Plant and animal responses Flashcards
What kind of stimuli do plants respond too?
Biotic (living) and abiotic (non-living)
How do plants respond to the threat of herbivores
Chemical defenses:
Tannins; Alkaloids; pheromones
Tannins
-Toxic to microorganisms / larger herbivores
-Found on upper epidermis of the leaf and makes it taste bad
-Roots = prevents infiltration of pathogenic microorganisms
Alkaloids
-Derived from amino acids
-Tastes bitter = feeding deterrent
-Located in growing tips and flowers / peripheral cell layers of stem and roots
Pheromones
-Chemicals released by one individual = influence behaviour/ physiology of another
What are some other examples of plant defences
-Deposition of thicker wax on leaves = higher temp
- Vascular tissue is lignified = windy
Tropism
Directional growth response, in which the direction of the response is determined by the direction of the external stimulus
Phototropism
Shoot grows towards light ( positive phototropic) which enables photosynthesis
Geotropism
Roots grow towards the pull of gravity
-Anchors in soil and helps of absorption of water (to keep cells turgid)
=Helps photosynthesis / cools the plant
=Also minerals i.e. nitrate which is needed for protein synthesis
Chemotropism
On a flower, pollen tubes grow down the style, attracted by the chemicals towards the ovary where fertilisation takes place
Thigmotropism
Shoots of climbing plants i.e. ivy wind around plants or toher solid structures for support
Positive tropic
If a plant responds to a stimulus
Negative tropic
If a plant responds away from a stimulus
Nastic responses
non-directional response to external stimuli
Thigmonasty
Non directional response in plants, to the stimulation of contact
Photoperiod
Plant response to day length, which influences what time of year the plant flowers
Plant hormones
Coordinate the plants responses to environmental stimuli
-Not produced in endocrine glands, but by cells in a variety of tissues in the plant
Amplify/cancel out
Synergy = amplify
Antagonistic = cancel out
What do plant hormones do within a plant
Amplify/cancel out the effects of different tissue
Used in:
-Cell division
-Cell elongation
-Cell growth
How are hormones transported around the plant
-Active transport
-Diffusion
-Mass flow in phloem/ xylem
Examples of plant hormones
-Cytokines
-Abscisic acid
-Auxins
-Gibberellins
-Ethene
Cytokines
-promote cell division
- Delay leaf senescence
-Overcome apical dominance
-Promote cell expansion
Abscisic acid
-inhibits seed germination and growth
-Causes stomata closure when their is low water availability
Auxins
-Promotes cell elongation (plant growth)
-Inhibits growth of side shoots
-Inhibits leaf fall
Gibberellins
Promotes seed germination and growth of stems
Ethene
Promotes fruit ripening
What were the researchers investigating with the role of auxin with plants
If the apex of the plant is broken the plant grows side branches from lateral buds that were previously dormant
Researchers suggested that auxins from the apical bud prevent lateral buds from growing
When the tip of the plant is removed, auxin in the shoot drop and lateral buds grow
How did the researchers test their first hypothesis with auxin
Scientists applied a paste that contained auxins to the end of the shoot and the lateral buds did not grow
What were the limitations of the researcher’s first method at investigating their hypothesis of the effect of auxin in plants
When exposed to oxygen cells on the cut end of the stem could have produced a hormone that promoted lateral bud growth
How did the researchers improve their method at investigating their hypothesis of the effect of auxin in plants
Applied a ring of auxin transport inhibitor below the apex of the shoot
=Lateral buds grow
What was the researchers conclusion after their improvement on the auxin experiment
Normal auxin levels in the lateral buds inhibit growth
Low auxin levels = promote growth
Whare the limitations of the researchers improvement to the auxin experiment
Auxin levels and growth inhibition may have no effect on one another
-Could be a third variable
-Auxin levels in lateral bud of a kidney bean was still high after apex had been cut
What was the researchers final conclusions
Two other hormones were involved: Abscisic acid / Cytokines
How do abscisic acid and auxin affect each other
abscisic acid = inhibits bud growth
-High auxin in shoot keeps abscisic acid levels high
- When tip is removed abscisic acid levels drop and lateral bids start to grow
