Module 5.1.5 Plant & Animal Responses Flashcards
What are the 4 types of plant growth & development?
Seed germination
Cell elongation
Apical dominance
Stem elongation
What are the 5 plant hormones?
Auxins (IAAs)
Gibberellins
Ethene
ABA
Cytokinins
What 2 processes is auxins involved in?
Cell elongation
Apical dominance
What happens in cell elongation?
Auxins are released by the meristem of the plant which bind to receptors on the cell surface membrane. H+ ions are then pumped into the cell through proton channels, decreasing the pH of the cell. This causes the cell to be more permeable to water so it becomes more flexible. The cell will end up absorbing more water, expanding the cell wall & causing cell elongation. The cell wall will then become turgid when the auxins are broken down as the cell matures
What is apical dominance?
Favouring apical shoot growth and inhibiting lateral shoot growth, caused by auxins
What is the apical shoot?
The main stem
What are the lateral shoots?
Shoots that branch off of the main stem
Why is apical dominance beneficial for the plant?
The shoots are better for competing for light since they are taller and get receive the maximum amount of light for photosynthesis & respiration
Why are the lateral shoots longer down the plant?
Auxins inhibit lateral shoot growth, as there is a smaller concentration of them down the plant, the lateral shoots are longer, makes a greater surface area for light to be absorbed
What is phototropism?
How a plant responds to light
What is geotropism?
How a plant responds to gravity
How are auxins involved in positive & negative phototropism?
Auxins molecules in a plant’s shoot move towards the shaded side which stimulates cell elongation. This causes the shaded side to grow at a faster rate than the rest of the plant, and as a result, bend towards the light. This ensures can get the maximum amount of sunlight it can, to increase respiration and produce more glucose. This is positive phototropism. The roots, however, will bend away from the light as they do not photosynthesise and have no stimulus, in a process known as negative phototropism.
How are auxins involved in positive & negative geotropism?
The plastids in the root cap of the roots will settle on the bottom side of the cell. This stimulates auxins to be produced which will cause cell elongation, causing the roots to bend towards the ground, due to gravity, as there is most likely water and nutrients there. This is called positive geotropism. However, the shoots will exhibit negative geotropism, as they will grow away from the gravitational pull of the ground, as there is most likely little sunlight there. This is known as negative geotropism
What 2 processes does auxins inhibit?
Fruit ripening
Abscission
What is abscission?
When leaves fall off the trees e.g. in autumn season
What processes does gibberellins help?
Stem elongation
Germination of cells
Stimulates pollen tube growth in fertilisation
How do gibberellins aid in seed germination?
Water is absorbed which stimulates seed germination. Due to the water uptake, the embryo synthesises gibberellin production. The aluerone layer then synthesises amylase in response to gibberellin production. Amylase then mobilises energy reserves and hydrolyses starch into maltose. Maltose is then hydrolysed into glucose which is respired to release ATP
How do gibberellins play a role in stem elongation?
Gibberellins increase the internode length so plants can get more sunlight -> maximum photosynthesis can occur
How are gibberellins linked to genes regarding height of the plant?
Some plants’ height is partially controlled by the Le gene. The dominant allele Le produces tall plants if present whereas the recessive allele le produces shorter plants if present in a homozygous plant. This gene regulates enzyme production that is involved in a pathway that for active gibberellin. Homozygous recessive plant end up being dwarves because no active gibberellin is formed so plants are unable to grow tall however, farmers may apply active gibberellin to stimulate growth in shorter plants
How may farmers have a role in preventing stem elongation?
Farmers may reduce the height of a plant because the stem isnt always eaten so it is useless for them. They may also reduce the stem to prevent crop damage in bad weather as taller plants are more prone to damage. Reducing the stem also reduces waste production
What processes does Ethene promote in a plant?
Abscission & fruit ripening
What type of relationship do auxins & Ethene have?
An antagonistic relationship -> they both oppose each other
What type of relationship do auxins & gibberellins have?
A synergic relationship -> both hormones work together
What does ABA (abscisic acid) do in a plant?
Maintains the dormancy of seeds & buds
Stimulates protective responses under stress -> (e.g. if its too cold, ABA may stimulate antifreeze production)
What type of relationship does ABA & gibberellins have?
