Chapter 2 - Transport In Plants And Transpiration Flashcards
What does the cross section of a plant root show?
The relative positions of vascular tissue
What is contained within the stele?
Mainly xylem tissue with a smaller amount of phloem tissue surrounded by the endodermis
What is outside the stele?
The cortex( a layer of undifferentiated cells) surrounded by the epidermis
What do xylems transport?
Water and inorganic ions
What does the phloem transport?
Organic molecules such as sucrose and amino acids
How are xylems specialised?
They have no end walls, no cell contents and are dead when fully formed
What is lignin?
An impermeable substance that thickens the secondary cell walls. It provides great strength the prevents the vessels form collapsing when under pressure, and for structural support. It is also waterproof which prevents leakage of water.
What are the two type of xylem?
Protoxylem (young) and metaxylem ( mature)
What are the two types of protoxylem?
Annular and spiral thickening. Lignin laid down in this way does not restrict the elongation of the xylem as growth of the root tips take place
What are the two types of metaxylem?
Reticulate or pitted thickening. The pitted vessels are almost completely covered in lignin and the pits allow water movement
What are the phloem cells concerned with transport?
Sieve tube elements aligned in a continuous row called the sieve tube.
Do phloem have end walls?
Yes but they are perforated with sieve pores to form sieve plates
How do we know that translocation is an active process?
Each sieve tube cell is closely associated with one or more companion cells which have a dense cytoplasm filled with mitochondria. The companion cells are linked to the sieve tube by plasmodesmata. Also metabolic inhibitors such as cyanide that stop respiration in plant cells also disrupt translocation
