CO2:
•
Usually, most of the CO2 absorbents are with -OH eg: NaOH or
KOH
•
Sources of CO2 are usually those with the -CO3 eg: CaCO3,
H2CO3
•
a non-chemical source: gas cylinder
•
the gas is supplied through a bubbler
•
to measure CO2 concentration: use probe with meter
Temperature:
•
method of controlling: use an electronic water-bath (a beaker of
boiling water)-depends on the experiment
•
use an electronic thermostat
•
heat screen*/ heat filter
*for uniform distribution of heat.
•
incubator
•
digital/mercury thermometer
•
for food tests, such as Benedict's test, the temp must be 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.
•
When making concentrations, the minimum number you should
make is 3. Ideally, the number of conc. you're going to make
must be 5.
•
mass must be the same when comparing two samples.
Measuring:
•
use mm calipers
•
a ruler- calibrated to cm or mm
•
measuring cylinders
•
syringe, pipette
•
weighing scale/ electronic balance
•
digital/mercury thermometer
•
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)
•
MOVEMENT AND TIME
1) measure distance moved at a certain time (or)
2) measure time taken for certain distance moved
•
VOLUME OF CAPILLARY TUBING:
1) mention the diameter
2) and the surface area
•
RATE OF TRANSPIRATION= DIAMETER (of capillary tubing)/
DISTANCE MOVED(by the droplet) orLENGTH
Reliability:
•
never use the same sample when you are going to repeat the
experiment
•
always reset- whenever resetting the exp. always refresh the
specimen with the same mass and volume you were using in
the first exp.
•
repeat and take average/ plot a graph
Accuracy:
•
use the right apparatus
•
gas syringe for measuring volume of gas
•
look at "Measuring" for more information
Plants:
•
always use same species
•
same developmental age
•
keep in mind the size of leaves, size of roots, and the number of
roots (and leaves).
•
ENVIRONMENTAL CONDITIONS:
1. light intensity
2. temperature
3. humidity
4. CO2 and O2 concentrations
5. wind
6. water
7. mineral content
•
same mass of germinating seeds
•
shoots of same size/length
•
when the plant is placed in water, the stem must be cut slanted
under water to prevent any air-locking
•
use of bung or air-tight screw to prevent evaporation of water
•
in some questions, you'll see a screw: it's there for resetting the
apparatus
•
accuracy factor: measure properly and cut using a thread
•
to control the surrounding temperature, plant experiments must
be done in a thermostatically controlled room
•
When using a suspension, always use either same mass or
same volume
•
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!
•
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
•
for accuracy: always cut out the same size of DNA fragments
•
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
•
in any experiment, you can only test for one factor at a time.
Varying Light:
•
same wattage of bulb & varying distances
•
same distance and varying bulb wattage
•
different number of lamps at same distance
•
a dark room with light of fixed illumination
•
lamp at same distance and use light filter with different
thicknesses.
Measuring Light Intensity:
•
light meter
•
light-dependent resistor
•
photometer
•
camera meter
•
photodiode
Methods of Eliminating Light:
•
card board box, black paper, dark room, black bag
•
place in a cupboard
Enzymes:
•
temperature, pH, and substrate concentration
•
When varying the concentration of the enzyme, then the
substrate concentration must be kept constant
•
temp control: use water bath
•
pH control: use buffer solution
Exp on Effect of Chemicals on Enzyme Action:
•
must think whether the chemical is an inhibitor
•
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
•
it always shows a change in it's original colour to mark the end
point of a reaction
•
the colour change of the indicator will always be mentioned in
the question only if it isn't mentioned in our syllabus
•
For any experiment: note colour change at a fixed time (or)
•
note the time taken for the colour change to take place
•
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
•
wrapping is also done to prevent evaporation
Humans:
•
measurement of height, sex, heart rate, disease
•
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
•
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!!!!
•
Food Availability and Disease!!!
Wind:
•
use a fan
•
for varying wind: vary the fan speed or the distance from the
specimen
Organism Growth:
•
source: corn syrup, glucose, protein, low grade NH3
•
never write nutrient broth
•
mention 2 examples at least
•
same amount or conc. of nutrient broth to the two sets of
specimen
•
the nutrient supply must be kept constant
•
mention flow rate through fermenter
•
For batch culture: note the amount of time the organism is left in
the fermenter
•
keep in mind the O2 supply, temperature, pH
•
sterility of the fermenter is very important [so that no other
organism grows and acts as a competitor]
•
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)
•
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?)
•
how will you vary (count bubbles? use gas syringe?)---always
ask yourself: is it a comparison
•
units--same volume, same mass, same concentration
•
What are the constants? How will you keep them constant?
•
give brief description of the steps; if time is required, BE
SPECIFIC.
•
inference: in some experiments you need a control, but don't
write anything which isn't required otherwise
•
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
•
so that anomalous results can be removed
•
permit variance from mean
•
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
•
use of a buffer solution to maintain pH
•
using sol of known conc. (by serial dilution)
•
comparing colours of solution by a colorimeter
•
larger number of known conc.
•
washing syringes and pipettes
•
mixing and stirring for uniformity to prevent settling of
suspension
•
in microscopy: eye-piece graticule
•
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
•
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
•
whatever factor is being used in the question is emitted from the
control
•
For counting chromosomes and making them visible, the
growing regions of the plant are cut
•
cut surface of the specimen
•
chromosomes are counted by placing cut surface under a high
power light microscope(with high magnification)
•
How to make chromosomes visible?
•
> add dye/stain them
•
> Examples of dyes:
1) methylene blue
2) aceto-carmine
3) aceto-orcein
https://www.xtremepapers.com/community/threads/biology-paper-5tips.27105/