Carbon Assimilation

1. 1- [blank_start]photosynthesis[blank_end] underpins the fundamental success of green plants
   - it is the nutrition source for virtually all organisms on earth > include the [blank_start]human[blank_end] population
   - the scale of photosynthesis is vast = 2 x10^11 [blank_start]tonnes[blank_end] of carbon fixed per year
   - surprising how little was known about photosynthesis until the final decades of the [blank_start]19[blank_end]th century > since the practice of agriculture was already several of thousands of years old
   
   [blank_start]Aristotle[blank_end] proposed the '[blank_start]Humus[blank_end]' mmm theory = the fact that plant life on earth could determine its own existence and only required nutrients from [blank_start]soil[blank_end], soil could sustain plant life with no other inputs what so ever
   - this was believed until the late 19th century
   
   THEN [blank_start]Stephen[blank_end] Hales (hale mary) said plants obtained a portion of their nurtrition from the air with [blank_start]light[blank_end] involved
   - Stephen [blank_start]hale[blank_end] said Aristotle's [blank_start]humus[blank_end] theory was probably wrong, and plants needed other sources
   - Stephen [blank_start]Hale[blank_end] is known as the father of plant physiology
   
   

   1. Aphotosynthesis
   2. Bhuman
   3. Ctonnes
   4. D19
   5. EAristotle
   6. FHumus
   7. Gsoil
   8. HStephen
   9. Ilight
   10. Jhale
   11. Khumus
   12. LHale
2. 2After Stephen [blank_start]Hale[blank_end] proposed the Humus theory by [blank_start]Aristotle[blank_end] was most likely wrong
   - Joseph Priestly and Ingen-[blank_start]Housz[blank_end] pushed things forward
   - Joseph [blank_start]Priestly[blank_end] and Ingen-Housz said air and [blank_start]light[blank_end] are both very important in photosynthesis
   
   finally Julius [blank_start]Mayer[blank_end]
   - deduced the energy used by green plant tissue was derived from the [blank_start]sun[blank_end] and that plants were able to transform radiant energy to a [blank_start]chemical[blank_end] form
   
   6CO2 + 6H2O --> C6H12O6 + 6O2

   1. AHale
   2. BAristotle
   3. CHousz
   4. DPriestly
   5. Elight
   6. FMayer
   7. Gsun
   8. Hchemical
3. 3It took another century to clarify structural and chemical details of photosynthesis after Julius [blank_start]Mayer[blank_end] deduced energy used by plants came from the sun and plants were able to convert it to [blank_start]chemical[blank_end] energy

   1. AMayer
   2. Bchemical
4. 4One really important thing to remember in terms of photosynthesis
   - a leaf is not filled with air but with [blank_start]water[blank_end]
   - this water poses a massive problem for carbon [blank_start]dioxide[blank_end] has to pass through from external environment to the chloroplasts
   - Carbon dioxide is quite [blank_start]insoluble[blank_end] in water and becomes even less soluble at [blank_start]higher[blank_end] temperatures
   - carbon dioxide is 10,000 times less diffusive in water than in [blank_start]air[blank_end]
   
   so because leaves are full of [blank_start]water[blank_end] this makes it harder for carbon dioxide to diffuse in
   - chloroplasts have to receive the [blank_start]soluble[blank_end] form of carbon dioxide (bicarbonate, HCO3-, and [blank_start]carbonate[blank_end], CO3-2-)

   1. Awater
   2. Bdioxide
   3. Cinsoluble
   4. Dhigher
   5. Eair
   6. Fwater
   7. Gsoluble
   8. Hcarbonate
5. 5What goes on in the stroma? C3 photosynthesis
   - [blank_start]carbon[blank_end] dioxide enters stroma and is fixed by [blank_start]RuBP[blank_end] via the enzyme [blank_start]rubisco[blank_end] through a carboxylation reaction (addition of carbon dioxide)
   - 5C sugar (RuBP) --> [blank_start]carboxylation[blank_end] --> 2 x 3C products
   - because the product = 2 x [blank_start]glyceraldehyde[blank_end]-3-phosphate has [blank_start]3[blank_end] carbons this is why it is called C3 photosynthesis
   - only discovered in 1961
   - [blank_start]most[blank_end] important process on earth
   - FACT: rubisco is the most abundant [blank_start]protein[blank_end] on earth but is very [blank_start]inefficient[blank_end]
   
