reaction?
Because all substrates have occupied an active site
what are the 4 factors that affect enzyme activity?
- temp
- pH
- enzyme conc
- substrate conc
how to set up control when measuring enzyme activity?
use distilled water or boiled enzyme solution instead of enzyme solution
how can colorimeter determine RoR of trypsin and milk?
as trypsin digests proteins in milk, milk becomes more translucent
value in colorimeter decreases as digestion increases
how to calculate RoR from time?
1/time
what is microscopy used for?
to increase magnification and resolution of object
what is the formula for magification?
I / A x M
how to use light microscope to observe and measure plant stem samples?
- calibrate eyepiece graticule and line it up with stage micrometer
- cut THIN transverse section of plant stem
- place on slide, add stain and cover slip. ensure no air bubbles
- set objective lens to lowest magnification
- draw it out
what are rules for label lines in biological drawings?
must use ruler and draw horizontal line
what are the magnifications of eyepiece and objective lenses?
10x eyepiece
objective comes in low, medium, high
what is the mitotic index of a sample?
ratio of cells undergoing mitosis to the total number of cells in a sample
what are some common risk assessment factors?
- scalpel/scissor - risk cuts
- acids/dyes - risk irritation
- glass equipment - risk cuts
how to find mitotic index of a garlic clove? (Core prac procedure)
- heat HCl in waterbath
- cut small sample of root tip using scalpel
- add stain (acetic orcein)
- Macerate with needle, make 1 thin layer
- cover slip, ensure no air bubbles#
- gently press tgt
where in plants can cells undergoing mitosis be found?
meristem tissues at root and shoot tips
what is the formula of mitotic index?
of cells w visible chromosomes / total ~ of cells in sample
why is garlic root tip placed in hot HCl? For mitosis observation
to dissolve middle lamellae, breaking up cellulose cell wall
so dye can stain
why is garlic clove sample squashed?
to flatten sample and reduce layers
what is the pollen tube?
path through stigma made by digestive enzymes so pollen grain can reach embryo sac and fertilise ovum
what is the cell-surface membrane made up of?
phospholipid bilayer
is selectively permeable
what is the purple pigment on beetroot cells called? how is it used?
betalain
permeability can be measured by intensity of pigment leaked
using colorimeter
what conditions are measured for beetroot membrane permeability?
range of temperatures: 0-70 C
filter out to colorimeter sample #
control cuvette using distilled water
what are 2 abiotic factors that affects permeability of cell membranes?
temperature
conc of solvents (ethanol)
what is the effect of temp on membrane permeability?
increasing temp = increase permeability (more extreme temps), as proteins in membrane denature to produce gaps
what is the effect of ethanol conc on membrane permeability?
higher = increase permeability, as it causes gaps to form in membrane
what is plasmolysis?
where plant cell begins to shrink away from cell wall (as water osmosise out of cell)
what is isotonic?
water conc in cell is equal to outside of cell
what is hypertonic?
water in cell is osmosising to outside of cell
cell becomes flaccid
what is hypotonic?
water is osmosising into cell
cell becomes turgid
what is the procedure to test for osmotic potential of plant cells?
5 concs of mineral salt solutions
place plant cells in them and soak for 20 mins (to reach equilibrium)
observe 25 cells under microscope, note how many are plasmolysed
how to dissect a locust?
remove exoskeleton
flood specimen with water, trachae show up silvery-grey
what are rules about biological drawings?
firm single line, no shading
use pencil
large diagram (half the space given at least)
what is used to measure the uptake of water?
potometer
what is used to measure liquid translucency?
colorimeter
what factors affect rate of transpiration?
- wind speed
- light intensity
- temp
- humidity
- SA
- water supply
how is rate of transpiration calculated?
distance of bubbles travelled in capillary tube
volume of water uptake = πr²
rate = volume/time
how to control light intensity?
distance between lamp and potometer
how to control wind speed?
using a fan/hair dryer near potometer at different speeds
how to control humidity?
wrap plastic bag around plant to maintain humid environment
How to control temperature in practicals?
Thermostatically controlled water bath
Describe how to use a micrometer to determine how many times bigger your drawing is than the actual cell? (4 marks)
- use eye piece graticule and line up
- calibrate stage micrometer
- divide length by magnification
- repeat measurements
- divide into lengths in drawing (apply Q!)
