Photosynthesis Notes

Energy for Life Processes
All organisms obtain and use energy to carry out the functions of life
o Energy comes from the sun
– (producers) make their own food
Heterotrophs – (
) obtain energy by eating autotrophs or other heterotrophs
Plants make their own food by converting
into chemical energy
o Use this energy for their own metabolic functions (respiration, growth and reproduction)
o Their stored energy becomes energy for consumers
Overview of Photosynthesis
o Autotrophs (plants)
o Photosynthesis – process by which
use light energy to produce ATP and
organic molecules (glucose) from inorganic molecules (CO2 and H2O)
Where does photosynthesis occur?
o Leaves  Leaf cell 
 Thylakoid Stroma (p. 103)
o Thylakoid – flat sac that contains chlorophyll (
that absorbs red and
blue light) where light-dependent reactions take place
 Light-Dependent reactions – where light energy is converted to chemical energy
o Stroma – fluid surrounding thylakoid where light-independent reactions take place
o To provide
(in form of organic molecules) upon which almost all life on Earth
o Three stages
1. Light Absorption – energy captured from sunlight
 LightReactions
2. Light energy converted to chemical energy (ATP and NADPH)
 LightReactions
3. Light-Independent Reactions – ATP and NADPH power synthesis of organic
molecules using CO2
What is in sunlight that plants can use?
Light is radiation energy (electromagnetic spectrum)
Different wavelengths represent different amounts of energy
o Smaller the wavelength the
the energy
o Gamma rays (smallest, highest energy) all the way to radio waves (largest, lowest
o Visible spectrum – in between – contains the light plants absorb
has highest energy, red lowest
 Green in the middle
o Light is reflected (you see this),
(pass through, you don’t see)
(you don’t see this), or transmitted
First Stage of Photosynthesis  Light Absorption (Light-Dependent Reactions)
Capturing the sun’s energy
Pigment – (found in thylakoid of chloroplast) molecule that absorbs light
o Like a sponge
Chlorophyll a – green pigment that is the primary light-absorbing pigment for photosynthesis
 Absorbs orange/red light
 Reflects
o Chlorophyll b – assists chlorophyll a
 Absorbs blue, reflects green
o Carotenoids – assists chlorophyll a
 Absorbs blue, reflects
o Electrons in chlorophyll now have energized electrons
 These energized electrons leave
and move on to next stage
Water – all the excitement causes water to be split into H+, O2 and electrons (e-)
o These electrons replace those lost from chlorophyll
is given off to atmosphere
Second Stage of Photosynthesis Conversion of Light Energy (Light Dependent Reactions)
Follow the electrons!
Electrons leave chlorophyll and hop onto the electron transport chain
o Still in the
o Series of reactions result in the production of ATP (energy) and NADPH (electron
 NADPH provides excited electrons for Stage 3
ATP and NADPH are released into stroma of chloroplast
Third Stage of Photosynthesis 
of Energy (Light-Independent Reactions)
Carbon atoms from CO2 and hydrogen atoms (from water) go through Calvin Cycle to produce
organic compounds (glucose) which will be stored in plant for their own use/other use
Overall Photosynthesis Reaction
H2O +
CO2  C6H12O6 +