Module 5.4 - Plant Responses and Hormones Flashcards
How do plants increase their chances of survival, behaviour wise? (3)
- They grown in the direction of light to maximise light absorption for photosynthesis
- Their roots and shoots grow in accordance to gravity
- Climbing plants have a sense of touch to help them climb and reach sunlight
How do plants protect themselves from herbivory? (2)
- Chemical defences
- Physical defence
Examples of chemical defences? (3)
- Alkaloids
- Tannins
- Pheromones
Herbivores? (1)
- Animals that eat plants
Alkaloids? (2)
- Bitter tastes, noxious smells or poisonous characteristics
- Deter or kill herbivores
Alkaloids nicotine? (3)
- Tobacco plants
- Poisonous to many insects
- Used in response to tissue damage
Tannins? (3)
- Taste bitter
- Can bind to proteins in the gut making plant hard to digest
- Deter animals from eating the plant
Pheromones? (2)
- Signalling chemicals released into the air in response to herbivore grazing.
- Cause nearby plants to start making chemical defences
Example of a pheromone in use? (3)
- When corn plants are being eaten by caterpillars
- They produce pheromones which attract parasitic wasps
- These wasps then lay their eggs in the caterpillars which eventually kills them
Example of a physical defence? (4)
- Plants are able to fold up in response to being touched
- If a single leaflet of the plant Mimosa pudica is touched, a signal spreads through the whole leaf, causing it to quickly fold up
- This may knock off any small insects feeding on the plant
- It may also scare off animals trying to eat it
Abiotic stress? (2)
- Anything harmful that’s natural but non-living like a drought
- Some plants respond to extreme cold by producing their own form of antifreeze
Antifreeze? (2)
- Carrots produce antifreeze proteins at low temperatures
- The proteins bind to ice crystals and lower the temperature that water freezes at which stops more ice crystals from growing
Tropism? (2)
- A tropism is the response of a plant to a directional stimulus
- Plants respond to stimuli by regulating their growth
Positive tropism? (1)
- Growth towards the stimulus
Negative tropism? (1)
- Growth away from the stimulus
Phototropism? (3)
- Growth of a plant in response to light
- Shoots are positively phototropic and grow towards light
- Roots are negatively phototropic and grow away from light
Geotropism? (3)
- Growth of a plant in response to gravity
- Shoots are negatively geotropic and grow upwards
- Roots are positively geotropic and grow downwards
Hydrotropism? (2)
- Plant growth in response to water
- Roots are positively hydrotropic
Thermotropism? (1)
- Plant growth in response to temperature
Thigmotropism? (1)
- Plant growth in response to contact with an object
How do plants respond to stimuli? (1)
- By using growth hormones
Growth hormones? (3)
- Chemicals that speed up or slow down plant growth
- Produced in the growing regions of the plant and they move to where they’re needed in the other parts of the plant
- Also called growth substances
Types of growth hormones? (2)
- Gibberellin
- Auxins
Gibberellin? (1)
- Gibberellin stimulates seed germination, stem elongation, side shoot formation and flowering
Auxins? (2)
- Stimulate the growth of shoots by cell elongation
- High concentrations of auxins inhibit growth in roots
Elongation? (1)
- Cell walls become loose and stretchy, so the cells get longer
Indoleacetic Acid (IAA)? (5)
- Auxin produced in the tips of shoots in flowering plants
- Stimulates cell elongation
- IAA is moved around the plant to control tropisms
- This results in different parts of the plants having different amounts of IAA
- The uneven distribution of IAA means there’s uneven growth of the plant
What are the uneven growths of a plant caused by uneven distribution of IAA? (2)
- Phototropism: IAA moves to the more shaded parts of the shoots and roots, so there’s uneven growth
- Geotropism: IAA moves to the underside of shoots and roots, so there’s uneven growth
How do IAA move across a plant? (2)
- Diffusion and active transport over short distances
- Via the phloem over long distances
What are auxins involved in? (2)
- Apical Dominance
- The growth of the apical bud is dominant over the lateral buds
Apical bud? (1)