   2 x glyceraldehyde-3-[blank_start]phosphate[blank_end] (G3P)
   - made using ATP and NADPH
   - used to make simple sugars
   - BUT some is used to [blank_start]regenerate[blank_end] RuBP

   1. Acarbon
   2. BRuBP
   3. Crubisco
   4. Dcarboxylation
   5. Eglyceraldehyde
   6. F3
   7. Gmost
   8. Hprotein
   9. Iinefficient
   10. Jphosphate
   11. Kregenerate
6. 6[blank_start]Rubisco[blank_end]
   - so abundant because it is so [blank_start]inefficient[blank_end]; in a leaf [blank_start]50[blank_end]-70% of soluble content = rubisco
   - the calvin-[blank_start]benson[blank_end] cycle/C3 pathway of photosynthesis
   - Rubisco = ribulose-1,5-[blank_start]bisphosphate[blank_end] carboxylase/[blank_start]oxygenase[blank_end]
   - the binding sites of rubisco are equally as capable of binding and fixing [blank_start]oxygen[blank_end]
   - 3:1 ratio of carbon dioxide fixed to oxygen = losing [blank_start]25[blank_end]% of potential CO2 fixed
   - when fixing [blank_start]oxygen[blank_end] some CO2 is released

   1. ARubisco
   2. Binefficient
   3. C50
   4. Dbenson
   5. Ebisphosphate
   6. Foxygenase
   7. Goxygen
   8. H25
   9. Ioxygen
7. 7Why do carbon dioxide and oxygen compete for rubisco? it is believed that...
   - carbon dioxide concentrations used to be so [blank_start]high[blank_end]
   - virtually [blank_start]no[blank_end] oxygen
   - over time oxygen levels have increased and carbon dioxide levels have [blank_start]decreased[blank_end]
   - early photosynthetic bacteria has no requirement to worry about [blank_start]competition[blank_end] with oxygen
   - but now the situation has reversed and it is a problem

   1. Ahigh
   2. Bno
   3. Cdecreased
   4. Dcompetition
8. 8SO when rubisco first evolved there was no [blank_start]oxygen[blank_end] in the atmosphere so the enzyme was [blank_start]efficient[blank_end], but more recently we need turbo-chargers to concentrate carbon dioxide around the enzyme [blank_start]rubisco[blank_end]

   1. Aoxygen
   2. Befficient
   3. Crubisco
9. 9[blank_start]Photorespiration[blank_end]: costly and efficient
   - why do plants still engage in this wasteful process?
   - the [blank_start]oxygenase[blank_end] function of [blank_start]rubisco[blank_end] is left over from previous times with lower atmospheric oxygen concentrations, now a hinderance due to evolution
   - must it must do something useful
   - [blank_start]photorespiration[blank_end] must serve a useful process for when transforming plants without out it they do [blank_start]not[blank_end] survive

   1. APhotorespiration
   2. Boxygenase
   3. Crubisco
   4. Dphotorespiration
   5. Enot
10. 10How many types of Photosynthesis are there?
    - 3: C3, C4, and CAM ([blank_start]crussulacean[blank_end] acid metabolism)
    
    C4 and CAM
    - have evolved in multiple lineages so many times quite [blank_start]quickly[blank_end]
    - but mainly evolved to try and minimise [blank_start]photorespiration[blank_end]
    - because C4 and CAM have evolved in so many plants so quickly its believed [blank_start]all[blank_end] plants are capable (have what they need) to transform into a C4 or [blank_start]CAM[blank_end] plant > this is debatable as this whether they all have the correct machinary

