OCR A-level Biology Practicals
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment) -
ANS-1. cut equal size pieces of beetroot and rinse them to remove any pigment released during
cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures. for the same length of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into cover for the colorimeter
6. measure the absorbance rate of each liquid
7. the more absorbance the more permeable the membrane was
\benefits of staining? - ANS-- make more organelles visible, chloroplasts, cell walls.
- increases contrast
- clearer images can be obtained.
\control variables for measuring rates of respiration in yeast - ANS-- temperature is controlled by
water baths
- availability of oxygen is controlled
- ph is controlled
\how can you improve methods generally - ANS-1. increase sample sizes to improve
accountability and repeatability
2. ensure same sample sizes for each comparison - for valid comparison
3. Continuous variables are controlled
\how to calibrate an eye-piece graticule - ANS-A stage micrometer is simply a slide with a set of
evenly-spaced markings, usually 0.1 mm apart. By viewing this stage micrometer with an
eyepiece graticule in place and using the desired objective lens it is possible to line up the
graticule markings with those on the stage micrometer. Thus it is possible to calculate the
calibration factor, indicating how far apart the graticule markings are when using this particular
objective lens. The stage micrometer can then be removed and the specimen slide put in its
place.
\how to ensure bacterial cultures are grown successfully - ANS-- aseptic techniques
- incubate at suitable temperature
- use ph buffer
- agitation
-lids secured but not sealed
\how to improve mounting samples onto cover slips? - ANS-squash slides to allow more light to
penetrate, uses wet mount to prevent dehydration of tissue, use sharp blade to cut thin enough
sample of tissue.
\how to prepare a wet mount - ANS-1.pipette a small drop of water onto the slide
2.use tweezers to place the specimen on top of the water drop
3.stand the coverslip upright on the slide next to the water droplet and carefully tilt and lower the
cover slide so it covers the.specimen to avoid air bubbles which may obstruct view.
6.stain the specimen by putting a drop of the stain next to the cover slip.
, \Practical 1 : Using a Light microscope to examine blood smears - ANS-Preparation:
1.) staining samples with methylene blue/ eosin
- staining to add contrast so it is easier to identify different parts of te cell
- for the electron microscope, the specimens are stained with lead
2.) mounting
- dry mount:
thinly sliced
use tweezers to pick up your specimen and put it in the middle of a clean slide
place a coverslip over the top of the specimen
Microscope
1. clip the slide containing the specimen onto the stage
2. select lowest powered objective lens
3. use coarse adjustment knob to bring he stage up to just below objective lens
4. look down the eyepiece and the coarse adjustment knob to move the stage so the image is
roughly in focus.
5. adjust the focus with the find adjustment.
knob until a clear image is obtained
6. swap to greater magnification with higher-powered objective lens
REMEMBER
- MAGNIFICATION = IMAGE SIZE / OBJECT SIZE
- stage micrometer is the bigger 'ruler'
- eye piece graticule is the smaller 'ruler'
\Practical 10: Using a potometer - ANS-1. cut a shoot underwater to prevent air from entering
the xylem. cut a slant to increase the surface are available for water uptake.
2. Assemble the potometer in the water and insert the shoot underwater, so no air can enter the
water.
3. remove the apparatus from the water but keep the end of capillary tube submerged in a
beaker of water.
4. check the apparatus is watertight
5 dry the leaves to allow time for shoots to acclimatise
6. remove the end of capillary tube from the beaker of water until one air bubble had formed, the
put the capillary tube back into the water.
7. record the starting position of the air bubble along the ruler.
8. start the stopwatch and record the distance moved by the bubble per unit time
9. rate of air bubble movement is the rate of transpiration
10. all other conditions must be kept constant. only one change should be variable.
\Practical 11: The effect of antibiotics on bacterial growth - ANS-1. dip disics in anitbiotics
2. place on bacterial culture
3. meausre inhibition zone
*Practical 8: The effect of temperature on membrane permeability (beetroot experiment) -
ANS-1. cut equal size pieces of beetroot and rinse them to remove any pigment released during
cutting.
