The Phloem and Translocation
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of plant cell structure and function and plant organ systems including the roles of leaves, roots and stem.
What is the function of a root hair cell?
To absorb water and mineral ions from the soil using a large surface area
Name the main organs in a plant and give one function of each.
Leaf – photosynthesis; Root – absorption; Stem – support and transport
What is the function of xylem tissue in plants?
To transport water and mineral ions from the roots to the leaves
Topic Explainer Video
Check out this @JoeDoesBiology video that explains the phloem and translocation, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Phloem and Translocation
What is Phloem?
- Phloem is a type of transport tissue found in plants.
- It moves dissolved sugars (mainly sucrose) made during photosynthesis from the leaves to the rest of the plant, including:
- Growing regions (for immediate use in respiration),
- Storage organs (like roots or tubers) where sugar can be stored as starch.
What is Translocation?
- Translocation is the movement of dissolved sugars through the phloem.
- It occurs in both directions (up and down the plant) to meet the needs of cells.
- Translocation is an active process, it requires energy from respiration.
- Translocation is important because sugars are made in the leaves during photosynthesis but need to be moved to other parts of the plant for respiration and storage.
Phloem structure
- Phloem vessels are made of living cells (unlike the xylem) that contain some cytoplasm.
- These cells form a tube used for transport.
- The cells have pores in their end cell walls called sieve plates, to allow sugars to pass from cell to cell.
- Next to the phloem cells are cells called companion cells. These cells have many mitochondria to provide the energy needed for translocation.
Key Terms
- Phloem – plant tissue that transports sugars.
- Translocation – movement of dissolved sugars around the plant via phloem.
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Exam Tip
When asked to explain phloem function, don’t just say "moves food". Use the correct term “dissolved sugars’ or ‘sucrose’.
Remember, unlike the xylem vessel, the phloem transports sugars both up and down the plant, or bi-directionally.
No answer provided.
Practice Question
Describe how the phloem is adapted for transporting sugars in plants.
(3 marks)
Model Answer:
- Phloem is made up of living cells.
- The cells form a tube.
- The end cell walls have pores / sieve plates that allow sugars to move between cells.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!