Photosynthesis

Overview of Photosynthesis (Page 2)

• Energy Requirement:

  • All living things need energy to survive.

  • Most energy comes from the sun.

• Autotrophs:

  • Organisms that create food using sunlight.

  • Examples: algae, plants, some protists, and prokaryotes.

  • Provide energy directly (herbivores) or indirectly (carnivores) to heterotrophs.

• Heterotrophs:

  • Must obtain energy from the food they eat.

• Photosynthesis Process:

  • Converts light energy into chemical energy in organic compounds (e.g., carbohydrates).

  • Important to understand the diagram illustrating this process.

Reactants and Products (Page 3)

• Reactants in Photosynthesis:

  • Carbon Dioxide (CO2)

  • Water (H2O)

• Products of Photosynthesis:

  • Glucose (C6H12O6)

  • Oxygen (O2)

• Stages of Photosynthesis:

  • Light Reactions:

    • Captures light energy and stores it as chemical energy in molecules like NADPH.

  • Calvin Cycle:

    • Forms organic compounds with CO2 and stored energy (ATP, NADPH).

Light Reactions (Stage 1) (Page 4)

• Location:

  • Occur in chloroplasts (thylakoids).

• Chloroplast Structure:

  • Thylakoids: flattened membrane sacs.

  • Grana: stacks of thylakoids.

  • Stroma: surrounding solution.

  • Lumen: space inside thylakoids.

Pigments and Light Absorption (Page 5)

• Pigments:

  • Compounds that absorb light, integral for photosynthesis.

• Types of Chlorophylls:

  • Chlorophyll a:

    • Main pigment for photosynthesis.

  • Chlorophyll b:

    • Assists chlorophyll a and absorbs light in the green spectrum.

  • Carotenoids:

    • Accessory pigments, reflect yellow, orange, and brown; visible when chlorophyll production stops.

• Absorption Spectrum:

  • Shows the wavelengths of light absorbed by different pigments.

Photosystems and Light Reaction Steps (Page 6)

• Photosystems:

  • Clusters of pigment molecules in thylakoid membranes.

  • Photosystem I (PSI) and Photosystem II (PSII) are key components.

• Steps of Light Reactions:

  1. Light energy absorbed in PSII, exciting electrons.

  2. Excited electrons are transferred to the primary electron acceptor.

  3. Electrons pass through the electron transport chain (ETC), pumping protons into the thylakoid.

Continuation of Light Reaction Steps (Page 7)

• 4. Light also absorbed by PSI, leading to further electron excitement and transfer.

• 5. Water is split to replace electrons; this produces oxygen.

• 6. Electrons combine with NADP+ and protons to form NADPH.

ATP Production in Light Reactions (Page 8)

• ATP:

  • The main energy currency, produced during light reactions via chemiosmosis.

• Chemiosmosis:

  • Utilizes the proton gradient across the thylakoid membrane for ATP formation.

• Summary of Light Reactions:

  • Oxygen is released from H2O.

  • NADP+ → NADPH (electron carrier).

  • ADP → ATP (via ATP synthase).

  • ATP and NADPH are used in the Calvin Cycle.

The Calvin Cycle (Stage 2) (Page 9)

• Function:

  • Enzyme-assisted reactions creating 3-carbon sugars from CO2.

• Carbon Fixation:

  • Process of converting inorganic CO2 into organic compounds.

• Calvin Cycle Process:

  1. ATP and NADPH enter the stroma.

  2. CO2 enters through stomata.

  3. ATP removes H+ from NADPH to assist in glucose formation.

  4. 6 CO2 needed to form one glucose molecule.

Factors Affecting Photosynthesis (Page 10)

• Light Intensity:

  • Increased intensity raises the rate of photosynthesis until a maximum is reached.

• Temperature:

  • Higher temperatures generally increase the rate until enzymes denature.

• Carbon Dioxide Levels:

  • Higher CO2 levels enhance the rate until it levels off.

Alternate Pathways for Carbon Fixation (Page 11)

• C4 Pathway:

  • Stomata partially close; functional in high O2 and low CO2 environments (e.g., corn, crab grass).

• CAM Pathway:

  • Stomata open at night to conserve water; store CO2 as organic compounds; released during the day for the Calvin Cycle.