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BIOL227 - Plant & Algae Diversity > Module 2 - Plant Physiology (Photosynthesis) > Flashcards

Module 2 - Plant Physiology (Photosynthesis) Flashcards

1
Q

Why should we care about photosynthesis?

A

Arguably one of the most important processes on Earth - provides food, habitats, fossil fuel & wood fuel energy, regulates the atmosphere (increased O2 and decreased CO2)

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2
Q

What is photosynthesis?

A

The conversion of light energy into chemical energy - the capture of light energy, and combination of CO2 and H2O to create sugars and O2 (by-product of H2O being split).

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3
Q

What is the basic chemical formula of photosynthesis?

A
  • Carbon dioxide + Water + light energy –> carbohydrates + 2 oxygen OR
    CO2 + 2H2O (electron donor) + light –> [CH2O] (carbs) + 2O2 (oxidised electron donor) + H2O (water)
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4
Q

What do the light dependent reactions capture and create?

A
  • Capture the energy of light to use it to make NADPH (H+ carrier)
  • Make ATP (energy storing molecule)
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5
Q

What does the light independent (dark) reaction convert and create? And where does it occur?

A
  • Converts NADPH and ATP to NADP+ and ADP
  • In the stroma of the chloroplast
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6
Q

Describe the major steps in the “Z” scheme (light reaction) and its main purpose

A
  • Chlorophyll and other pigment absorb photons
  • Electrons are created by splitting water into H+ and O2 (photolysis)
  • Electrons are moved through PSII to create ATP after a series of electron donations
  • PSI absorbs photons and takes electrons further through the electron transport chain and electron donations to create NADPH
  • Main purpose of light reactions is to create ATP and NADPH that are used in dark reactions
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7
Q

What does the light independent reaction start off with? What are the basics of this reaction? What are the products used for?

A
  • Starts off with the NADPH created in the light reactions
  • Enzyme RuBisCo transforms CO2 from seawater/atmosphere to create sugars
  • Sugars created will eventually be used for metabolic fuel in cellular respiration or creation of new tissues
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8
Q

During the first step of the light-independent reaction, what does RuBisCO do?

A

The enzyme RuBisCO welds one carbon atom from a CO2 molecule with the RuBP chain (five carbons) to build an initial six-carbon sequence.

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9
Q

Why is RuBisCO not efficient at its job? And why is photorespiration costly? How have certain plants overcome this problem?

A

It evolved during a time with low atmospheric O2 concentrations, therefore carboxylase activity competes with oxygenase activity - high oxygen concentration leads to the switch from photosynthesis to photorespiration. C4 and CAM plants have overcome this by having CCMs, and either separating carbon fixation spatially or temporally.

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10
Q

What do CO2-concentrating mechanisms do?

A

Concentrate CO2 at the site of RuBisCO

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11
Q

What are abundant and limiting in the terrestrial and marine/freshwater environment?

A

Terrestrial: CO2 abundant (diffuses rapidly), water can be limiting
Marine/Freshwater: Water abundant, CO2 limiting (diffuses slowly)

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12
Q

What is the C3 plants’ process of photosynthesis?

A

RuBisCO welds CO2 to RuBP to create 2, three carbon phosphoglycerates (PGAs)
- Non-CCM photosynthesis

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13
Q

Why is the C3 process inefficient in arid environments?

A
  • Loss water through stomata, although closing them to stop water loss prevents CO2 uptake, and photorespiration occurs (adding oxygen instead of CO2 to RuBP)
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14
Q

What is the process of C4 plants? And why is it more efficient in arid environments?

A
  • Creates a 4-carbon molecule in mesophyll
  • Concentrates CO2 at RuBisCO in the mesophyll. Carbon fixation occurs in the spatially isolated bundle sheath cells
  • Costs more ATP than C3, but conserves more water and limits photorespiration
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15
Q

What is the process of CAM plants? And how are they particularly adapted for extremely arid environments?

A
  • Seperates process temporally: stomata open at night, CO2 reacts with PEP to form malate
  • Malate is stored in vacuoles until daytime when stomata close, where it is then decarboxylated and CO2 is released into Calvin cycle.
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16
Q

What environments do C3 plants thrive in? And why might this be?

A
  • Where sunlight is moderate, temperatures are moderate, and water is plentiful
  • They evolved when atmospheric CO2 levels were high, and therefore fall into photorespiration and a loss of carbon and nitrogen in warm environments
17
Q

What do C4 plants use less of compared to C3 plants? And what advantage does this give them?

A
  • Nitrogen, as C4 plants largely use PEPC instead, which needs much less nitrogen compared to RuBisCO
  • Therefore C4 have an advantage in places where nitrogen is limited
18
Q

What are the two main ways that algae uptake carbon dioxide? And why is one way not considered to be a true CCM? When is this strategy inefficient?

A

1) Via energized direct uptake (true CCM) through antiports and/or symports –> Requires less energy than CO2 diffusion
2) Catalyzed external conversion of HCO3- into CO2 to enhance diffusion (not a true CCM) - the enzyme carbonic anhydrase externally catalyzes the conversion of HCO3- to CO2
- Does not concentrate/elevate CO2 levels at site of Rubisco, although costs less energy than energized uptake.
- Not a good strategy when pH is high/CO2 levels are low

19
Q

How might having a CCM or a suite of different CCM components be advantageous in algal species?

