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.
Safety: Goggles- protect eyes from stain and acid, Lab coat- protect clothing from stain. Care when cutting root tip.
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
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.
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.)
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.
- 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.