BIOL371 PLANT THEME 5 EXAM QUESTIONS AND ANSWERS
WITH COMPLETE SOLUTIONS
Auxin
promote growth
Gibberellins
stimulate growth and stems elongation
Cytokinins
enhance growth and retard aging
Ethylene
gaseous hormones that regulates a range of responses including senescence
Brassinosteroids
regulate plant growth responses
Abscisic acid
suppresses growth, influences responses to environmental stress
Jasmonates
regulate growth, have roles in defence
Oligosaccharins
promote synthesis of phytoalexins in injured plants, role in regulating growth
Sytemin
only in tomato, roles in defence, triggering jasmonate-induced chemical defences
Salicylic acid
, triggers synthesis of pathogenesis-related proteins, general defences
Auxins (4)
1. mainly indoleacetic acid (IAA)
2. synthesized in: shoot apical meristem, young stems, leaves
3. function: promote cells elongation, govern growth responses to light and gravity
4. accumulate on the opposite side of a light source
Acid-growth hypothesis
explains how auxins regulate plant cells expansion
Acid-growth hypothesis step 1
auxin acts on cell: auxin triggers pumping H+ into cell wall (acdifying cell wall)
Acid-growth hypothesis step 2
crossbridges break: expansins activated > break crossbridges between cellulose
microfibrils
Acid-growth hypothesis step 3
cell expansion: cellulose microfibrils loosen > wall becomes extensible > cell can
expand
Acid-growth hypothesis from step 1 to 3
turgor pressure increases
Phototropism (4)
1. growth responses to directional light source (bend toward light)
2. blue light receptors trigger auxin transport
3. auxin moves to the dark side
4. auxin stimulates cells to elongate more quickly > bend
WITH COMPLETE SOLUTIONS
Auxin
promote growth
Gibberellins
stimulate growth and stems elongation
Cytokinins
enhance growth and retard aging
Ethylene
gaseous hormones that regulates a range of responses including senescence
Brassinosteroids
regulate plant growth responses
Abscisic acid
suppresses growth, influences responses to environmental stress
Jasmonates
regulate growth, have roles in defence
Oligosaccharins
promote synthesis of phytoalexins in injured plants, role in regulating growth
Sytemin
only in tomato, roles in defence, triggering jasmonate-induced chemical defences
Salicylic acid
, triggers synthesis of pathogenesis-related proteins, general defences
Auxins (4)
1. mainly indoleacetic acid (IAA)
2. synthesized in: shoot apical meristem, young stems, leaves
3. function: promote cells elongation, govern growth responses to light and gravity
4. accumulate on the opposite side of a light source
Acid-growth hypothesis
explains how auxins regulate plant cells expansion
Acid-growth hypothesis step 1
auxin acts on cell: auxin triggers pumping H+ into cell wall (acdifying cell wall)
Acid-growth hypothesis step 2
crossbridges break: expansins activated > break crossbridges between cellulose
microfibrils
Acid-growth hypothesis step 3
cell expansion: cellulose microfibrils loosen > wall becomes extensible > cell can
expand
Acid-growth hypothesis from step 1 to 3
turgor pressure increases
Phototropism (4)
1. growth responses to directional light source (bend toward light)
2. blue light receptors trigger auxin transport
3. auxin moves to the dark side
4. auxin stimulates cells to elongate more quickly > bend
