Plant responses Flashcards
what roles does auxin have
cell elongation,
apical dominance,
root growth
how does cell elongation operate and what experimental evidence is there
increases cell wall stretchiness, enabling water absorption and cell expansion
auxin application causes pH to decrease. Enzyme that increase cell wall flexibility work best in acidic conditions
how does apical dominance operate and experimental evidence
promotes growth of the main shoot and inhibits lateral shoots
lateral shoots grow faster when the apex (tip) of main shoot (site of auxin production) is removed
how does root growth operate and what experimental evidence is there
low auxin concentrations promote root elongation
application of small quantities of auxin stimulates root growth; high concentration inhibits growth
what are the roles of gibberellins
stem elongation,
seed germination
how does stem elongation operate and what experimental evidence is there
stimulates cell elongation and division
gibberellins concentrations and plant height show a positive correlation
how does seed germination operate and what experimental evidence is there
activates genes for amylase and protease enzymes, which break down food stores in seeds
mutant seeds that lack gibberellin genes and seeds exposed to gibberellin inhibitors do not germinate
what does ethene do to plants
promotes leaf fall (abscission) and fruit ripening
what does abscisic acid do to plants
works in opposition to gibberellins to stop seed germination
state 3 roles of auxin (3 marks)
cell elongation,
apical dominance/shoot growth,
root growth,
(photo)tropism(s),
ethene released/fruit ripening,
prevention of abscission/leaf fall
suggest 2 similarities and 2 differences between ways in which plant and animal hormones operate (4 marks)
Similarities:
cell signalling molecules,
receptors,
idea of often working as antagonist (eg glucagon and insulin, gibberellin and ABA)
Differences:
animals have endocrine glands/plants lack glands,
animal hormones move in blood and plant hormones move in xylem/phloem through cells,
animal hormones produce effectors more rapidly
give abiotic and biotic factors that plants respond to
abiotic: factors:
day length change,
cold weather,
water shortage
Biotic:
herbivory
give the plant responses and mechanism for day length change
leaf loss (abscission): reduced light exposure-reduced auxin-increased ethene sensitivity-increased cellulase production-cell walls digested at abscission zone
flowering (either when days become shorter or longer): relative proportion of 2 phytochrome photoreceptors (Pfr and Pr) dictates when flowering begins, Pfr=accumulates in the day and is converted back to Pr at night
give plant responses and mechanism for cold weather
solutes produced as antifreeze: reduced temp and day length switch certain genes on or off (i.e. epigenetic control of transcription)
give plant responses and mechanism for water shortage
stomatal close: release of ABA causes stomata to close
give plant responses and mechanisms for herbivory
physical structures: eg evolution of thorns, barbs, spikes and inedible tissue
chemical defence: eg toxic compounds such as tannins, alkaloids and terpenoids.
pheromones warn other plants (or regions of same plant) of an attack
describe the defenses plants have evolved against herbivory (4 marks)
physical defenses,
thorns/barbs/spikes, stings,
fibrous/inedible tissue,
chemical defenses,
named toxic compound,
pheromones for communication between plants
explain how leaf fall is initiated in some plants as day length increases (4 marks)
auxin concentration reduced,
increased ethene sensitivity (in abscission zone),
cellulase/digestive enzyme gene switched on/transcribed,
increased cellulase production,
cells walls digested in abscission zone
suggest how a plant is able to prepare for a pathogenic attack when a neighbouring plant becomes infected (2 marks)
pheromones enable communication between plants,
neighbouring plant produces callose (before infection)
define tropism
growth or movement in response to an environmental stimulus
give examples of positive and negative tropism
positive: phototropism
Negative: geotropism
describe the mechanism that controls phototropism in plants, including roles of auxin
shoot apex produces auxin, which diffuses (or actively transported) down the shoot
auxin concentration will be greater on shaded side of shoot/side receiving less light
auxin causes shaded cells to elongate/expand because their cell walls are loosened/stretched
cell walls are loosened because H+ ions pumped into walls, lowering pH, which increases activity of expansion (proteins that mediate the loosening of cell walls)
cells elongate more on shaded side than brighter side of shoot
shoot therefore bends towards the light
how can phototropism be investigated
vary light intensity (seedlings grown in darkness, all round light or unilateral light)
grow seedlings in unilateral light and vary light wavelengths using filters
vary auxin concentration (by removing shoot apex or introducing additional auxin to one side of plant)
describe how geotropism can be demonstrated using a clinostat (2 marks)
plant is grown on its side,
constant rotation,
idea that gravitational force is felt evenly by all parts of the plant,
roots and shoots grow straight, horizontally
