CO2: •
Usua Usually lly,, most most of of the the CO2 CO2 abso absorb rben ents ts are are wit with h -OH -OH eg: eg: NaOH NaOH or or KOH
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Sour Source ces s of CO2 CO2 are are usua usuall lly y thos those e with with the the -CO -CO3 3 eg: eg: CaCO CaCO3, 3, H2CO3
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a nonnon-ch chem emic ical al sour source ce:: gas gas cy cyli lind nder er
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the the gas gas is supp suppli lied ed thro throug ugh h a bubb bubble ler r
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to meas measur ure e CO2 CO2 conc concen entr trat atio ion: n: use use pro probe be with with mete meter r
Temperature: •
method method of cont contro rollin lling: g: use use an electr electroni onic c wate waterr-bat bath h (a (a beak beaker er of boiling water)-depends water)-depends on the experiment
•
use an an el electronic th thermostat
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heat screen*/ heat fil filter
*for uniform distribution of heat. •
incubator
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dig digita ital/m l/merc ercury ury ther thermo mome mete ter r
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for food food tes tests, ts, such such as as Bene Benedic dict's t's test, test, the the temp temp must must be above above 80'C.
Time: Always mention: - the method of timing ( stopwatch/ wall clock) - precise time -mention the time according to the need (Teacher's advice: Don't be vague when mentioning the time period; be sensible, realistic and precise! )
Sample Size: •
the larger the sample size, the more reliable the results.
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When making concentrations, the minimum number you should make is 3. Ideally, the number of conc. you're going to make must be 5.
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mass must be the same when comparing two samples.
Measuring: •
use mm calipers
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a ruler- calibrated to cm or mm
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measuring cylinders
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syringe, pipette
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weighing scale/ electronic balance
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digital/mercury thermometer
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MEASURING PLANT LENGTH1) use ruler 2) use a thread (remind me to explain what this means if i didn't by the end of this post please)
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MOVEMENT AND TIME 1) measure distance moved at a certain time (or) 2) measure time taken for certain distance moved
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VOLUME OF CAPILLARY TUBING: 1) mention the diameter 2) and the surface area
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RATE OF TRANSPIRATION= DIAMETER (of capillary tubing)/ DISTANCE MOVED(by the droplet) or LENGTH
Reliability: •
never use the same sample when you are going to repeat the experiment
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always reset- whenever resetting the exp. always refresh the specimen with the same mass and volume you were using in the first exp.
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repeat and take average/ plot a graph
Accuracy: •
use the right apparatus
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gas syringe for measuring volume of gas
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look at "Measuring" for more information
Plants: •
always use same species
•
same developmental age
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keep in mind the size of leaves, size of roots, and the number of roots (and leaves).
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ENVIRONMENTAL CONDITIONS: 1. light intensity 2. temperature 3. humidity 4. CO2 and O2 concentrations 5. wind
6. water 7. mineral content
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same mass of germinating seeds
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shoots of same size/length
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when the plant is placed in water, the stem must be cut slanted under water to prevent any air-locking
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use of bung or air-tight screw to prevent evaporation of water
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in some questions, you'll see a screw: it's there for resetting the apparatus
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accuracy factor: measure properly and cut using a thread
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to control the surrounding temperature, plant experiments must be done in a thermostatically controlled room
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When using a suspension, always use either same mass or same volume
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in a question on dry mass (and you're dealing with seeds): the water is removed (evaporated) by placing seeds in an incubator or oven but never use bunsen flames-it damages the seed!
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when cutting the leaf in discs for comparing the rate of photosynthesis (or cutting anything, such as a potato): 1) the size and cross-section must always be the same
2) always cut the curved edges out and cut out a flatter surface from the centre
DNA: •
if the question is on electrophoresis, the distance is always taken
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for accuracy: always cut out the same size of DNA fragments
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restriction enzymes are used to cut at any specific place
Light: •
Keep three things in mind: 1) keeping light constant 2) varying it 3) excluding it
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in any experiment, you can only test for one factor at a time.
Varying Light: •
same wattage of bulb & varying distances
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same distance and varying bulb wattage
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different number of lamps at same distance
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a dark room with light of fixed illumination
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lamp at same distance and use light filter with different thicknesses.