    1. Acrussulacean
    2. Bquickly
    3. Cphotorespiration
    4. Dall
    5. ECAM

11. 11[blank_start]C4[blank_end] Photosynthesis
    - looks very different to C3 plants
    - they have [blank_start]circular[blank_end] (round) mesophyll cells
    - this anatomy is known as [blank_start]Kranz[blank_end] Anatomy (structure of C4 plants); spongy [blank_start]mesophyll[blank_end] cells are clustered in a ring around the leaf [blank_start]veins[blank_end] (blood)
    - around the veins are bundled [blank_start]sheath[blank_end] (insulation) cells which contain large [blank_start]chloroplasts[blank_end]
    - whereas the spongy mesophyll have few if any [blank_start]chloroplasts[blank_end] unlike in C3 plants
    - spongy mesophyll cells are filled with PEPC ([blank_start]phosphoenol[blank_end]-pyruvate [blank_start]carboxylase[blank_end]) which fixes carbon [blank_start]dioxide[blank_end] from the outside and is then shuffled across in to the bundle [blank_start]sheath[blank_end] cells

    

    1. AC4
    2. Bcircular
    3. CKranz
    4. Dmesophyll
    5. Eveins
    6. Fsheath
    7. Gchloroplasts
    8. Hchloroplasts
    9. Iphosphoenol
    10. Jcarboxylase
    11. Kdioxide
    12. Lsheath
12. 12What goes on inside C4 plant cells?
    - complete machinery differentiated between [blank_start]2[blank_end] cell types
    - spongy [blank_start]mesophyll[blank_end] are filled with PEPC (phosphoenolpyruvate [blank_start]carboxylase[blank_end]) in massive adundance, this enzyme fixes the carbon [blank_start]dioixde[blank_end] coming in from the oustide
    - mesophyll cells are the [blank_start]first[blank_end] point the carbon dioxide reaches after entering stomata
    - this PEPC is fixed to [blank_start]malate[blank_end] (2nd to last product of TCA) in the mesophyll cells
    
    This [blank_start]malate[blank_end] (TCA Product) is shuffled across to the bundled [blank_start]sheath[blank_end] cells where it is broken down to release the [blank_start]carbon[blank_end] dioxide and pyruvate
    - this carbon dioxide is then fed to [blank_start]rubisco[blank_end] (enzyme) and the [blank_start]C3[blank_end] normal cycle begins
    - the [blank_start]pyruvate[blank_end] is recycled to reproduce PEPC
    
    

    

    1. A2
    2. Bcarboxylase
    3. Cmesophyll
    4. Ddioixde
    5. Efirst
    6. Fmalate
    7. Gmalate
    8. Hsheath
    9. Icarbon
    10. Jrubisco
    11. KC3
    12. Lpyruvate
13. 13The beauty of [blank_start]C4[blank_end] photosynthesis is there is no oxygen, it minimises rubiscos capability to fix to [blank_start]oxygen[blank_end]
    - rubisco is present with [blank_start]pure[blank_end] carbon dioxide so [blank_start]cannot[blank_end] combine with oxygen because carbon dioxide is in such a [blank_start]high[blank_end] concentration = this is referred to as '[blank_start]turbo[blank_end]-charging' photosynthesis
    - this minimises [blank_start]photorespiration[blank_end] (rubisco combining with oxygen) almost totally
    - this makes the plant much [blank_start]more[blank_end] efficient and outcompetes equivalent [blank_start]C3[blank_end] species
    - very high rate of photosynthesis will [blank_start]outcompete[blank_end] C3 plants due to increased efficiency
    - C4 plants are especially successful in [blank_start]warmer[blank_end] climates

    1. Aoxygen
    2. BC4
    3. Cpure
    4. Dcannot
    5. Ehigh
    6. Fturbo
    7. Gphotorespiration
    8. Hmore
    9. IC3
    10. Joutcompete
    11. Kwarmer
14. 14Distribution of C4 Plants
    - around ~2-3% of higher plants have evolved into [blank_start]C4[blank_end] plants
    - Generally [blank_start]tropical[blank_end] in origin
    - >50% of [blank_start]grass[blank_end] species are C4
    - most of the worlds [blank_start]weeds[blank_end] are C4 e.g. Spartina anglica
    - they are economically important
    
    SO: C4 plants have carry out barely any [blank_start]photorespiration[blank_end], they have a higher [blank_start]temperature[blank_end] optimum