How do Cytokines and auxin affect each other
Cytokines promote bud growth
-When directly applied overrides the apical dominance effect
-High levels of auxin make shoot apex a sink for cytokines produced in the roots
-When apex removed, cytokines can spread even;y around the plant
What is apical dominance
Inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the plant shoot
How was stem elongation researched
Fungus caused disease, which made rice grow tall
-Fungal compounds = gibberellins (GA3)
-Tested on many diff plants and made them grow tall
Limitations of stem elongation experiment
Just because GA3 causes cell elongation does not mean that it does so in nature
How did researchers overcome this limitation (Gibberellins)
Compared GA1 Le with GA3 le = plants with GA1 grew taller
Why did the plants with GA1 grow taller
Le gene = length
Codes for an enzyme that activates GA20 (inactive) to GA1 (active
le (recessive) = non-functional enzyme so no active gibberellin produced
Internodes
Where the leaves develop as the stem grows
Where do gibberellins also cause growth
In the internodes by stimulating cell elongation (by loosening cell walls) and cell division (stimulating production of the protein that controls the cell cycle)
Seed germination pathway
1) Seed absorbs water and embryo releases gibberellin
2) Travels to aleurone layer in endosperm of the seed
3) Gibberellin activates production of amylase (starch to glucose)
4) Provides a substrate for respiration of the embryo
5) Embryo grows
6) Glucose also used for protein synthesis
Steps of cell elongation (auxin)
1) Meristematic cells produce auxins, diffuse towards the zone of elongation down the concentration gradient
2) Auxin binds to receptors on cells, open protein channels on plasma membrane, H+ enters
3)influx of H+ = lower pH ; cell wall becomes more flexible
4) Water moves into the cell and expands the cell without bursting it
5) Cell elongates
6) Auxin leaves = broken down
7) Cell wall becomes rigid again
Main role of auxins
+ apical shoot growth
- lateral shoot growth
=allows for better photosynthesis throughout the plant
Main role of stem elongation
+gibberellins
+ internodes
= Taller plants / better competition for light
=allows for better photosynthesis throughout the plant
What are the meristems
Immature cells in the plant that are still capable of division
Different types of meristems and their roles
1) Apical meristems in the apex = root/shoots getting longer
2) Lateral bud meristems in the buds = side shoots longer
3) Lateral meristems in a cylinder around roots/ shoots = roots/ shoots getting wider
4) In some plants intercalary meristems (located between the nodes) = shoot getting longer
Darwin
Did a series of experiments which confirmed that a chemical messenger from the shoot tip is responsible for the phototropic responses
Darwin experiments
-Control = towards the light
-Tip removed = straight
-Opaque cap = straight
-Transparent cap = towards light
-Base covered by opaque shield = towards the light
Boysen-Jenson
Water and/or solutes need to be moved backwards from the shoot trip for phototropism to happen
Boysen-Jenson experiment
When a permeable gelatine block was inserted behind shoot tip = positive phototropism
When an impermeable mica block was inserted = no phototropic response
Experiment that investigates phototropic responses
1) Experiment plant in test tube with water, cotton wool plug, illumination on one side, roots and shoots marked every 10mm
2) 10x replicates with illumination on all sides
=Plant with illumination on one side bent towards the light as shady parts have elongated more
Experiment that investigates geotropic responses
1) Control plant spun slowly by a klinostat
-Shows effects of gravity is applied equally to all sides of the plant
= Both roots/shoots grow horizontally
2) Experimental plant, klinostat is off so gravity can be applied to one side
= Root bends downwards as upper side of the root has elongated more than the lower side
=Shoot bends upwards as lower side of the root
has elongated more than the upper side
Went
Discovered a chemical messenger existed and could stimulate a phototropic response artificially
Went experiment
Confirmed hypothesis by using agar blocks all impregnated with different concentrations of auxin and all gave the same response
=Cell elongation is proportional to the concentration of auxin
Auxin’s role in cell elongation conclusions
Auxin produced at apex of shoot in zone of elongation
light=all sides= auxin promotes shoot growth evenly
