Part I: Energy & Transport
The Energetics of Plant Life
Plants are the primary producers of nearly all terrestrial ecosystems, converting solar energy into chemical energy through photosynthesis. This part explores the biophysical and biochemical basis of how plants acquire water and minerals, harvest light, and fix atmospheric CO2 into organic molecules. These processes underpin all of plant metabolism and growth.
Water movement through the plant is governed by thermodynamic gradients expressed as water potential. Light capture involves specialized pigment–protein complexes embedded in the thylakoid membrane, while carbon fixation relies on the enzyme RuBisCO — the most abundant enzyme on Earth — operating within the stroma of chloroplasts.
~1%
Solar energy captured by photosynthesis
120 Gt C/yr
Global terrestrial CO₂ fixation
~50%
RuBisCO as fraction of leaf nitrogen
Lecture Companions: Light & Dark Reactions
Five undergraduate lectures developing the photosynthetic light reactions (PSII, PSI, electron transport, photophosphorylation) and the dark reactions / Calvin cycle — review before the chapter-by-chapter treatment below.
Light Reactions
19A. Introduction to the Light Reactions
19B. The Light Reactions
19C. Tying Up Loose Ends
Dark Reactions & Calvin Cycle
20A. Introduction to the Dark Reactions
20B. The Calvin Cycle
Chapters in Part I
Chapter 1: Water & Mineral Transport
Water potential (\(\Psi = \Psi_s + \Psi_p + \Psi_g\)), osmosis, root pressure, transpiration–cohesion–tension theory, mineral ion uptake via the Nernst equation, and aquaporin structure and function.
Chapter 2: Photosynthesis — Light Reactions
Chlorophyll absorption, PSII water-splitting, electron transport chain (PQ, cyt b6f, PC), PSI, ferredoxin, NADP⁺ reductase, chemiosmotic ATP synthesis, and the Z-scheme.
Chapter 3: Calvin Cycle & Carbon Fixation
RuBisCO kinetics with O₂ competitive inhibition, the three phases of the Calvin cycle, stoichiometry (3CO₂ + 9ATP + 6NADPH → G3P), and light-dependent regulation via thioredoxin.
Key Equations in Part I
Water potential: \(\Psi = \Psi_s + \Psi_p + \Psi_g\)
Proton motive force: \(\Delta\tilde{\mu}_{H^+} = -2.3RT\,\Delta pH + F\,\Delta\Psi\)
RuBisCO with O₂ inhibition: \(v = \frac{V_c [CO_2]}{K_c\left(1 + \frac{[O_2]}{K_o}\right) + [CO_2]}\)