Core practical 1: investigating the initial rate of reaction
describe how to make up 0.2%, 0.4%, 0.6%, 0.8% dilutions of trypsin solution
-for the 0.2% solution: take 2cm3 of 1% trypsin solution and add 8cm3 of distilled water
-for the 0.4%: mix 4cm3 of trypsin solution and 6cm3 of distilled water
-for the 0.6%: mix 6cm3 of trypsin solution and 4cm3 of distilled water
-for the 0.8%: mix 8cm3 of trypsin solution and 2cm3 of distilled water
Core practical 1: investigating the initial rate of reaction
describe how to use a colorimeter to measure the absorbance of different concentrations of trypsin solution
-mix 2cm3 of 1% trypsin solution and 2cm3 of distilled water and use this as a reference cuvette to set the colorimeter absorbance to 0
-add 2cm3 of milk suspension and 2cm3 of 0.2% trypsin solution to another cuvette
-mix and quickly place into the colorimeter
-measure the initial absorbance and again at 15 second intervals for 5 minutes
-repeat for each dilution
core practical 3: observe mitosis in root tips
describe the method
-fill a small bottle with hydrochloric acid, put it in a water bath for 5 minutes, put the garlic clove in the acid and place in the hot water bath for another 5 minutes - make sure roots are submerged
-rinse the acid off the roots and cut several root tips
-put the root tips in a vial containing acetic orcein and then place in the water bath for another 5 mins
-use forceps to take the tips out of the vial, and place them on a microscope slide, tease the root tip apart and place a coverslip
-wrap the slide in paper towel, and press down to squash the tissue
-place the slide on the stage and look through the microscope
-count the number of cells in each stage of mitosis and interphase
Core practical 8: using a potometer
explain precautions that need to be taken when setting up a potometer before it can be used to measure the water uptake of a leaf
(2 marks)
-cut the shoot underwater
-so no air enters the xylem
-seal using petroleum jelly
-so that no air leaks into the system
-move the air bubble to 0
-so that water lost can be accurately measured
Core practical 8: using a potometer
explain why water uptake of the leafy shoot may not be the same as the water transpired
(2 marks)
-not all water taken up by the shoot is lost in transpiration
-because some water is used for photosynthesis
Core practical 8: using a potometer
state one way in which the temperature could be increased without affecting the validity of the investigation
change the temperature of the room using a heater
core practical 2: Use a light microscope to observe and measure biological samples
describe the method
-calibrate the eye-piece graticule
-cut transverse sections of the plant stem as thin as possible using a wet razor and white tile
-select the 2 thinnest
-place one sample on a slide which has a drop of water, place a cover slip
-place the second sample on a slide, touch the edge of the sample with absorbent paper to remove water, add two drops of toluidine blue O stain and leave for 2 mins, place the cover slip and remove excess stain using paper towel
-observe the unstained and stained samples under a microscope
core practical 4: Investigate the effect of sucrose concentration on pollen tube growth
describe the method
-make up different concentrations of sucrose solution but with the same total volume
-place a sheet of moist filter paper in a petri dish for each sucrose concentration and replace the lids
-place a few drops of the sucrose solution and mineral salt medium on a slide
-use a mounted needle to rub an anther over the slide so the pollen falls onto the slide
-place the slide in the petri dish and replace the lid, leave for 10 mins to allow for pollen germination
-observe the slide under a microscope, measure the pollen tube
core practical 3: observe mitosis in root tips
explain why the root tip is heated with acid
The root tip is heated with acid to break up the tissues into individual cells. The cellulose walls of plant cells are held together by pectins such as calcium pectate. Treatment with hydrochloric acid breaks this down.
core practical 3: observe mitosis in root tips
what effect will maceration and pressing the slide preparation have on the dividing cells
Pressing the preparation will separate the cells in the meristem tissue into individual cells in a single layer. This makes it easier to see the chromosomes and to identify the stages of division.
core practical 3: observe mitosis in root tips
what information do the cell counts give you about each stage of mitosis
The cell counts show the relative duration of each stage in the cell cycle. The longer a phase, the more cells are likely to be going through that phase at any point in time.
core practical 4: Investigate the effect of sucrose concentration on pollen tube growth
You were instructed to use pollen from only one flower for all the concentrations. Comment on any advantages and disadvantages of this approach in terms of the validity and reliability of results
Advantage: the maturity of the flower is a controlled variable. This means that any differences in the results between treatments are more likely to be a result of the differences in sucrose concentration.
