Photosynthesis and its Regulation Lecture Notes PDF
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University of Saskatchewan
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Summary
These lecture notes provide an overview of photosynthesis, including pigments, the light-dependent and independent reactions, and how it is regulated. The document also covers adaptations to stress as well as alternative pathways for plants such as C4 and CAM photosynthesis.
Full Transcript
Lecture summary notes - photosynthesis and its regulation 1. Pigments: Pigments are chemical substances that absorb specific wavelengths of light, giving them distinct colors. Types of pigments: Chlorophylls: Green pigments ess...
Lecture summary notes - photosynthesis and its regulation 1. Pigments: Pigments are chemical substances that absorb specific wavelengths of light, giving them distinct colors. Types of pigments: Chlorophylls: Green pigments essential for photosynthesis (e.g., chlorophyll a and b). Carotenoids: Orange, yellow, or red pigments involved in photoprotection and photosynthesis (part of antenna complexes). Flavonoids: Photoprotection, fruit color, coloring to attract pollinators Anthocyanins: Water-soluble pigments providing color and UV protection. 2. Pigment Locations: Found in plastids (chloroplasts and chromoplasts) and vacuoles. Pigments contribute to functions such as attracting pollinators, deterring herbivores, and protecting against UV radiation. 3. Photosynthesis Overview: Divided into light-dependent reactions (occur in the thylakoid membranes) and light- independent reactions (Calvin cycle in the stroma). Light-dependent reactions: Capture light energy to generate ATP and NADPH. Involve Photosystems I and II, electron transport chains, and water splitting. Electrons move from water to NADPH ETC generates proton gradient for photophosphorylation (production of ATP via ATP synthase as H+ flows from thylakoid lumen to stroma). Light-independent reactions: Use ATP and NADPH to fix CO2 into carbohydrates via the Calvin cycle. 4. Regulation of Photosynthesis: Factors influencing photosynthesis include stomatal conductance, mesophyll conductance, leaf anatomy, chloroplast number, and location. Stomatal opening/closing is regulated by turgor pressure changes driven by ion movement in and out of guard cells. 5. Adaptations to Environmental Stress: Cyclic Photophosphorylation: Generates additional ATP under high light intensity or low CO2 conditions. Pigment accumulation: Protects against excess light by absorbing it before it reaches chloroplasts. 6. Photorespiration: A wasteful process caused by Rubisco’s oxygenase activity under high temperatures or low CO2 levels. Releases CO2 and consumes ATP without producing sugars. Mitigated by C4/CAM photosynthesis and cyclic photophosphorylation 7. Alternative Photosynthetic Pathways: C4 Photosynthesis: Spatially separates CO2 fixation (mesophyll cells) via PEP carboxylase from the Calvin cycle (bundle sheath cells). Common in grasses. CAM Photosynthesis: Temporally separates CO2 fixation by PEP carboxylase at night from the Calvin cycle during the day. Closes stomata during day, opens at night. Common in succulents like cacti.