A
  • CCMs overcome the low CO2 concentration and slow diffusivity in water
  • Having a CCM can be more or less efficient in certain environments, and could be advantageous over neighboring species
20
Q

What conditions are terrestrial plant CCMs favored?

A
  • Low water
  • High temperature
  • Low nitrogen
21
Q

What do algal CCMs require and what conditions are they favored in?

A
  • CCM use requires high light and high nutrients
  • CCM use favored at higher temps and lower CO2 concentrations
22
Q

Non-CCM algal species tend to increase as:

A
  • Light decreases
  • Nutrients decrease
  • CO2 increases
  • Temperature decreases
23
Q

What is one of the most limiting nutrients for terrestrial plants? And how do they take this up?

A

Nitrogen!
- Obtained from soil via plant roots (Nitrite > Nitrate > Ammonium), and can be increased through symbiosis with nitrogen-fixing microorganisms within nodules

24
Q

What other important nutrients are required by plants? And how do they take these up?

A
  • Include potassium, magnesium, calcium, copper, iron, manganese, cobalt, sodium, zinc
  • Most of the sulfur in plants is from sulfate absorbed via a H+ -SO42- symporter from soil
  • HPO42- in the soil is absorbed by roots via a H+ -HPO42- symporter (usually for ATP creation)
25
Q

What are the main nutrients taken up in algae? And how do they do so?

A
  • Nitrate, phosphorus and sulfate uptake all requires ATP use and energized uptake
  • Nitrate and sulfate also require NADPH use to energize reactions within the cell into useable forms of N and S
26
Q

How does calcification occur? And why is it so important in the ocean?

A
  • Calcification is the process of bicarbonate and calcium uptake from seawater and subsequent precipitation of minerals within the calcifying fluid
  • An important process of creating reefs and provides benefits to organism structure/defense
27
Q

What are the two main techniques for measuring calcification?

A
  • Total alkalinity anomaly technique measures changes in total alkalinity
  • Buoyant weight measure the weight of CaCO3 material precipitated over longer time periods (is more accurate)
28
Q

Why might ocean acidification impact calcification?

A
  • Ocean acidification decreases seawater CO32- (carbonate) and increases protons (H+)
  • H+ and/or carbonate concentrations in seawater could increase dissolution of exposed skeleton
  • Higher H+ in seawater makes it more difficult for calcifications to occur, by changing internal pH (i.e. H+ concentrations)
29
Q

How do we determine CCM presence/absence?

A

“The C3 vascular land plants relying on diffusion of CO2 from the bulk atmosphere through the diffusion boundary layer, stomata etc. up to Rubisco have organic matter that is severely depleted in 13C relative to the atmospheric CO2. One reason for this is the more rapid carboxylase activity of Rubisco with 12C than with 13C.”

30
Q

Based on 13C levels, how do we determine whether a plant has a CCM or not?

A
  • If delta13C is from 0% to -10%, there is direct HCO3- uptake only (CCM)
  • if delta13C is from -30% to -10%, there is a possible mixture pf HCO3- and CO2 uptake
  • If delta13C is greater than -30%, there is CO2 uptake only (Non-CCM)
31
Q

How do reefs “grow”?

A

Complicated!
- Many different types of reefs (e.g. with or without coralline algae, or fully composed of coralline algae)
- Different parts of the reef built in different ways
- Timescales are important

32
Q

What are the gross calcium carbonate producers in the ocean?

A
  • Corals
  • Coralline algae
  • Sediment producers
  • Sediment input from hydrodynamics (e.g. currents)
33
Q

How is calcium carbonate removed from these systems?

A
  • Physical: storms, wave action, currents, sediment export
  • Chemical: dissolution of sediments/reef framework
  • Biological: bioerosion - sponges, parrotfish, cyanobacteria, endolithic algae, sea urchins, borers (e.g. mussels)
34
Q

What are the two methods of measuring carbonate production?

A
  • Census based: organism covers, organism calcification rates, bioerosion rates, rugosity, reef porosity (specific)
  • Hydrochemical: measure changes in total alkalinity flux over time or space on the reef
35
Q

Why is there so much between reef variability of carbonate production?

A
  • Different reefs have different contributions of: organism cover, organism calcification rates, bioerosion rates, sediment production
36
Q

How will climate change impact carbonate production?

A
  • Decreased coral calcification, coralline algal calcification, and coral cover
  • Increased sediment dissolution
  • Changes in bioerosion rates
37
Q

From the results of a recent study on projected reef net production, what did they find reefs under RCP8.5 that still had net accretion tended to have in common?

A
  • Most were in the Pacific
  • Had initially high rates of net carbonate production
  • Had high contribution of coralline algae to their net production
38
Q

Why is coralline algae important? And how could further studies expand on its key role in reef ecosystems?

A
  • Can calcify at similar rates to corals
  • Contribution to reef growth and net carbonate production likely very largely underestimated
  • Solutions to improving coralline algal contributions

BIOL227 - Plant & Algae Diversity (2 decks)

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