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Plant physiology! Flashcards

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1
Q

Why is Arabidopsis Thaliana a model organism?

A

1) Small
2) first diploid genome that has been completely sequenced
3) Rapid life cycle
4) short generation time
5)Prolific seed production and easy cultivation
6) easy to manipulate
7) Self-pollination (hermaphroditic)

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2
Q

what are the parts of a germinating seed?

A

cotyledon (mono or dicot - like leaves), hypocotyl (initial stem) and root

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3
Q

what is etiolation?

A

Elongated, pale green to yellowish growth due to low light intensity or darkness, extended hypercotyl, unfolded cotyledon
Happens when a seed germinates in the dark

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4
Q

what is a phytochrome? What can it absorb?

A

a chemical photo-receptor in plants that is used to detect light, absorbs red and far-red light most strongly (600-750nm) as most useful for photosynthesis, can also absorb blue light (350-500nm) & UVA radiation

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5
Q

what are the parts of a phytochrome?

A

photosensory domain (contains chromophore phytochromobilin) and regulatory domain

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6
Q

what is phytochromobilin? What can it convert between?

A

a chromophore, senses if light is far red or red, converts between pr and pfr version (photoreversiblity), these are cis/trans isomers, pi bond
Found in the photosensory domain of a phytochrome

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7
Q

what happens to phytochrome in far red light?

A

far red light causes cis/trans isomerisation that converts pr to pfr form, this changes protein structure so that NLS is exposed
Therefore, the phytochrome moves to nucleus, and changes gene expression, triggers germination
FAR LIGHT -> PFR FORM -> NUCLEUS -> GENE EXPRESSION

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8
Q

what is evidence for phytochrome changes?

A

GFP - in light you can see it move to the nucleus

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9
Q

what is photo reversibility?

A

pr - inactive form (it absorbs red light during the day to convert it to pfr),
pfr - active form (absorbs far-red light throughout the night to convert it to pr)

  • its in equilibrium, some in each form at all times
    Basically day time turns the phytochrome into pfr, so it germinates
    Night time turns the phytochrome into pr, so it etiolates
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10
Q

what is phyA mutant?

A

plant has a mutated phytochrome so can’t detect light or pfr can’t enter the nucleus and act as a transcription factor.
- has a dark phenotype, looks etiolated
Like wildtype etiolated seed

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11
Q

when will seeds germinate?

A

in red light
- chlorophyll absorbs red light but can’t reach ground bc absorbed by higher trees so unproductive to germinate until a gap in trees
- otherwise only far-red light will reach ground which keeps phytochrome in pr inactive form, so will stay in cytosol and not move to nucleus so won’t affect gene expression

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12
Q

What are circadian rhythms?

A

biological clock, responds to external factors to conserve energy, clock genes are activated in the day and protein builds up, it is a negative feedback mechanism, inhibited at night due to build up of protein
Living on a rotating planet is biologically stressful

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13
Q

what is the period?

A

time between peak to peak

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14
Q

what is the amplitude?

A

half the height from trough to peak (height of the peak from resting)

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15
Q

what is the phase?

A

a specific point in a cycle

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16
Q

what is a northern blot?

A

Analyzes RNA fragments (mRNA) on a gel electrophoresis using a probe, tracks how fast genes are switched on or off (measures transcription levels as the intensity of the signal relates to the relative amount of mRNA)

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17
Q

how to identify clock components?

A

use reporter protein e.g luciferase (from fireflies, lights up), add a promoter used in the clock so can see when its active and then create mutants to track which proteins used and changed

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18
Q

what is entrainment?

A

the process of taking external signals and feeding it into biological system
- if plant is in the dark, the clock gets out of sync
- each cell has a clock of its own

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19
Q

how does phytochrome entrain the clock?

A

it senses presence of light (dawn) and moves into nucleus, acts as a transcription factor, if no light then doesn’t happen and gets out of sync

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20
Q

What is turgor pressure for?

A

mechanical stability and physiological processes

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21
Q

what are nutrients dissolved in?

A

soil solution

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22
Q

in diffusion and osmosis, is there still the same number of solutes on each side?

A

yes

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23
Q

what are the 3 types of water potentials that add to give overall water potential Psi?

A

solute potential, pressure potential and gravitational potential

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24
Q

what is cytoplasm held by?

