5.5 Plant Responses Flashcards
What do tannins do?
- Make leaves taste bad
- Make roots less easy for pathogens to enter
What is the difference between biotic and abiotic environmental components?
Biotic=Living
Abiotic=Non-living
Why must plants respond to their environment?
It may help them live long enough to reproduce
What are alkaloids?
Nitrogenous bases that have physiological effects on animals e.g. nicotine
What is a pheromone?
A signalling chemical that can produce a response in another organism.
What is a tropism?
A directional growth response in which the direction of the response is determined by the direction of the external stimulus
What is phototropism and why is it needed?
Plant shoots grow towards light, enabling them to photosynthesise
What is geotropism and why is it needed?
Roots grow towards gravity’s pull, allowing them to be anchored to the soil and take up water and minerals
What is thigmotropism and why is it useful?
Shoots climbing plants, such as ivy, wind around other plants or structures for support
What is a nastic
response?
Non directional response to external stimuli
What is a negative tropic response?
A plant responding away from a stimulus
What are plant hormones?
Chemical messengers that can be transported away from where they are made to act in other parts of the plant.
How can you ensure that hormones only act upon the correct tissues?
Specific hormones bind to specific receptors with complementary shapes on the membranes of particular cells
What are the effects of cytokinins?
- Promote cell growth
- Delay leaf ageing
- Overcome apical dominance
What are the effects of abscisic acid?
- Inhibits seed germination and growth
- Causes stomatal closure
What are the effects of auxins?
- Promote cell elongation
- Promote apical dominance
- Inhibit leaf abscission (fall)
What are the effects of gibberellins?
- Promote seed germination
- Stem elongation
What is the effect of ethene?
Promotes fruit ripening
How do hormones move long distances around the plant?
Mass flow in phloem or xylem
What is apical dominance?
Inhibition of lateral bud growth by auxins.
What does rooting powder do?
Encourage root growth
What does rooting powder contain?
Auxins and talcum powder
What would happen to the plant if there wasn’t any apical dominance?
The plant would grow in all directions, becoming bushy, and photosynthesis wouldn’t be efficient enough.
Why can’t plant cells divide as readily as animal cells?
They are limited by the cellulose cell wall
What are meristems?
A particular place in the plant where there are still groups of immature cells capable of dividing
Which plant hormone causes stomatal closure at times of water stress?
Abscisic acid
What hormone causes seed germination?
Gibberellins
What hormone effects leaf loss?
Auxins
What are expansins?
Cellulose cell wall loosening enzymes
What pH is optimum for expansins?
Acidic (low pH)
What plant hormone causes cell elongation?
Auxins
What plant hormone causes stem elongation?
Gibberellin
How does gibberellin stimulate cell elongation?
By loosening cell walls
How does gibberellin stimulate cell division?
By stimulating production of a protein that controls the cell cycle
What is the difference between Auxin and Gibberellin in their growth effects?
- Auxin controls tropic growth from nodes and buds
- Gibberellin controls stem elongation (growth in internodes)
What does a DELLA protein do?
Binds to transcription factors, making them useless. It effectively stops protein synthesis and growth
What are transcription factors?
Proteins that initiate gene transcription for protein synthesis
How does cutting the tip of a shoot allow lateral growth?
When the tip with high auxin concentration is cut abscisic acid levels drop and growth is allowed in lateral buds.
(High abscisic acid=lateral growth inhibition)
How does mimosa pudica respond to touch?
A signal is spread from the touched leaf causing it to quickly fold up to prevent mimosa pudica from being eaten.
What is the function of IAA (Indoleacetic acid) ?
It moves around the plant to control tropisms, by stimulating cell elongation. It has an uneven distribution so that plant can grow unevenly.
How does IAA (Indoleacetic acid) move around the plant for long distances?
Phloem tubes
How does IAA help phototropism?
IAA moves to shaded parts of the shoots, making the cells on that side elongate and the shoot bends towards the light.
How does IAA help geotropism?
IAA moves to the underside of shoots, making cells elongate and the shoot grows upwards.
Why does covering the tip of a shoot make it grow straight upwards rather then towards the light?
The tip is most sensitive to light and because the tip is covered it’s not in contact with light so grows straight up
When investigating geotropism, why must you insure your shoots are covered?
Because if light reaches the shoots this will effect your results due to phototropism.
How do you investigate geotropism?
Have planted shoots and place them at different angles
Why is it that in a tall plant, side shoots grow near the bottom?
The auxin concentration near the bottom is low so it’s effect of inhibiting side shoot growth is not effective
Why do you need a control experiment?
You need something untreated so that you can compare and see if the effect from the independent variable is not from any other factor.
How to gibberellins stimulate seed germination?
They trigger the breakdown of starch into glucose, which the seed embryo can use to respire and make energy to grow.
Why does abscisic acid prevent seed germination?
Because it inibits gibberellin action
What does synergistic mean?
When 2 things can work together to have a big effect e.g. auxin and gibberellins can work together to make a plant really tall
What does antagonistic mean?
When 2 things oppose eachothers actions e.g. when gibberellins stimulate side shoots growth and auxins inhibit side shoots growth
What is leaf abscission?
Leaf loss
Why do deciduous plants lose leaves in the winter?
Helps to conserve water lost from their leaves during water stress- soil water may be frozen
What triggers leaf loss?
Shortening day length in autumn
How do auxins effect leaf loss?
They inhibit leaf loss
How does ethene effect leaf loss?
Ethene promotes leaf loss
What is the process of stomatal closure?
It opens ion channels which let the water potential inside the cell rise, so water leaves the cell by osmosis- this makes it flaccid closing the stomata.
What is the process for fruit ripening?
Ethene stimulates enzymes which break down cell walls, chlorophyll, and starch into glucose.
How can auxins be used in weed killers?
They make weeds grow long stems and grow too fast which they can’t supply so they die.
What are the advantages of taking cuttings?
It’s quick, cheap and easy to keep taking cuttings from the same plant
What is a coleoptile?
A seedling a few days after germination
Where is the zone of max cell elongation?
Just below the tip
How does auxin increase stretchiness of the plant cell wall?
By promoting active transport of H+ ions into the cell wall
How do H+ loosen the plant cell wall?
They decrease the pH allowing expansin enzymes to work at their optimum
How do expansins stretch cell walls?
They break bonds within the cellulose fibres, making the cell wall less rigid
What are phototropins?
Proteins that act as receptors for blue light, found in meristematic cells
Phototropins become _________ when hit by blue light.
Phosphorylated
What is in a vascular bundle from inside outwards?
Xylem
Cambium
Phloem