Why are electron microscopes used instead of light microscopes to look at viruses? (2 marks)
- electron microscopes have higher resolution and magnification
- bcs it has shorter wavelengths
outline a method for extracting photosynthetic pigments
grind a leaf with pestle and mortar
+ extraction solvent like propanone
then paper chromatography
outline how paper chromatography can be used to separate photosynthetic pigments?
- use capillary tube to dot extracted pigment on start line (drawn w pencil)
- dip paper in solvent
- allow solvent to run until it reaches the other end of paper
how to calculate Rf values for paper chromatography?
distance moved by pigment / distance moved by substance
How to use counting squares to count cells?
Count cells in grid,
And middle line of left and bottom of the grid
What is the inaccuracy in counting cells?
- hard to decide if cell is touching line (e.g. double counted)
- counts both dead and living cells
When Q asks you to comment on the validity of a conclusion and standard deviation involved, think…
- Does SD and data overlap?
- if yes, it’s invalid
- if not, it’s valid - Give reason why this could happen
Explain why streak plating on selective media is a suitable method for isolating the salmonella. (4 marks)
- Streak plating only allowing gram -ve to grow
- So it spreads bacteria in agar individually,
- So colonies grow separately
- When extracting, only one type of bacteria will be picked up
How to find exact data values if given a table but my exact data isn’t on the table?
Plot a graph
Find value on graph (line of best fit)
Explain why decreasing temp affects rate of respiration of maggots. (2 marks)
Less kinetic energy in enzymes
So collisions between enzymes and substrates less likely to take place
Why do we use controls?
For comparison
Explain the effect of ethanol on plant cell membranes. (2 marks)
Ethanol damages/dissolves phospholipids (as it is polar)
So membrane becomes more permeable
Why do we have to rinse disc of beetroot/leaf?
To remove excess pigments as it would affect measurements
When to accept or reject null hypothesis in Chi square test?
If Chi2 value > p value (p=0.05 unless stated otherwise)
It is significant enough to reject null hypothesis,
As less than X% probability the difference is due to chance
Then link to Question’s conclusion
If chi2value < p value, accept H0
How to make sure respirometer test is valid.
- control temp using thermostatically controlled water bath
- use colour liquid in glass tube
- use KOH/soda lime (to absorb CO2)
- use πr2d
- use metric ruler
- repeat
Which stage in the aerobic respiration produces 4 CO2 for each glucose?
Krebs
What do you use to extract plant pigments? (Grinding wise)
Pestle and mortar
How do you produce a plan drawing?
Outline organism/thing
Do not draw details
What do mitotic index mean?
Ratio of cells dividing out of all cells
Higher value (closer to 1) = more cell dividing
What is sucrose’s effect on pollen tube growth?
Higher sucrose conc = higher rate of pollen tube growth
Increased germination as more sucrose supply for respiration
What does it mean by turgid cells?
Cell with High water content
What do turgid and plasmolysed cells look like under a microscope? Why?
Turgid: brick shape, full of water so enough pressure against rigid cell wall to keep structure
Plasmolysed: dense cluster in middle of cell, away from cell wall
Why does increase in temp increase rate of respiration?
Increase KE and enzyme activity
So increase oxygen uptake to supply for increased activity
What colour filters affect rate of photosynthesis (negatively) the most?
Green decreases it most
Red light is blocked
Plants don’t use much green light (as reflected by their colour as they reflect green light
What factors affect distance travelled by pigments in chromatography?
