-
7/28/2019 Bio Practicals
1/3
GRAPHS:
1.the value which is varying is always on the y-axis while the
constant value is on the x-
axis.
2.no unbroken lines
3.it must be neat and thin
4.the points can be joined using a ruler or by hand
5.do not draw beyond the plotted points.
6.blobs or centre points more than 1mm are NOT acceptable
7.if zero is present in the reading, your graph MUST pass
through zero.
8.label both axis
9.use appropriate units
10.use appropriate scale
11.use sharpened pencil to plot
12.plot the dots within circles, of equal sizes, must be clear
and not too big.
SOURCES OF ERRORS:
1.temperature not controlled
2.pH not controlled or not measured accurately
3.difficulty in judging the colour.
4.difficulty in having the same time
5.inaccuracy in preparing serial dilution
6.inaccuracy of equipment, for e.g. pipette/syringe
7.too short time.
8.evaporation of the solution which can cause the concentration
to change.
LIMITATIONS OF ERRORS
1.measure the volume accurately using syringe with narrow range
of calibration
2.repeat more times at each pH/conc./temp
3.use range of pH/conc./temp
4.accurate specific measuring devices
5.use colorimeter to measure the degree of colour change.
6.use buffer to control pHs
7.use of water bath/thermostat to control temp
8.use thermometer to measure the temp.
9.thermostatically controlled environment.10.repeat with each
conc.
11.volume of the sample(e.g. enzyme/substrate. must be the
same.. because as
volume increases, conc also increases
12.keep only one factor different, and all others must be the
same.
-
7/28/2019 Bio Practicals
2/3
RELIABILITY
1.take minimum of 3 readings
2.repeat with more pH/conc/temp and find out their mean
ACCURACY
1.seeing electronic thermostat
2. use of pipettes instead of measuring cylinders
KEY
1.read the whole question till the end
2.decide number of readings to take
3.don't go for more or less than 3 readings per conc/vol of any
ques.
4.make a table
5.write down the UNITS in each column of the table...e.g.
conc/cm^3 , temp/C
MICROSCOPY (IMPORTANT)
1.proportion of thickness must be correct.
2.draw the organelles where u see them, dont just draw anywhere
within the cell
never draw what u know.
3.whenever u see the plant cells, draw the cell walls.
4.IN PLAN DIAGRAMS, NO DRAWING OF ANY CELLS, AND NO SHADING...if
u'll do either
of them, You'll lose the whole mark
5.when asked to draw 2 cells, draw the ones that are easiest to
draw. And dont draw
more than 2 cells
6.fraw the adjacent (touching. cells.
7.drawing should be large, unshaded.
8.in plan diagrams show the relative thickness of each
layer.
9.draw the exact shape, if its oval or round or has wavy
outlines
10.label the diagram...simplest thing to label is cytoplasm,
nucleus and cell membrane.
11.if its a trachea cell, then label goblet cells, cilia, blood
vessels, muscular tissue,
cartilage cells (lacunae.
12. when asked to compare 2 diagrams....make a table (drawing a
table itself has 1
mark .....put at least one similarity
-
7/28/2019 Bio Practicals
3/3
MAGNIFICATION
1.Measure the length of the object youre asked to measure in the
question.
2.Your measurement will probably be in centimeters, you have to
convert it to the same
unit as the actual length provided in the question (usually
micrometers, m).
3.To convert from cm to m, take the observed value in cm,
multiply it by 10000.
4.Now you have an observed value in m, substitute it in the
formula, and then
substitute the actual in the formula to get the
magnification.
MAKING TABLESIndependent Variable in the first column....and
observations or dependent variables in
other columns.....in question 1 of exam..two kinds of questions
can be set....one
involving quantitative observations like most enzyme experiments
and other involving
qualitative observations like food-tests...as far as
observations for qualitative data are
concerned...these will include most probably color changes
during course of
investigation...so a likely error for these experiments can be
difficulty in judging b/w
different colors with your improvement being the use of
colorimeter to measure color
intensity.....
ERRORS IN MESUREMENTS
1.irregular in shape
2.difficulty in focusing3.preperation is squashed
