Biology 2601A/B Lecture Notes - Lecture 11: Xylem, Vacuole, Phloem
Phloem
- Phloem is interconnected with the xylem
- Phloem transports photosynthates and signalling molecules (hormones and RNA) from
source (generates materials) to sink (consumes materials)
Structure
- Phloem are composed of living cells
- Individual cells of the phloem are called sieve elements which are
connected by sieve plates and act like pipes
- Sieve elements are alive, ut don’t have nuleus,
vacuole, filaments, microtubules, or ribosomes
- They need a companion cell which has a nucleus, vacuoles, etc
companion cell = life support of sieves (responsible for ATP
synthesis, protein synthesis, metabolic regulation of sieve elements)
- Phloem loading and unloading occurs through companion cell
- Phloem is under high positive turgor pressure
-
Individual sieve element
*Sieve tube elements
have mitochondria,
plastids, + smooth ER
- At the end of the sieve
elements are sieve plates
(allow for end-to-end
connection of phloem)
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