Chapter 16- Plant responses Flashcards
(27 cards)
Define a tropism
Directional growth shown by plants in response to environmental cues
Name the four most important plant hormones
Auxins
Gibberellins
Ethene
Abscisjc acid (ABA)
What are the main roles of auxins?
CONTROL cell elongation, stimulate the release of ethene, abscission (leaf fall)
What are the main roles of gibberellin?
CAUSE stem elongation, trigger the mobilisation of food stores in a seed at germination, stimulate pollen growth tube
What are the roles of ethene?
Promote abscission, causes fruit to ripen
What are the roles of ABA?
Maintains dormancy in seeds and buds, stimulates cold protective responses, stimulates stomatal closing
Describe the process and hormones involved in seed germination
A seed absorbs water, the embryo is activated and produces gibberellins, producing enzymes that break down food stores in the seed. Food is used to produce ATP and grow materials. ABA helps to control by acting as an antagonist to gibberellins
Describe what evidence there is to prove the role of gibberellins
Seeds that do not produce gibberellins do not germinate
If gibberellin inhibitors are applied, seeds do not germinate, and if removed they do
Give an example of an auxin used as a growth stimulant
Indolucteaic acid (IAA)
How do auxins have an impact on growth of the main shoot
Auxins lower the pH to the optimal pH so cells can keep the walls very elastic. After maturing, plants destroy auxins- walls become more rigid and cells don’t expand and grow
What do we mean by the term apical?
The primary shoot
What other effects can auxins have?
High concentrations support apical dominance by suppressing growth of lateral shoots
Low concentrations promote root growth
How are gibberellins involved with elongation of plant stems?
They affect the length of the internodes- regions between the leaves on the stems
Define synergism and antagonism
Antagonism- two hormones work in opposite effect to each other determining a balance
Synergism- different hormones working together to give a greater response than they would’ve otherwise
What are the main forms of abiotic stress?
Seasonal changes
Daylight sensitivity
Decrease in temperature
Why do deciduous plants lose their leaves in the winter?
It takes more energy to support their leaves than the amount of glucose produced by photosynthesis
Describe photoperiodism
Plants sensitive to a lack of light in their environment resulting from a pigment called phytochrome. Falling light levels leads to falling auxin levels
How do plants respond to ethene hormone?
At the base of a leaf stalk is the abscission zone, which are cells sensitive to ethene. Ethene initiates gene switching in the cells producing new enzymes which weaken the abscission zone. The leaf falls and fatty material is deposited at the leaf stalk, preventing pathogen entry
How do plants respond to major drops in temperature?
Produce organic molecules and chemicals which effectively act as an antifreeze by lowering the freezing point in cytosol
Name and describe the three chemical responses plants have developed in defense to animals
Tannins- produce a bitter taste that puts animals off eating leaves, also toxic to insects
Alkaloids- Bitter, nitrogenous compounds that affect the metabolism of animals that ingest them (drugs) eg caffeine, nicotine
Terpenoids- Form essential oils, but also act as neurotoxins
Define a pheromone
A chemical made by an organism that affects the behaviour of another animal of the same species
How do plants use pheromones to communicate?
Used to ‘tell’ other plants in the same species of any danger
What is a VOC and how do plants use them as a defensive system?
Volatile organic compounds, mimic pheromones but between plants and other species
eg- cabbages attacked by caterpillars produce a chemical that attracts parasitic wasps
How can we prove that a shoot tip detects the light stimulus?
Lightproof cover placed over the shoot tip resulting in no response
