5.5 Plant Resposes Flashcards
What do plants respond to?
external stimulus’ that are biotic (living) or abiotic (non living)
Do plants have sense organs?
No, instead they’re able to detect changes then produce relevant changes as a response.
Physical defences of plants
Cellulose cell wall, waxy cuticle, guard cells, callose
Cellulose cell wall
Physical barrier.
Lignin thickening of cell walls - waterproof and indigestible
Waxy cuticle
Prevents water from collecting on the surface (pathogens need water)
Guard cells
Can close the stomata
Callose
Large polysaccharide that is deposited in sieve tubes at the end of the growing season. Blocks the flow so that pathogens can’t spread.
Chemical signals of plants when they’re in danger
Tannins, alkaloids, pheromones
Tannins
chemical released in leaves that make the leaves taste bad and they’re toxic to microbes so it prevents the entry of pathogens.
Alkaloids
Chemical released in leaves that make the leaves taste bitter
Poison and affect the metabolism of insects which ingest them.
Pheromones
chemicals released by one plant that tells the nearby plants if there’s danger or limiting resources etc
Directional responses
Aka tropism
grows towards or away from that stimulus
Types of tropism
Phototropism
Geotropism
Chemotropism
Thigmotropism
Phototropism
plant grows towards the light if positively and grows away from light if negatively phototropic
Geotropism
roots of the plant grows towards gravity if positively and grows away from gravity if negatively geotropic
Chemotropism
plant grows towards the chemicals if positively and grows away from chemicals if negatively chemotropic
Chemotropism example
fertilisation in a plant, the embryonic sac of the plant releases chemical which promotes the growth of the pollen towards it
Thigmotropism + example
grows towards support e.g. shoots wind around other plants or solid structures to gain support
Another name for non directional responses
Nastic responses
Example of nastic response
some plants e.g. mimosa pudica have leaves and when you touch them the leaves close = thigmonastic response = caused by local bio electrical signals (not plant hormones)
Do plants have glands
No
Neurotoxin
a chemical that interferes with the ability of neurones to conduct nerve impulses
Cytokinins effects
Promote cell division
Delay leaf senescence
Overcome apical dominance
Promote cell expansion
Promote growth of side shoots
Abscisic acid effects
Inhibits seed germination and growth
Causes stomatal closure when the plant is stressed by low water availability
Auxins
e.g. IAA (indole-3-acetic acid) effects
Promote cell elongation
Inhibit growth of side-shoots
Inhibit leaf abscission (leaf fall)
Gibberellins effects
Promote seed germination and stem elongation
Prevents leaf abscission
Promotoe fruit development
Ethene effects
Promotes fruit ripening
Senescence
Aging
Apical dominance
when the apical bud keeps on growing upwards
What happens to the lateral buds when there’s less auxin
They grow
When do apical buds grow?
When there’s high to normal auxin levels
How to make the plant grow sideways
Apical bud can be cut = auxin from the apical bud prevented lateral buds from growing = when shoot is cut, auxin levels drop and the buds grow.
Growth from lateral buds
Grows sideways
Where are the apical buds located
At the top of the plant
What do auxins promote
Apical dominance = The auxins that are produced at the growing tip at the apex (i.e. the top) of a plant stem cause the stem to grow upwards and also stop lateral (side) buds from growing
What does cytokinins do the opposite of?
Auxins
What does Abscisic acid inhibit
Seed germination
Where is auxin produced
In the apical bud
Abscisic acid in terms of growth
high auxin keeps abscisic acid levels high. When auxin is removed, abscisic acid levels drop and buds start to grow.
Cytokinins in terms of growth
high levels of auxin cause cytokinins to move to the shoot apex. When apex is removed, cytokinin spreads evenly around the plant and causes bud growth.
Similarity and difference in the way humans and plants secrete hormones
- both work in same way in terms of complementary receptors
- humans = endocrine glands and
plants = Cells in different tissues release the hormone = most are peptide hormones which is why they look for a target receptor
Difference in way hormone reaches destination in humans and plants
Humans = travels through blood via diffusion
Plants = active transport, mass flow, diffusion
How did scientists find out that gibberellins promote growth?
- found a dwarf plant and a normal plant and compared the genes and realised one had the genes to make gibberellin and one didn’t
- The one that didn’t have the genes when given gibberelinic acid it grew taller which shows that gibberelinic acid is the cause for stem elongation
- The allele was responsible for producing an enzyme that converts GA20 to GA1
- If you find a way to synthetically add that enzyme you can recreate that condition
How do gibberellins cause seed germination
- When a seed absorbs water the embryo releases gibberellin which allows the production of the enzyme amylase (breaks down starch into glucose)
- Glucose acts as a substrate for respiration and it can be used for protein synthesis = enables growth
Germination
mobilisation of food reserve and promotion of growth
Dormancy
stage in which a seed will not germinate.