Measuring Light Intensity: •
light meter
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light-dependent resistor
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photometer
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camera meter
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photodiode
Methods of Eliminating Light: •
card board box, black paper, dark room, black bag
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place in a cupboard
Enzymes: •
temperature, pH, and substrate concentration
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When varying the concentration of the enzyme, then the substrate concentration must be kept constant
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temp control: use water bath
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pH control: use buffer solution
Exp on Effect of Chemicals on Enzyme Action: •
must think whether the chemical is an inhibitor
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when dealing with beads of enzyme: always use the same number/ same mass of beads
KEY: Remember the 4 factors affecting enzyme activity plus the effect of inhibitor
Indicator: •
used to show the presence of a substrate
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it always shows a change in it's original colour to mark the end point of a reaction
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the colour change of the indicator will always be mentioned in the question only if it isn't mentioned in our syllabus
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For any experiment: note colour change at a fixed time (or)
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note the time taken for the colour change to take place
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when repeating the experiment, always replace/refresh the indicator with the same volume and concentration that was used in the previous experiment
(Two of the points that i didn’t know how to title) •
the specimen is always wrapped to exclude a certain environmental factor when an absorbent, such as CO2, is added
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wrapping is also done to prevent evaporation
Humans: •
measurement of height, sex, heart rate, disease
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Reliability factors: 1) age group 2) gender 3) body mass/size 4) genetics/race 5) state of health 6) time of the day the test is being conducted 7) any tolerance or addiction 8) use of any stimulant or depressant 9) metabolism: Metabolic activity decreases with age!!!
Population: •
sigmoid curve: drawing, labelling, and the reasons behind every phase
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What decreases population? 1) destruction of habitat 2) disease 3) food availability
4) migration and emigration 5) increase in predators 6) increase in parasite 7) lesser nesting places 8) hibernation 9) accumalation of toxic waste 10) for plants: -> increased grazing -> environmental factors: natural disasters, soil erosion -> deforestation: causes soil erosion •
IMPORTANT LIMITING FACTORS!!!!
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Food Availability and Disease!!!
Wind: •
use a fan
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for varying wind: vary the fan speed or the distance from the specimen
Organism Growth: •
source: corn syrup, glucose, protein, low grade NH3
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never write nutrient broth
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mention 2 examples at least
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same amount or conc. of nutrient broth to the two sets of specimen
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the nutrient supply must be kept constant
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mention flow rate through fermenter
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For batch culture: note the amount of time the organism is left in the fermenter
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keep in mind the O2 supply, temperature, pH
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sterility of the fermenter is very important [so that no other organism grows and acts as a competitor]
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sterility is important in both batch and continuous culture- in fact, every time you set up a batch culture, sterility must be maintained
Planning Questions: •
decide what the experiment is on (like diffusion, osmosis, photosynthesis)
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use the same apparatus; describe what you're going to vary and what must be kept constant- decide which is the dependant and independent variable (eg light intensity? CO2 conc.? or gas produced?)
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how will you vary (count bubbles? use gas syringe?)---always
ask yourself: is it a comparison •
units--same volume, same mass, same concentration
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What are the constants? How will you keep them constant?
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give brief description of the steps; if time is required, BE SPECIFIC.
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inference: in some experiments you need a control, but don't write anything which isn't required otherwise
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precautions (FREE MARK!!!)
Reliability: > give time for calibration (Calibration time is adjusting time) >Repeat 3 times to be certain that the results are consistent-do not change the parameter >large sample size
Why repeat? •
increases the certainty that the results are consistent
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so that anomalous results can be removed
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permit variance from mean
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to take an average
Accuracy: •
means measuring in a reliable manner. Eg 1) weighing scale 2) thermometer 3) vernier caliper 4) measuring cylinder 5) gas syringe
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use of a buffer solution to maintain pH
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using sol of known conc. (by serial dilution)
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comparing colours of solution by a colorimeter
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larger number of known conc.
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washing syringes and pipettes
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mixing and stirring for uniformity to prevent settling of suspension
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in microscopy: eye-piece graticule
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to measure the surface area, the specimen is placed on a grid, where the full squares, half or more than half are taken into consideration
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FILTERING AND CENTRIFUGING: the suspension spins and the more dense sinks at the bottom
Control: •
in an experiment with living organisms, the control must be a dead organism
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whatever factor is being used in the question is emitted from the control
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For counting chromosomes and making them visible, the growing regions of the plant are cut
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cut surface of the specimen
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chromosomes are counted by placing cut surface under a high power light microscope(with high magnification)
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How to make chromosomes visible?
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> add dye/stain them
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> Examples of dyes: 1) methylene blue 2) aceto-carmine 3) aceto-orcein
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