bio practicals

8. Tensile strength

• range of tensile lengths → 5,10,20

• sam width, plant type cross section etc.

• conditions the same → temp, humidity etc.

• how masses added→carefully, small weights added one at a time etc

• adding masses until fibre breaks

• description of appropriate safety precaution with reason → blanket pillo under weight to protect table, add with care and ensure hands are, scalpel → care + cutting board

A scientist investigated the effect of calcium chloride concentration on pollen tube growth

use a range of 6 solutions of calcium chloride / from 1 – 6 au (1) (bc in table in q)

• use of sucrose solution / boric acid (1)

• controlled variable (1)

• place pollen {on agar plate / in hanging drop} (1)

• leave for 1 hour (1)

• use a microscope and (calibrated) graticule to measure pollen tube length (1)

• repeat readings at each calcium chloride concentration to allow calculation of mean (1)

Compare and contrast the structures of these two hearts. (4)

Similarities, any two of:

• both have valves, strings, atria, ventricles, chambers (2)

Differences, any two of:

• both ventricles have a larger (internal) volume in the DCM heart (1)

• (in both ventricles) the {wall / muscle} is thinner in the DCM heart (1)

• the septum is thinner in the DCM heart (1)

• strings different

Describe how comparative measurements of the vitamin C content of the leaves from two spinach plants could be made. (5)

• use equal {size pieces / masses} of spinach (for both plants) (1)

• extratction method → grinding(amount of time) + adding a volume of water

• measure out {equal / same / stated} volume of (standard) DCPIP solution

• add spinach (extract) until no blue colour remains / becomes colourless / decolourises (1)

• record volume of extract used (1)

• use calibration curve/ explain how to use formula eg. conc. vitamin C = vol. of standard Soln. vit C ÷ volume of food extract added

Methid of beetroot permeabilty (5)

• {equal sized / same shaped} pieces of (beetroot) tissue cut (1)

• washed in water (until no more pigment lost) (1)

• placed in (same / stated) volume of water (1)

• placed in a range of temperatures 5 oC to 30 oC (1)

• left for {stated / suitable / same} time (1)

• samples of the liquid (around the discs) were removed (and placed in colorimeter cuvette) (1)

• repeat (at each temperature) {to get mean / SD

Describe a procedure for the accurate determination of the diameter of a cell/Devise a method to determine the cross-sectional area of a fibre

• a (transverse) section/layer/slice of the fibre is cut (1)

• ensure section is flat (1)

• (using a light microscope find cell) under low power (1)

• then view under high power (1)

• calibrate eyepiece graticule / use of stage micrometer

• count number of (eyepiece) graticule units over the cell (1)

• convert eyepiece graticule units (to microns using calibration) (1)

• measure diameter at different positions / orientations (1)

• area calculated using πr2 (1)

Describe a procedure to compare the percentage germination of pollen collected by the two methods used in this investigation ( both resault in the collection of pollen grains)

• methods used (to observe germination of pollen grains → cavity slide/agar plate

• sucrose solution added (1)

• sufficient time → 15 min-5 days → 30 min

• temp/ph/sucrose solution controlled

• ensure same plant variety/species → biotic variable

• view through microscope / count germinated & non-germinated / count germinated & total (and work out percent) (

• be careful with pollen alergy

Describe a safe method to observe the stages of mitosis in these roots.

• cut root tip

• (root tips) placed in (warm) acid (1)

• (root tips) then placed in named stain → toluidine blue /methylene blue

• (root tip placed on a microscope slide and) {macerated / teased / described} / squashed

• use of high power (on a microscope) (1)

• insing tips in water / wearing gloves / goggles

Describe how this investigation could be modified to determine if the differences between … are significant

• each treatment should be repeated (1)

• {all conditions / named condition} should be kept constant (1)

• (mean and) SD calculated / error bars (1)

• look for overlap in SDs / perform t-test

anti microbrial properties of stuff

description of how bacteria are cultured (1) → (bacteria grown (on nutrient agar) / bacterial lawn} / bacterial broth (1)

description of how extracts are added to culture (1) → cut wells

control of (1) → e.g disc size /extract volume / solvent volume

incubate at suitable temperature for suitable time (1) → temp. <37, time 1 day to 7 days

appropriate measurement of resaults → zone of inhibition (1)

e.g. disinfect equipment, flame equipment,goggles, gloves, tie back long hair (1)

description of the use of all three solutions to grow onions (1)

• description of a relevant biotic factor kept constant → mass/age/variety(1)

• description of a relevant abiotic factor kept constant → temp/ph(1)

• appropriate measurement of {plant parts / plant} made at start and finish (1)

• after {same/ specified / stated} time (1

Describe a safe method to prepare and examine the structure of human cheek cells.

• e.g. bud into disinfectant/sterile/fresh bud/toothpick/wear gloves/ goggles/safe use of microscope/slides/careful use of bud/stain to prevent injury

• use of cotton bud (1)

• followed by use of stain/dye (1)

• place cells (on slide) under coverslip (1)

• use of high power of microscope (1)

A student investigated the water potential of potato tissue by measuring the change in mass of pieces of potato in a range of concentrations of salt solutions. how?

cut pieces of same {size / surface area / potato} (1)

 find mass of each piece before and after soaking (1)

 soak pieces in solutions for {same length of time / stated time} (1)

 blot dry before weighing (1)

 repeat for each solution (1)

 description of how percentage change calculated (1

Devise a procedure to determine the concentration of reducing sugars in a sweet potato.

• use {standard / known} {mass/volume} of sweet potato / use a standard volume of sweet potato extract / volume of extraction liquid (1)

• carry out reducing sugar test → adding benidicts reagent + heating

• filter the solution / remove precipitate} (after the test is carried out) (1)

• {weigh the precipitate remaining in the filter paper / measure intensity of blue color in filtrate}

• convert this {mass / intensity} to a concentration of reducing sugar / compare colour of tube contents precipitate with a colour chart quali

Describe a method for estimating the soluble protein concentration in the beakers in step 4.

use biuret reagent / do biuret test (1)

remove meat from solution(s) / take sample of solution(s) / filter solution(s) (1)

use {known / same/ equal} volume of (meat) solution / use {known / same/ equal} volume of (biuret) reagent (1)

produce (colour) standards using known protein concentrations / compare the {colour / result} to colour standards (1 → could make calibration curve