Q.In Gymnosperms, the activity of sieve tubes are controlled by
a. Nearby sieve tube members.
b. Phloem parenchyma cells
c. Nucleus of companion cells.
d. Nucleus of albuminous cells.

Step 1. Recall that gymnosperms lack true sieve tubes and companion cells. The chapter's phloem section explains that sieve elements occur as two types - sieve cells (the more primitive type, found in pteridophytes and gymnosperms) and sieve tubes (found only in angiosperms, each paired with a companion cell). Since gymnosperms have sieve cells, not sieve tubes, and sieve cells by definition have no companion cells, option (c), nucleus of companion cells, cannot be correct for a gymnosperm.

Step 2. Eliminate options (a) and (b). Nearby sieve tube members (a) is not applicable either, since gymnosperms do not have sieve tube members at all, only sieve cells. Phloem parenchyma cells (b) are a separate, storage-focused cell type in phloem and are not described as regulating sieve-element activity in any group.

Step 3. Identify the actual regulating cell. The chapter specifically introduces albuminous cells as cytoplasmic, nucleated parenchyma cells associated with the sieve cells of gymnosperms, and states that albuminous cells in conifers are analogous to the companion cells of angiosperms - meaning they perform the equivalent regulatory/nutritive role for the sieve cell that a companion cell performs for a sieve-tube element, even though they are not derived the same way.

Step 4. Confirm the answer. Since gymnosperm sieve cells have no companion cells of their own, it is the nucleus of the associated albuminous cell that functionally takes over that regulatory role, matching option (d).

Recognise that gymnosperms have sieve cells (not sieve tubes) with no companion cells, then identify albuminous cells as the companion-cell analogue that regulates them.

• Picking 'nucleus of companion cells' by assuming every phloem conducting cell has a companion cell, without recalling that companion cells are specific to the angiosperm sieve tube.
• Not recognising 'albuminous cells' and 'Strasburger cells' as the same structure described by two different names.