simple dilution is when all dilutions have the same amount of the original sample but serial dilutions only the first dilution has some of the first sample and the rest just have some of the preceeding sample i hope you understandheyy
when do we used simple dilutions and when do we use serial dilutions ??
Assalamu 'Alaykum Everyone!CO2:
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.
- 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
*for uniform distribution of heat.
- 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
- digital/mercury thermometer
- for food tests, such as Benedict's test, the temp must be above 80'C.
- the method of timing (stopwatch/ wall clock)
-mention the time according to the need
(Teacher's advice: Don't be vague when mentioning the time period; be sensible, realistic and precise! )
- 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
DIAMETER (of capillary tubing)/ DISTANCE MOVED(by the droplet) orLENGTH
- RATE OF TRANSPIRATION=
- 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
- CO2 and O2 concentrations
- 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.
Measuring Light Intensity:
- 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
- camera meter
Methods of Eliminating Light:
- card board box, black paper, dark room, black bag
- place in a cupboard
Exp on Effect of Chemicals on Enzyme Action:
- 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
KEY: Remember the 4 factors affecting enzyme activity plus the effect of inhibitor
- must think whether the chemical is an inhibitor
- when dealing with beads of enzyme: always use the same number/ same mass of beads
(Two of the points that i ddint know how to title)
- 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:
Metabolic activity decreases with age!!!
- age group
- body mass/size
- state of health
- time of the day the test is being conducted
- any tolerance or addiction
- use of any stimulant or depressant
- sigmoid curve: drawing, labelling, and the reasons behind every phase
- What decreases population?
- destruction of habitat
- food availability
- migration and emigration
- increase in predators
- increase in parasite
- lesser nesting places
- 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!!!
Right now..am going to sleep, but please don't reply until i'm done posting everything..thanks a lot...
- use a fan
- for varying wind: vary the fan speed or the distance from the specimen
Yeahh thankssimple dilution is when all dilutions have the same amount of the original sample but serial dilutions only the first dilution has some of the first sample and the rest just have some of the preceeding sample i hope you understand