5.1.5 - Plant And Animal Repsones Flashcards
What is abiotic stress?
Plant stress due to non-living components of their environment
How do abiotic factors affect leaf loss in all plants?
Temps and light affect photosynthesis - when demand for glucose becomes greater than glucose produced during PS, leaves are lost.
How do abiotic factors affect leaf loss in trees only?
Wind is more likely to blow trees over when full of leaves so in winter they lose all leaves to remain dormant until days lengthen and temps rise.
What is photoperiodism?
The way plants are sensitive to a lack of light in their environment.
What is phytochrome?
A light-sensitive pigment that determines night length to day length
What are the 2 forms of phytochrome?
Pr and Pfr
What do lengthening of dark periods trigger?
- leaf abscission
- period of dormancy
What do falling light levels result in ?
1 Falling concentrations of auxin
2 leaves respond to by producing the hormone ethene
3 Ethene-sensitive layers in abscission zone (AZ) undergo gene switching
4 New enzymes produced
5 Enzymes weaken and digest cell walls of separation layer (outer layer of AZ)
How is the plant protected from pathogens after leaf abscission?
1 vascular bundles sealed off
2 fatty acid materials build protective layer under separation layer
3 Protective scar formed
What is the role of the separation zone?
Respond to hormonal cues: retain water and swelling - more pressure for abscission to happen
How does a decrease in temperature affect plants?
Cells freeze = membranes disrupted = die
How do plants prevent freezing?
1 cytoplasm and cell sap have solutes = lower freezing point
2 some produce polysaccharides, amino acids and proteins to act as anti-freeze
3 can produce chemicals = frost resistant ( genes activated in sustained fall in temp - reversed with sustain spell of warm weather)
What is the main mechanism plants use to overcome stresses of heat and water availability?
Stomatal control
What hormone is responsible for stomatal control?
ABA
What releases hormone ABA?
Leaf cells and roots
What does ABA do?
1 plant under abiotic stress
2 ABA binds to receptors on membrane of guard cells
3changes in ionic concentration
4 changes turgor
5 stomata CLOSE
What is herbivory?
The process by which herbivores eat plants
Physical defences against herbivory
- thorns
- barbs
- spikes
- fibrous + inedible tissue
- hairy leaves
- stings
Chemical defences against herbivory
- tannins
- alkaloids
- pheromones
What are tannins and what are their functions?
- part of group called phenols
- have bitter taste = discourages herbivory
- toxic to insects (inactivate digestive enzymes in saliva)
What are alkaloids and what are their functions?
- bitter-tasting, nitrogenous compounds
- affect metabolism and can poison animals
- e.g. nicotine, caffeine morphine and cocaine
What are pheromones and what are their functions?
Chemical made by organism, affecting behaviour of others of same species
Give examples where trees use pheromones
- if attacked by insects, release pheromones to be absorbed by OTHER leaves and branches. Stimulates release of other chemical defences to protect themselves from attack.
- Evidence: if under water stress, roots release chemical to communicate with other plants
What are volatile organic compounds ?
- act like pheromones
- between themselves and other organisms
- made when plant detects attack via chemicals in saliva of insect -> gene switching
Name a plant that folds in response to touch and can be seen with the naked eye
Mimosa pudica
What are all of the defences that a mimosa pudica has
- physical : sharp prickles in stem
- chemical : alkaloid toxin
- touch: fold down and collapse
What is the purpose of leaves folding in response to touch?
- dislodges small insects that land in leaves
- can frighten off larger herbivore
How do mimosa pudica a recover after folding ?
- takes 10-12 mins
- potassium ion movement into specific cells followed by osmotic water movement
Where can geotropic responses be investigated?
In shoots and roots
What is used to investigate geotropic response?
A clinostat
How are clinostats used?
- slowly rotates 4revs per hours so that gravitational stimulus is applied evenly so root and shoot grow straight
What do Petri dishes do?
- stick to wall of lab
- seeds inside
- rotate 90° at intervals
- geotropic response that seedlings grow are seen in 2 hours
What is a tropism?
A directional growth response in which is determined by the direction of an external stimulus
What’s the difference between positive and negative tropism?
Positive - response TOWARDS a stimulus
Negative - response AWAY from stimulus
Define geotropism
A response in plant growth caused by gravity
Define phototropism
A response in plant growth or bending caused by light
Define hydrotropism
A response in plant growth or bending caused by water
Define thigmotropism
A response in plant growth caused by touch e.g. vines
Define chemotropism
A response in plant growth caused by certain chemicals
E.g. pollen tubes grow down flower’s stigma, towards ovaries for fertilisation due to chemicals
What are the roles of gibberellins?
- seed germination
- stem elongation
Define germination
The sprouting of a seed, spore or other reproductive body - usually after a period of dormancy
Describe the process of germination
1 conditions are what is required
2 seed begins to absorb water
3 embryo veins to release gibberellins
4 gibberellins diffuse into aleurone layer and stimulate cells to synthesis amylase
5 amylase hydrolyses starch in endosperm leading to maltose molecules that are converted into glucose
6 glucose used for respiration so the plant is metabolically active and can germinate
What is the antagonist to gibberellins and what does it do ?
ABA hormone inhibits the production of amylase, maintaining dormancy
List the commercial uses of plant hormones
- hormonal control of ripening
- hormonal rooting powders and micropropagation
- hormonal weed killers
How do hormones control ripening?
Ethers is released harvested climacteric fruits which triggers a series of chemical reactions including a greatly increased respiration rate.
How is controlled ripening used commercially?
When producing the perfectly ripe climacteric fruit, they are harvested when they are fully formed but long before they are ripe as they are harder and less likely to get damaged in transport. When wanted to sell, they are exposed to ethene gas under controlled conditions to ripen them for the supermarket shelves .
How do hormones act as rooting powders and affect micropropagation ?
When cutting shoots off of the tip of a plant, if dipped in auxins and placed in soil, the chance of a roots forming and propagation occurring is increased
How is the use of hormonal rooting powders and micropropagation used commercially ?
Many plants are grown from a few cells, saving money for horticultural and agricultural businesses.
How do hormones act as weed killers?
Synthetic auxins target broad-leaves dicots, which are what most weeds are. The hormone affects their metabolism and the growth rate increases, becoming unsustainable so they die.
How are hormonal weed killers used commercially ?
Farmers and gardeners use the synthetic auxins as they are cheap, low toxicity ti mammals and are selective (narrow-leaved crop plants are unaffected and so have no competition)
Define apical dominance
The process whereby auxins produced at the growing tip at the apex allows growth upwards but also inhibits lateral (side) buds from growing
Explain experiments used to control apical dominance
1 apical bud of 1st test plant = decapitated
2 lateral buds grow
3 genetically identical 2nd plant = decapitated but immediately replaces top with agar block containing auxin
4 restoration of inhibition of lateral bud growth
In what ways can you investigate the effect oh hormones on plant growth?
- apply different hormones to cut ends of stems or roots at different concentrations
- grow seedlings hydroponically ( witching nutrient solutions eater than soil )
USE SERIAL DILUTIONS TO OBSERVE DIFFERENT CONCENTRATIONS OF DIFFERENT HORMONES
What experimental evidence is there for gibberellins controlling stem elongation and germination?
- Rice was isolated gibberellins which produced the same spindly growth in plants.
- discovered shirt stem plants = little to no gibberellins; scientists bred many dwarf varieties of plants (gibberellin synthesis pathway interrupted) and this keeps them short so less risk of damage by weather / harvesting
