OCR a level biology A PAGs

How does the callibration of a microscope work? (PAG1)

eye piece graticule acts as a ruler (always the same), then a stage graticule is added and they are lined up and the number of divisions and therefore equivalence can be found.

Why is staining used? (PAG1)

Staining in microscopy is used to provide detail, and to provide distinguish/contrast

What are the 2 types of mounts in microscopy? (PAG1)

wet mount and dry mount

How do you use a light microscope (PAG1)

select the lowest powered objective lens, use coarse adjustment to move towards lens, focus using the fine adjustment.

What are the common rules in drawing and labeling a cell in microscopy? (PAG1)

no shading

large

label lines

straight lines with no arrow

use a scale

pencil

What are the safety precautions when doing dissections? (PAG2)

take care

goggles

non-latex gloves (as chemicals)

apron

dispose of waste appropriately and safely

How do you dissect a heart? (PAG2)

insert fingers into the 4 chambers to identify wall thickness, therefore which is each chamber and right/left, identify vessels, cut along lines to look in left ventricle and atrium, make a similar cut on the right, use a ruler to measure wall and draw an image with a scale

How do you do a plant dissection? (PAG2)

white tile, scalpel, cut cross-section of stem, use tweezers to place half in tap water, stain, wash off, create wet mount

What colour does toulidine blue turn different plant organs? (PAG2)

Phloem​ - red

Xylem​ - green/blue-green

Parenchyma​ - red-purple

how to do random sampling? (PAG3)

random sites selected, e.g. use a graph and pick random coordinates

prevents bias, but may result in uneven sampling

How to do stratified sampling? (PAG3)

divide into groups and then sample randomly

prevents small populations being missed, more equal

can lead to over-representation

How to do opportunistic sampling? (PAG3)

areas are chosen to sample

quicker but large bias

How do you do systematic sampling? (PAG3)

samples are taken at set distances e.g. transect

good method of biodiversity, may miss species

How do you calculate species diversity? (PAG3)

random sampling, then use Simpson's diversity index

How do you calculate species abundance? (PAG3)

random sampling, multiply up the sample size

How do you do conduct a practical looking at the effect of temperature on the rate of reaction? (PAG4)

different water baths, equal volumes of hydrogen peroxide in each test tube, buffer, water bath, add catalase, measure volume of oxygen produced with an upturned measuring cylinder and a delivery tube

How does enzyme concentration affect the rate of reaction? (PAG4)

KI and I2 into a spotting tile, use serial dilutions to change amylase conc., add starch and start timer, add to spotting tile every 10s, stop timer once the solution isn't blue/black anymore

How does substrate concentration affect the rate of reaction? (PAG4)

different serial dilutions of hydrogen peroxide, add catalase and measure the amount of oxygen produced using an upturned measuring cylinder and a delivery tube.

How do you do serial dilutions? (PAG4)

e.g. dilution factor of 2

5 boiling tubes with distilled water (except 1st), start with 2% catalase, 4cm3 to first, then add 2cm of this into the next and so on

How do you use a colorimeter? (PAG5)

switch colorimeter on to stabilize, select red filter (benedicts and water bath which should turn red with glucose - complementary), use a cuvette filled 3/4 with distilled water to calibrate to 0, use a pipette to put sample in cuvette, read absorbency, higher absorbency means higher conc.

How do you use a potometer (PAG5)

measure rate of transpiration, cut water underwater at a slant, assemble underwater, and then leave the capillary tube underwater still, watertight, dry leaves, acclimatize, remove capillary tube, record starting position of bubble, start stop watch and measure bubble movement every 30s

How to separate chlorophyll pigments using chromatography? (PAG6)

grind up leaves, with propanone as the solvent, add to test tube with petroleum jelly and shake, use top layer with a capillary tube/pipette and place dot on pencil line, dry and repeat, place the TLC plate in the solvent, once at the top remove paper and allow to dry

