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Assalamu 'Alaykum Everyone!
A brother, dornam , had asked for tips and advice on preparing for the Biology Paper 5 that's coming up. So I decided to share some practical techniques with the rest of you guys so that we're all even..
The tips were dictated to my classmates and I by our biology teacher, who had gone through all the marking schemes of the years from 2007 ( I think) and onward..however, the year 2011 and 2012 may not be included.
CO2:
- Usually, most of the CO2 absorbants 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
- 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
- incubator
- digital/mercury thermometer
- for food tests, such as Benedict's test, the temp must be above 80'C.
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.
- use mm calipers
- a ruler- calibrated to cm or mm
- measuring cylinders
- syringe, pipette
- weighing scale/ electronic balance
- digital/mercury thermometer
- MEASURING PLANT LENGTH-
- use ruler
- use a thread (remind me to explain what this means if i didn't by the end of this post please)
- MOVEMENT AND TIME
- measure distance moved at a certain time (or)
- measure time taken for certain distance moved
- VOLUME OF CAPILLARY TUBING:
- mention the diameter
- and the surface area
- RATE OF TRANSPIRATION=
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
- use the right apparatus
- gas syringe for measuring volume of gas
- look at "Measuring" for more information ^^
- 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:
- light intensity
- temperature
- humidity
- CO2 and O2 concentrations
- wind
- water
- 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):
- the size and cross-section must always be the same
- always cut the curved edges out and cut out a flatter surface from the center
- 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
- Keep three things in mind:
- keeping light constant
- varying it
- excluding it
- in any experiment, you can only test for one factor at a time.
- 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.
- 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
- 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
- must think whether the chemical is an inhibitor
- when dealing with beads of enzyme: always use the same number/ same mass of beads
Indicator:
- used to show the presence of a substrate
- it always shows a change in it's original color to mark the end point of a reaction
- the color change of the indicator will always be mentioned in the question only if it isn't mentioned in our syllabus
- For any exp: note color change at a fixed time (or)
- note the time taken for the color 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 exp
)- 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
- measurement of height, sex, heart rate, disease
- Reliability factors:
- age group
- gender
- body mass/size
- genetics/race
- state of health
- time of the day the test is being conducted
- any tolerance or addiction
- use of any stimulant or depressant
- metabolism
Population:
- sigmoid curve: drawing, labelling, and the reasons behind every phase
- What decreases population?
- destruction of habitat
- disease
- food availability
- migration and emigration
- increase in predators
- increase in parasite
- lesser nesting places
- hibernation
- accumalation of toxic waste
- for plants: -> increased grazing -> environmental factors: natural disasters, soil erosion -> deforestation: causes soil erosion
- IMPORTANT LIMITING FACTORS!!!!
- Food Availability and Disease!!!
- use a fan
- for varying wind: vary the fan speed or the distance from the specimen
