Photosynthesis
Key terms:
Photosynthesis – is a synthesis of organic chemicals by using the energy of
sunlight.
Autotroph – is an organism that gets its energy from nonliving source
Chemoautotroph – organisms that gets its energy from chemicals
Heterotroph – is an organism that gets its energy from living source
Organisms that do photosynthesis in different ways - Plants, green algae,
unicellular protist, cyanobacteria (first photo synthesizers), and purple sulfur
bacteria
Everything is round and flat because of maximum energy needed
Structure:
 Chloroplast is where photosynthesis happens
 Has chlorophyll, which is in thylakoid
 Stacks/Layers of thylakoid are called grains
 Liquid around are called stroma (inner and outer membrane)
First part (Absorption Spectrum):
 Its about transferring energy
 How do we capture sunlight?
 Light reaction and dark reaction
o Reactions that require sunlight and reactions that don’t
 Transport chain
 Calvin cycle does not require sunlight (dark reaction)
 Electron carrier: NADPH
 Photophosphorylation: The creation of ATP by using sunlight
 Carbon fixation: fixation – sequester/taking the atom or molecule out
from the atmosphere and sticks it to the sugar molecule
 Electromagnetic radiation – it's a type of energy (light)
o Energy that travels as a wave (radio waves)
o There’s the range or spectrum that plants can reflect/absorb the
light
o Our eyes can see visual spectrum
 The peak is absorbing and the low ones are reflected
 Green light is the slowest
 Plants that are born at the bottom of the jungle usually use carotenoid
 Chlorophyll – The important one is the porphyrin ring with carbon tails
and with a center of magnesium atom, which is used to absorbing light
 Light moves in photons (a measurable unit of light).
o Light hits the molecule (ground level)
o The Mg/electron gets excited (more energy)
o When electron doesn’t gets excited, then heat and light is emitted
C6H12O6 + 6O2 <- 6CO2 + 6H2O
Second part:
 Photosystem – the light shines, it gathers the energy from one chlorophyll
to another
 Dichlorophyll A molecule with two stuck together
 Photo system 2 sits in the thylakoid, transferring the energy to the central
P680 (two chlorophyll stuck together)
 There’s a water splitting water splits water into oxygen hydrogen and
electron
 The electron picks the energy from the P680
 The electron goes to the pump which pumps H+ into the thylakoid by
using the energy from electron
 Photosystem 1 is the second one. It has chlorophyll A collecting energy.
The center of it is P700 (center of the photosystem 1)
 The electron comes and pick the energy from the P700 because the
energy is concentrated in the center
 The electron gets recharged and then the NADP reductase makes NADPH
by taking electron (NADHP + (H+) + e-) [anabolism]
 Now, we’re reducing H+ in the stroma in two ways
 ATP synthase is sitting in the thylakoid and its making ATP by ADP + P
from the membrane potential of the H+ inside the thylakoid
 Its making ATP by the high concentration inside the thylakoid and out to
the stroma
 The end products in the stroma is NADPH and ATP
 Then, calvin cycle happens in the stroma
 Cyclic in two ways:
o Electrons in the transport chain just cycling inside the thylakoid
after P700
o Electrons in the photosynthesis: cycling inside the thylakoid after
P700 and the breaking down of NADPH (NADPH + (H+) + e-) in the
Calvin cycle
 10.17 diagram:
o Photosystem II is collecting energy from light and then the energy
is concentrated in the P680
o End products: NADPH and ATP (energy carrier) by
photophosphorylation
 Calvin Cycle:
o 3-5-carbon compounds – ribolose biphosphate (RUBYP)
o Rubisco – enzyme that allows plants to do photosynthesis. Carbon
fixation. Has low affinity for carbon. It gives carbon to each 3-5carbon compounds -> 3-6-carbon compounds.
o Then it becomes 6-3-carbon compounds (3 phosphoglycerate
(molecules is on the 3rd carbon)
o We want to add phosphate by substrate phosphorylation. 6ATP is
broken down to ADP. 1-3-biphosphoglycerate
o We use NADPH is broken down to NADP + H. the release of energy
to rearrange the atoms. Glyceraldehyde 3 phosphate.
o Now 6-3-GP’s, its energetic
o We take out one of the 3’s so we end up with 5-3-GP

o We’re gonna use 3ATP to rearrange to 3-5-carbon RUBYP’s
o G3P x 2 = glucose
Different types of photosynthesis:
o Carbon dioxide
o Water
o Sunlight
o Stomata (hole in the leaves),
o Plants in the dessert C4 respiration (thick leaves):
 It takes in the carbon dioxide at night
 PEP carboxylase takes the CO2 out of the air and holds onto
it until the plants are ready to use. Higher affinity for CO2.
 During daytime, the stomata closes and PEP carboxylase
gives the CO2
 Handles things by location
o Palasade and mesophylls (spongy). Vascular tissues with bundle
sheaf cells are around of the vascular tissues and the mesophyll
cells mostly do photosynthesis
o Crussalacean acid metabolism (CAM): its an organic compound. Its
separated by time. Transport chain at daytime and Calvin cycle at
night time.
 Using chemicals to hold CO2
 Gives CO2 to the plant during calvin cycle