- The shoot tip at the top of a flowering plant
Auxins and apical buds? (2)
- Auxins stimulate growth of apical bud
- Auxins inhibit growth of side shoots from lateral buds
Why is apical dominance important? (3)
- Prevents side shoots from growing
- This saves energy & prevents side shoots from same plant competing with the shoot tip for light
- Allows a plant in an area where there are loads of other plants to grow tall very fast to reach the sunlight
What happens if you remove the apical bud? (2)
- The plant won’t produce auxins
- Side shoots will start growing by cell division and cell elongation
How can you demonstrate that apical dominance is controlled by auxin? (2)
- Replace the tip with a source of auxin
- Side shoot development is inhibited
What happens to the concentration of auxin as they move away from the apical bud? (2)
- At the bottom of the plant auxins become less concentrated
- Side shoots will start to grow
Gibberellins? (3)
- Produced in young leaves and in seeds
- Stimulate seed germination, stem elongation, side shoot formation and flowering
- Don’t inhibit plant growth in any way
Role of gibberellins in stem elongation? (2)
- Help plants to grow tall
- If dwarf variety of plant is treated with gibberellins then it will grow to the height of tall variety
How do gibberellins stimulate seed germination? (2)
- By triggering the breakdown of starch into glucose in the seed
- The plant embryo in the seed then use the glucose to begin respiring and release the energy it needs to grow
How can seed germination be prevented? (1)
- Gibberellins are inhibited by the hormone abscisic acid
Auxins and gibberellins are synergistic? (2)
- They work together to have a really big effect
- Auxins and gibberellins work together to help plants grow tall
Auxins and gibberellins are antagonistic? (2)
- They oppose each other’s actions
- Gibberellins stimulate the growth of side shoots but auxins inhibit the growth of side shoots
Deciduous plants? (1)
- Plants that lose their leaves in winter
Why is losing leaves helpful for deciduous plants? (3)
- Helps plants to conserve water during the cold part of the year
- Difficult to absorb water from frozen soil
- There’s less light for photosynthesis
Abscission? (2)
- Leaf loss
- Triggered by the shortening day length in autumn
Role of auxins in abscission? (3)
- Inhibit leaf loss
- Auxins are produced by young leaves
- As the leaf gets older, less auxin is produced, leading to leaf loss
Role of ethene in abscission? (6)
- Stimulates leaf loss
- Ethene is produced by ageing leaves
- As the leaves get older, more ethene is produced
- Abscission layer develops at the bottom of the leaf stalk
- Ethene stimulates cells in the abscission layer to expand
- This breaks the cell walls and causing the leaf to fall off
How do plants reduce water lost through transpiration? (1)
- Close their stomata using guard cells
Role of guard cells in reducing water loss? (3)
- Guard cells found on either side of a stomatal pore
- When the guard cells are full of water, they are turgid and the pore is open
- When the guard cells lose water, they are flaccid and the pore closed
What hormone is responsible for making the pore close? (1)
- Abscisic acid (ABA) triggers stomatal closure
How does ABA work? (7)
- Binds to receptors on the guard cell membranes
- Causes ion channels to open
- Ca2+ enters cytosol from vacuole
- Increased concentration of Ca2+ in cytosol causes other ion channels to open
- This allows ions to leave the guard cells & raises the water potential of the cells
- Water then leaves the guard cells by osmosis
- Guard cells become flaccid and stomata closes
Ethene’s use in the fruit industry? (2)
- Stimulates enzymes that breaks down cell walls, chlorophyll and convert starch into sugars
- Makes the fruit soft, ripe and ready to eat
Auxins’ use as a weed killer (herbicides)? (2)
- Make weeds produce long stems instead of lots of leaves
- Make weeds grow too fast - they can’t get enough water or nutrients so they die
Auxins’ use as a rooting hormone? (3)
- Auxins make a cutting grow roots
- Cutting can be planted and grown into a new plant
- Cuttings can be taken from one original plant and treated with rooting hormones so lots of the same plant can be grown quickly and cheaply from just one plant
