Describe four types of Phloem tissue

Answer: Phloem is a complex tissue that transports food in plants. The four types of Phloem tissue are sieve tubes (living, transport food), companion cells (control sieve tubes), phloem parenchyma (stores food), and phloem fibres (dead, provide support). Except for phloem fibres, all components are living and essential for food conduction.

Explanation:

The phloem is a complex permanent tissue responsible for the transport of food in plants. It is made up of four main types of elements. Here are the four types of Phloem tissue:

1. Sieve Tubes: These are long, tube-like structures arranged longitudinally. Their end walls are perforated to form sieve plates. They lack a nucleus but are living and help in the transport of food materials, mainly sucrose.
   
2. Companion Cells: These are specialized parenchymatous cells closely associated with sieve tube elements. Each sieve tube element has a companion cell beside it. They have a nucleus and control the activities of the sieve tubes.
   
3. Phloem Parenchyma: These are living cells found in the phloem. They store food materials and other substances like resins, latex, and mucilage. They also help in the lateral transport of food.
   
4. Phloem Fibres (or Bast Fibres): These are dead, sclerenchymatous fibres that provide mechanical support to the plant. Among all phloem elements, they are the only ones that are dead at maturity.
   

These four components together perform the function of translocation of food in plants.

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