Photosynthesis
Photosynthesis is a process which
light energy is used in the synthesis of
organic molecules.
What is the equation for
photosynthesis?
Water + carbon dioxide +light energy
=
Oxygen + glucose
The role of chloroplasts in
Photosynthesis.
• Chloroplast is an organelle in the leaf of a
plant that contain the thylakoid cells and the
stroma. These are shown on the following
diagram.
• Here 2 important reactions take place. The
light dependant reactions take place in the
thylakoid cells and the light independent in
the stroma.
Chloroplasts
What happens in the light
dependent reactions.
• Electrons in the chloroplast gain energy
from sunlight , this energy is used to add a
phosphate group to ADP making ATP.
• The energy is used also used in the
photolysis of water to split it into oxygen
and hydrogen molecules
• The electrons, protons and energy for the
light dependent reactions are used to make
NaDPH2.
• The ATP/NADPH2 from the Light
Dependent reactions enter the light
independent reactions.
What happens in the light
independent reactions.
The light independent reactions
occur at night for only a few seconds
due to limited amounts of ATP and
supply of NADPH2.
Role of NADPH2 and ATP
Energy from ATP and electrons from
NADPH2 are used to reduce carbon
dioxide and build it to sugars
The following cycle is called the
Calvin cycle.
• This is called Fixing the carbon dioxide.
The carbohydrates(sugars) are in a form of
RuBP.
• The following cycle is called the Calvin
cycle.
• What happens in the Calvin cycle?
• RuBP with the addition of carbon dioxide
splits into 2 moles of GP. For GP to be
turned to Carbohydrates it requires ATP and
NADPH2. The NADPH2 give up its
electrons which enter the GP molecules
making GALP.
GALP
GALP is converted to a whole series
of mostly sugars, some lipids and
some Proteins.
• Also some GALP is regenerated back to
RUBP if sufficient amounts of NADPH2
and ATP are provided.