Phloem and xylem have low quantities of:

Question

BlackTom AI · Accepted Answer

Phloem and xylem are vascular tissues specialized for transport; their saps are dominated by water and by dissolved sugars or mineral ions, so the overall nitrogen content is relatively low.

1) Relevant knowledge points and concepts
- Xylem transports mainly water and dissolved mineral ions upward from roots; its sap is largely water with inorganic ions and very low concentrations of organic nitrogen compounds.
- Phloem transports photosynthates (mostly sucrose) and some organic solutes (including amino acids and signaling molecules) from sources to sinks; phloem sap is rich in sugars and water but contains only modest amounts of nitrogenous compounds.
- Nitrogen in plants exists as inorganic ions (nitrate, ammonium) and organic forms (amino acids, proteins); however, compared with water and sugars, total nitrogen content in vascular sap is low.

2) Step‑by‑step reasoning
- Identify what each tissue carries: xylem = water + minerals; phloem = sugars (sucrose) + some amino acids + water.
- Compare the four answer choices against the known composition:
  - Water: abundant in both xylem and phloem.
  - Sugar: abundant in phloem (major transported solute).
  - Amino acid: present in phloem but in relatively small amounts compared with sugars; xylem contains very little organic amino acids.
  - Nitrogen (as an element/total nitrogenous content): present only in small concentrations in sap (most plant nitrogen is in leaf/seed/structural tissues, not in transport sap).
- Therefore the component present in low quantities in both xylem and phloem is nitrogen.

3) Calculations
- No numeric calculation is required; this is based on qualitative composition of vascular sap.

4) Why the correct answer is correct
- Both vascular tissues are dominated by water and, for phloem, sugars; total nitrogen (organic and inorganic forms combined) in sap is low relative to these major constituents, so “Nitrogen” is the correct choice.

5) Why other options are incorrect
- Amino acid: present, especially in phloem, so not universally “low” in both tissues.
- Sugar: abundant in phloem (the main transported solute).
- Water: abundant in both xylem and phloem.

Conclusion: The correct answer is Nitrogen, matching the provided answer.

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