Biology Tuition Singapore O Level Biology Tuition – Transport in Flowering Plants Common Misconception

Misconception 1

Xylem vessels have lignified walls and are often referred to as impermeable

Correct Concept 1

Xylem vessels cannot be impermeable or else nothing can pass through them. The lignin exists only as spiral rings. It is not coated all over the walls. For example, the pits of the walls are not lignified and substances can pass through them. Lignin is only present to increase the rigidity of the walls and provide mechanical support to them, but not to change their permeability

Misconception 2

Both xylem vessels and phloem sieve tubes are made of dead cells

Correct Concept 1

Only xylem vessels are made of dead cells. Mature sieve tube elements are living cells that have degenerate protoplasm (protoplasm that has lost most of its organelles). They are sustained by companion cells

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