Lecture 12

Question 1

Lignin made of

Answer 1

Complex polymer of phenylpropane units

Question 2

Lignin Purpose

Answer 2

-Hydrophobic mesh bonds to cellulose and waterproofs the wall,
-Prevents wall enlargement and adds mechanical strength,
-Resists microbial attack,
-It was one of the most important
prerequisites of the evolution of large
upright-growing terrestrial plants,
-Most abundant organic material
on earth after cellulose,
-Lignin stains red with phloroglucinol

Question 3

Primary vs Secondary Cell Walls

Answer 3

• Secondary walls are less hydrated because they contain fewer pectins and hemicelluloses and because lignin is hydrophobic,
• Secondary walls are less plastic because of the rigidity conferred by lignin,
• Microfibrils in the secondary wall layers are more highly organized and different wall layers usually have a different pitch, which further strengthens the entire wall
• Secondary walls are birefringent (refract light) due to their crystalline arrangement

Question 4

Primary pit fields become ??? with secondary wall added

Answer 4

Pit Membranes

Question 5

Bordered pit pairs

Answer 5

Pit membrane with torus in Gymnosperms

Question 6

Simple pit pairs

Answer 6

No torus

Question 7

Wood anatomical features observed in RLS

Answer 7

-Bordered pit distribution in axial tracheids,
-Morphology of half-border pit-pairs (between ray parenchyma cells and
axial tracheids),
-Types of rays: Presence of ray tracheids

Question 8

Sclerenchyma Purpose

Answer 8

Strengthening tissue in a plant, formed from cells with thickened, typically lignified, walls

Question 9

Sclerenchyma Attributes

Answer 9

• Usually dead cells at maturity,
• With secondary walls containing simple pits,
• Permanently differentiated Found all over the plant body,
• Provide rigid support for mature organs

Question 10

Collenchyma vs Sclerenchyma

Answer 10

• Collenchyma: Thin primary walls with some areas of secondary thickening. Particularly in regions of new growth,
• Sclerenchyma: Thick lignified secondary walls and often die when mature

Question 11

Sclereids:

Answer 11

Reduced form of sclerenchyma cells with highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants

Question 12

Fibers Purpose

Answer 12

Dead at maturity and function as support tissue. Associated with vascular bundles

Question 13

Fiber Types

Answer 13

Septate, Phloem, Xylem, Gelatinous (little/no Liginifaction)