Questions: Part A In which of the following ways do plant hormones differ from hormones in animals? Plant hormones function as only paracrine signals. Plant hormones may travel through the air as a gas. Plant hormones may be transported from the hormone producing cell to the responding cell through a vascular system. Plant hormones typically travel from the hormone producing cell to an adjacent responding cell through gap junctions.

The answer is the second one: Plant hormones may travel through the air as a gas.

Explanation for each option:

1. Plant hormones function as only paracrine signals.
   This is incorrect. While plant hormones can act locally (paracrine), they can also act at a distance, similar to endocrine signals in animals. They are not limited to paracrine signaling.

2. Plant hormones may travel through the air as a gas.
   This is correct. Some plant hormones, such as ethylene, can diffuse through the air as a gas, which is a unique feature compared to most animal hormones.

3. Plant hormones may be transported from the hormone producing cell to the responding cell through a vascular system.
   This is incorrect. While plant hormones can be transported through the plant's vascular system (xylem and phloem), this is not a unique feature that differentiates them from animal hormones, as animal hormones also travel through the circulatory system.

4. Plant hormones typically travel from the hormone producing cell to an adjacent responding cell through gap junctions.
   This is incorrect. Plants do not have gap junctions; these are structures found in animal cells. Plant cells communicate through plasmodesmata, but this is not the typical mode of hormone transport.

In summary, the unique aspect of plant hormones compared to animal hormones is their ability to travel through the air as a gas, as seen with ethylene.