An antagonistic relationship
What does cytokinins do in a plant?
Promotes cytokinesis & is produced in cells that are actively growing.
Reduces plant senescence & promotes lateral growth
What is Plant senescence?
Gradual ageing of a plant
How are cytokinins beneficial for plant growth?
Cytokinins increases more mitosis which makes more cells which increases plant growth
What type of relationship does cytokinins & auxins have?
A synergistic relationship
What are some commercial use of auxins?
Sprayed on developing fruits to prevent abscission & fruit ripening
Sprayed onto flowers to initiate fruit growth without fertilisation (parthenocarpy -> promotes growth of seedless fruits)
Applied to cut end of a shoot to stimulate root production
Synthetic auxins -> used as selective herbicides
What are the commercial use of gibberellins?
Sprayed onto fruit crops to promote growth
Sprayed onto citrus trees -> allows fruit to stay on the trees longer
Sprayed onto sugar cane to increase the yield of sucrose
Brewing -> GA sprayed onto barley seeds to make them germinate, amylase is produced, starch is broken down into maltose, the action of yeast on the maltose produces alcohol
What are the commercial uses of cytokinins?
Delay leaf senescence -> sprayed to prevent leafs from yellowing
Can be used in tissue culture to mass produce plants
Can break dormancy in some seeds
What is some evidence of plant hormones?
Gene manipulation -> mutate genes to make a hormone
Disrupt production pathway (stop hormone production & see results)
Cut the shoot tip (remove meristem -> remove auxins & observe the changes, apply hormones externally & see the further changes (best for auxins))
What is a Nastic movement & why does it occur?
a rapid, reversible & non-directional response to stimuli (e.g. temp.)
due to changes in turgidity/growth in the plant (K+ ion conc.)
How does a nastic movement occur?
Electrical potentials across cell membranes signal plant @ base of the mimosa leaf to rapidly lose water -> leaf droops
What is an example of a plant that does nastic movements?
Mimosa pudica
Venus Flytrap
Who are the four scientists that did experiments on plant hormones?
Darwin
Boysen-Jensen
Paal
Went
Explain Darwin’s experiment about plant hormones?
He cut tip of a coleoptile (seedling) and placed an opaque tip on top & saw no curvature of the seedling towards the light
What were the conclusions of Darwin’s experiments?
Growth stimulus is produced in the tip & transmitted to the zone of elongation
Cells on the shaded side elongate more than the cells on the other side
Explain Boysen-Jensen’s experiment about plant hormones?
A sheet of mica was placed into the shaded side of the coleoptile & saw no curvature, & place a sheet on the light side (saw a curvature), repeated this with gelatine (removed seed tip) & saw a normal phototropic curvature.
What were the conclusions of Boysen-Jensen’s experiment?
Materials which aren’t permeable to water can stop curvature response in some circumstances, materials that are don’t interfere with the curvature response
What was Paal’s experiment about plant hormones?
He removed the plant tip & replaced it on 1 side of the coleoptile stump, found the growth curvature occurs without a light stimulus
What were the conclusions of Paal’s experiment?
The growth substance was chemical in nature & had diffused from the tip which stimulated growth
What was Went’s experiment on plant hormones?
He placed coleoptile tips on gelatine & then discarded them. Gelatine was cut up into smaller blocks & placed on 1 side of the coleoptile stump. The coleoptile bends in total darkness & the angle can be measured
What were the conclusions of Went’s experiment?
The angle of curvature is related to the number of tips used
Number of tips used is related to auxin concentration in the gelatine/agar
The curvature response is due to a chemical which moves from the tip & helps cell elongation
Explain how ABA works on the plant in times of stress
- Plant detects change in environment e.g. lack of water, and secretes ABA
- ABA binds to receptors -> inhibits proton pumps
- ABA binding stops proton pumps, preventing H+ from leaving guard cells
- Calcium ions (Ca2+) enter guard cells
- Calcium ions -> act as second messengers:
- Negatively charged ions and potassium (K+) ions leave the guard cells
- Potassium ions prevented from entering
- Water potential in guard cells increases
- Water leaves -> osmosis
- Guard cells become flaccid -> closing stomata
What 3 different experiments can you perform to test for auxins in a plant & what is observed in each one?
