A Levels Biology (9700)•9700/13/M/J/24

Explanation
Sieve Element Structure in Phloem
Steps:
- Recall sieve elements are elongated phloem cells with porous sieve plates for sap flow.
- Identify key visible features in a longitudinal electron micrograph: thick cell wall, sieve plate (end wall with pores), and cytoplasm.
- Evaluate labels: must include wall, cytoplasm, and sieve plate; avoid non-essential organelles like mitochondria, which are sparse.
- Match options to standard diagram: C includes all essentials without extras.
Why C is correct:
- Sieve elements feature a cell wall perforated by sieve plates and contain cytoplasm for mass flow of nutrients, per phloem transport definitions.
Why the others are wrong:
- A omits cytoplasm, essential for visualizing sap movement.
- B labels mitochondrion, not a prominent or defining sieve element feature.
- D adds mitochondrion, incorrect as sieve elements have reduced organelles.
Final answer: C
Topic: Structure of transport tissues
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