Plant hormones Flashcards
What is a hydrotropism?
Plant growth in reponse to water. Roots are positively hydrophobic.
Why do plants respond to the changes in environment?
Increases their chances of survival e.g.
- they sense the direction of light and grow towards it ro maximise photosynthesis
- they sense gravity, so their roots and shoots grow in the right directions
- climbing plants have a sense of touch, so they can find things to climb and reach the sunlight
What is herbivory?
Being eaten by animals (including insects)
What do plants use against herbivory?
Chemical defences. For example they can produce toxic chemicals in response to being eaten.
What are examples of chemical plants release to prevent being eaten by herbivory?
Alkaloids and tannins
What do alkaloids do?
Chemicals with bitter tastes, noxious smells or poisonous characteristics that deter or kill herbivores, e.g. tobacco plants produce the alkaloid nicotine bin response to tissue damage. Nicotine is highly poisonous to many insects.
What do tannins do?
Taste bitter, and in some herbivores (e.g. cattle and sheep) they can bind proteins in the gut, making the plant hard to digest. Both of these things deter animals from eating the plant
What are pheromones and why do plants release them?
Release them in response to herbivory
Signalling chemicals that produce a response to other organisms
What are examples of pheromones?
- Some plants release alarm pheromones into the air in response to herbivore grazing. This can cause nearby plants that detect these chemicals to start making chemical defences such as tannins.
- When corn plants are being eaten by caterpillars, they can produce pheromones which attract parasitic wasps. These wasps then lay their eggs in caterpillars, which eventually kills them.
What can some plants do in response to being touched?
Fold up
What is an example of plants that are able to fold up?
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 helps protect the plant against herbivory by:
- Helps to knock small insects off that we’re feeding on the plant
- Helps to scare animals trying to eat it
What is abiotic stress?
Anything harmful that’s natural but non-living, like a drought
Example of how plants responding to abiotic stress makes them more likely to survive?
Carrots produce their own antifreeze proteins at low temperatures- the proteins bind to ice crystals and lower the temperature that water freezes at, stopping more ice crystals from growing.
What is a tropism?
The response of a plant to a directional stimulus ( a stimulus coming from a particular direction).
Plants respond to stimuli by regulating their growth.
What is a positive tropism?
Growth towards the stimulus
What is a negative tropism?
Growth away from the stimulus
What is phototropism?
The growth of the plant in response to light
What part of the plant is positively phototropic and what does this mean?
The shoots, means they grow towards the light
What part of the plant is negatively phototropic and what does this mean?
The roots and it means they grow away from the light
What is geotropism?
The growth of the plant in response to gravity
What part of the plant is positively geotropic and what does this mean?
The roots and it means they grow downwards
What part of the plant is negatively geotropic and what does this mean?
The shoots, means they grow upwards
What is hydrotropism?
Plant growth in response to water
What part of the plant is positively hydrotropic?
Roots
What is thermotropism?
Plant growth in response to temperature
What is thigmotropism?
Plant growth in response to contact with an object
What are growth hormones?
Chemicals that speed up or slow down plant growth
What is gibberellin and what does it do?
A growth hormone
Stimulates seed germination, stem elongation, side root formation and flowering
What is auxin and what does it do?
A growth hormone
Stimulates the growth of shoots by cell elongation- where the cell walls become loose and stretchy, so the cells get longer
What can high concentrations of auxins cause?
Can inhibit the growth in roots
