Photosynthesis
- Photosynthesis is carried out by a number of different organisms: plants, algae,
bacteria and some protists.
- These organisms all contain the green pigment called chlorophyll and are called
Photoautotrophs
- These green plants using Chlorophyll will be able to convert light energy into glucose
within the chloroplast.
- Photosynthesis overall reaction is : _______________________________________
Light Reactions ~ Overview
1. Pigments embedded in thylakoid membrane absorb energy from sunlight and give
electrons to membrane proteins. These proteins are organized into into 2
photosystems.
2. Movement of electrons and H+ ions leads to production of NADPH and ATPElectrons
released by pigments are replaced by splitting of H2O (photolysis) producing O2
Overall, this results in the formation of ATP + NADPH ~ used in the Calvin Cycle to
construct Glucose.
If you were to take a cross section of a leaf we are able to see the photosynthetic cells,
which contains the chloroplasts.
A cross section of a chloroplast show the thylakoid membrane system and stroma
(surrounding fluid).
Photosynthesis has 2 main stages:
1. Light Reactions ~ ____________________________________________________
- Light energy is captured by pigment molecules and then use it to made NADPH and
ATP.
- In this process water molecules are split and then generate oxygen to be released to
environment.
2. Calvin Cycle ~
____________________________________________________
- Here high energy electrons carried by NADPH and energy store in ATP are used to
convert CO2 into carbohydrates like glucose.
- This process will also assemble lipids and proteins.
Light Trapping Pigments:
- The function of photosynthetic pigments is to
capture energy from photons of sunlight.
- Like waves, photons of light have a characteristic
wavelength (the distance covered in one cycle of
the wave)
- The most energetic photons travel at shorter
wavelengths. Compare red light (long
wavelength) with blue light (short wavelength).
Although the amplitude of each wave is the
same, there are many more waves per unit time
for blue light.
- Blue light packs more energy per
photon than red light does.
- A photosynthetic pigment is sensitive to a specific
range of the spectrum. The electrons within the
pigment are excited by a specific wavelength of
light.
- Chlorophyll a and chlorophyll b absorb blue and
red wavelengths of light, while reflecting and
transmitting wavelengths in the middle of the
visible spectrum (green and yellow).
- Leaves appear green because the “chlorophylls”
are the most abundant pigments, but other
pigments are hidden beneath this overpowering
green colour.
- The carotenoids some of the blue and green wavelengths. The phycobilins absorb
most of the green, yellow and orange wavelengths.
- In autumn, the chlorophylls breakdown revealing the presence of the other pigments.