Photosynthesis Explained in Detail


  1. Introduction
  2. Where does this happen?
    1. Leaves
    2. Chloroplasts
  3. Soil, Water, and Light
  4. Light
  5. Pigments
  6. Light-dependent Reactions
  7. Light-independent reactions
  8. Summary
  9. C4 Plants and CAM Plants
  1. Introduction

Photosynthesis (PS) = The ability to make food (sugars) in presence of sunlight. = Process in which the sun’s energy is used to fix (attach) CO2 into organic compounds. = Process in which the sun’s energy is used to REDUCE CO2 into organic compounds.

Reduction – gain of 1 or more e- (gain of H+ atom)

Oxidation – loss of 1 or more e- (loss of H+ atom)

e- often travel with an H+.

Autotrophs – self-feeders – includes plants, algae, some bacteria. All are photosynthetic

PS: 6CO2 + 12H2O à C6H12O6 (glucose) + 6 H2O + 6O2

Reduction, function is to make the glucose.

~250 billion metric tons of sugar is produced every year. A bit over ½ is in the oceans.

Overall PS steps:

  1. Capture sun’s energy
  2. Make ATP + NADPH (e- carrier, different than the other ones)
  3. Uses ATP + NADPH to make sugar
  1. Where does this happen?

Majority of PS occurs in leaves


Top of leaf covered by cells

See notes in book

Vascular tissue –

Xylem – moves up

Phloem – moves down – see notes & fig 8.1

In the chloroplasts is where PS is occurring

Chloroplasts – See notes

  1. Soil, Water, & Light.

Section 8.2 – C.B. van Niel – 1930’s

Purple sulfur bacteria

CO2 + 2H2S à(w/ light) made CH2O (sugar unit, C6H12O6) + H2O + 2S

CO2 + 2H2A à(CH2O + H2O + 2A

CO2 + 2H2O à(CH2O) + H2+O + O2

Read this section in book.

Is light necessary for ALL of photosynthesis?

  1. Light dependent reactions
    1. Sun’s energy is used to make ATP + NADPH
    2. Light-independent reactions – Calvin Cycle (RECENTLY been determined to not be completely light-independent
      1. ATP + NADPH are used to make sugar