Module 5.1.5 - Plant responses Flashcards
What do plants respond to?
- changes in environment
- abiotic stress
- herbivory
What are changes in the environment?
Phototropism - grows towards light
Gravitropism - roots grow down, shoots grow up
Phygomotropism - sense of touch
What is abiotic stress?
- non living factor, causes harm
- plants either survive or dies
e.g. drought, too much water, high/;low temps, change in light intensity, day/season length
What are chemical responses to herbivory?
Tannins - toxic to microorganisms and larger herbivores, bad tasting
Alkaloids - found in growing tips and flowers, taste bitter
Terpenoids - antibacterial and antifungal properties
What are pheremones?
Chemical released that affect behaviour of
others of same species
What is leaf loss in deciduous trees?
- changes in day length causes changes in light and temp
- during autumn, glucose needed to release energy needed to protect plant from freezing is greater than glucose produced by photosynthesis
- trees lose leaves and remain dormant until spring
- due to antagonistic response of auxin and ethene
How does auxin cause leaf loss in deciduous trees?
- inhibits leaf loss
- produced by young leaves
- less produced as leaf gets older
What is tropism?
Directional growth towards an external stimuli
What is a nastic response?
Non directional response to external stimuli
How does ethene cause leaf loss in deciduous trees?
- stimulates leaf loss
- older leaves produce more ethene
- causes formation of abscission layer by causing cells to expand and break cell walls
- stimulates production of enzymes called cellulase (breaks down cellulose and cell walls)
How do plants control their response?
- coordinate responses to environment
- not produced in endocrine glands but by cells in variety of tissues
- when hormones reach target cells, they bind to receptors on plasma membrane which can influence cell division, cell elongation or cell differentiation
What is auxin?
Plant hormone, made in tip of growing shoots/roots, unequally distributed in response to light/gravity, elongates roots, shortens shoots
Why does the shaded part of a plant bend towards the light?
Has more auxin
Where is auxin produced and what does it do?
- at bottom of roots due to gravity
- prevents growth of root cells so opposite side continues to grow and elongate causing curve
What is the growth of apical bud dominant over?
Lateral bud
How does apical dominance happen?
- if plant shoot tip is cut, plant grows from lateral bud
- auxins from apical bud prevent lateral buds from growing when shoot is cut
- auxin levels drop and buds grow
What are plant hormones involved in?
Germination of seeds, growth of stems, ripening of fruit and falling of leaves
What gas is used to ripen climatic fruits?
Ethene
What are climatic fruits?
Continue to ripen after harvesting due to peak of ethene production triggering series of chemical reactions
What are some examples of climatic fruits?
Bananas, tomatoes, mangoes, avocadoes
What are non-climatic fruits?
Don’t produce large amounts of ethene, don’t ripen as much after picking
What are some examples of non-climatic fruits?
Oranges, strawberries, watermelon
Why are fruits harvested when fully formed but not long before ripe?
- Less easily damaged during transport as they are harder
- prevents wastage during transport and increase time available to be sold - exposed to ethene gas to ripen to be sold
What is hormone rooting powders and micropropagation?
- auxin affects shoots and roots growth
- auxin on cut shoots stimulates production of roots
- dipping cut stems into hormone rooting powder increases chances of roots forming and successful propagation taking place
- plant hormones essential as control production of mass new cells and then differentiation of clones into tiny new cells
What are hormonal weedkillers?
- weeds interfere with crop plants, competing for light, space, water and minerals
- balance of hormones enables plants to grow
- synthetic auxin acts as very effective weedkillers
- broad leaved plants absorb auxin and their metabolism is affected, growth rate increases and becomes unsustainable/dies
- narrow leaved plants aren’t affected, continue to grow normally, freed from competition
What is synthetic auxin?
Simple, cheap to produce, decreases toxicity to mammals
What can produce seedless fruits?
Auxin
What can promote fruit dropping in plants?
Ethene
What does cytokinin do?
Used to prevent ageing of ripened fruits and products, micropropagation to control tissue development
What does gibberellin do?
Delay ripening and ageing in fruits, improve size/shape in fruits, speed up malting process in beer brewing
- initiate seed germination, end seed dormancy, promote flowering, increase length of stem
