Plant responses and hormones Flashcards
What are the three ways plants respond to changes in their environment?
• grow towards light to maximise light absorption for photosynthesis
• sense gravity so roots and shoots grow in the right direction
• climbing plants have a sense of touch so they can climb to find sunlight
What are the two toxic chemical defences to herbivory?
1) Alkaloids - deter or kill herbivores
2) Tannins - deter herbivores
What are two examples of pheromones that plants release in response to herbivory?
• alarm pheromones alert nearby plants to produce chemicals such as tannins
• Pheromones which can attract parasitic wasps to kill caterpillars by laying eggs in them
What is one example of a plants physical response to being touched?
Mimosas leaves quickly fold up when it is touched to protect against herbivory and knock off small insects
What is a tropism?
The response of a plant to a stimulus coming from a particular direction
What is positive tropism?
Growing towards the stimulus
What is negative tropism?
Growing away from the stimulus
What is phototropism?
The growth of a plant in response to light
In regards to phototropism, what are shoots and roots?
Shoots are positively phototropic and roots are negatively phototropic
What is geotropism?
The growth of a plant in response to gravity
In regards to geotropism, what are shoots and roots?
Shoots are negatively geotrophic and roots are positively geotrophic
What is hydrotropism? Give an example of a positively hydrotrophic plant part.
Plant growth in response to water - roots are positively hydrotrophic
What is thermotropism?
plant growth in response to temperature
What is thigmotropism?
Plant growth in response to contact with an object
What a growth hormones in plants?
Chemicals that speed up or slow down plant growth
Where are growth hormones produced in plants?
Growing regions - Shoot tips and leaves
What does gibberellin do?
Stimulates seed germination, stem elongation, side shoot formation, and flowering
What do auxins do?
Stimulate the growth of shoots by cell elongation
What is the problem with a high concentration of auxins?
It will inhibit growth in the roots
Where does IAA move in the shoots and roots in phototropism?
In the shoots, it moves to the shaded side and in the roots, it moves away from the light
Where does IAA move in the shoots and roots in geotropism?
In the shoots, it will move to the shaded side so the shoot can grow upwards and in the roots it will continue to grow down
What would be the result of placing a cap on a shoot?
It will not move towards the light, and it will grow upwards
What would be the result of placing foil around a shoot, but not on the tip?
The tip would bend towards the light, but not the rest of the shoot
What is apical dominance?
The prevention of the growth of sides shoots from lateral buds, so the shoot tip continues to grow
How does inhibiting side growth lead to apical dominance?
Energy isn’t used up growing sides shoots, so the plant can grow tall very fast
Which hormone, auxins, or gibberellins, can inhibit plant growth?
Auxins
What are gibberellins inhibited by and why?
Abscisic acid to prevent seed germination
What does auxins and the gibberellins being synergistic mean? Give an example.
They work together to have a really big effect - Plant growing tall
What does auxins and gibberellins being antagonistic mean? Given an example.
They oppose each other’s actions - gibberellins stimulate side shoot growth, but auxins inhibit it
What are deciduous plants?
Plants that lose their leaves in the winter
What does plants losing their leaves in the winter do?
Helps them to conserve water during cold parts of the year as soil may be frozen and there is less light for photosynthesis
What is leaf length triggered by?
The shortening of the days in the autumn
How is leaf loss controlled?
Auxins inhibit leaf loss - less auxin produced = leaf loss
Ethene stimulates leaf loss - stimulates cells in abscission layer to expand and break the cells walls = leaf falls off
Why do plants need to close their stomata?
To reduce water loss through transpiration
What makes guard cells open and close stomata?
Guard cells full of water - turgid - pore is open
Guard cells lose water - flaccid- pore is closed
What does abscisic acid do to somata?
Triggers their closure by binding to receptors and allowing calcium ions to enter and cause other channels to open, raising the water potential so water leaves via osmosis
How is ethene used commercially?
Ethene ripens fruit by breaking down cells walls so bananas are transported before ripe and exposed to Ethene on arrival
What are the two ways auxins are used commercially?
1) used in selective weed killers to make weeds grow too fast - can’t get enough water and nutrients
2) used as rooting hormones so cuttings can be cut and grown quickly and cheaply