What is needed to produce gibberellins
Abiotic factors e.g. water, temperature and light stimulates seeds to produce gibberellins
What causes seeds to germinate?
Gibberellins will allow seeds to come out of dormancy
What causes seeds to be dormant
Abscisic acid helps to maintain seed dormancy by inhibiting the production of amylase
Do auxins stimulate growth in early germination
Yes but high concentration will inhibit germination
Auxin experiment control
when there’s light the plant is growing towards the light
Auxin experiment when the tip was cut
No directional growth
Auxin experiment When tip was covered by an opaque cap
No directional growth
Auxin experiment When there’s a transparent cap
Growing towards light
Auxin experiment When bottom of stem was covered by opaque shield
Plant was still growing towards the light = base doesn’t have something that promotes phototropism
Auxin experiment When tip was separated by gelatin block (permeable)
Phototropism still occurs
Auxin experiment When tip is separated by mica block (impermeable)
No directional growth = movement was important
Conclusion of auxin experiment
- Something produced at the tip is involved in phototropism
- if you shine light to auxin it always moves towards the shaded side + promotes growth and other side doesn’t grow as much so it bends towards the light
How does auxin promote the stretchiness of the cell wall
- Promotes active transport of hydrogen ions from the plasma membrane into the cell wall
- This lowers the pH of the cell wall where it becomes the optimum pH for the enzyme expansins to work
- Expansin works by breaking the bonds in cellulose
- Hydrogen ions disrupt the hydrogen bonds within cellulose so the cell wall becomes less rigid and takes on more water = stretchy + can expand
What’s responsible for moving auxins to the shaded side
Phototropin 1 and 2 (enzymes)
Auxin’s role in geotropism in the roots
- In the roots auxin accumulates on the lower side + inhibits cell elongation so the upper side starts growing more + bends downwards
Auxin concentration to promote growth in the roots and shoots
Low to promote growth in roots and high in shoots
Creating serial dilutions
- start with a stock solution and take 1 cm^3 and add 9 cm^3 of water which makes it 1/10 diluted
- Then take 1cm^3 this solution and add 9cm^3 water to this which makes it 1/100 diluted and repeat
Auxin as rooting powder
before planting it encourages root growth
IRL uses of auxins
As rooting powder
Promotes growth of seedless fruit
Used as a herbicide
Auxin as a herbicide
causes weeds to grow so fast that they can’t handle it + die
IRL use of cytokinins
- Delay aging and prevent the yellowing of lettuce leaves
Gibberellins IRL uses
- delay aging if citrus fruits = can be in shops for longer
- Can work with cytokinins to improve the shape of apples
- Makes grapes bigger + less compact
- Can be used in brewing and sugar production
- sugar production
- plant breeding
Gibberellins in brewing and sugar production
it produces amylase that breaks down starch into maltose
Promotes growth of sugar canes
Gibberellins in plant breeding
speed up process of seed formation + use this knowledge to create giberrelin inhibitors to keep flowers short or delay germination
Irl uses of ethene
- promotes ripening of apples, tomatoes and citrus fruit
- Promotes fruit drop in cotton, cherry and walnut
- Promotes female sex expression in cucumbers
- Promote lateral growth in some plants
Ethene in promoting female sec expression in cucumbers
more likely to be pollinated + decreases the chance of self pollination
How do plants respond to drought
- by shutting stomata or dropping their leaves
- When there’s low water availability for the plant the hormone Abscisic acid is released + promotes Stomatal closure.
How do plants respond to freezing
- by producing an antifreeze chemical in their cells that decreases the formation of ice crystals that can destroy plant cells if allowed to form within them
A
B
Why does light increase stem and root growth
More carbs produced during photosynthesis
Light may trigger growth and germination
Phototropism in stems and roots
Positive in stems, negative in roots
In the investigation, the students controlled light, temperature and mineral concentration.
State one other factor that the students should have controlled in this investigation.
When looking at phototropism
Water Availability, soil pH, size of plant
Amyloplasts are heavy
Binding of amyloplasts with ER releases Ca2+
Ca2+ stimulates growth
Root grows to side of Ca2+ release
Auxin and gibberellins given to trees and effects observed:
- shorter roots
- grew taller
- all began to grow within two days of eachother
- had fewer and shorter side branches
- retained their fruit and leaves for longer
Explain each observation
Why’s gibberellins classed as a plant hormone
- chemical messenger produced in one part of plant but has effects in another part
- affects activity of target cells
- long lasting effects
1 = light intensity = diff light intensities could lead to variation in phototropism = use same distance from lamp every time
2 = no repeats = can’t calculate mean/do statistical tests = repeat at least twice
