practicals P1

Question 1

ways of measuring the rate of enzyme activity

Answer 1

• 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

Question 2

variables in enzyme experiments

Answer 2

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)

Question 3

effects of temperature on enzyme activity

Answer 3

vary temperature using a waterbath or beaker with ice

measure using thermometer

control all other variables

Question 4

effects of substrate/enzyme concentration of enzyme activity

Answer 4

stock solutions diluted to make necessary concentrations
- dilution series

Question 5

effects of pH on enzyme activity

Answer 5

use buffer to maintain pH

check buffer doesn’t affect rate of reaction - use control

Question 6

how to calculate rate of reaction

Answer 6

change in DV
over
time

if DV is time then = 1 over time

Question 7

how to calculate rate of reaction on graph

Answer 7

linear - calculate gradient
curved - draw tangent then calculate gradient

g = change in Y
over change in X

Question 8

how to prepare root tip cells to view mitosis

Answer 8

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

Question 9

what is the mitotic index?

Answer 9

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

Question 10

how to calculate cells in stages of mitosis

Answer 10

number of cells in stage
over
number of cells

x length of cell cycle

Question 11

how to calculate magnification

Answer 11

actual = size over magnification
I
M A

Question 12

How to measure light concentration without colorimeter

Answer 12

Use known concentration of X
Prepare dilution series
Compare to colour standards = concentration

Question 13

eyepiece graticules and stage micrometer

Answer 13

graticule - fitted onto eyepiece, scale with numbers, no unit

micrometer - placed on stage, accurate scale with units
used to work out division of graticule

Question 14

how to prepare slide

Answer 14

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

Question 15

how to prepare plant tissue for osmosis

Answer 15

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

Question 16

how to calculate % change in mass

Answer 16

final mass - initial mass
over
initial mass
x100

(as a ratio = final over initial)

Question 17

how to plot calibration curve

Answer 17

% change in mass on y
concentration of solution on x

Question 18

why does increasing concentrations of alcohol increase pigment?

Answer 18

phospholipids dissolve in alcohol

increased concentration = more dissolve so more pigment leaves

eventually lose structure

Question 19

why does increasing temperature increase pigment?

Answer 19

rate of diffusion increases so pigment leaving increases

phospholipids have more kinetic energy = more fluid

eventually proteins denature = large quantities of pigment

Question 20

control variables

Answer 20

time
volumes/ surface area
temperature
pH
type of plant material

Question 21

how to use calorimeter

Answer 21

measure absorbance
calibrate with distilled water
use opposite colour to sample
(blue for red beetroot)

Question 22

risk assessment with dissections

Answer 22

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

Question 23

aseptic techniques

Answer 23

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

Question 24

zone of inhibition

Answer 24

larger zone = better substance is at killing microbe

measure diameter

control using disc soaking in distilled water - should have no effect on growth

Question 25

chromatography

Answer 25

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

Question 26

biochemical test for reducing sugar (eg monosaccaride such as glucose and maltose/lactose)

Answer 26

add benedicts heat in water bath positive = coloured precipitate blue - brick red (depending on conc.) use excess to make sure all sugar reacts

Question 27

biochemical test for non-reducing sugar (eg sucrose)

Answer 27

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

Question 28

biochemical test for starch

Answer 28

add iodine dissolved in potassium iodide solution positive = orange to blue/black

Question 29

biochemical test for lipid

Answer 29

test for lipids/fats add ethanol shake add water positive = milky emulsion intensity = concentration

Question 30

biochemical test for proteins

Answer 30

add sodium hydroxide (alkaline) add copper (II) sulphate solution postive = purple]negative = stays blue