Photosynthesis Unit
Photosynthesis
= a process that captures energy from sunlight to make sugars that store chemical energy
- plants absorb visible light for photosynthesis
- appears white but is made of a variety of colors (ROYGBIV) = visible spectrum
- pigment = a compound that absorbs light
- different colors absorb different colors of light
- chlorophyll = a molecule in chloroplasts that absorbs visible light
- two types: chlorophyll a (primary pigment)
chlorophyll b (accessory pigment)
- absorb mostly red and blue light
- neither a nor b absorbs green light (this is why plants appear green – color is reflected)
- carotenoids (accessory pigments) – contain yellow, orange, red, brown pigments
- in plants, chlorophylls are much more abundant than other pigments
- in fall, plants lose their chlorophylls (carotenoids then become visible)
Light Reactions
- capture energy in sunlight and transfer it
- take place in thylakoid membrane of chloroplast
- chlorophyll absorbs energy from sunlight
- water is broken down (into H+ ions, electrons, and oxygen)
- oxygen is released as a waste product
- NADPH is formed (functions like ATP = energy) when electrons are added to NADP+
- energy is transferred to make ATP (when H+ ions diffuse)
- overall, oxygen is given off as a waste product, NADPH and ATP are formed
Dark Reactions (Calvin Cycle)
- energy (NADPH and ATP) from light reactions make sugars
- occurs in stroma of chloroplast
- does not need sunlight
- carbon dioxide is needed
- a simple sugar, glucose, is formed from carbon dioxide and energy from ATP and NADPH
- overall, glucose, NADP+, and ADP are created. NADP+ and ADP go back to the light reactions
Equation of Photosynthesis
6CO2
(carbon dioxide)
+
6 H2O
(water)

C6H12O6
+
(sugar = glucose)
6O2
(oxygen)
Functions of Photosynthesis
- ultimately produces food for all organisms
- provides materials for plant growth/development
- simple sugars become starch and cellulose (found in cell walls)
- helps regulate Earth’s environment
- removes carbon dioxide from atmosphere
Factors that Affect Photosynthesis
1) Light Intensity – as light intensity increases, photosynthesis increases to a point
2) CO2 Concentration – as CO2 Concentration, photosynthesis increases to a point
3) Temperature – as temperature increases, photosynthesis will increase to a point, then a decrease will
occur if temperatures continue to increase