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Biology Practical Tips
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, ur graph MUST pass through
zero.
8.label both axis!
9.use appropriate units10.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.temp nt controlled
2.pH not controlled or nt measured accurately
3.difficulty in judging the colour.
4.difficulty in having the same time5.inaccuracy in preparing
serial dilution
6.inaccuracy of equipment, fr 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./temp3.use range of
pH/conc./temp
4.accurate specific measuring devices
5.use colorimeter to measure the degree of colourness.
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..cuz as
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volume increases, conc also increases
12.keep only one factor different, and all others must be the
same.
Reliability.....take minimum of 3 readings!
repeat with mre pH/conc/tempand find out their mean
Accuracy.....seing electronic thermostat
use of pippettes 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 table5)write down the UNITS in each coloumn of the
table...e.g. conc/cm^3 ,
temp/C
MICROSCOPY!!!
1)propotion 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, u'll lose the whole mark!!
5)when asked to draw 2 cells, draw the ones that are easiest to
draw. and
dont draw more then 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
outlines10)label the diagram...simplest thing to label is cytopasm,
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 atleast one similarity
ERRORS IN MESUREMENTS!
1)irregular in shape