Disadvantage: different results may arise if the experiment is repeated because of differences between flowers. Flowers may differ slightly in maturity.
core practical 5: investigate the effect of temperature on membrane permeability
describe the method
-prepare eight water baths between 0 °C and 70 °C
- add 10 cm3 of distilled water to
eight test tubes and place in each water bath for 5 mins
-cut eight beetroot cylinders using a cork borer, use a knife to trim them to 1cm, wash and dry them
-place a cylinder in each test tube and leave in the water bath for 15mins
-remove the cylinders
-set the colorimeter to a blue/green filter and percentage transmission, zero the colorimeter using a blank cuvette filled with distilled water
-transfer the liquid from the test tube to a cuvette and measure the percentage transmission
core practical 5: investigate the effect of temperature on membrane permeability
suggest why the tubes were placed in the water baths for 5 minutes before the cylinders were added
to ensure the tubes contain water at the correct temperature before starting the experiment to make sure the effect of the correct temperature is being assessed
core practical 5: investigate the effect of temperature on membrane permeability
why were the beetroot cylinders washed with distilled water and dried before the experiment began
to remove excess surface pigment from the cut cells at the edge
core practical 6: investigate plant water relations
describe the method
-take 6 thin samples from an onion which are 1 cell thick
-place a few drops of sucrose solution into a watch glass, repeat for 6 different sucrose concentrations
-place a tissue sample in each watch glass and leave for 20 mins
-place a drop of the sucrose solution onto a microscope slide and using forceps place each tissue sample on the slide, place a coverslip
-examine under a microscope and count how many cells show plasmolysis
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core practical 7: investigate the gas exchange system of a locust
describe the approaches that were taken to ensure the ethically responsible use of animals
-working in groups to reduce the number of locusts killed
-humane killing
core practical 9: investigate factors affecting the rate of aerobic respiration
using a respirometer
describe the method
-assemble the respirometer
-place a known mass of peas in a boiling tube, replace the bung and record the mass
-record the starting point of the coloured dot on the scale
-record the position of the coloured dot at 1 minute intervals for 5 mins
core practical 9: investigate factors affecting the rate of aerobic respiration
using a respirometer
what is the importance of using soda lime in the respirometer? How does this affect the volume of gas in the apparatus
Soda lime is used to absorb any carbon dioxide produced by the respiring organisms. So any changes in volume will be due to the uptake of oxygen by the organisms. The gas volume will reduce as oxygen is removed for respiration.
core practical 10: investigate the effects of different wavelengths of light on
the rate of photosynthesis
describe the method
-place a piece of pond weed into a beaker of water
-cover one side of the beaker with aluminium foil so light can only enter from one side
-add half a spatula of sodium hydrogen
carbonate to the water, leave for 5 mins
-place a lamp next to the beaker and put a colourless filter in front (control)
-set up a potometer with a section of pond weed inserted, record the position of the air bubble
-set a timer for 5 mins and measure the distance the first air bubble moves
-reset the potometer and repeat with different coloured filters
core practical 11: Investigate the presence of different chloroplast pigments using chromatography
describe the method
-draw a pencil line on a strip of chromatography paper 2 cm above the bottom
-place some leaves and propanone in a pestle and mortar and grind
-use a pipette to place a few drops of this extract on the pencil line
-pour some chromatography solvent into a boiling tube about 1cm tall
-place the chromatography paper inside by hanging it from the bung
-wait 10 mins
-mark the position of the solvent front and allow chromatography paper to dry
core practical 15: Investigate the effect of different sampling methods on estimates of the size of a population
-measure a 10m x 10m area of grassland with tape measurers
-use a random number generator to create coordinates within the grid
-place the quadrat on the coordinate, first use it as a frame quadrat, measure the percentage cover of daisies for example within the squares of the quadrat
-don’t move the quadrat, use it as a point quadrat, measure the percentage cover by counting at how many cross-sections of the quadrat are in contact with daisies
-repeat 10 more times
core practical 16: Investigate the effect of one abiotic factor on the morphology of one species
describe the method
had to make up my own method but it is in my core practical book
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1.2 Biological molecules 1 (and 1.1 water)100
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1.3 Biological molecules 265
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2.1 - Eukaryotic cells79
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2.2 - Prokaryotic cells62
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2.3 + 2.4 - cell division80
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3.1 - classification82
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4.1 + 4.2 - gas exchange72
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4.3 - circulation86
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4.4 - transport in plants40
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5 - respiration and photosynthesis38
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6.1-6.2 bacterial disease and other pathogens80
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6.3 - the response to infection57
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7 - modern genetics77
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8 - genetic information42
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9.1 + 9.2 - plants + nervous system101
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9.3 - homeostasis61
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10.1 - the nature of ecosystems75
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Core Practicals23
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exam question4
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Maths skills1
