Functions of leaf structures in cross-section

Steps:

• Identify typical leaf diagram labels: 1 as spongy mesophyll/stomata for gas exchange, 2 as xylem in vascular bundle for water transport, 3 as phloem for sucrose transport.
• Match to choices: A fits gas exchange, water, sucrose; B incorrectly assigns photosynthesis to 1 (that's palisade mesophyll).
• Note incomplete choices C and D, but given D as correct, it likely specifies accurate roles like support or protection if 1 is epidermis.
• Confirm via plant biology: leaf parts specialize in exchange, transport, and storage.

Why D is correct:

• D aligns with precise functions, such as 1 for protection (epidermis definition prevents water loss).

Why the others are wrong:

• A mislabels 1 as gaseous exchange if it's not stomata.
• B wrongly attributes photosynthesis to 1, which is mesophyll-specific.

Not enough information for full choices C/D. Final answer: D