Question

To test the effect of an auxin on plant growth, the auxin was dissolved in a gelatin block. Several plant seedlings were prepared and growth was measured every five days.

Plant	Growth after 5 days	Growth after 10 days
1	15 mm	29 mm
2	4 mm	9 mm
3	5 mm	10 mm
4	14 mm	31 mm
5	8 mm	20 mm

What proves that auxin is necessary for plant growth?

• A. Plant 1 grew faster than Plants 2 or 3.
• B. Plant 4 grew faster than Plants 2 or 3.
• C. Plant 5 grew faster than Plant 1.
• D. Plant 3 grew faster than Plant 2.
• E. Plant 5 grew faster than Plant 4.

Answer 1

The correct option is B Plant 4 grew faster than Plants 2 or 3.

Growth rate in intact plant 1 is 3 mm per day which is reduced in plant 2 upon removal of tip to 1 mm per day. The growth rate is resumed to 3 mm per day upon application of auxin as in plant 4. This means plant tip contain auxin and removal of tip resulted in truncated growth. Also, comparing the growth rates, plant 4 exhibit 3.1 mm growth rate after auxin application while plants 2 and 3 (plants with removed tip) showed only 0.9 mm and 1 mm growth rate per day. This proves that auxin is necessary for plant growth.

Therefore, the correct answer is option B.