Plant Responses Flashcards
stimulus
a change in the environment that causes response in an organism
plant growth regulators
chemicals (hormones) that control plant growth
auxins
hormones that regulate growth in plants
tropism
a response to a stimulus
phototropism
growth of a plant in response to light
geotropism
the growth response of a plant to gravity
thigmatropism
the growth response of a plant to touch
hydrotropism
the growth response of a plant’s roots to water
chemotropism
the growth response of a plant to chemicals
adverse external environment
surroundings which are harmful to organisms
stock solution
solution of known concentration
serial dilution
a series of dilutions of stock solution of known concentration
external factors that regulate growth
light intensity: required for energy for photosynthesis
day length: causing plants to flower
gravity: shoots grow up, roots grow down
temperature: affects enzyme activity
internal factors that regulate growth
plant growth regulators:
produced and secreted from: meristem
how transported: through vascular tissues in the stem
active in small amounts
how plant growth regulators and hormones in animals are alike
slow response and transmission speed
produced in one site and active in another
effect is widespread (in more than one part of the plant)
types and use of plant regulators: growth promotors
auxins
site of production: shoot tip + root tip
site of action: zone of elongation
example: indoleacetic acid (IAA)
auxins function
involved in phototropism (regulatory) and apical dominance (inhibitory)
higher concentration causes more growth, faster rate of cell division
IAA
indoleacetic acid
site of production: meristem tissue at root tip and shoot tip
functions: causes stem and root lengthening
stimulates fruit formation
describe apical dominance
apical bud produces auxin
auxin moves down through vascular tissue
allows the plant to grow vertically by inhibiting lateral bud growth and side branching
mechanism of response : phototropism
stimulus: sunlight
1. IAA produced in meristem
2. diffuses to shady side of stem
3. cells on shady side elongate more than the sunny side (more IAA present)
4. stem bends toward the sun
causes of unequal distribution of auxin
shoot: light shining in different directions
causes auxin to diffuse to shady side
types and use of plant regulators: growth inhibitors
ethene
abscisic acid
ethene
inhibitor site of production: ripe fruit functions: -promotes ripening of fruits -promotes leaf fall and plant aging
abscisic acid
inhibitor site of production: stem, leaves functions: -inhibit germination: allows germination -cause stomata to close in dry conditions and retain water
commercially prepared growth regulators
gibberellins: production of seedless fruit
ethene: ripening of fruit, breaks down chlorophyll
benefits of plant growth regulators to horticulturists
promote ripening
seedless fruit formation
micropropagation
micropropagation
rapid multiplication of a plant using tissue culture methods which produce large numbers of identical plants
advantage of phototropism
plant grows toward light providing more energy which increases photosynthesis rate
advantage of geotropism
ensures roots always grow down to the soil
anchor the plant
advantage of chemotropism
stimulates the pollen tube growth leading to fertilisation during sexual reproduction
advantage of thigmatropism
provides support to plant for growth eg ivy on tree
advantage of hydrotropism
allows plant roots to absorb more water
positive tropism
growth response towards the stimulus
benefits as it provides best growing conditions
eg positive geotropism, roots grow with gravity
negative tropism
growth response away from the stimulus
eg negative geotropism, shoots grow against gravity
plant adaptations for protection
structural or anatomical adaptations
chemical adaptations
why: protection against ingestion by herbivores, disease from pathogens, water loss
structural/anatomical adaptations
- spines, thornes
-stop animals from eating them eg cacti, nettles - guard cells
-change shape when they lose water, stomata close
controls transpiration rate
chemical adaptations
- toxic chemicals/poisons
- kill pests that eat them - heat shock proteins
- protect enzymes at high temperatures/pH outside optimum range
- allow proteins to fold correctly - stress proteins: response to invading pathogens
- damage micro organisms/ form a strong cell wall to stop the pathogen
results of experiment in control
the roots and shoots have grown as the seed itself has produced IAA
depending on the concentration of IAA solution, the roots and shoots in the control are longer than those that inhibited growth, and shorter than those that stimulated growth
roots after experiment
lower conc. - stimulation, more growth
higher conc. - less growth
shoots after experiment
lower conc. - less growth
higher conc. - stimulation
experiment
plant used: cress seeds
why serial dilution: IAA works at very low concentrations so must be diluted, small amounts are difficult to make
safety: wear gloves when handling IAA as it is toxic
control
no IAA just distilled water
