Lecture 6

Question 1

Mechanisms for cell expansion (3)

Answer 1

Cell wall loosening (breaks cross links, slides fibres)
Uptake of water
Wall thickness maintenance

Question 2

Components of the cell wall (

Answer 2

Cellulose microfibrils
Matrix polysaccharides
Glycoproteins (ex. Extension)

Question 3

Methods of cell wall loosening by breaking linkages (2)

Answer 3

Cleaving hemicellulose bonds with XET

Cleave H-bonds bw MFa and hemicellulose with expansion proteins

Question 4

Mechanism of stomatal opening/closing

Answer 4

OPENING:
Guard cells accumulate solutes -> decreases GC osmotic potential -> water potential pulls water in -> increase turgor pressure -> GCs expand and open

CLOSING:
Guard cells lose osmotica in surrounding apoplast/subsidiary cell -> water potential increases in adjacent cells -> water rushes out of GCs -> decrease turgor pressure in GCs -> GCs deflate and close

Question 5

What is radial micellation?

Answer 5

Spiral wall thickening that prevent swelling in radial direction and force cells to elongate

Question 6

Stomata open in response to what? What is opening enhanced by?

Answer 6

Demand (if need more CO2)

Opening enhanced by: photosynthesis, light, low atmospheric CO2

Question 7

Transpiration and Water Use Efficiency equations

Answer 7

T = leaf conductance x water vapour gradient

E = g(🔺W)

WUE = photosynthesis (A)/ transpiration (E)

Question 8

Midday stomata closure (2)

Answer 8

Hydropassive: high transpiration rates deflates GCs and decreases their

Hydroactive: inhibitors (ex. ABA) are released from mesophyll cells/roots causing stomatal closure

Question 9

Benefits of using sucrose/sucrose derivates (2)

Answer 9

Safe (are non reducing sugars that can’t accumulate)

Efficient (for one ATP used, many carbons enter the phloem)

Question 10

What is invertase? CWIN? CIN? SUS? VIN?

Answer 10

Invertase is a group of enzymes that catalyze the hydrolysis of sucrose into glucose + fructose

Cell Wall Acid Invertase: uptake by monosaccharide sugar found in the cell wall
Cytoplasmic Invertase: uptake by sucrose/proton symport into the cytoplasm
SUS: also found in the cytoplasm but breaks sugars down to UDPG (not glu) + fructose
VIN: found in the vacuole

Question 11

What is catalpol?

Answer 11

A volatile monoterpene that is bitter and toxic to deter insects trying to steal nectar (favoured pollinators are insensitive to it)

Question 12

3 Phases of Nectar Formation + Secretion

Answer 12

Phase 1: carbohydrate unloading and storage in a nectar (apoplastic/symplastic transfer)

Phase 2: carbohydrate processing (carbs getting packaged into secretory vesicles)

Phase 3: secretion (out the stomata)

Question 13

Process of a developing bean seed

Answer 13

Zygote develops into multicellular embryo w 2 cotyledons -> endosperm is swallowed up by cotyledons at seed maturity -> cotyledons fn in carb + N storage for germinating seed

Question 14

What do high hexose/sucrose concentrations stimulate? (2)

Answer 14

Embryonic cell division
Development of transfer cells (E2748 gene)
Switch from cell division to cell expansion
Upregulation of genes involved w starch synthesis

Question 15

What new tissues arise from primary meristems procambium and ground tissue?

Answer 15

PC: fascicular cambium

Ground parenchyma: interfasicular cambium

Question 17

Cell types that make up the vascular cambium (2)

Answer 17

Fusiform initials (axial system)

• II° xylem/II° phloem
• source of cells for conduction, translocation, support

Ray initials (radial system)

• parenchyma cells
• cells that move material to/from xylem and phloem, stores nutrients

Question 18

What is an annual ring? What two types of xylem does it result in?

Answer 18

One season’s worth of growth

Early xylem: wider/thin cell walls, larger cells
Late xylem: narrower/thick cell walls, smaller cells

Question 19

What is wood? What two systems is it made of? What two types of wood are there?

Answer 19

Wood = secondary xylem

2 systems: axial (vertical), radial (horizontal)

Sapwood (outer conducive part of wood; light in colour)
Heartwood (inner non-conductive part; dark)!

Question 20

What new tissues arise from secondary meristems vascular cambium and cork cambium?

Answer 20

VC: form wood/bark tissue
CC: outer zone of bark