How to distinguish amino acids using chromatography? (PAG6)

put amino acid dot on the paper on the pencil line, add into a beaker with solvent, fume cupboard, remove once solvent is up, dry, ninhydrin agent, measure RF value

How to conduct electrophoresis? (PAG6)

restriction enzymes to fragment the DNA, agrose gel in gel tray, well side needs negative electrode, buffer, use a micro pipette with DNA and loading dye in the wells, power source at 100V, smaller fragments will move faster, leave for 30mins, tip out excess buffer, cover with staining solution and bands should be visible,

What are some examples of sterile techniques? (PAG7)

wash hands

disinfect work area

bunsen burner to sterilise air

use to sterilise equipment

open agar plate as little as possible

How do you test the effect of temperature on membrane permeability? (PAG8)

beetroot at equal sizes in 5cm3 of water, different water baths at a set amount of time, carry out colorimetry with a blue filter, higher absorbency, more pigment, more permeable

How to test for reducing sugars? (PAG9)

benedicts, water bath, it will go from blue to brick-red dependent on the concentration (may go orange/yellow/green with lower conc.)

How to test for non-reducing sugars? (PAG9)

HCl, water bath, neutralise with NaHCO3, benedicts and water bath, blue to red.

How to test for lipids? (PAG9)

ethanol, shake, distilled water, shake again, positive will show a cloudy emulsion

How to test for proteins? (PAG9)

NaOH and CuSO4, blue to purple

How to test for starch? (PAG9)

test tube, sample, iodine, orange to blue/black

How do you use a spirometer? (PAG10)

breath in and out of tube into oxygen chamber, chamber moves up and down, rotating drum, notates on a trace, upwards slope means breathing out, downwards mean in.

How to investigate heart rate? (PAG11)

find pulse on forearm of resting heart rate, gentle exercise for 5 mins e.g. walking, measure heartbeat and again every minute, record time taken to return to normal, repeat with different people

How do you detect electrical activity in muscles? (PAG11)

2 electrodes to each muscle, connect to amplifier and computer, contract muscle by lifting arm, graph should spike, lift a weight and amplitude will increase. carry on, muscles will become fatigued, so amplitude will continue to increase as the brain is working harder.

How to investigate phototropisms? (PAG11)

planted wheat shoots, prepare by covering 3 tips with foil, 3 without and 3 with the bases wrapped, leave to grow in sunlight for 2 days. measure growth and direction

How to investigate geotropisms? (PAG11)

petri dishes with cress seeds, water and cotton wool. place dishes at different angles without light and in a moist warm environment. leave for 4 days and measure growth and direction.

How to look at the role of auxins in apical dominance? (PAG11)

for 10 plants cover tip with auxin paste, for another 10 cover the tips with paste not containing auxin's, and the last 10 as a control. after 6 days log the number of side shoots on the plants. The auxin's should have less

How to investigate the role of gibberllins in stem elongation? (PAG11)

water 20 plants with dilute gibberllins, and the other 20 leave as controls. leave to grow for 28 days. every 7 days measure the stem growth

how to use a respirometer? (PAG11)

. Place a coloured liquid with detergent added to it into the manometer tube, Connect apparatus with the taps open, measure mass of small organisms, Place the living organisms in the apparatus, Place the whole apparatus in a water bath​, Record the starting level of the syring​e. This should be near the top of the scale​, Mark the starting levels of the manometer fluid​ in the manometer with a marker pen. Close the taps​ and leave the apparatus in the water bath for a set time period (e.g. 10 mins), Measure the new level of the manometer fluid​ and calculate the change in level ​of manometer fluid. 10. Push down the syringe barrel to reset the manometer fluid. The change in volume in the syringe​ (measured by the change in level of the syringe plunger) is equal to the volume of oxygen absorbed by the organisms​, Calculate the oxygen absorbed per minute per gram of organism

How do you calculate an RF value?

distance travelled by spot/distance travelled by solvent

How do you calculate percentage change?

change ÷ original x 100