Photosynthesis+R

Photosynthesis

Overview of Photosynthesis

  • Uses light energy, H2O, and CO2 to produce food.

  • Releases O2 as a byproduct.

  • Chemical reaction:

    • Light + 6 CO2 + 6 H2O → C6H12O6 + 6 O2

Chlorophyll

  • Most common pigment used in photosynthesis.

Absorption of Light by Chloroplast Pigments

  • Absorption Spectrum includes:

    • Chlorophyll a and b

    • Carotenoids

  • Wavelength ranges:

    • 400 nm to 700 nm

Chloroplast Structure

  • Photosynthesis occurs in two main areas:

    • Thylakoid membrane

    • Stroma

  • Structure overview:

    • Outer membrane

    • Inner membrane

    • Thylakoid

    • Stroma

Key Processes in Photosynthesis

  • Photosystem II

  • Photosystem I

  • Calvin Cycle (with carbon fixation)

Photosystems

  • Embedded in the thylakoid membrane.

  • Contain chlorophyll for light absorption.

  • Light energy moves electrons.

Photosystem II

  • Light excites electrons in chlorophyll.

  • Electrons return to ground state, releasing energy.

  • Energy transferred to p680 chlorophyll, which then loses electron to primary electron acceptor.

  • Electrons replenished by splitting water, producing O2.

Electron Transport Chain (ETC)

  • Electron passed to ETC, pumps H+ into thylakoid space.

  • Facilitated diffusion back into stroma produces ATP via ATP synthase.

Photosystem I

  • Excited by light, transfers energy to p700 chlorophyll.

  • p700 loses electron to primary electron acceptor and is replenished by electrons from ETC (from p680 and water).

  • Electrons can be transferred to NADP+ to form NADPH or undergo cyclic electron flow for additional ATP production.

Calvin Cycle

  • Occurs in the stroma.

  • Involves:

    • Carbon Fixation (using RuBisCo)

    • Glucose Production

    • Regeneration of RuBP

  • Reaction:

    • RuBP + CO2 + ATP + NADPH → RuBP + Glucose

Photorespiration

  • Occurs due to RuBisCo's reaction with O2 instead of CO2.

  • Results in "garbage" product and waste of ATP and NADPH.

Stomata and Guard Cells

  • Stomata regulate gas exchange (O2 in, CO2 out).

  • Guard cells control opening and closing to manage water loss (transpiration).

  • Closing stomata can lead to O2 build-up, disrupting glucose production.