Phloem Flashcards
What is translocation?
The movement of sugars and other organic compounds from sources to sinks
Is the translocation of phloem an active or passive process?
an active process requiring an input of ATP
What are sieve tubes?
Column of living cells that make up the phloem
What are the 2 main types of cells that compose sieve tubes?
Sieve element cells
Companion cells
What are sieve element cells?
Long and narrow cells that are connected together to form the sieve tube
What are companion cells?
Provide metabolic support for sieve element cells and facilitate the loading and unloading of materials at source and sink
Why do sieve element cells need to be connected by plasmodesmata to a companion cell?
Sieve elements contain limited cytoplasm with a few mitochondria and other organelles, but the nucleus, vacuole, cytoskeleton, and many other structures are broken down
Why do sieve elements have no nuclei and reduced number of organelles?
To maximize the space for the translocation of materials
What are sieve elements connected by?
Connected by sieve elements at their transverse ends
What increases the SA:Vol of companion cells?
An infolding plasma membrane
What are sieve elements largely filled with?
Phloem sap
What is a source in translocation?
where the organic compounds are synthesised – this is the photosynthetic tissues (leaves)
What is a sink in translocation?
where the compounds are delivered to for use or storage – this includes roots, fruits and seeds
What is symplastic loading?
Materials can pass into the sieve tube via interconnecting plasmodesmata
What is apoplastic landing?
materials can be pumped across the intervening cell wall by membrane proteins
