Intro to Photosynthesis
Green Book – 4.2 and 4.3
Blue Book – Chapter 6
Reviewing Why We Need
Photosynthesis
• Photosynthesis is the process that feeds the
biosphere.
• Photosynthesis feeds the entire world either
directly or indirectly.
• Sun -> Autotrophs (producers) ->
Heterotrophs (consumers and decomposers)
Plant Anatomy
• All green parts of the plant, including stems, contain
organelles called chloroplasts.
• Chloroplasts get their color from a pigment called
chlorophyll.
• There are about a half million chloroplasts per square
millimeter of leaf surface.
• Most chloroplasts are located in the mesophyll, the tissue
in the interior of the leaf.
– Mesophyll cells each contains 30-40 chloroplasts
• Gas exchange happens through a structure in the leaf
surface called stomata.
– Carbon dioxide enters
– Oxygen exits
Chloroplasts
• All green parts of the plant, including stems,
contain organelles called chloroplasts.
– A double membrane encloses each chloroplast,
keeping the stroma (dense fluid that fills each
chloroplast, sort of like cytoplasm) contained.
– A mass of interconnected membranes, called
thylakoids, are housed inside the chloroplasts and are
surrounded by stroma. This is where chlorophyll is
strored.
– Sometimes, thylakoids are found in stacks. These
stacks are called grana.
What Happens on a Molecular Level?
6 CO2 + 6 H2O + Light Energy ->
C6H12O6 + 6 O2
Two Stages of Photosynthesis
• There are two stages
of photosynthesis:
– Light Reactions
– The Calvin Cycle
Light Reactions
• Light reactions are the steps of photosynthesis
that convert solar energy to chemical energy.
– Chlorophyll absorbs energy from the sun.
– Energy is transferred across the thylakoid
membranes through the splitting of water.
– Oxygen is released.
– Energy is transferred to ATP.
Light Independent Reactions
(Calvin Cycle)
• ATP from the light reactions is used to make
sugar. This occurs in the stroma of the
chloroplasts.
– CO2 is added to make bigger molecules.
– A molecule of glucose is formed and is used to
store energy.
Crash Course - Photosynthesis
• https://www.khanacademy.org/partnercontent/crash-course1/partner-topic-crashcourse-bio-ecology/crash-coursebiology/v/crash-course-biology-108