Structure and functions of phloem

What does phloem do?

Living tissue that transports food in the form of organic solutes around the plant- supplies cells with sugars+amino acids

How are phloem sieve tubes similar to xylem?

Made up of cells joined end to end to form a long hollow structure- but they aren’t lignified in phloem

What happens to the areas in between cells?

Walls become perforated to form sieve plates- let phloem contents through

What happens when large pores appear in cell walls?

Tonoplast (vacuole membrane), nucleus and other organelles break down

What dos the phloem become filled with?

Phloem sap and the mature phloem cells have no nucleus

What are companion cells?

Form with sieve plates elements, linked to them via plasmodesmata, maintain their nucleus and organelles

What features do companion cells have?

Transport proteins in plasma membrane, lots of mitochondria (provide ATP) for active transport of assimilates in/out, plasmodesmata

What are plasmodesmata?

Microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells

Describe companion cells

Very active, act as a life support system for sieve tube cells which lose normal functions

What else does phloem tissue contain?

Supporting tissues like fibres and sclerids- cells with very thick walls

What do sieve plates with sieve pores do?

Allows for the continuous movement of the organic compounds

What does cellulose cell wall do?

Strengthens the wall to withstand the hydrostatic pressures that move the assimilates

what does noorganelles do?

Maximises the space for the translocation of the assimilates

What does thin cytoplasm do?

Reduces friction to facilitate the movement of the assimilates