Practicals

Question 1

method to investigate substrate concentration effecting initial rate of reaction
( same for enzyme concentration)

Answer 1

• use a range of at least 5 substrate concentrations
• use an enzyme conc/volume that won’t limit rate
• measure volume of gas produced/ colour change/ product
• use tangent

Question 2

Describe how to use a light microscope

Answer 2

start with lowest magnification objective lens
put slide on stage - secure with stage clips
use focus to move stage close to the lens
adjust focus and light intensity to get clearest image

Question 3

Describe the eyepiece graticule

Answer 3

see through ruler in the eyepiece

no units

Question 4

describe the stage micrometer

Answer 4

a slide with 1 um markings

Question 5

describe how to use the stage micrometer

Answer 5

set magnification
record how many eyepiece graticule units is equal to one micrometer
dont change magnification
view specimen and use scale to calculate actual size

Question 6

What is the root tip squash used for?

Answer 6

calculate mitotic index/ see mitosis

Question 7

Method - Root tip squash

Answer 7

use a fixative to prevent enzyme action 
remove 1 mm of the root tip 
add stain (nile blue)
add cover slip without trapping air 
squash vertically

Question 8

slide preparation

Answer 8

add distilled water to a microscope slide
the sample has to be thin
water molecules holds in place by adhesion
stain
add cover slip

Question 9

why do we use stains

Answer 9

identify types of cells/ different cells

stains make the sample absorb more light - visible

Question 10

What is the Mitotic index and how is it calculated?

Answer 10

used to investigate the % of cells undergoing mitosis

(no of cells in mitosis/ total no of cells) x 100

Question 11

where is the mitotic index high?

Answer 11

at growing regions (meristem)

Question 12

what are common issues with calculating mitotic index?

Answer 12

use a fixative, use a stain, multiple layers of stains

Question 13

how could you use mitotic index to investigate the use of herbicide?

Answer 13

use a range of 5 herbicide concs, control all variables, plot mitotic index of graph, use lowest conc when mitotic index is 0

Question 14

Describe identifying the water potential of plant tissue

Answer 14

prepare serial dilution from a stock solution 
cylinders of plant tissue with the same SA 
weigh mass @ start 
submerge for 1 hour 
blot dry with a paper towel 
weigh again and calculate the % change 
plot calibration curve and estimate 
isotonic when % change = 0

Question 15

equation to calculate volume of stock required with serial dilution

Answer 15

(total amount/ stock concentration)x desired conc

Question 16

what is a colourimeter?

Answer 16

instrument that quantitatively measures the colour intensity of a solution (measures absorbance/ transmission)

Question 17

cuvette

Answer 17

rectangular test tube for colourimetry

Question 18

Colourimeter method

Answer 18

use a blank for comparison
make a calibration curve by plotting samples
read off unknown value to find concentration

Question 19

what is serial dilution used for?

Answer 19

calibration curves, viable cell count

Question 20

10 fold serial dilution

Answer 20

add 1cm of original to 9 cm of distilled water (repeat)

Question 21

what does a potometer measure?

Answer 21

rate of transpiration

Question 22

control (potometer)

Answer 22

light intensity/ wavelength
temperature
air movement/ humidity

Question 23

equation for transpiration rate

Answer 23

(distance bubble moves x cross sectional area) / time taken

Question 24

common errors with potometer

Answer 24

water used for turgidity
used for photosynthesis 
respiration makes water 
not all stomata covered/ leaves removed 
air bubbles in xylem 
error in reading

Question 25

what is the affect of freezing on membrane permeability?

Answer 25

carrier proteins and protein channels defirm when frozen

cell membrane is damaged by ice crystals

Question 26

what is the affect of cold temperatures on membrane permeability?

Answer 26

low kinetic energy - phospholipids are close together, decreasing membrane permeability

Question 27

what is the affect of warm temperature on membrane permeability?

Answer 27

increases kinetic energy, phospholipids move more, more space, increasing permeability

Question 28

hot temperatures affecting membrane permeability

Answer 28

carrier proteins denatured

Question 29

what is the affect of a solvent on membrane permeability?

Answer 29

dissolve the phospholipids in the cell membrane

loses its structure increasing permeability

Question 30

Method = Investigate the affect of solvent/temperature on membrane permeability

Answer 30

cut a piece of tissue
standardise the source and rinse thoroughly
use a range of at least 5 concentrations/ temperatures
control all other variables
measure colour change using a colorimeter set to absorbance
use a distilled water blank
repeat 5 times

Question 31

safety precautions for dissection

Answer 31

use scissors instead of scalpel where possible
replace blade covers
make cuts with blades facing away from you
wear safety goggles
sterilise equipment

Question 32

Method investigating microbial growth

Answer 32

evenly distribute bacteria on an agar plate
use a range of 5 conc
keep all other variables controlled
use aseptic techniques
use a single species of bacteria
incubate for 24 hours at 25 c to avoid cultivating harmful bacteria
repeat 5 times

Question 33

Calculating the clear zone of an uneven area?

Answer 33

use mean diameter to calculate pi x radius squared

Question 34

what is the importance of aseptic techniques

Answer 34

• avoids presence of unwanted microorganisms
  no competition for nutrients
  no decrease in yield
  prevents escape of microorganisms

Question 35

aseptic technique

Answer 35

disinfect work area
flame innoculating loop
flame glass bottle mouth
replace lids quickly