lecture 2 (photosynthesis and nutrient cycles)

Question 1

describe the equations and general process of oxygenic photosynthesis

Answer 1

light reactions: (splitting water, producing ATP)
H2O + NADP+ADP+Pi -> O2 +ATP +NADPH
light independent reactions: (C fixation)
CO2 + NADPH + H + ATP -> CH2O + NADP+H2O + ADP+Pi
overall reaction:
CO2+H2O -> CH2O + O2

Question 2

does photosynthesis always produce O2? briefly describe the difference between oxygenic and non oxygenic photosynthesis

Answer 2

no, can produce sulphur instead of oxygen
CO2+2H2S -> CH2O + H2O+2S

Question 3

describe the roll of aquatic algae in carbon sequestration

Answer 3

part of the carbon cycle:
phytoplankton take up through PP, sometimes retained in surface waters and recycles CO2 into surface waters. some sinks out through fecal matter, marine snow, sloppy feeding etc. can be mixed back up or sequestered in sediments

Question 4

what is the range of wavelengths for light that are used by algal pigments?

Answer 4

between 400-700nm

Question 5

what does PAR stand for?

Answer 5

photosynthetically active radiation (the range of visible light)

Question 6

what are the general functions accomplished by each part of the cell for photosynthesis (antennae complex, photosystems 1&2, chloroplast stroma)

Answer 6

antenna complex -> resonance transfer of light
photosystem 2 -> splitting water
photosystem 1 -> production of NADPH
chloroplast stroma -> fixation of carbons into sugars

Question 7

what is the main photosynthetic pigment?

Answer 7

chlorophyll a

Question 8

how does the antennae complex work?

Answer 8

“satellite dish”, energy transfers from pigment molecule to pigment molecule until it reaches the reaction center (Chl a)

Question 9

what is the function of carotenoids (and give two examples)

Answer 9

anti-oxidants to protect from UV radiation
eg. carotenes, xanthophylls

Question 10

what wavelengths go deepest

Answer 10

blue

Question 11

how does light quality and quantity change with depth?

Answer 11

near the surface light “quality” (wavelength) is good, since there is still all wavelengths. this decreases with depth, as different wavelengths attenuate at different depths (red first, blue last)
“quantity” (intensity) of light is a function of water clarity. light penetrates deeper in clear waters than in turbid water

Question 12

describe three strategies of algae to deal with variations in light level

Answer 12

1. phototaxis -> moving towards light using photoreceptors (eg. rhodopsin, phytochrome) and flagella
2. accessory pigments -> optimize photosynthesis and protect from photodamage
3. mixotrophy -> using multiple feeding methods to get enough “food” (eat other things when light is low)

Question 13

what is the pivotal photosynthetic pigment in algae?

Answer 13

chlorophyll A

Question 14

what are the main roles of accessory pigments in algal cells?

Answer 14

to optimize photosynthesis by harvesting wavelengths not absorbed by chl a
protecting from photodamage from excess light (carotenoids)

Question 15

draw the absorbtion spectra for carotenoids, chl a and chl b

Answer 15

wavelengths from 400-700
chl a: mid then peak about 450 and steep decline, low until smaller peak ~675nm
chl b: low, peak around 490 (higher than chla), low then lower peak around 690nm
carotenoids: medium then two peaks ~475 and 500nm, then low for rest

Question 16

describe 3 evolutionary adaptations that allowed algae to utilize CO2 in lower concentrations than those present in early earth

Answer 16

colonization of terrestrial habitats (higher diffusion of CO2 from air)
evolution of enzyme RuBisCo that catalyzes incorporation of inorganic CO2 into reduced organic compounds
evolution of carbon concentrating mechanisms

Question 17

why is it important to expose rubisco enzyme to high levels of CO2 around its active site?

Answer 17

in order for Rubisco to function as a carboxylase and convert CO2 into reduced organic compounds

Question 18

what is photorespiration?

Answer 18

binding of O2 at the active site of Rubisco, which oxidizes it and causes loss of organic C

Question 19

define specificity and turnover rate in Rubisco

Answer 19

specificity: ratio in selectivity of CO2 over O2 (higher = more specific)
turnover rate: rate of turnover Kcat (how fast)
trade off between these -> can be one or the other

Question 20

describe with a diagram the CCM in cyanobacteria

Answer 20

HCO3- is taken up through active transport (using ATP) or through plasma membrane transporters with Na
CO2 diffuses into the cell, converted into HCO3- by NADPH in the thylakoid membrane
charged HCO3- is trapped in the cell, must be converted to CO2 for photosynthesis use
in the carboxysome HCO3- +H -> CO2+H20 conversion takes place, using enzyme carbonic anhydrase to speed it up. rubisco is in there and uses CO2 for PP (some leakage occurs)

Question 21

describe with a diagram the CCM in eukaryotic cells

Answer 21

several types of CA enzymes, has pyrenoids instead of carboxysomes.
HCO3- is converted to CO2 with CA enzyme. CO2 diffuses in, HCO3- is transported into cytosol, then the chloroplast.
can also be converted into C4 compound before entering chloroplast. CO2 is released from the C4 compound for fixation through RuBisCO

Question 22

what is the function of CCMs?

Answer 22

to increase the CO2 supply to Rubisco

Question 23

why are CCM required by modern algae?

Answer 23

because algae evolved in a high CO2 world, and now is much lower

Question 24

indicate 5 commonly required mineral nutrients by algae, describing function/location of these nutrients in algal cells

Answer 24

N -> amino acids, nucleotides, chlorophyll, phycobillins
P-> ATP, DNA, phospholipids
Na -> nitrate reductase
Co -> Vitamin b12
Mg -> chlorophyll

Question 25

describe with a diagram the basic steps in the process of nitrate vs ammonium utilization by algae

Answer 25

both are taken in by active transport. NO3- is usually more available, but more energetically expensive. Nitrate reductase (which needs Iron) reduces it to NH4+.
this is important for cells but not that abundant ->converted to reduced organic nitrogen used for protein and chlorophyll synthesis

Question 26

which oceans are iron limmited?

Answer 26

Arctic, equatorial pacific, and Southern oceans

Question 27

describe how calcification, HCO3 utilization and photosynthetic processes are linked

Answer 27

combine to make net equation
2HCO3 + Ca -> CaCO3 + CH2O + O2
calcification:
CO2+Ca2+H2O-> CaCO3+2H
HCO3 utilization:
2H + 2HCO3-> 2CO2+2H2O
photosynthesis:
CO2+2H2O+8protons ->CH2O + H2O+O2

Question 28

how can sulfur released from algal cells affect earths climate?

Answer 28

they release DMSP which can contribute to warming of the atmosphere