AP BIOLOGY

Detailed explanation-1: -Phloem sap travels through perforations called sieve tube plates. Neighboring companion cells carry out metabolic functions for the sieve-tube elements and provide them with energy.

Detailed explanation-2: -Phloem parenchyma cells, called transfer cells and border parenchyma cells, are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they also function in the transport of foods.

Detailed explanation-3: -Phloem is a complex permanent tissue. It transports organic food inside the body of the plant bidirectionally. It consists of four types of cells called sieve tubes, companion cells, phloem parenchyma and phloem fibres.

Detailed explanation-4: -Companion cells – transport of substances in the phloem requires energy. One or more companion cells attached to each sieve tube provide this energy.