Download Photosynthesis

Photosynthesis (in a nutshell)

The energy originally from sunlight is
transformed and used to combine CO2 and
H2O into Glucose (C6H12O6) or other plant
molecules (cellulose, amino acids, etc.)
Structures
Photosynthesis occurs only in plants and a
small number of single-celled organisms
(like algae).
 To be able to photosynthesize, you must
have a specific organelle: the Chloroplast.

Chloroplasts
Inside each chloroplast
are what look like stacks
of green pancakes.
 Each pancake is called a
thylakoid.
 The stacks of thylakoids
are known as grana.
 The empty space inside
the chloroplast is called
the stroma.

Chlorophyll
Each chloroplast’s thylakoids are lined with a
special sun-absorbing pigment.
 This pigment is known as chlorophyll.
 It is what allows the plant to absorb sunlight
which is used to power photosynthesis

 It also is what makes the plant green.
 Chloroplasts use red & blue light and reflect green
Photosynthesis

Photosynthesis has
two components:
 A) Photosystem II
○ 1. The absorption of sunlight
and water (H2O)
○ 2. The removal of hydrogen
atoms from water using the energy of sunlight
○ 3. The use of this hydrogen to power ATP production in each
thylakoid’s ATP Synthase.
 B) The Calvin Cycle
○ 1. The absorption of CO2
○ 2. The use of ATP to power the production of G3P from CO2
and Rubisco (5 carbon molecule) in the stroma.
○ 3. The use of G3P to make sugars, amino acids, fats, and all
other components of the plant.
Photosynthesis
Photosystem II
1. Sunlight (primarily red
& blue wavelengths) is
absorbed by chlorophyll
pigments in the
chloroplasts. Water (H2O)
is absorbed by the
chloroplast
2. The sunlight is used to
separate hydrogen from
oxygen. Oxygen is
released as O2. H+ is
stored in each thylakoid.
3. The hydrogen
absorbed by the thylakoid
is used to power ATP
Synthase, which makes
ATP from ADP and Pi
Click for explanations
Calvin Cycle
The Calvin Cycle is powered
by ATP (not shown)
1. CO2 is absorbed.
Carbon is separated from
oxygen. O2 is released.
2. The remaining carbon
atom is combined with 5carbon Rubisco (from the
previous cycle)
3. The 6-carbon molecule
is split into two 3-carbon
molecules (G3P). One
G3P is used to make
sugars or other plant
molecules. The other is
paired with 2 carbon
atoms to re-make
Rubisco.
Click for explanations
Photosynthesis (PSII & Calvin)
Research

Regulation of photosynthesis in
developing leaves of soybean
chlorophyll-deficient mutants
Cai-Zhong Jiang, et al, Iowa State Univ
This team used soybeans that were
missing one gene (out of two genes
total) for chlorphyll production.
 These plants were lighter green than the
control. Why?

Research
Jiang created the plants through genetic
crosses.
 ¼ of the plants were dark green
(normal), ½ were light green, and ¼
were yellow. The yellow plants always
died.
 Why were some yellow?
 Why did the yellow always die?

Research
Jiang’s team also found that plants with
half as much chlorophyll produced half
as much Rubisco.
 Why might this be? Why would this be
good for a plant?