The solubility of the pigment
How does streak plate isolate individual colonies? (5 marks)
- flame wire loop with Bunsen
- streak sample on sterile agar
- at least 3 streaks in total
- second and third streaks must pass through lines of previous streaks
- incubate and pick out individual colonies with wire loop
Why is bacteria incubated at 30C at school? (2 marks)
- above would be similar to human body temp
- risk of growing human pathogens and infection students
How can a scientific community evaluate a new idea? (2 marks)
- repeat experiments to validate findings
- peer review
When temperature is mentioned, must discuss…
ENZYMES
Explain why the double envelope of chloroplasts in an electron micrograph cannot be seen as 2 separate membranes. (2 marks)
- bcs resolution is not high enough
- membranes too close together to be distinguished
Describe how you would dissect a locust to make sure every gas exchange system is visible. (3 marks)
- pin locust
- cut the body open
- submerge in distilled water
How to increase validity of measuring grass cover. (3 marks)
- use larger quadrat
- use random number generator
- place quadrat at random coordinates
- to achieve a consistent measure of mean
Explain how genetically modifying mosquitoes to be fluorescent can be used to produce a large population of them. (4 marks)
- identify mosquitoes that are fluorescent
- because they contain the gene and are genetically modified
- interbreed them
- repeat for generations
- by selecting offspring that have the GM gene
Explain why the Brazilian Government advises people to use mosquitoes nets even if they have already contracted the Zika Virus. (2 marks)
- mosquitoes spread other diseases
- to prevent people to be bitten
- prevent spread to uninfected people
Explain why an electron microscope, rather than a light microscope, was used to produce a photograph. (2 marks)
Has higher resolution
Bcs wavelength of e-s are shorter
When analysing data in a table,
Say something about each column
When is chi2 test used
To find difference between 2 variables if difference is by chance
When is spearman’s rank test used
To find correlation
When is simpson’s index used
To measure biodiversity
What is the guideline for drawing graphs?
SLAPU(K)
Scale
Line of best fit
Axis (independent on x, dependent on y axis)
Points
Units
(Key - sometimes when more than 1 line is drawn)
How should leaves used in transpiration investigations be prepared? (2 marks)
- dry leaves, as wet reduces diffusion
- cut under water to prevent blocking xylem
Explain the possible health benefit of converting glucose into fructose for use in sweet tasting drinks. (2 marks)
- less needed for same sweet effect
- so less caloric intake
- so reduce obesity
Describe how you could use chromatography to separate plant pigments. (3 marks)
- add pigments to start line
- dry and repeat
- place paper in ethanol
- let solvent run to reach near top
What stain is used to see stages in mitosis?
Acetic orcein
Describe how to prepare a microscope slide of root tissue to show stages of mitosis. (4 marks)
- add warm acid
- remove acid w water
- tease / macerate cells
- add acetic orcein stain
- add cover slip
Devise a method to investigate the effect of waterlogged soil on mitosis in root cells. (4 marks)
- use waterlogged and non waterlogged soil
- same plant species
- control temp using thermostatically controlled water bath
- leave for same period of time eg 5 weeks
- take cells from same part of root tips
Waterlogged soil lacks oxygen.
Explain why a lack of oxygen in waterlogged soil could reduce the growth of a plant. (4 marks)
So respiration is inhibited
So ETC inhibited
So less ATP synthesis
So less active transport of mineral ions
So less protein synthesis
Describe how a microscope should be used to observe the stomata using the high power lens. (3 marks)
- locate specimen using low power objective lens
- focus using low/medium power objective lens
- only use fine focus with high power lens
Describe how nail varnish peel samples should be taken to allow a valid comparison between mean numbers of stomata. (2 marks)
- apply on same age of leaves
- on the same surface / area of leaf like the top part of leaf
Analyse data to explain how fewer stomata might affect the growth of coffee plants. (3 marks)
Less CO2 intake
So less carbon fixed to make glucose
And less ATP synthesised to transport mineral ions
So less protein synthesis / DNA
Explain why samples of a pathogenic microorganism is exposed to radiation before injected as vaccine. (2 marks)
To kill / inactivate
So less risk of infection
Describe how vaccination enabled people to have active artificial immunity. (5 marks)
MHC present antigens becoming APC
APC bind to CD4 receptor
Activate and produce T memory cells
Produce B lymphocytes
Differentiate into Plasma cells that release antibodies
Explain how a drug resistant bacteria may evolve. (3 marks)
Mutations happens randomly
Produce proteins/enzymes that make drug ineffective
So resistant organisms pass on allele
Drug is the selection pressure
Describe how atherosclerosis develops in coronary arteries. (3 marks)
Damage to endothelium caused by high blood pressure
Trigger inflammatory response
Deposits cholesterol
Form atheroma
What are the conditions for the hardy-weinberg equation?
