Figure 1. The effect of karrikins (KAR) and trimethylbutenolides (TMB) on seed germination in Lactuca plants. Error bars represent ±2
.
Fires frequently occur in some ecosystems and can destroy all above-ground vegetation. Many species of plants in these ecosystems respond to compounds in smoke that regulate seed germination after a major fire. Karrikins (KAR) and trimethylbutenolides (TMB) are water-soluble compounds found in smoke that are deposited in the soil as a result of a fire. KAR and TMB bind to receptor proteins in a seed. In a study on the effects of smoke on seeds, researchers recorded the timing and percent of seed germination in the presence of various combinations of KAR and TMB. The results are shown in Figure 1.
In a second investigation into the effect of available water on seed germination after a fire, researchers treated seeds with KAR or TMB. The treated seeds were then divided into two treatment groups. One group received a water rinse and the other group received no water rinse. The seeds were then incubated along with a group of control seeds that were not treated. The results are shown in the table.
EFFECT OF CHEMICAL TREATMENT AND WATER RINSE ON GERMINATION
| Treatment Group |
Chemical Treatment |
Water | Germination Result | |
| KAR | TMB | |||
| 1 (control) | − | − | − | Control result |
| 2 | + | − | − | Different from control |
| 3 | − | + | − | Different from control |
| 4 (control) | − | − | + | Control result |
| 5 | + | − | + | Different from control |
| 6 | − | + | + | Same as control |
The researchers made the following claims about the effect of KAR and the effect of TMB on seed germination relative to the control treatment.
- KAR alone affects the timing of seed germination
- KAR alone affects the percentage of seeds that germinate
- TMB alone affects the timing of seed germination
- TMB alone affects the percentage of seeds that germinate
Provide support using data from Figure 1 for each of the researchers' claims.
Make a claim about the effect of rinsing on the binding of KAR to the receptor in the seed and about the effect of rinsing on the binding of TMB to the receptor in the seed. Identify the appropriate treatment groups and results from the table that, when compared with the controls, provide support for each claim.
There is intense competition by plants to successfully colonize areas that have been recently cleared by a fire. Describe ONE advantage of KAR regulation and ONE advantage of TMB regulation to plants that live in an ecosystem with regular fires.
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