Chapter 1: Introduction

• Photosynthesis is the process by which plants convert sunlight, carbon dioxide, and water into glucose and oxygen.

• Photosynthesis is a vital process for sustaining life on Earth.

• There are two main reactions in photosynthesis: the light-dependent reactions and the light-independent reactions (Calvin cycle).

• The light-dependent reactions convert sunlight into energy.

• The light-independent reactions (Calvin cycle) use the energy from the light-dependent reactions to convert carbon dioxide into glucose.

• Photosynthesis is a complex and inefficient process.

Chapter 2: The Calvin Cycle

• The light-independent reactions in photosynthesis are also known as the Calvin cycle.

• The Calvin cycle is a series of chemical reactions that convert carbon dioxide into glucose.

• Photosynthesis is essentially respiration in reverse.

Chapter 2: Called Chlorophyll

• Photosynthesis needs water, carbon dioxide, and sunlight

• Water is absorbed by the roots of metovascular plants

  • Metovascular plants have pipelike tissues called xylem

  • Xylem conducts water, minerals, and other materials to different parts of the plant

• Carbon dioxide enters and oxygen exits through stomata in the leaves

• Plants keep oxygen levels low inside their leaves

  • Reasons for keeping oxygen levels low will be discussed later

• Chlorophyll absorbs individual photons from the sun

Plant Cells and Chloroplasts

• Plant cells have plastids, unlike animal cells

• The most important plastid is the chloroplast

  • Chloroplast has a complicated internal structure

• Chlorophyll is stored in membranous sacs called thylakoids

• Thylakoids are stacked into grana

• The chloroplast has a lumen inside the thylakoid and a stroma outside the thylakoid

• Thylakoid membranes are phospholipid bilayers

  • Phospholipid bilayers maintain concentration gradients of ions and proteins

Chapter 3: Convert The Energy

• Photon created by fusion reactions of the sun hits a molecule of chlorophyll

  • Photon ends its 93,000,000 mile journey

  • Photon slaps into a molecule of chlorophyll

• Light dependent reactions

  • Chlorophyll absorbs the energy from the photon

  • Electron gains energy and gets excited

  • Electrons have nowhere to put the energy

  • Photo excitation occurs when energy is gained by electrons from a photon

• Photosynthesis converts the energy of electrons into something usable by the plant

  • First chlorophyll is part of a complex called photo system 2

  • Photo system 2 contains 99 different chemicals

  • Over 30 individual chlorophyll molecules in photo system 2

  • Photo system 2 is the first of 4 protein complexes needed for light dependent reactions

Chapter 4: Electrons Lose Their Energy

• PS 2 and protein complexes in the light-dependent reactions are located in the thylakoid membrane

• Electron transport chain is where energized electrons lose their energy

  • PS 2's chlorophyll transfers excited electron to a mobile electron carrier protein

  • Chlorophyll then splits water molecule (H2O) to replenish the lost electron

  • Byproducts of water splitting are hydrogen ions (protons) and oxygen

• This reaction is essential for producing oxygen and allowing us to breathe

Chemicals in Food

• All life is made of chemicals

• Chlorophyll creates the air we breathe

• Chemical does not necessarily mean carcinogen

Chapter 5: Bit Of Energy

• All energized electrons from PS 2 have been picked up by electron carriers

  • Transported to the cytochrome complex

  • The cytochrome complex serves as an intermediary between PS 2 and PS 1

  • The cytochrome complex uses a bit of energy from the electron to pump another proton into the thylakoid

• The thylakoid is being charged like a battery

  • Pumping the thylakoid full of protons creates a concentration gradient

  • The protons push their way through an enzyme called synthase

  • Synthase uses the energy to pack an inorganic phosphate onto ADP, making ATP

• Electrons are entering lower energy states as they move along the electron transport chain

• Electrons get re-energized upon delivery to photosystem 1

Chapter 6: The Calvin Cycle

• PS 1 and PS 2 are mixtures of proteins and chlorophyll molecules

  • Electrons get excited by photons and hitch a ride onto another electron carrier

  • An enzyme combines 2 electrons and 1 hydrogen ion with NADP plus to form NADPH

• After light-dependent reactions:

  • Chemical energy in the form of ATPs and NADPHs is produced

  • Oxygen is also produced as a byproduct

• The Calvin Cycle (light-independent reactions)

  • Occurs in the day, not necessarily in the dark

  • Uses energy from ATPs and NADPHs to produce something useful for the plant

  • Begins in the stroma of the chloroplast

  • Phase 1: Carbon fixation

    • CO2 is fixed to ribulose bisphosphate (RUBP)

    • Enzyme called ribulose 15 bisphosphate carboxylase oxidase (Rubisco) helps in this process

Chapter 7: Dependent Reactions Plants

• A one-celled organism evolved an enzyme called Rubisco to convert inorganic carbon into organic carbon

  • Rubisco allowed the organism to take in CO2 from the atmosphere

  • Rubisco was not very efficient, but better than relying on chemically formed organic carbon

  • The organism produced a large amount of Rubisco to compensate for its inefficiency

• Rubisco became the dominant form of life on Earth

  • Plants, through light-dependent reactions, increased the amount of oxygen in the atmosphere

  • Rubisco, designed in a world with low oxygen levels, started to have issues

• Rubisco started to produce a toxic byproduct called phosphoglycolate

  • Phosphoglycolate interfered with enzyme functions, including those involved in the Calvin cycle

  • Plants had to develop specialized enzymes to break down phosphoglycolate into glycine and other useful compounds

• Plants continue to produce large amounts of Rubisco

  • It is estimated that there are 40,000,000,000 tons of Rubisco on the planet at any given time

Chapter 8: Need Some Energy

• Calvin Cycle

  • Ribulose bisphosphate (RUBP) gets a CO2 added to it

    • Creates an unstable 6 carbon chain

    • Breaks apart into 2 molecules of 3 phosphoglycerate

  • Phase 2: Reduction

    • Requires energy

    • ATP adds a phosphate group to 3 phosphoglycerate

    • NADH adds electrons

    • Results in 2 molecules of glyceraldehyde 3 phosphate (G3P)

  • G3P

    • High energy, 3 carbon compound

    • Can be converted into various carbohydrates

    • Glucose for short term energy storage

    • Cellulose for structure

    • Starch for long term storage

  • Regeneration

    • Requires 5 G3P to regenerate 3 RUBPs

    • Requires 9 molecules of ATP

    • Requires 6 molecules of ADPH

Chapter 9: Conclusion

• All these chemical reactions and chemical energy

• Conversion of 3 RUBPs into 6 G3Ps

  • Only one G3P gets to leave the cycle

  • Other G3Ps needed to regenerate the original 3 ribulose bisphosphates

• Regeneration is the last phase of the Calvin cycle

• Plants turn sunlight, water, and carbon dioxide into every living thing

  • Talking, playing, climbing, loving, hating, and eating

References

• Selected references for further information

Review and Questions

• If you don't understand, check the references or rewatch the video

• Hopefully, upon review, things will make more sense

• Leave any questions in the comments below