A plant laboratory tested ways of producing potato plants by micropropagation. Fig. 1 shows the stages: a small shoot-tip explant is placed on sterile nutri...
Question 1 Report
A plant laboratory tested ways of producing potato plants by micropropagation. Fig. 1 shows the stages: a small shoot-tip explant is placed on sterile nutrient jelly, many shoots form, and rooted plantlets are transferred to compost. Table 1 gives results after six weeks for explants placed in different light conditions. Each treatment used 30 explants from the same disease-free parent plant.
| Light condition | Explants forming shoots out of 30 | Mean shoots per successful explant |
|---|---|---|
| Darkness | 18 | 2.1 |
| 12 h light each day | 27 | 5.4 |
| 24 h light each day | 24 | 4.0 |
(a) Use Table 1 to calculate the percentage of explants forming shoots in 12 h light each day. Show your working. [2]
(b) Describe the effect of the three light conditions on the number of shoots produced. [3]
(c) Explain why the laboratory used explants from the same parent plant. [2]
(d) Complete this statement about the process. The cells of the new potato plantlets have the same ______ as cells in the parent plant because they were produced by ______. [2]
(e) Suggest two conditions the laboratory should control when comparing the light treatments. [2]
Answer Details
(a) Calculate the percentage:
\[\frac{27}{30}\times100=90\%\]
The percentage of explants forming shoots in 12 h light each day is 90% [2].
(b) Darkness gives the fewest successful explants and the lowest mean number of shoots [1]. Twelve hours of light each day gives the highest values, 27 successful explants and 5.4 shoots per successful explant [1]. Twenty-four hours of light gives lower values than 12 h light, but higher values than darkness [1]. [3]
(c) Explants were taken from the same parent plant to keep genetic variation constant, so they have the same genes [1]. Differences between treatments are therefore more likely to be caused by light condition [1]. [2]
(d) The cells of new potato plantlets have the same genes, or genetic information [1], as parent cells because they are produced by mitosis [1]. [2]
(e) Any two controls gain [2]: use the same nutrient jelly or growth-regulator concentration; keep temperature the same; use the same size or type of explant; allow the same growth time; and use the same volume of nutrient medium.
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