Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 8: Photosynthesis - Coggle Diagram
Chapter 8: Photosynthesis
overview of photosynthesis
photosynthesis is the process by which plants, algae, and photosynthetic bacteria capture light energy and use it to synthesize carbohydrates
during photosynthesis, carbon dioxide, water, and energy are used to make carbohydrates and oxygen
heterotrophs and phototrophs
heterotrophs = must obtain organic molecules in their food, whereas autotrophs make organic molecules from inorganic compounds
phototrophs
photoautotrophs use the energy from light to make organic molecules
An energy cycle occurs in the biosphere in which photosynthesis uses light, CO2, and H2O to make organic molecules, and the organic molecules are broken back down to CO2 and H2O via cellular respiration to supply energy in the form of ATP
in plants, the leaves are the major site of photosynthesis
reactions that harness light energy
light is a form of electromagnetic radiation that travels in waves and is composed of protons with discrete amount of energy
electrons can absorb light energy and be boosted to a higher energy level (an excited state)
photosynthetic pigments include chlorophylls a and b as well as carotenoids, which absorb light energy in the visible spectrum to drive photosynthesis
during linear electron flow, electrons from PSII follow a pathway along an ETC in the thylakoid membrane which generates H+ electrochemical gradient that is used to make ATP
light energy striking PSI boosts electron to a very high energy level that results in the synthesis of NADPH
during cyclic photophosphorylation, electrons are activated in PSI and flow through the ETC back to PSI. This cyclic electron flow produces an H+ electrochemical gradient that is used to make ATP
molecular features of photosynthesis
in light- harvesting complex of PSIl:
pigment molecules absorb light energy that is transferred to the reaction center via resonance energy transfer
high-energy electron from P680* Is transferred to a primary electron acceptor
an electron from water then replaces the electron lost by P680* and O2 is produced
synthesizing carbohydrates via the calvin cycle
the Calvin cycle is composed of 3 different phases = carbon fixation, reduction and carbohydrate production, and regeneration of RuBP
ATP is used as a source of energy and NADPH as a source of high-energy electrons to incorporate CO2 into a carbohydrate
variations in photosynthesis
C3 plants incorporate CO2 into RuBP to make 3PG which is a three carbon molecule
photorespiration occurs when the
level of O2 is high and that of CO2 is low
, which happens under
hot and derby conditions
. During this process, some O2 is used and CO2 is liberated.
Photorespiration is inefficient because it reverses the incorporation of CO2 into an organic molecule
some C4 plants avoid photorespiration by incorporating CO2 first (via PEP carboxylase) into a four-carbon molecule, which is pumped from Mesophyll cells into bundle-sheath cells. This maintains a high concentration of CO2 (minimizing photorespiration) in bundle-sheaths cells, where the Calvin cycle occurs
CAM plants (a type of C4 plant) prevent photorespiration by fixing CO2 into a four carbon molecule at night, then running the Calvin cycle during the day with their stomata closed to reduce water loss