In assessing organ growth, which pairing is most appropriate?

The correct option is Pollen tube - Length.

Explanation

Growth is defined as an irreversible permanent increase in the size of an organ or its parts. Because measuring the increase in protoplasm directly is difficult, growth is quantified using parameters proportional to it, such as fresh weight, dry weight, length, area, volume, and cell number. The choice of parameter depends on the structural nature of the organ.

Analysis of Options:

• Pollen tube - Length is Correct: The growth of a pollen tube is primarily linear as it travels through the style. Therefore, it is measured in terms of length.
• Dorsiventral leaf - Length is Incorrect: A dorsiventral leaf is a laminar (flat) structure. Its growth is most accurately assessed by measuring the increase in surface area rather than length alone.
• Pollen tube - Surface area is Incorrect: While the surface area of a pollen tube increases during growth, the standard metric for its assessment is length.
• Stem internode - Fresh weight only is Incorrect: A stem internode grows primarily through elongation. Therefore, length is the most appropriate measure. Relying on "fresh weight only" is inaccurate because fresh weight can fluctuate with water status and does not capture the directional nature of internodal elongation.

Key Takeaway:
Specific parameters are used to measure growth for different plant parts: length for pollen tubes and roots, surface area for leaves, and cell number for meristematic activity (e.g., in maize roots).