    1. AC4
    2. Btropical
    3. Cgrass
    4. Dweeds
    5. Ephotorespiration
    6. Ftemperature
15. 15CAM ([blank_start]crussulacean[blank_end] acid metabolism) Photosynthesis
    - variant of photosynthesis with a [blank_start]temporal[blank_end] (time) separation
    - about 7% of plants have [blank_start]CAM[blank_end] photosynthesis
    - discovered at newcastle university
    - Stomata are open at [blank_start]night[blank_end] and closed during the [blank_start]day[blank_end] (unlike other plants)
    - effectively the same mechanism/pathway as C4 but instead of having different [blank_start]cell[blank_end] types in CAM you have a [blank_start]night[blank_end]/day separation between what goes on
    
    At night = stomata are [blank_start]open[blank_end] (unlike any other plant on earth); carbon dioxide is taken in, fixed by PEPC ([blank_start]phosphoenolpyruvate[blank_end] carboxylase) into malate
    - [blank_start]malate[blank_end] then accumulates over the course of the night (massive change in acidity)
    - malate is broken down in the [blank_start]day[blank_end] when the stomata are closed
    - malate is broken down into carbon dioxide and [blank_start]pyruvate[blank_end]
    - carbon dioxide combines with [blank_start]rubisco[blank_end] and forms sugars in the normal pathway
    - [blank_start]pyruvate[blank_end] is recycled to regernate PEPC

    1. Acrussulacean
    2. Btemporal
    3. CCAM
    4. Dnight
    5. Eday
    6. Fcell
    7. Gnight
    8. Hopen
    9. Iphosphoenolpyruvate
    10. Jmalate
    11. Kday
    12. Lpyruvate
    13. Mrubisco
    14. Npyruvate
16. 16[blank_start]CAM[blank_end] Photosynthesis
    - can fix carbon dioxide in a completely [blank_start]oxygen[blank_end] free environment behind stomata during the day
    - added advantage if you don't lose any [blank_start]water[blank_end] at the same time as you are [blank_start]fixing[blank_end] carbon dioxide (as stomata are closed
    - this is [blank_start]turbo[blank_end]-charged C4 photosynthesis
    - many [blank_start]desert[blank_end] species e.g. cacti and succulent plants employ this, they need big [blank_start]vacuoles[blank_end] to accumulate malate (TCA)

    1. ACAM
    2. Boxygen
    3. Cwater
    4. Dfixing
    5. Eturbo
    6. Fdesert
    7. Gvacuoles
17. 17C3 plant e.g. [blank_start]rice[blank_end]
    C4 plant e.g. [blank_start]maize[blank_end]
    CAM plant e.g. [blank_start]Agave[blank_end]
    
    CAM plants use 1/[blank_start]5[blank_end]th the amount of water to create the same amount of plant biomass = increased water use efficiency
    
    FACT: some plants are CAM [blank_start]all[blank_end] the time, others can switch; start as C3 plants and flexibly switch into CAM as they [blank_start]need[blank_end] it

    1. Arice
    2. Bmaize
    3. CAgave
    4. D5
    5. Eall
    6. Fneed
18. 18Ecology and Evolution of CAM Plants
    - an adaptation to [blank_start]drought[blank_end]
    - diversity of CAM plants is greatest in tropical [blank_start]rainforests[blank_end]
    - ~7000 species of CAM [blank_start]orchid[blank_end]
    - there are aquatic CAM plants > evolved as a carbon [blank_start]dioxide[blank_end] concentrating mechanism
    - CAM inducible in some arid-zone species
    
    There are massive opportunities in CAM in crop production
    - CAM plants as biofuel for under-utilised arid and semi-arid marginal land

    1. Adrought
    2. Brainforests
    3. Corchid
    4. Ddioxide
19. 19Summary
    - [blank_start]Rubisco[blank_end] > most abundant protein on earth
    - Majority of plants use ‘wasteful [blank_start]C3[blank_end] pathway of photosynthesis’
    - Rubisco [blank_start]inefficiency[blank_end] led to the evolution of CCMs
    - C4 plants (3%) – [blank_start]spatial[blank_end] separation of carboxylases (PEPC and Rubisco)
    o Flourish in hot, tropical areas
    - CAM plants (7%) – [blank_start]temporal[blank_end] separation of carboxylases
    o Flourish in water and/or CO2 limited environments
    

    1. ARubisco
    2. BC3
    3. Cinefficiency
    4. Dspatial
    5. Etemporal

Description

Plant Biology Quiz on Carbon Assimilation, created by sophie waddington on 18/05/2018.

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sophie waddington

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