AP BIOLOGY

Detailed explanation-1: -The primary phloem tissue that gives the plant stability, rigidity, and strength is called the sclerenchyma. Both fibers and sclereids, two types of sclerenchyma, have thick secondary cell walls and are typically dead when they reach maturity.

Detailed explanation-2: -Phloem consists of four elements: Sieve tubes, companion cells, phloem parenchyma and phloem fibres. Except for phloem fibres, all other elements are living. Phloem fibres are thick-walled, elongated spindle-shaped dead cells which possess narrow lumen. They provide mechanical support to the plant.

Detailed explanation-3: -Final answer: Phloem fibre is dead tissue.

Detailed explanation-4: -Explanation: Phloem fibres possess narrow lumen and they are thick-walled elongated spindle-shaped dead cells. They provide mechanical support to the tissue. Phloem parenchyma is thin-walled living cells of parenchyma.