Topic 9 Control Systems Flashcards
Why are embryos removed from seeds in CP14?
embryos are natural Gibberellin producers, so taking it away we can use known Gib. conc to conduct investigation
reducing validity
why would contamination present a biohazard when growing the seed in agar?
Fungi and bacteria may also produce amylase, presenting a clear zone but reduces validity
Why are there clear zones around seeds when growing in starch agar?
Gibberellin is a transcription factor, involved in synthesis of amylase
by aleurone layer around the endosperm
hydrolysing starch into maltose
how do plants grow?
cell division and cell elongation
what are 3 main plant growth chemicals?
auxins, cytokinins an gibberellins
what do auxins do?
effects plant cell walls, promote cell elongation
how do auxins increase the plasticity of the cell wall?
ENTERS CELL, TRAVEL INTO NUCLEUS
auxin binds to receptor sites, and pumps H+
reduced pH break bonds between adjacent cellulose microfibrils
what is the acid growth hypothesis?
- auxin molecules bind to receptor protein
- ATP synthase pumps H+ into cell wall
- loosen bond between cellulose microfibres
- K+ travels into cytoplasm
- water osmosise down, stretching cell
What does auxin promote and inhibit, and how does the concentration distribute across the plant?
Conc decreases down
Promotes vertical growth and inhibits lateral growth
What do cytokinins promote and how?
Lateral bud growth , cell division in roots and shoots
Acts by attaching to receptors, triggering transcription factors to switch on/form
What is synergy in terms of plant pigments and give an example
Complimenting each other
Auxin and Gibberellin
What is antagonistic in terms of plant pigments and give an example
Inhibit each other / work oppositely
Auxin and cytokinins
How does cytokinins and auxin conc distribute in plants?
Auxin top heavy, decreases down
Cytokinins bottom heavy, decreases up
Which seed half has amylase activity?
Half with embryo
Shows clear zone on agar
As it contains gibberellin
Suggest and explain how to investigate IAA in agar affects the growth of shoots. (5 marks)
- record height of shoot
- calc difference in height
- shoots w IAA are taller than control
- because IAA diffuses down
- so higher IAA conc causes more growth
- due to more cell elongation
- deems of acid growth hypothesis
What is photomorphogenesis
process where plant development is controlled by the levels and type of light
What is photoperiodism in plants? And what are they controlled by?
Response of a plant to relative lengths of light and dark
Controlled by pigment called phytochrome
What are phytochromes used for?
Initiating flowering, germination and shoot growth
How do phytochromes work?
They are Conjugated proteins
With highly reactive photoreceptors
That absorbs light or particular wavelengths,
Causing conformational change
What colour are phytochromes?
Blue green
What are 2 forms of phytochromes?
Pr (inactive)
And
Pfr (active)
How is Pr and Pfr interconverting?
Pr -> Pfr in natural light
Pfr -> Pr in the dark
What are long day plants and their characteristics?
Bloom when days are longest
Nights are shortest
What are short day plants and their characteristics?
Bloom in spring, when days are shorter
which phytochrome stimulates which plant to flower?
PFr stimulates long day plants
Pr stimulates short day (long night) plants
[Pfr spells longer so longer day - vice versa]
What are benefits to plants being able to respond to changes in day length? (3 marks)
- flowering/development at the right time
-so flowers when insects are available - day length changes to set a pattern, e.g. always short days in winter, long in summer
- other stimuli are less regular eg temp
How do auxins affect the synthesis of enzymes? (3 marks)
- auxin binds w receptor in cell
- transcription factor becomes active/activated
- transcription factor binds to DNA/promoter
- switches on transcription
HOW does gibberellin affect growth of plants?
- gibberellin binds to cell surface receptors
- act as transcription factor
- activate protein synthesis
- causing cell elongation & division
how do auxins and cytokinins control the growth of lateral buds? (3 marks)
- auxin is released from the terminal bud
- and diffuses down the stem to inhibit cytokinin action
- cytokinin stimulates lateral shoot growth
- is produced from base of shoot
how does the structure of cell membrane affect the transport of auxin? (2 marks)
- uncharged auxin can diffuse through the hydrophobic/nonpolar fatty acid tails
- -ve charged auxin has to move through protein channels/carrier proteins
what is the mechanism by auxin and expansin to cause cells to elongate? (3 marks)
- lower pH = elongation increases
- bcs expansin is activated by lower pH
- weaking intermolecular bonds between cellulose molecules
- cell takes in water -> expand
Explain how red and far red light affects the germination of lettuce seeds. (Given lettuce seeds germinate when red is the last or only wavelength received) (4 marks)
- red light stimulates conversion from Pr -> PFr
- far red inhibits conversion Pr -> PFr
- PFr is the active phytochrome
- switches on gene for germination, activating enzymes involved
- last wavelength determines form of phytochrome present as conversion is reversible
Suggest benefits to plants being only able to respond to changes in day length. (3 marks)
- so will flower at the right time
- when insects are also available
- a regular stimulus, day length is a set pattern in seasons
Explain how auxin affects the synthesis of enzymes. (3 marks)
- auxin binds with receptors in cell (nucleus)
- transcription factor (TF) activated
- TF binds to DNA
- switches on transcription
How does Gibberellin affect growth on plant cells? (3 marks)
- Gibberelin enters nucleus
- act as / activates transcription factor
- cause cell elongation
what takes up majority of a grain cell?
endosperm
Explain how charged and uncharged auxin travels through cell surface membrane? (2 marks)
- uncharged auxins travel through uncharged fatty acid tails
- charged auxins move through carrier proteins / protein channels
Describe the mechanism (of auxin and expansin) that causes cells to elongate. (3 marks)
- at lower pH, elongation increases
- as expansin is activated by lower pH
- weakeining bonds between cellulose
- water enters and expands cell
Explain how seed banks can help to conserve the genetic diversity of plant species. (2 marks)
- large number of seeds collected and stored from many different plants
- ensures large gene pool in seed collected
Compare the central nervous system and the peripheral nervous system. (3 marks)
Both have
- neurones
- contain synapses
CNS/PNS
- no branches / somatic and autonomic
- no / has sensory and motor input
- processes info / no
How does IAA stimulate cells to synthesise proteins? (4 marks)
- IAA enters cell
- travels through cytoplasm to nucleus
- joins promotor region
- switches on gene
- activity at promoter region
- forms mRNA
- translation produces protein
How does acetylcholine lower HR? (3 marks)
- from the parasympathetic system
- slows down heart rate
- binds to receptors on SAN
- lower frequency of depolarisation
Given that lettuce are short day plants, explain how red and far red light affects the germination of lettuce seeds. (4 marks)
- red light stimulates Pr to Pfr
- far red light stimulates Pfr to Pr
- Pfr is the active phytochrome
- genes involved in germination are switched on
- enzymes involved in germination are synthesised
Why do chemicals affecting translation have a bigger effect in pollen tube growth than chemicals affecting transcription?
mRNA already present
To synthesise proteins and enzymes needed for growth of pollen tube
Explain why plants grown from germinating seeds may not flower at the same time of year as they would have done in their county of origin. (2 marks)
Flowering is affected by day length
Phytochromes respond to light exposed
Explain how the seed viability test would be different for some seeds from other parts of the world, stored at the same seed bank. (3 marks)
- different conditions
- such as temperature, humidity
- if correct conditions not used, viable seeds may still not germinate