- no mutation
- mating randomly
- no selection pressure
What procedures are used to collect valid data using a colorimeter for photosynthetic pigments? (4 marks)
- calibrate to obtain 0 absorbency using reference curette with distillled water
- same light intensity
- use red filter
- use tubes with clean sides, no scratches
- same vol and conc of x and y
Explain the effect of one concentration of thrombin on the conversion of fibrinogen to fibrin. (2 marks)
less slows RoR
but final fibrinogen converted will be the same
as enzymes can be reused
just takes longer to form
fibrin will be produced more slowly
(Or reverse)
Explain why the stem would be a different colour after placing in a beaker of stain? (2 marks)
- stain has been taken up by xylem
- as xylem transports water
Describe the procedure for the accurate determination of the diameter of cell A using a microscope. (5 marks)
- use light microscope under low power to identify specimen
- then use high power to view cell
- calibrate eyepiece graticule using stage micrometer
- count number of graticule units over cell
- convert units using calibration
- measure diameter at different positions
Describe a procedure to compare the percentage germination of pollen collected. (5 marks)
- observe germination of pollen grain using agar plates
- add sucrose solution
- for 12 hours
- control temperature in incubator
- control biotic eg same plant variety
- ## view through microscope
How to increase validity of this investigation involving temperatures and enzymes on a graph? (4 marks)
- repeat
- calculate SD and plot error bars on graph
- keep all conditions constant
- calculate t-test
Explain why it is important to measure the volume of oxygen in the first 10 seconds. (2 marks)
- it is the initial rate of reaction
- substrate is not limiting yet
A student was given a 1 moldm-3 sucrose solution. How can the student use this to make a 0.8moldm-3 sucrose solution?
8:2 / 4:1
sucrose:distilled water
Describe steps taken by student to see pollen grains using a microscope. (3 marks)
- pollen grains put in sucrose solution
- place on microscope slide
- use low power lens first to identify specimen then increase magnification
Explain why a student plotted standard deviations on a graph. (2 marks)
- It is the range of values around the mean
- no overlap gives an indication of significant difference
Why is temperature controlled when investigation involves enzymes?
To control enzyme activity
Explain why no oxygen was produced when boiled liver was added to hydrogen peroxide but raw liver does. (3 marks)
- enzyme denatured
- H bonds / disulphide bonds broken
- shape of active site changes
- no longer complementary to bind to substrate
Explain why it is important ot measure the volume of oxygen in the first 10 seconds. (2 marks)
- It is the initial rate of reaction
- substrate is not limiting
How to measure water content of soil?
Sample at regular intervals
Weigh, dry, reweigh till constant mass
What is used to absorb carbon dioxide in investigation of respiration?
Soda lime
Why would you cover the dissected locust with water? (1 mark)
So trachea / gas exchange system is clearly visible
Which bacteria stains red and why?
Gram Negative
Because it has thiN Peptidoglycan cell wall
At what temperatures should culturing bacteria be stored in in an incubator?
Under 30C
Explain why decreasing the temperature affects the rate of respiration of maggots. (2 marks)
- less kinetic energy
- so less frequent collisions of enzymes and substrates
What is the null hypothesis?
THERE IS NO DIFFERENCE BETWEEN EXPECTED AND OBSERVED _____ (depends on context)
Describe how you could use chromatography to separate pigments in plant leaves. (3 marks)
- add extract/pigment to start line
- draw start line with pencil
- concentrate spot - dot, dry, repeat
- place paper in solvent like ethanol
- allow run till near top of paper
- obtain solvent front
Why must we use dry leaves and cut stem under water when conducting an investigation using a photometer, measuring rate of transpiration?
- dry leaves as wet reduces rate of diffusion
- cut under water to prevent air getting into xylem, affecting the results
- to maintain validity of investigation!
Explain how the student could convert transpiration rate using units mm3cm-2min-1 in a 5 minute period test using potometer . (3 marks)
Find volume πr^2 h
Divide by total area of leaves
Divide by time (5 mins)
Why is rate of transpiration much higher in moving air than still air? (2 marks)
- moving air moves water molecules away from leaves
- INCREASES concentration gradient
What stain is used in mitosis?
Acetic orcein
Devise a procedure, using electrophoresis, to compare the amplified DNA of humans and Neanderthals. (4 marks)
- Use restriction endonucleases to cut DNA samples into fragments
- Load DNA samples to agarose
- Run electric current through
- Add markers to visualise bands (like fluorescent dye)
- Compare positions of bands produced
Explain how results from electrophoresis can provide evidence for interbreeding between Homo Sapiens and Neanderthals. (2 marks)
- compare the location and number of bands from results
- similarities in bands’ positions indicates interbreeding (in the past)