When light on one side auxin goes to shaded side, which causes cells to elongate there quicker
=Shoot bends towards light
How does light cause the redistribution of auxin
-Auxin
2 enzymes identified:
1) Phototropin 1
2) Phototropin 2
-Activity promoted by blue light
Blue light
Main component of white light and causes a phototropic response
P1 effect on auxin
1) More P1 on light side than shaded
2) Gradient thought to cause redistribution of auxin in the plant
Why does P1 affect auxin
1) P1 effects PIN proteins in plasma membrane which causes the efflux of auxin from each cell
2) This sends auxin in different directions in the shoot dependant on the PIN proteins location in the plasma membrane
How is the activity of PIN proteins controlled
-Molecule called a PINOID
theory: phototropins affect the activity of the PINOID which affects PIN activity
Recent research: Many only work for pulse induced phototropism (short bursts of light) with another independent mechanism able to operate in continous light
Auxin in geotropic responses in the roots (Went)
When a shoot lies flat the auxin accumulates on the lower side where it inhibits cell elongation
-Upper side continues to grow and bends downwards
=Contrasts shoot where auxin promotes cell elongation on lower side = shoot bends upwards
Root/shoot cells (auxin)
Exhibit different responses to the same concentrations of auxin
How do you create a serial dilution
1) 10 boiling tubes with bungs
2) Using a syringe add 10ml of auxin solution at 100 parts per million in the first boiling tube
3) Using a separate syringe add 9ml of distilled water to four test tubes
4) Remove 1ml of auxin from tube 1 and add to tube 2
5) Repeat process between tubes 2-3, 3-4, 4-5
6) Shake vigoursely
=All jars now contain auxin solution each 10x more dilute than the last
Auxin (Commercial uses)
1) Prevents leaf drop (artificial auxins)
2) Promotes flowering
3) Promotes fruit drop in high conc (get rid of small fruit)
4) Promotes roots growth (cutting plant placed in rooting power before planting)
5) Growth of seedless fruit by unpollinated flowers with auxin
=Auxin promotes ovule growth = triggers automatic production of auxin in developing fruit which helps complete development
6) Used as herbicides
How does auxin act as a herbicide
Artificial so plant finds it hard to break auxin down
Promotes shoot growth so much that stem buckles and dies
Cytokines (commercial uses)
-Prevents yellowing of yellow leaves after harvest as delays elaf senescence
-Used in tissue culture to help mass produce plants
How does cytokines mass produce plants in a tissue culture
Promotes bud and shoot growth from tissue from parent plant, which produces short shoot/side branches
=Split into smaller plants
=Each grown separately
Gibberellins (commercial uses)
1) Delay leaf senescence in citrus fruits = extends time fruit can be left unpicked
2) Gib + Cytokines = apple elongation to improve shape
3) Elongate grape stalks so the grapes become less compact and can grow bigger
Gibberellins (brewing)
Starch - maltose - malt
1)Starch to maltose (amylase switched on by natural gibberellins = extra speeds up process)
2) Maltose to malt 9drying and grinding the seeds)
Gibberellins (sugar production)
Spraying gibberellins between the internodes of sugar can make the stem elongate = stem is where sugar stored = more sugar available
=Increases sugar yield up to 10 tonnes per acre
Gibberellins (plant breeding)
Difficult to plant breed conifers as takes long time to become fertile
-Gibberellins speed up process by inducing seed formation on younger trees
-Biennial plants (only flower 2nd year) gibberellins can induce seed production
Gibberellins (prevent plants from growing)
Spray with gibberellin synthesis inhibitors
=Prevents lodging
What’s lodging
In wet summers stems bend over due tot he weight of water on seed heads =Difficult to harvest
Ethene (commercial uses)
Gas so cannot be used directly = use an acid which slowly releases ethene
1) Speeds up ripening of apples, tomatoes, citrus fruits
2) Promotes fruit drop in cotton, cherry, walnut
3) Promotes female sec expression in cucumbers
=reduces chances of self-pollination which makes them bitter
4) Promotes lateral growth = compacts flower stems
How to store fruit
Low temp, little O2, High CO2 prevents ethene synthesis
=Prevents fruit ripening
Nicotine selective advantages
Nicotine deters grazers so plant can continue to reproduce however metabolic resources are diverted to nicotine production
