Cloning Plants
Design of an experiment to assess one factor affecting the rooting of stem-cuttings
- Stems can be cut so that roots develop from the cut end of the stem
- This is a way of cloning plants artificially, used routinely by gardeners and horticulturalists
- In most plants, a stem cut below a node is the ideal place to cut
- A node is the position where leaves branch off the stem
- Leaves below this point are removed
- The bottom section of the stem is inserted into compost or water
- Compost must be sterilised beforehand by heating
- Compost should be well watered and aerated
- Hormone rooting powder may assist the process of rooting
- A plastic bag with holes cut in it is used to cover the plant, to prevent excessive water loss
- Rooting takes a few weeks until the cutting is rooted independently in its soil
- The success of rooting is variable and can be tested by experimentation
Worked example
Design an experiment to assess the effect of adding hormone rooting powder to a plant cutting before rooting.
Step 1: Decide the independent variable
This is what I, as a scientist, alter. This is whether to use hormone rooting powder or not when planting out cuttings
Step 2: Decide the dependent variable
This is what I will measure at the end of the experiment. This will be the mass of root matter formed by the cuttings. The root matter will be removed using a sharp scalpel and weighed on an accurate lab balance
Step 3: How will the amount of root formation be measured?
This can involve cutting away all the root material and weighing it
Step 4: What variables should be kept constant for a valid investigation?
Species of plant, brand of compost used, mass of compost used, the sterilisation method of the compost used, pot size, length of cutting, approx leaf surface area present, light intensity, temperature, size/material of the plastic bag, size/number of holes in the plastic bag and time taken for the growth of plants
Step 5: How many different types of plants should be used?
A plant species should be chosen for rooting experiments that form roots readily in water or a solid medium. Basil plants (Ocimum basilicum) are readily available, inexpensive and form roots easily
Step 6: How many cuttings should be used for each treatment
Ideally, three repeats (minimum) for each treatment. This allows repeats for the identification of anomalies and calculation of a reliable mean
Step 7: Draw out a blank results table to frame the results
This helps to refine the experimental design before lab work starts
Blank Results Table
Step 8: Data processing
How will I process the data I generate to give meaningful conclusions?
Calculate a % change in the mean mass of root material from using no rooting powder to using rooting powder
Step 9: Improvements to the experiment
Drying the root material in an oven at 50℃ to determine the dry mass of root material. This removes variation caused by possible fluctuations in root tissue’s water content
Conduct more repeats to improve the reliability of the data
Perform experiments on different plants or by using a different brand of rooting powder/combinations of plant hormones