Boundless Biology by Lukas Waller

3.4 - CAM and C4 plants

C4 Plants * Examples: Maize, sugarcane, sorghum. * Adaptation: Found in hot, dry environments to minimize photorespiration. * Key Enzyme: PEP carboxylase, which has a high affinity for CO₂ and does not react with O₂, reducing photorespiration. Pathway: * CO₂ + PEP (3C) → Oxaloacetate (4C) → Malate (4C). * Malate is transported to bundle-sheath cells, where CO₂ is released for the Calvin cycle. CAM (Crassulacean Acid Metabolism) Plants * Examples: Pineapple, cacti, succulents. * Adaptation: Found in arid environments; adapted to conserve water. * Stomata Behavior: Stomata open at night to minimize water loss. * Key Enzyme: PEP carboxylase, similar to C4 plants, used for initial carbon fixation at night. Pathway: * CO₂ + PEP → Oxaloacetate (4C) → Malate (4C), which is stored in vacuoles as malic acid overnight. * During the day, malic acid is broken down to release CO₂ for the Calvin cycle.

3.3 - Calvin Cycle (LIR)

Location: Takes place in the stroma of the chloroplast. * Phases of the Calvin Cycle: 1. Carbon Fixation: 2. Reduction Phase: 3. Regeneration of RuBP: * Key Enzyme: * RuBisCO is the primary enzyme, acting as both a carboxylase and an oxygenase. * Can bind to CO₂ (carboxylation) or O₂ (oxygenation), the latter leading to photorespiration, which reduces efficiency. * Energy Requirement: * For each full turn of the cycle (producing 1 G3P): * To produce one glucose molecule, the cycle must run twice, requiring: * Products: * G3P is the direct product, which can be used to form glucose and other carbohydrates. * Photorespiration Issue: * Occurs when RuBisCO fixes O₂ instead of CO₂, leading to wasteful energy loss. * More likely in hot, dry climates when stomata close to conserve water. * Adaptations: * C4 and CAM plants have evolved mechanisms to minimize photorespiration and improve efficiency, which will be explored further.

3.2 - Light Dependent Reactions

Things To Remember * Cyclic Photophosphorylation occurs as a means to produce additional ATP rather than ATP and NADPH. This is because the Calvin Cycle (next episode) requires more ATP than NADPH. * PSI = Photosystem 1, PSII = Photosystem 2 Diagrams * Noncyclic Photophosphorylation: ⁠https://cdn.kastatic.org/ka-perseus-images/faeb1179a538a3a8106fa5f3b9bd90c92f9834a7.png⁠ [https://cdn.kastatic.org/ka-perseus-images/faeb1179a538a3a8106fa5f3b9bd90c92f9834a7.png] * Cyclic Photophosphorylation: https://cdn.kastatic.org/ka-perseus-images/d47991f2cf9c7a4fc22f055b60793af8c341991f.png [https://cdn.kastatic.org/ka-perseus-images/d47991f2cf9c7a4fc22f055b60793af8c341991f.png] Quizzes * https://quizlet.com/30876000/light-dependent-reactions-light-independent-reactions-flash-cards/ [https://quizlet.com/30876000/light-dependent-reactions-light-independent-reactions-flash-cards/]

3.1 - Intro to Photosynthesis

Key Terms, try drawing these out. A) Leaf Anatomy * palisade layer * cuticle layer * spongy layer * vascular bundle (xylem/phloem) * stomata * guard cells * epidermis (upper/lower) B) Chloroplast Anatomy * membrane (inner/IMS/outer) * thylakoid membrane * thylakoid lumen * thylakoid lamella * granum C) When do stomata open and how do they do so? Topics not covered in-depth: * Sunlight triggers [K+] ion movement which requires ATP from the plant in order to open guard cells.