5 - MZH - Plant responses Flashcards
State 2 ways in which plants use to produce coordinated responses
- Chemical communication molecules (hormones)
- Growth substances/ regulators
give 5 examples of plant reponses
- Seed germinating in suitable conditions - ensure optical growth
- Shoots growing upwards and roots downwards
- Plants growing adaptively with respect to light and variations in water content of the soil
- Responding to seasons in order to flower at the right time
- Responding to predation or abiotic stress
Define Abiotic stress + example
Abiotic stress = Somethign that’s potentially harmful to a plant that’s natural but non-living
E.g. drought - water stress
Define Herbivory
Herbivory = Process of animals eating plants
What are pheromones?
Pheromones = A signalling chemical, released by one plant, that affects the response of others
If this plant releases pheromones into its environment neighbouring plants can start producing defensive chemicals befoe they themselves are attacked
Give an example of a plant responding to abiotic stress
Carrots:
Produce antifreeze at low temperatures
- Proteins bind to ice crystals and lower the temperature that water freezez at ∴ stopping more ice crystals from growing
Different responses given by plants in response to herbivory and pathogenic microorganisms? (4)
Physical defences
Chemical defences - Tannins, alkaloids and pheromones
Leaf folding - Mimosa pudicans
Responses to herbivory/ pathogenic microorganisms:
Physical defences
- Thorns
- Spikes
- Hairy leaves
- Stings
Goal = Make themselves unappetising to predator
Responses to herbivory/ pathogenic microorganisms:
Chemical defences
Alkaloids:
- Chemicals derived from amino acids and taste bitter, smell noxious or have poisonous characteristics that deter or kill herbivores
- Located = outer leaves of stems and roots
- E.g. Tobacco plants produce the alkaloid nicotine (which is poinsonous to many insects) in response to tissue damage
Tannins:
- Tastes bitter
- In some herbivores (cattle, sheep) they can bind to proteins in the gut, making the plant hard to digest
Pheromones = A signalling chemical, released by one plant, and can affect the responses of others
- Some plants release alarm pheromones into the air in response to herbivore grazing. Allows nearby plants to detect these chemicals and start making chemical defences
- When corn plants are eaten by caterpillars, the produce pheromones which attract parasitic wasps. These wasps lay their eggs in the caterpillars, which eventually kill them
Responses to herbivory/ pathogenic microorganisms:
Leaf folding
Mimosa pudicans - is a sensitive plant which has leaves that collapse in towards the stems if touched and are protects by sharp spines
Define Tropism
Tropism = Directional growth reponse of plants determined by a stimulus
What is the difference between a positive/ negative tropism?
Positive tropism = Respons towards the stimulus
Negative tropism = Response away from the stimulus
Name the 5 types of tropism you need to know and name the stimulus that accompanies each type of tropism
What are nastic responses?
Example?
Nastic responses = Non-directional responses to external stimuli e.g. collapsing of leaves on mimosa
Phototropism
How is it useful?
Positive phototropism = Plant shoot responding by growing towards light
- Shoot phototropisms are controlled by plant hormones called Auxin e.g. IAA
- For a plant to respond to light it needs a photoreceptor molecule that’s sensitive to light changes
Geotropism
How is it useful?
- Roots grow towards the pull of gravity
- Response anchors the roots
- Helps them to support the above ground structures
- Helps in the uptake of water and mineral salts
Chemotropism
How is it useful?
On a flower pollen grains grow down the style, attracted to chemicals so they can enter the ovary and fertilisation can take place
Thigmotropism
How is it useful?
- Shoots of ivy and other climbing plants wind round other plants or solid structures to gain support
- The tendrils of sweet peas wrap around objects they touch allowing the plant to gain support + climb
Give the basic summary of the communication system of flowering plants (3)
Sensor (receptor) → Plant hormone → Effector
Compare animal hormones and plant hormones
List 3 ways in which plant hormones move around the plant?
- Active transport
- Diffusion
- Mass flow in phloem and xylem vessels
Name the 5 plant hormones you need to know
Cytokines
Abscisic acid (ABA)
Auxins e.g. IAA - Indoleacetic Acid
Giberellines
Ethene
Plant hormones and their effects: (4)
Cytokines
- Promote cell division
- Delay leaf senescence
- Overcome apical dominance
- Promote cell expansion
Plant hormones and their effects: (3)
Abscisic acid (ABA)
- Inhibits seed germination + growth
- Causes stomatal closure when the plant is stressed by a shortage of water
- Stimulates cold protective responses
- e.g. production of antifreeze
Plant hormones and their effects: (3) + example
Auxins
E.g. IAA - Indoleacetic acid
- Promote cell elongation (taller!)
