A plant breeder grew orchid tissue in sterile boxes. Fig. 1 shows one original cell producing a small group of cells. Table 1 gives the number of plantlets ...
Question 1 Report
A plant breeder grew orchid tissue in sterile boxes. Fig. 1 shows one original cell producing a small group of cells. Table 1 gives the number of plantlets formed from one piece of tissue.
| Week | Number of plantlets |
|---|---|
| 2 | 4 |
| 4 | 16 |
| 6 | 64 |
(a) What process produces the extra cells in Fig. 1? [1]
(b) Describe the trend in the number of plantlets. [1]
(c) Give two advantages of producing orchid plants in this way. [2]
The table below shows results from a study of radiation exposure and cell division in cultured human blood cells. Fig. 1 shows a cell with chromosomes arranged at the centre before they separate.
| Radiation dose / arbitrary units | Cells completing mitosis / % |
|---|---|
| 0 | 94 |
| 2 | 71 |
| 4 | 39 |
(a) Describe the relationship shown in Table 1. [1]
(b) What is the name of the stage in Fig. 1 when chromosomes line up at the cell centre? [1]
(c) Explain why radiation that damages DNA can reduce successful mitosis. [2]
(d) Give one reason why this experiment should use cells from the same tissue type. [1]
Answer Details
Orchid tissue culture
- (a) Mitosis produces the extra cells. [1]
- (b) The number of plantlets increases and doubles every two weeks: 4, 16, then 64. [1]
- (c) Two advantages are that many plants can be made quickly and the plants are genetically identical with desired features. Conserving rare plants is also acceptable. [2]
Radiation and mitosis
- (a) As radiation dose increases, the percentage of cells completing mitosis decreases, from 94% at zero dose to 39% at dose 4. [1]
- (b) Chromosomes lined up at the cell centre are in metaphase. [1]
- (c) Radiation can damage DNA, so it may not be copied correctly. This can stop cell division or produce abnormal daughter cells. [2]
- (d) Cells should come from the same tissue type because cells from different tissues naturally divide at different rates. [1]
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