practicals P1 Flashcards
ways of measuring the rate of enzyme activity
- gas produced - how fast the product is made eg gas released into upside down cylinder
- biochemical tests - how fast substrate broken down eg testing for starch using amylase, none left = broken down
- change in mass
- change in pH
- colour change
variables in enzyme experiments
temperature
concentration of enzyme
pH (use buffers)
substrate concentration
keep all same except independent
control - repeat with denatured enzyme (check it is making change in DV)
effects of temperature on enzyme activity
vary temperature using a waterbath or beaker with ice
measure using thermometer
control all other variables
effects of substrate/enzyme concentration of enzyme activity
stock solutions diluted to make necessary concentrations
- dilution series
effects of pH on enzyme activity
use buffer to maintain pH
check buffer doesn’t affect rate of reaction - use control
how to calculate rate of reaction
change in DV
over
time
if DV is time then = 1 over time
how to calculate rate of reaction on graph
linear - calculate gradient
curved - draw tangent then calculate gradient
g = change in Y
over change in X
how to prepare root tip cells to view mitosis
cut 1cm from the tip of a growing root
- tip as that is meristem, so mitosis is happening
used mounted needle to spread cells on slide - thin so light can shine through
add stain - makes chromosomes easier to see
place cover slip gently - don’t smear or will damage chromosomes
what is the mitotic index?
proportion of cells undergoing mitosis
(high rate may mean cancerous growth)
no. of cells with visible chromosomes (undergoing mitosis)
over ——–
total number of cells visible
how to calculate cells in stages of mitosis
number of cells in stage
over
number of cells
x length of cell cycle
how to calculate magnification
actual = size over magnification
I
M A
How to measure light concentration without colorimeter
Use known concentration of X
Prepare dilution series
Compare to colour standards = concentration
eyepiece graticules and stage micrometer
graticule - fitted onto eyepiece, scale with numbers, no unit
micrometer - placed on stage, accurate scale with units
used to work out division of graticule
how to prepare slide
pipette small drop of water onto slide
use tweezer to place thin specimen (light through)
add a drop of stain
carefully lower cover slip, one side then the other to avoid air bubbles
press down firmly - thin layer so light can pass through
how to prepare plant tissue for osmosis
cut safely using cork borer
= same surface area
dry cylinders before weighing to remove cytoplasm from cut cells
dry before weighing to remove surface water
how to calculate % change in mass
final mass - initial mass
over
initial mass
x100
(as a ratio = final over initial)
how to plot calibration curve
% change in mass on y
concentration of solution on x
why does increasing concentrations of alcohol increase pigment?
phospholipids dissolve in alcohol
increased concentration = more dissolve so more pigment leaves
eventually lose structure
why does increasing temperature increase pigment?
rate of diffusion increases so pigment leaving increases
phospholipids have more kinetic energy = more fluid
eventually proteins denature = large quantities of pigment
control variables
time
volumes/ surface area
temperature
pH
type of plant material
how to use calorimeter
measure absorbance
calibrate with distilled water
use opposite colour to sample
(blue for red beetroot)
risk assessment with dissections
equipment sharp
- cut onto board not hand
- cut away from you
disinfect
- tools in disinfectant, blade down
- surface
- hands with soap
dispose of parts and equipment in separate bin
aseptic techniques
prevent contamination
- wash hands with soap
- disinfect working area
use bunsen burner flame
- equipment sterilised
- neck of bottle
- glass spreaders in alcohol first
- not remove pertinent dish lid, lifted
- tape, allows o2 in, no microbes out
incubate at 25c - prevents harmful pathogens growing
zone of inhibition
larger zone = better substance is at killing microbe
measure diameter
control using disc soaking in distilled water - should have no effect on growth
chromatography
separate mixtures into individual components
relies on differences in solubility
- higher solubility = travel further
larger molecules move slower = seperated
can be used to separate monosaccharides
add to line on paper - in pencil so doesn’t run/mix with the ink
suspend above solution
biochemical test for reducing sugar
(eg monosaccaride such as glucose and maltose/lactose)
add benedicts
heat in water bath
positive = coloured precipitate
blue - brick red (depending on conc.)
use excess to make sure all sugar reacts
biochemical test for non-reducing sugar (eg sucrose)
obtain negative reducing sugar test
break down non-reducing into monosaccharides first
add dilute HCl (acid)
heat in water bath
neutralise with sodium hydrocarbonate (alkali)
carry out Benedict’s for reducing sugar
positive = coloured precipitate
blue - brick red
biochemical test for starch
add iodine dissolved in potassium iodide solution
positive = orange to blue/black
biochemical test for lipid
test for lipids/fats
add ethanol
shake
add water
positive = milky emulsion
intensity = concentration
biochemical test for proteins
add sodium hydroxide (alkaline)
add copper (II) sulphate solution
postive = purple]negative = stays blue
