lecture 7

Question 1

what is a vascular bundle?

Answer 1

a strand of primary xylem and primary phloem often enclosed by a bundle sheath of parenchyma or sclerenchyma fibres

Question 2

what are the functions of xylem?

Answer 2

transport of water and minerals from root to shoot

Question 3

what are the functions of phloem?

Answer 3

• transport of sugars, nutrients, and signaling molecules from shoot to root
• long-distance signaling (movement of signaling molecules such as hormones and mRNA)

Question 4

what are the cell type criteria for tracheary elements?

Answer 4

1. cell wall: secondary cell walls, lignified; lots of pits of varied patterns and shapes
2. cell shape: cylindrical with varied (but often large) diameters; end walls sloped to varying degrees
3. status at maturity: dead
4. cytoplasm: cytoplasm and plasma membrane gone at maturity
5. distribution in plant body: in vascular tissue only

Question 5

what are the cell types found in xylem?

Answer 5

• tracheary elements (tracheids and vessel elements)
• fibres
• parenchyma

Question 6

what are the cell types found in phloem?

Answer 6

• sieve elements (sieve cells and sieve-tube elements)
• sclerenchyma (fibres and sclereids)
• parenchyma

Question 7

how do tracheary elements differentiate?

Answer 7

programmed cell death

Question 8

how do vessel elements differ from tracheids?

Answer 8

• shorter and wider
• better conductors
• have perforation plates on end-walls
• evolutionarily more advanced

Question 9

what are the cell type criteria for sieve elements?

Answer 9

1. cell wall: primary cell walls only. many plasmodesmata (not pits)
2. cell shape: close association between sieve-tube elements and companion cells (STE are cylindrical and elongated while CC are elongated)
3. status at maturity: living. STE organelles mostly degraded but stay alive thanks to CC
4. cytoplasm: STE appear empty, but filled with phloem sap (dissolved sugars, nutrients, signaling molecules). CC dense cytoplasm
5. distribution in plant body: in vascular tissue only

Question 10

what is a sieve plate?

Answer 10

portion of cell wall between adjacent sieve tube elements, many sieve pores; simple or compound

Question 11

simple vs compound sieve plates

Answer 11

simple: entire plate is a single sieve area
compound: plate has multiple sieve areas

Question 12

what are sieve-tube element/companion cell morphologies?

Answer 12

• end-walls sloped to varying degrees
• simple or compound plates at ends
• variation in pattern of lateral sieve areas
• companion cells can be one or more per element

Question 13

protoxylem vs metaxylem

Answer 13

protoxylem: first to form, differentiation completes before elongation of the organ has completed
metaxylem: begins formation later than protoxylem, differentiation completes after elongation of the organ has completed

Question 14

what happens to the remaining procambium after stem vascular bundle maturation?

Answer 14

goes dormant, or retains meristematic activity, forming the fascicular cambium for secondary growth