Remove the tips of the apical stem: apical stem no longer grows & theres an increase in lateral growth
The tips are covered => auxin moves to all parts of the stem so all parts start to grow
The tips are lit form one side -> positive phototropism
What is a tropism?
The movement/growth away or towards a stimulus
What is a positive tropism?
movement/growth towards stimulus
What is a negative tropism?
movement/growth away from stimulus
Why are tropisms important for the plant?
To increase & maximise the survival of a plant -> reproduction
What are the circadian rhythms of a plant?
It determines when buds form into flowers & close for the night (achieved by light sensors & hormone levels)
What is phenology?
When most plants grow in the summer, but lay dormant/die in the winter
Why is it important that plants can sense the presence, direction, amount, angle & duration of light?
It can determine circadian rhythms or the phenology of the plant
What is hydrotropism?
Growth related to water concentration
What is positive & negative hydrotropism?
Positive -> root growth towards water
Plant roots can drown in oversaturated soil -> negative: root growth away from water
What is thigmotropism?
Growth related to physical touch
What is positive & negative thigmotropism?
Positive -> growth towards an object (plant wrapping round an object)
Negative -> roots grow away from objects in the soil
What is chemotropism?
Growth related to chemical concentration
What is thermotropism?
Growth related to temperature
What are the two different defences that plants have towards herbivory?
Physical
Chemical
What are some of the physical defences that plants have?
Thorns, spikes, tough bark, tiny hairs
What are some of the chemical defences that plants have?
Tannins
Alkaloids
Terpenoids
Pheromones
Volatile Organic Compounds
How do tannins defer insects?
They have a bitter taste & are toxic to insects
How do alkaloids defer predators?
They have a bitter taste & are poisonous to animals (affect the metabolism)
What are some examples of alkaloids?
Caffeine
Nicotine
How do terpenoids defer predators?
They are toxic to insects & fungi (act as neurotoxin/repellent)
What are pheromones?
Chemicals released out of an organism that affect the social behaviour of other members of the same species
What are pheromones?
Chemicals released out of an organism that affect the social behaviour of other members of the same species
How do pheromones help other plants protect from predators?
When a plant is being attacked, they release pheromones to other neighbouring plants of the same species to make callose
What are volatile organic compounds (VOCs)?
They are similar to pheromones but affect other species
How do VOCs protect plants?
They can attract predators of the pest that is attacking them
What happens when a plants experiences changes in seasons?
Abscission
Explain the process of abscission
Photochromes in the plant detect falling light levels. Auxin production from the meristems is decreased as a response. This causes the leaves to respond by increasing ethene production that diffuses down the base of the leaf stalk. These cells are sensitive to ethene, so the ethene activates genes in the cells abscission zone to produce digestive enzymes (cellulase). Cellulase then digests the cell wall of the separation zone of the plant. This causes the vascular bundles to seal of and fatty deposits to occur. Finally, secondary factors such as the wind help the leaf fall off the plant.
What do photochromes do in a plant?
They control seed germination, flowering & abscission
Why is abscission beneficial for a plant?
It reduces the energy needed to maintain the leaves in the winter
The fallen leaves insulate the roots so they dont end up freezing
The rotten leaves provide minerals for the soil
What does a plant do when there is water stress?
Closes the stomata
Describe how a plant responds to lack of water
The root hair cells detect low water levels in the soil, so they start to produce ABA which is transported up the stem towards the rest of the plant & leaves. The ABA binds to complementary receptors on the surface of guard cells. This causes a conformational change which opens ion channels & ions diffuse out of the plant. Water then leaves the guard cells by osmosis, which cause the water potential to become lower outside than inside the plant. This makes the guard cells become flaccid, so they respond by closing
Describe how a plant responds to lack of water
The root hair cells detect low water levels in the soil, so they start to produce ABA which is transported up the stem towards the rest of the plant & leaves. The ABA binds to complementary receptors on the surface of guard cells. This causes a conformational change which opens ion channels & ions diffuse out of the plant. Water then leaves the guard cells by osmosis, which cause the water potential to become lower outside than inside the plant. This makes the guard cells become flaccid, so they respond by closing