A

plasmodesmata

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25
what is plasmodesmata made of?
desmotubules
26
what is the pressure potential of a flaccid cell?
zero, no pressure against cell wall as cell is floppy
27
what solute potential does 0.1M of solute equal to?
-0.244MPa
28
If solute potential was -0.4 in a flaccid cell, what would the water potential be?
-0.4 because theres no pressure potential is a flaccid cell
29
where does water move from and to?
high to low water potential until can't expand anymore e.g plasma membrane so then pressure is added and potential pressure becomes +ve
30
What is cavitation?
Negative pressure is too great so causes water column to break and air cavities form in the xylem - stops water flow - too many cavitations causes drought
31
When is bulk flow transport used?
For long distances
32
What is the soil-plant-air-continuum?
continuum of water from soil to plants to air - lots of transpiration and gas exchange loses water out stomata
33
What is aperture? What affects it?
How open stomata are - changes on environmental conditions
34
How are plants waterproof?
Due to waxy cuticle on epidermis made of cutin
35
What is a plant called when it has no stomata?
Speechless - it will die because can't get CO2 in
36
What is a plant called when it has too many stomata?
Too many mouths - may have too high transpiration rate and lose too much H2O
37
What is transpiration rate based on? What can affect it?
Water VAPOUR concentration gradient - affect by temp and humidity
38
What is leaf stomatal resistance?
Diffusional resistance from leaf air spaces to atmosphere
39
What is boundary layer resistance? When is it thickest?
Air on the surface of the leaf - thickness depends on air movement - still air = thicker boundary layer = slower transpiration rate
40
What is pressure driven bulk flow?
Negative hydrostatic pressure and cohesion pulling water up under negative tension - takes lot of energy - cohesion-tension theory
41
What are the two types of vessel in xylem?
Tracheids and vessel elements
42
What are tracheids?
Thin vessels next to each other - have bordered pits to allow lateral movement
43
What are vessel elements?
Thicker vessels on top of each other - more vulnerable to cavitation
44
Which type of plant only have tracheids?
Gymnosperms like conifers
45
how do you track cavitation?
Use MRI to see vessels, the white spots indicate cavitation/embolism - can track when water is added
46
How to solve cavitation?
Positive root pressure - roots pump solutes in xylem at night so water potential is lowered - water then moves from high to low water potential so water goes into root from soil
47
What is a major disadvantage about rubisco in the Calvin cycle?
It uses oxygen as well as CO2 so PCE builds up which is a waste product and it becomes toxic and messes up metabolic pathways
48
How is PCE removed?
Photorespiration
49
What molecules can rubisco use?
CO2 and O2 because of similar shape - but want to limit the use of O2 because it causes waste products + photorespiration
50
How to reduce photorespiration?
Concentrate carbon around rubisco Reduce oxygenate activity Reduce energy wasted in rubisco
51
What are the 3 types of photosynthesis?
C3 C4 CAM
52
what is C4 photosynthesis?
includes specialist Kranz anatomy and metabolism used to fix carbon around rubisco to stop using oxygen so less photorespiration - carbon fixation in one cell - mesophyll cell - Calvin cycle in another cell - bundle sheath cell Spatial separation of initial carbon fixation and carbon fixation into the calvin cycle
53
Where is C4 photosynthesis used?
In hot countries otherwise there is little photorespiration so no point in C4 as it takes more energy
54
Which plants use C4 photosynthesis?
Mostly monocots - grasses, maize, sugarcane
55
What are the two cells used in C4?
mesophyll cells - cells on outside of vascular bundles bundle sheath cell - cells on inner ring around vascular bundles
56
How are the 2 specialised cells in C4 different in C3?
In C4, closer spacing and bigger bundle sheath cells to maximise Calvin cycle
57
Which cells contain rubisco?
Only bundle sheath cells
58
What is the C4 mechanism?
1. Co2 diffuses into mesophyll cell and turned into HCO3 2. HCO3 is fixed (turned into an organic molecule) by PEPC into C4 acid 3. C4 diffuses into Bundle sheath cells through plasmodesmata. 4. Decarboxylase decarboxylates C4 acid into C3 and releases CO2 into chloroplast of bundle sheath cell so CO2 is concentrated around rubisco 5. Calvin cycle happens with Co2 and rubisco and then C3 diffuses back into mesophyll cells 6. restarts
59
How are the bundle sheath cells specialised?
They have Suberin around them which is airtight and waterproof so CO2 can't diffuse out and O2 can't diffuse in
60
What is PEPC?
A biotin containing enzyme that can differentiate between O2 and CO2, unlike rubisco - its substrate is H2CO3 - its made from pyruvate and C3 which is recycled - uses energy to make
61
What is Kranz anatomy?
Rubisco is only in bundle sheath cells Closer spacing of cells in C4 Bigger bundle sheath cells BS cells covered in Suberin
62
Why don't all plants use C4?
Last step of C3 diffusion back into mesophyll cell and recycled into PEPC takes a lot of energy which only outweighs the energy cost of photorespiration in hot countries because at lower temps, there's little photorespiration so C4 takes too much energy then and not much point - so normally only in plants in hot countries bc then its worth the energy as photorespiration is higher and less waste produced by using PEPC instead of just rubisco
63
What happens to rate of photorespiration in lower temps and why?
It decreases because the solubility of oxygen and CO2 change so at lower temps, O2 is less soluble to rubisco uses it less - less photorespiration = less waste
64
Why is rubisco inefficient in C3?
It catalyses carboxylation as well as oxygenation (not what plants want)
65
