Plant Responses Flashcards
What is Phototropism
Growth towards light
What is Thigmotropism
Growth in response to touch stimulus
What is geotropism
Growth in response to gravity
What is Hydrotropism
Growth towards water
Why do plants respond to their environment
To avoid abiotic stress
Maximise photosynthesis
Obtain more resources
Avoid grazing/disease
Ensure germination is done in suitable conditions
What are the chemical defences of plants
Tannins - toxic to microbes, taste bitter to animals
Alkaloids - taste bitter
Pheromones - signalling molecules released in response to grazing to alert other plants
What is a tropism
Directional growth in response to external stimuli
What are Nastic responses
Non-directional responses to external stimuli
What is photoperiodism
Responses to day length or photoperiod
What controls plant responses
Hormones produced in small quantities in a variety of tissues
What is the role of auxins
Inhibit leaf abscission and lateral growth
promote cell elongation
Produced at apices and transported to zone of elongation
What is the role of gibberellins
Promote seed germination and stem growth
What is the role of abscisic acid
Stomatal closure
Inhibits seed germination and growth
What is the role of ethene
Promotes fruit ripening
What is the role of cytokinins
promotes cell division
What causes phototropism
Auxins move towards shaded area of shoot and promote those cells to elongate. This causes the shoot to be towards the light
How do auxins elongate cells
It increases the stretchiness of the cell wall by using a hydrogen pump to cause H+ to accumulate in cell wall
This causes a lower pH there and disrupts H+ bonds within cellulose, causing the wall to be less rigid
This means the cell can expand as it takes o water
Where does negative phototropism occur
In roots
How does negative phototropism occur
Auxins transported to shaded side, causing elongation to be inhibited there so that the root bends away from light
What is abscission
leaf or fruit fall from the plant
How is abscission caused
Auxin production decreases and ethene production increases
This causes production of cellulase - cell wall digested in abscission zone
Petiole separates from stem
What is apical dominance
When auxins from apex inhibit lateral growth
How do gibberellins promote seed germination
Seeds absorb water and embryo releases gibberellin
Gibberellin causes amylase to produce
Amylase breaks down starch into glucose
Glucose used for respiration so embryo can grow
How does abscisic acid cause stomatal closure
ABA binds to receptors on guard cell membranes
This causes K+ ions to leave the cell and the water potential of the cell increases
Water leaves guard cell by osmosis and stomata closes