- Inhibit growth of side shoots
- Inhibit leaf abscission (leaf fall)
Plant hormones and their effects: (4)
Gibberellins
Promote:
- Seed germination
- Stem elgongation
- Side shoot formation
- Flowering
Plant hormones and their effects: (2)
Ethene
Promotes:
- Fruit rippening
- Leaf abscission
What are auxin and gibberellins described to be?
Give an example of each
Synergenic - They work together to have a really big effect
- e.g. Work together to make the plant grow really tall
They can also sometimes be called antagonistic - Oppose each other’s action
- e.g. Gibberellins stimulate growth of side shoots but auxine inhibit the growth of side shoots
What are plant meristems?
Plant meristems = Regions of undifferentiated cells capable of mitosis
- They’re the souce of new cells for plant growth
NOTE: They’re the stem cells equivalent in plants
What is apical dominance?
Apical dominance = The apical bud (tip of the plant) grows more than the side shoots
Auxin and apical dominance + how it happens
Apical dominance
- In many plants, side shoots don’t grow if the main shoot is growing, this is because the apical bud (shoot tip) is dominant over the lateral buds that can grow into side shoots.
- Energy is not used to grow side shoots so benefits plants
- Allows plant to grow vertically faster to reach more light + prevents too many side shoots from developing which would make the leaves shade each other
- If apical bud is cut off, low conc of auxin at tip, stimulates lateral buds to grow into side shoots
- E.g. when plant or hedge is pruned
Experimental evidence for the role of auxins in apical dominance
-
If apical bud (shoot tip) cut off and IAA is applied:
- IAA is an example of auxin
- Lateral buds don’t grow into side shoots
- IAA replaces the natural auxin and inhibits lateral bud growth
-
If growing shoot is turned upside down:
- Lateral buds grow into side shoots
- Auxin is unable to diffuse to the lateral buds against gravity
-
If a ring of auxin transport inhibitor is applied below the apical bud
- Lateral buds grow into side shoots
Gibberellins + stem elongation
- Most plants produce gibberellins to regulate stem elongation
- When genetically dwarf plants are treated with gibberellic acid (GA) - stems elongate considerably
Gibberellins + seed germination
When seeds absorbs water, the embryo releases gibberellins which trigger the production of amylase which can hydrolyse starch → glucose
Abscisic acid (ABA) + leaf abscission (leaf fall)
ABA is a plant hormone that stimulates the production of ethene - ethene stimulated leaf fall
Production of ABA triggers:
- Cells in the layer at the base of the petiole (leaf stalk) seperate from each other
- A protective layer of cells with wax in their walls forms on each side of the abscission layer to prevent infection + water loss
- Vascular tissue is sealed
- Leaf is broken off by a mechanical force e.g. wind
Commercial uses of Auxin (4)
- Sprayed on to fruits to inhibit abscission
- So that fruits can be harvested together when ripe
- Sprayed on to flowers before pollination
- To stimulate the development of seedless fruit
- Stem or leaf cuttings are dipped into auxin “rooting powder”
- Root powder stimulates root development
-
Synthetic auxins can be used as selective herbicides to kill broad-leaved weeds in a cereal field
- Weeds grow too rapidly to support themselves ∴ fall over and die
Commercial uses of Ethene (3)
-
Speeds up fruit ripening in apples, tomatoes and bananas
- Fruit is picked when unripe + transported when hard so less damage caused
- Promote fruit drop in cotton, cherry and walnut
-
Promote female development in cucumbers
- Reduces self-pollination which makes cucumbers bitter
Commercial uses of gibberellins (5)
-
Delays senescence (ageing) in citrus fruits
- Can be left longer before being picked ∴ extend their availability
- Stimulates stem elongation in bunches of grapes
- Each grape can grow larger
- Stimulated stem elongation in sugar cane
- More sugar can be stored
- Stimulates germination of barely seeds
- Amylase converts starch → maltose to be used in brewing
- Promotes seed production in young plants e.g. Conifers
