BIOL Exam 2D - Photosynthesis

BIOL-1020, Zanzot, Chapter 10 Photosynthesis

photosynthesis

process that converts solar energy into chemical energy

photosynthesis

• nourishes almost entire living world (direct/indirectly)

• maintains O₂ concentration in atmosphere (enabling aerobic respiration

autotrophs

plants, algae, cyanobacteria

organisms capable of photosynthesis (1:4)

cyanobacteria

• responsible for the first surge in O₂ concentration in the atmosphere

• cell first engulfed by eukaryotic cell (endosymbiont theory)

autotrophs

organisms that sustain themselves w/o eating anything derived from other organisms (so through photosynthesis)

heterotrophs

organisms that obtain their org. material from other organisms

dependent on photo autotrophs, humans

chloroplasts

in the mesophyll, carry out photosynthesis

stomata

• microscopic pores where CO₂ enters and O₂ exits (plants)

  • gas exchange in leaves of plants

chlorophyll

green pigment

thylakoid

disc that holds chlorophyll

• site of light dependent rxns

grana

stacks of thylakoids

• split H₂O into H₂ + O₂

• H₂ e- are added into sugar molecules

• O₂ is a by-product

what chloroplasts do in photosynthesis

6CO₂ + 12H₂O + light → C₆H₁₂O₆ + 6O₂ + 6H₂O

(inverse of cellular respiration)

formula for photosynthesis

photons

discrete energy particles

electromagnetic radiation

travels in rhythmic waves

wavelength, frequency, energy particles

(3) traits of electromagnetic radiation

wavelength

determines type of electromagnetic energy

frequency & wavelength

inversely proportional

visible light

photo pigments absorb ___ wavelengths and reflect the areas we see

light reactions & Calvin cycle

(2) essential components of photosynthesis

light reactions

1. splits H₂O

2. releaes O₂

3. reduce NADP+ (e^- acceptor) to NADPH

4. make ATP from ADP

photo part of photosynthesis

Calvin cycle

• begins with carbon fixation

• forms sugar from CO₂ using ATP & NADPH

• in the stroma

carbon fixation

incorporating CO₂ into organic molecules

cyclic e^- flow

e^- cycle back from Fd to the PSI reaction center

only uses photosystem I

linear e^- flow

• involves both PSI & PSII

• produces ATP and NADPH using light energy

• primary pathway

ATP only

cyclic e^- flow products

ATP, NADPH, O₂

linear e^- flow products

photosystems

consist of a reaction-center (protein)complex surrounded by light-harvesting complexes

PSII

rx center chlorophyll (P680)

acts first in linear e- flow

PSI

rx center chlorophyll (P700)

acts second in linear e- flow

chemiosmosis

produces ATP through high concentration of H⁺ ions inside the thylakoid lumen

both double membrane energy-converting organelles that make p⁺ gradients for energy production

similarities in structure of chloroplasts and mitochondria

1. carbon fixation

2. reduction (of C)

3. regeneration of RuBP (CO₂ acceptor)

(3) parts of Calvin Cycle

G3P (glyceraldehyde 3-phosphate)

product of the Calvin Cycle (sugar)

rubisco

central in photosynthesis

inefficient

most abundant enzyme

photorespiration

alt. method of C fixation in hot, dry climates

dehydration causes plants to close the stomata to not lose water (plasmolyze)

why photorespiration occurs

C3 plants

reduces CO₂ access & O₂ buildup, plant does not anything

C4 plants

avoid cellular respiration spatially, through separation of O₂ and rubisco

• special mesophyll and bundle sheath cells (Kranz Anatomy)

• PEP carboxylase produces CO₂

how C4 plants avoid photorespiration

PEP carboxylase

adds CO₂ to Calvin Cycle to avoid photorespiration, but uses ATP

CAM plants

avoid photorespiration temporally, through separation of O₂ and rubisco

opening stomata at night to store CO₂ for Calvin cycle during the day

how CAM plants avoid photorespiration

stroma

fluid in chloroplast

• site of light independent rxns