Reading values from tables, graphs, and diagrams — ACT practice questions

A mountain plant opens its flowers after sunrise, but on many clear days the flowers partly close near midday and reopen late in the afternoon. Researchers recorded the percentage of fully open flowers at 8 a.m., 10 a.m., noon, 2 p.m., and 4 p.m. On a clear day, the percentages were 92%, 81%, 34%, 28%, and 76%, respectively. Air temperatures were 12°C, 18°C, 25°C, 27°C, and 19°C, while ultraviolet (UV) index values were 1, 3, 7, 8, and 3. Soil moisture decreased from 31% at 8 a.m. to 24% at 4 p.m.

On an overcast day, the corresponding open-flower percentages were 90%, 86%, 79%, 75%, and 82%. Air temperatures were 12°C, 17°C, 23°C, 25°C, and 18°C. UV index values were 0.5, 1, 2, 2, and 1. Soil moisture again decreased from 31% to 24%. The researchers followed the same 200 marked flowers on both days. They also counted pollinator visits during 10 min observation periods. Clear-day counts were 45, 38, 8, 5, and 31; overcast-day counts were 41, 39, 29, 26, and 34.

Four students proposed explanations.

Student 1

Flowers close when declining soil moisture lowers the water content of petals. Cloud cover matters only if it slows water loss.

Student 2

Flowers close when air temperature rises above about 22°C. Closing protects reproductive tissues from heat damage.

Student 3

Flowers close when the UV index rises above about 5. Closing shields pollen from UV radiation; temperature is not the trigger.

Student 4

The plant responds to pollinators. The main pollinator visits rarely at midday on clear days but continues visiting during overcast weather. Flowers close when visits become infrequent because remaining open then provides little reproductive benefit.