What is CAM photosynthesis?
Temporal (time) separation of initial carbon fixation by PEPC and fixation by rubisco - does one thing at night and another in the day - ALL IN ONE CELL BUT SEPARATED BY NIGHT AND DAY (and also slightly env conditions)
66
What is the CAM mechanism?
Night: 1. CO2 diffuses into stomata at night and converted into C4 by PEPC 2. C4 pumped into the vacuole to be stored AS MALIC ACID and filled overnight 3. Stomata shut at dawn Day: 4. C4 decarboxylated by decarboxylate into C3 and CO2 is released 5. CO2 is used by rubisco in Calvin cycle and C3 is recycled into PEPC
67
Why is CAM photosynthesis used?
To maximise CO2 uptake and minimise water loss
68
CAM ways to minimise water loss
Thick cuticles Large vacuoles Stomata with small apertures Sunken stomata Pits - creates deeper boundary layer - humid to reduce rate of transpiration Succulents in semi-arid environments
69
What are CAM switchers?
Some species are obligate CAM plants but some can switch between C3 and CAM - use CAM when water is scarce and switch back when it is abundant - may also be used due to salinity and temp
70
What is the ice plant?
An inducible CAM plant - can induce it to CAM and then bring it back to C3 - responds to salinity and drought - can see pathways and enzymes
71
Do CAM plants have bundle sheath cells?
Yes
72
What is the cofactor for chlorophyll?
Mg2+
73
What are the 3 categories of nutrients for plants?
Macronutrients Secondary nutrients Micronutrients
74
What are the 3 macronutrients?
Nitrogen Phosphorus Potassium - hence the NPK fertiliser
75
What is nitrogen used for?
Nucleic acids, amino acids, growth
76
What is phosphorus used for?
ATP, nucleic acids, sugar phosphates, phospholipids
77
What is potassium used for?
Osmotic relations, signalling, enzyme cofactors
78
What are the 3 secondary nutrients?
Sulphur, calcium, magnesium
79
What is sulphur used for?
Some amino acids
80
What is calcium used for?
Cell signalling, enzyme cofactor
81
What is magnesium used for?
Cofactor of chlorophyll - if not enough, not enough chlorophyll and plant turns yellow
82
What are the 3 micronutrients?
Iron, boron and then grouped together: zinc, copper, manganese and molybdenum
83
What is iron used for?
Cytochromes - absorb light
84
What is boron used for?
Holds cell walls together
85
What are zinc, copper, manganese and molybdenum used for?
Enzyme cofactors
86
What's special about the tea plant?
Aluminium is usually toxic to plants but tea needs aluminium to grow more
87
What is chlorosis?
Lack of Mg --> not enough chlorophyll and plant turns yellow
88
What is the critical zone?
Point for concentration of nutrients at which if you go below, you get a rapid drop off of growth
89
What is the adequate zone?
Zone where concentration of nutrients is right - saturated - even if add more doesn't do anything to plant growth - toxicity is after this zone
90
What roots do dicots have?
A tap root which ephemeral feeder roots branch off
91
What do ephemeral feeder roots do?
Bring in nutrients in one area and once no more nutrients, they die to save energy and then more grow from the tap root in another area with nutrients
92
What are the roots like in monocots?
Fibrous root system everywhere
93
What are the layers in a root?
Stele in the middle which includes pericycle, xylem and phloem Then endodermis Then cortex Then epidermis
94
How does the cortex compare in mono and dicots?
Cortex is thicker in dicots
95
What are the 3 nutrient pathways?
apoplast symplast vacuolar/ tonoplast
96
What is the apoplast pathway?
Through cell walls - continuous diffusion from soil through cortex - has to move to symplast pathway when reach casparian strip
97
What is the symplast pathway?
Cytoplasm (linked by plasmodesmata) - transport by transporter ions into root and diffuse through cytoplasm.
98
What is the tonoplast pathway?
Through the vacuole
99
What is the casparian strip?
A strip of Suberin around the endodermis that blocks the apoplastic route - controls what goes in and out of the xylem and what goes out into cells - is waterproof - has specialised transporters - allows xylem to have a higher nutrient conc than in soil as ions can be pumped into symplast
100
How do carnivorous plants get nutrients? What are their adaptations?
From insect falling in and getting dissolved by acid - have a ridge/ lip which is smooth so they can slip in - have downwards pointy hairs so insects can't climb up - they can have nectar around the ridge to lure insects in - trigger hair can release of enzymes to digest insect
101
What are channel transporters?
Used for diffusion - have a set specificity of pore size and negative or positive amino acids lining the channel - charged - sometimes gated so pores open or close in response to signals
102
What are carrier proteins?
Use facilitated diffusion - pores not completely across membrane - highly selection and slower than channels - have a conformation change to allow molecule through
103
What are the two potassium phases?
Low K+ phase - active transport - low capacity - slower rate - H+/K+ symporter High K+ phase - low affinity but high capacity - passive diffusion - voltage gated
104
when is metabolic rate its highest?
In the day
105
What is the solute potential of pure water?
0 Otherwise it is always negative Add solute and solute potential decreases Remember, water moves from high potential to low
106
What pressure potential does pure water at atmospheric pressure have?
0 A turgid cell has positive pressure potential
107
What is the second point of ion control in plants?
Xylem loading Specialised transporters expressed in the pericycle and xylem parenchyma
108
How is nitrogen uptake coupled to the clock?
Nitrogen typically enters the root as nitrate via nitrate transporters mRNA transcripts of nitrate transporter genes peak just before the start of the day

Organisms and environment (17 decks)

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