Plant Responses Flashcards
How do plants increase their survival chances against herbivores?
They protect themselves using toxic chemicals, communication with other plants and physical responses
How do some plants deter pests?
Plants produce alkaloids and tannins in their leaves that deter pests
Alkaloids are found in nicotine and taste bitter and are poisonous
Tannins taste bitter and interfere with digestion
What are alarm pheromones?
plants release alarm pheromones to warn other plants of herbivores
This stimulates them to synthesise toxic chemicals.
Other pheromones attract predators to eat pests
What does the mimosa pudica do in response to touch?
It folds up its leaves in response to touch
This helps to knock off or scare any insects
How do plants respond to cold temperatures?
Plants synthesise antifreeze proteins that prevent ice crystals from forming
What are tropisms?
They are a response by an organism in a particular direction caused by external stimulus
Plants show phototropism and geotropism
What is phototropism?
a directional response to sunlight
Plant shoots show positive phototropism and grow towards the sun
Roots show negative phototropism and grow away from the sun
What is geotropism
A directional response to gravity
Plant shoots show negative geotropism and grow against the force of gravity
Plant roots show positive geotropism and grow with the force of gravity
what do auxins do?
Auxins promote cell elongation in shoots but have opposite effect in roots
One of the most important growth factors is auxins such as indoleacetic acid
Other than auxins, what growth factors are also important?
Gibberellins - stimulate seed germination and flowering
Abscisic acid (ABA) - helps plants respond to environmental stress and is involved in stomatal closure
Cytokinins - stimulate cell division and cell differentiation
Ethene - stimulates flowering and fruit ripening
What is indoleacetic acid (IAA)?
a type of auxin which allows plants to respond to light and gravity
Enters the nucleus and binds to promoter region of DNA
Acts as transcription factor which activates or inhibits the transcription genes for proteins involved in cell elongation of growth
Transported in phloem
What does IAA do in shoots?
IAA accumulates on the shaded side of the shoot and activates genes involved in cell elongation
Activated genes are transcribed into proteins
Cell walls become looser and stretchy, causing the cells to become longer than the cells on the sunny side
Shoot bends towards the sun
What does IAA do in roots?
IAA accumulates on the more shaded side but it inhibits the growth of cells
More cells on non shaded side so root grows away from sun
How does IAA regulate geotropism?
IAA accumulates on the underside of shoots and roots
In shoots, IAA causes cell elongation which causes it to bend upwards against gravity
In roots, IAA inhibits cell growth which causes roots to grow downwards with gravity
What is apical dominance?
The growth of the apical bud at the expense of the side shoots growing
Promoted by auxins
How do auxins promote apical dominance?
Auxins prevent the growth of side shoots to save energy and prevent competition for light between the main shoot and side shoots
Less energy used for side shoots so more used so the plants grows taller and maximise sunlight absorbtion
What happens when the apical bud is removed?
Auxin levels drop which causes side shoots to start growing.
If the tip of shoot is replaced by an agar block containing auxin, the growth of side shoots is inhibited
What are gibberellins?
plant hormones that stimulate seed germination, growth of side shoots, stem elongation and flowering
stimulate the breakdown of starch into glucose
What is leaf abscission?
Controlled by hormones of deciduous trees in winter
Trees loose leaves in colder temperatures to conserve water during when there is less photosynthesis
How does leaf abscission occur?
Auxin inhibits leaf abscission and ethene promotes abscission
Auxin levels drop and ethene rises
when ethene reaches a certain levels, the abscission layer develops at the base of the leaf stalk
The cells in the layer expand in response to ethene and the cell walls break and the leaf breaks off
How do guard cells control the closing and opening of stomata?
When guard cells of full of water they become turgid which pushes the stomatal pore open
When guard cells lose water they turn flaccid and close the stomatal pore
How is the guard cell controlled?
Controlled by the plant hormone abscisic acid (ABA)
ABA binds to receptors on guard cell membrane causing calcium ion channels to open
Influx of calcium ions causes potassium ion channels to open and potassium ions leave the guard cell
Water potential in guard cell increases and water moves out of cell by osmosis. Guard cell becomes flaccid and pores close
What are commercial uses of plant hormones?
Auxins are used in rooting powders
Auxins used in herbicides
Ethene is used to control fruit ripening
