What is the Plant Vascular System?
The plant vascular system is a network of tubes that runs through roots, stems, and leaves, transporting water, minerals, and sugars throughout the plant. Two main tissues make this possible: xylem, which moves water and minerals upward from roots to leaves, and phloem, which distributes sugars from leaves in all directions. Together, they form the plant's 'circulatory system.'
The vascular system consists of xylem and phloem. Xylem transports water and minerals from roots upward via transpiration pull; phloem transports sugars from leaves in both directions via active transport. Both are essential for plant survival.
- •Dead cells (vessels and tracheids)
- •Transport: water + minerals UPWARD
- •Mechanism: transpiration pull
- •Location: center of stem/root
- •Wood is mostly xylem
- •No active energy (passive)
- •Living cells (sieve tubes + companion)
- •Transport: sugars in BOTH directions
- •Mechanism: active transport + pressure
- •Location: outer layer of stem
- •Bark contains phloem
- •Requires ATP energy (active)
Step-by-step worked examples
A plant is 50 cm tall. If water rises at 5 cm/hour via xylem, how long does water take to reach the top of the plant?
Plant height = 50 cm Water rise rate = 5 cm/hour Time = height ÷ rate = 50 ÷ 5 = 10 hours
A leaf produces 20 g of sugar per day. If phloem distributes sugar to 4 growing regions equally, how much sugar goes to each region?
Total sugar = 20 g Growing regions = 4 Sugar per region = 20 ÷ 4 = 5 g
In winter, a tree's phloem carries stored sugars from the root (40 g) upward. By spring, the root has used 15 g. How much remains?
Initial sugar = 40 g Used = 15 g Remaining = 40 − 15 = 25 g
Flashcards
Quick quiz
Q1.Which is NOT a function of xylem?
Q2.Phloem transport requires…
Q3.If you girdle a tree (remove all phloem but leave xylem), what happens?
Q4.Where is phloem located in a stem?
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Common mistakes
Xylem and phloem transport the same substances. — Correct: Xylem transports water and minerals UP; phloem transports sugars in BOTH directions.
Water travels through xylem via active transport. — Correct: Xylem uses passive transpiration pull; phloem uses active transport.
Phloem cells are dead, like xylem cells. — Correct: Phloem cells are living; xylem cells are dead. Living cells in phloem do the work of active transport.
Once sugar reaches a leaf, it stays there. — Correct: Sugars are continuously transported via phloem from photosynthetic leaves to growing regions and storage organs.
FAQ
How can water travel upward against gravity?
Water evaporates from leaves (transpiration), creating negative pressure (tension) that pulls water up xylem. This is called transpiration pull.
What would happen if phloem were blocked?
Sugars could not reach roots, stems, or flowers. Roots would starve, growth would stop, and the plant would eventually die.
Can xylem transport sugars?
No. Xylem cells are dead tubes; they lack the active mechanism needed. Phloem, with living cells, does this job.
Why do trees lose their leaves in fall?
Deciduous trees close off phloem to leaves to preserve sugars in roots and stems. Leaf loss also reduces water loss via transpiration.