2. Place the five pieces in five different test tubes, each with the same volume of water
3. Place each test tube in a water bath set at different temperatures. for the same length of time
4 remove the pieces of beetroot from the test tubes, leaving just the coloured liquid
5. take the small volume of each coloured liquid and put it into cover for the colorimeter
6. measure the absorbance rate of each liquid
7. the more absorbance the more permeable the membrane was
\benefits of staining? - ANS-- make more organelles visible, chloroplasts, cell walls.
- increases contrast
- clearer images can be obtained.
\control variables for measuring rates of respiration in yeast - ANS-- temperature is controlled by
water baths
- availability of oxygen is controlled
- ph is controlled
\how can you improve methods generally - ANS-1. increase sample sizes to improve
accountability and repeatability
2. ensure same sample sizes for each comparison - for valid comparison
3. Continuous variables are controlled
\how to calibrate an eye-piece graticule - ANS-A stage micrometer is simply a slide with a set of
evenly-spaced markings, usually 0.1 mm apart. By viewing this stage micrometer with an
eyepiece graticule in place and using the desired objective lens it is possible to line up the
graticule markings with those on the stage micrometer. Thus it is possible to calculate the
calibration factor, indicating how far apart the graticule markings are when using this particular
objective lens. The stage micrometer can then be removed and the specimen slide put in its
place.
\how to ensure bacterial cultures are grown successfully - ANS-- aseptic techniques
- incubate at suitable temperature
- use ph buffer
- agitation
-lids secured but not sealed
\how to improve mounting samples onto cover slips? - ANS-squash slides to allow more light to
penetrate, uses wet mount to prevent dehydration of tissue, use sharp blade to cut thin enough
sample of tissue.
\how to prepare a wet mount - ANS-1.pipette a small drop of water onto the slide
2.use tweezers to place the specimen on top of the water drop
3.stand the coverslip upright on the slide next to the water droplet and carefully tilt and lower the
cover slide so it covers the.specimen to avoid air bubbles which may obstruct view.
6.stain the specimen by putting a drop of the stain next to the cover slip.
, \Practical 1 : Using a Light microscope to examine blood smears - ANS-Preparation:
1.) staining samples with methylene blue/ eosin
- staining to add contrast so it is easier to identify different parts of te cell
- for the electron microscope, the specimens are stained with lead
2.) mounting
- dry mount:
thinly sliced
use tweezers to pick up your specimen and put it in the middle of a clean slide
place a coverslip over the top of the specimen
Microscope
1. clip the slide containing the specimen onto the stage
2. select lowest powered objective lens
3. use coarse adjustment knob to bring he stage up to just below objective lens
4. look down the eyepiece and the coarse adjustment knob to move the stage so the image is
roughly in focus.
5. adjust the focus with the find adjustment.
knob until a clear image is obtained
6. swap to greater magnification with higher-powered objective lens
REMEMBER
- MAGNIFICATION = IMAGE SIZE / OBJECT SIZE
- stage micrometer is the bigger 'ruler'
- eye piece graticule is the smaller 'ruler'
\Practical 10: Using a potometer - ANS-1. cut a shoot underwater to prevent air from entering
the xylem. cut a slant to increase the surface are available for water uptake.
2. Assemble the potometer in the water and insert the shoot underwater, so no air can enter the
water.
3. remove the apparatus from the water but keep the end of capillary tube submerged in a
beaker of water.
4. check the apparatus is watertight
5 dry the leaves to allow time for shoots to acclimatise
6. remove the end of capillary tube from the beaker of water until one air bubble had formed, the
put the capillary tube back into the water.
7. record the starting position of the air bubble along the ruler.
8. start the stopwatch and record the distance moved by the bubble per unit time
9. rate of air bubble movement is the rate of transpiration
10. all other conditions must be kept constant. only one change should be variable.
\Practical 11: The effect of antibiotics on bacterial growth - ANS-1. dip disics in anitbiotics
2. place on bacterial culture
3. meausre inhibition zone
