Biology Unit 2 Core practicals

Revision cards to give a brief overview of the methods, reasons for these steps, control variables and the safety involved with the practicals- where needed.

(For edexcel exam board)

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Observing Mitosis- garlic/onion root tip...


  • cut off the first 5 mm of the garlic root tip- this is where mitosis occurs
  • soak the root tip in 5cm3 hydrochloric acid- this breaks down the connective tissue.
  • wash with distilled water and dry with filter paper- removes acid to stop whole cells from being destroyed.
  • break up root with a needle and place on glass slide
  • Add drops of stain e.g. toluidine blue or orcein- highlights chromosomes
  • place a coverslip over the top and gently press down- makes it one cell thick for ease of viewing.
  • Add more stain and warm- to intensify the stain
  • Observe for stages of mitosis.

Control variables: volume of stain added, volume of acid.

SafetyGoggles- protect eyes from stain and acid, Lab coat- protect clothing from stain. Care when cutting root tip.

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Observing Mitosis

The duration of each stage of mitosis can be calculated using the equation below.

Duration of a stage = (percentage of cells in that stage x cell cycle time) / 100

remember what to look for in the stages of mitosis!

Prophase- centrioles at opposite poles(sides) chromosomes visible

Metaphase- chromosomes lined up at cell equator with spindles attached 

Anaphase- chromosomes being pulled apart with spindles contracting

Telophase- chromosomes become invisible and  nuclear envelope reappears

Cytokinesis- two nuclei visible at opposite sides of the cell


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Tensile Strength of fibres e.g. celery

Method:- plant would need to soak in water for a week - easier to extract fibres

  • Extract plant fibre
  • Suspend fibre between two clamp stands
  • Hang a 50g weght from the fibre
  • Keep adding weights one at a time untill fibre breaks.
  • Record the force used by hanging the used weights on a newton meter.
  • Record resulsts
  • Repeat experiment several times and calculate average.

Control variables: length of fibres used, diameter/thickness of fibres used, the mass of weights added, distance of seperation of clamp stands.

Safety: use a pillow to cushion weights when they fall to stop from squishing feet. Note: the lighter the weights, the more precise measurement of the point that it snaps.

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Plant mineral defieciencies- mung bean


  • cover test tubes in tin foil- prevents bacterial growth
  • fill each one with a different solution- each lacking in a certain mineral e.g. nitrate or phosphate
  • Use a control solution lacking no minerals
  • cover top of tube in cling film
  • make a whole in the cling film and place the root of mung bean through so that it is resting in solution
  • leave for a week

Controls: same volume of solution, same amount of light and temp. Size of container, same plant, solution lacking no minerals as a comparison.

(you can do this experiment differently by using different concentrations of a certain mineral e.g. nitrate in each tube to test the effects.  For this you would need a control soultion with 0 concentration of nitrate.)

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Antimicrobial properties of plants e.g. mint or ga


  • Get extract from plant you're testing e.g. mint by crushing dry plant in pestle and mortar with 10cm3 of ethanol
  • filter off the ethanol
  • Spread E.coli bacteria evenly out on agar plate
  • dip sterillised paper discs in extract and leave to dry.
  • place paper discs in plate and put tabs of tape on
  • incubate to encourage bacteria growth
  • Measure the diameter of the space of inhibition around the discs

Control Variables: use a disc not soaked in any extract as a comparison, volume of extract absorbed, size of paper discs, put discs in at same time.

Safety: Don't incubate at 37^c - body temp. and would encourage pathogenic (harmful) bacteria to grow. Aseptic technique- stops spreading of bacteria.

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  • Take a seedling and divide it into the top(cotyledon), the root and the shoot - to compare growth of different sections of plant
  • Make hot agar gel and pour into 3 tubes and leave to set
  • plant the tip of each section in to jel
  • Cover with cling film- to prevent bacteria growth
  • Leave for a few days- allows time for growth
  • observe- the cotyledon should develop into new plant-totipotency

Control: sunlight and temp.  cuttings from same plant, volume of agar and nutrients in the agar.

Safety: temp. below 37^c otherwise pathogenic bacteria growth.  care with cutting plant and pouring hot agar to prevent burning.

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Naya Patel

are these unit 2 edexcel bio experiments?


This is really really useful, you have made good notes. Well done 

Lizzie Keys

Naya Patel wrote:

are these unit 2 edexcel bio experiments?

 Yes they are all of the practicals that you will need to know for the edexcel exam.

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