B3.2.18 (HL)—Phloem adaptations
Phloem sieve tubes and companion cells transport sucrose and amino acids from sources to sinks by active loading and pressure flow.
- Syllabus
- First assessment 2025
- Objective
- B3.2.18
- Level
- HL
Exam analysis
Chance of appearing17%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–4
Common command terms
- Identify
- Label
- Outline
- Describe
- Explain
Scoring notes
- Common mistake
- Saying organic compounds move in xylem as well as phloem.
Recent exam appearances
November 2025Paper1A ["HL"] · TZ125[ 1 ]B3.2.18 (HL)—Phloem adaptations
May 2024Paper1 ["HL"] · TZ133[ 1 ]B3.2.18 (HL)—Phloem adaptations
May 2024Paper2 ["HL"] · TZ22(b)[ 2 ]B3.2.18 (HL)—Phloem adaptations
November 2023Paper1 ["HL"] · TZ229[ 1 ]B3.2.18 (HL)—Phloem adaptations
May 2023Paper2 ["HL"] · TZ18(b)[ 7 ]B3.2.18 (HL)—Phloem adaptations
Practice this objective
Coverage 2014–2025 · Updated 15 Jul 2026
Concept essentials
- Phloem transports sucrose and amino acids from sources to sinks.
- Companion cells help load solutes into sieve tubes using energy.
- Water enters loaded phloem by osmosis, raising hydrostatic pressure.
- Pressure gradients drive mass flow through sieve tubes.
- Sieve plates and plasmodesmata support movement through phloem tissue.