Photosynthesis
• Converts solar energy into the chemical
energy of a carbohydrate in this way:
• Solar energy + carbon dioxide + water →
carbohydrate + oxygen
• Photosynthetic organisms include plants,
algae, and certain bacteria.
• These organisms are called producers;
they synthesize organic molecules from
raw materials.
Photosynthetic organisms
•
1)
2)
3)
4)
Nearly all life is dependent on solar energy
because:
Photosynthetic organisms use solar energy to
produce organic nutrients.
Almost all organisms depend either directly
or indirectly on these organic nutrients to
sustain themselves.
Photosynthetic organisms provide food for
other organisms, known as consumers.
The bodies of plants became the coal or other
fossil fuels used today.
Structure and Function of Chloroplasts
• Chloroplasts are the organelles that carry on
photosynthesis.
• Mesophyll cells in the middle of a leaf house
chloroplasts
• Mesophyll cells are protected from drying out
by a waxy cuticle.
• Pores called stomata allow CO2 and O2 to
enter the leaf.
Mesophyll cells of a leaf
Structure of Chloroplasts
• Bounded by a double membrane.
• The inner membrane encloses a large central
space called the stroma that houses enzymes used
to reduce CO2 to carbohydrate.
• A membranous system of thylakoids lies within
the stroma; some thylakoids are stacked into
grana; thylakoids contain chlorophyll and other
pigments.
• Chlorophyll and other pigments absorb solar
energy.
Chloroplast structure
Visible Light
• Radiant energy from the sun (solar energy) can
be described in terms of its wavelength and its
energy content.
• The colors in visible light range from violet
(the shortest wavelength and highest energy) to
blue, green, yellow, orange, and red (the
longest wavelength and lowest energy).
Visible Light Spectrum
• Pigments (chlorophylls and carotenoids) found
within photosynthesizing cells, are capable of
absorbing various portions of visible light.
• Both chlorophyll a and chlorophyll b absorb
violet, blue, and red light best.
• Carotenoids absorb light in the violet-bluegreen range and reflect yellow or orange
• Leaves appear green because green light is
reflected and only minimally absorbed.
In the fall when the pigment chlorophyll breaks down, the
remaining pigment (carotenoids) become unmasked,
reflecting the colors like orange and yellow
•Photosynthesis is an oxidation-reduction reaction,
or redox reaction for short.
•Oxidation is the loss of electrons; hydrogen atoms
are removed from glucose.
•Reduction is the gain of electrons; oxygen atoms
gain electrons.
•Remember OIL RIG (oxidation is loss, reduction
is gain)
Overview of Photosynthesis
• A simplified overall equation for
photosynthesis is:
• Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
• During photosynthesis, water molecules are
oxidized; they lose electrons (e-) along with
hydrogen ions (H+).
• Also, CO2 is reduced and gains electrons given
up by H2O.
• Electrons from H2O are energized by the sun.
Two Sets of Reactions
• Photosynthesis is divided into two sets of
reactions, as implied by the term
“photosynthesis”:
• “Photo” refers to the light-dependent (needs
light) reactions that capture energy from the
sun
• Photosystem II
• Photosystem I
• “Synthesis” refers to the light-independent
(does not need light) reactions that produce
carbohydrate (glucose).
• Calvin Cycle
Overview animation of light-dependent reactions (photosystem II & I)
http://www.youtube.com/watch?v=eY1ReqiYwYs&feature=related
Overview of light-independent reactions (Calvin cycle)
http://www.youtube.com/watch?v=mHU27qYJNU0
A photosynthesis rap!!!!!!!!!
http://www.youtube.com/watch?v=Wi60tQa8jfE
Song: http://www.youtube.com/watch?v=OYSD1jOD1dQ
Enzyme involved
•NADP+
•Nicotinamide adenine dinucleotide phosphate
•Accepts 2 electrons and H+ to become NADPH
The ATP cycle
Light-Dependent Reactions
• Light energy is absorbed by chlorophyll
molecules.
• ATP, NADPH, and oxygen are produced.
• Water is split to produce oxygen, hydrogen
ions, and electrons
• Photosystem II occurs first
• Photosystem I occurs second
• Both occur within the thylakoid membranes
inside the chloroplast
•Photosystem II
•The electrons are excited by incoming light energy
(from the sun).
•These excited electrons are passed through a series
of electron carriers.
•Energy from these excited electrons is used to pump
hydrogen ions from the stroma to the thylakoid space.
•Hydrogen ions diffuse across the membrane from
the thylakoid space to the stroma through ATP
synthase
•As H+ pass through ATP synthase, the energy from
these ions generates ATP (used up later in
photosynthesis during light-independent Calvin
Cycle).
Photosystem I
• Electrons are excited by incoming light energy
(from the sun).
• These excited electrons are passed through a
series of different electron carriers from
photosystem II.
• As electrons pass down this chain, they
combine with the molecule NADP+ to form
NADPH
Light-dependent Photosystem II and
Photosystem I - Electron transport system
LIGHT-DEPENDENT REACTION
Requires Light and
Water
WHAT IT DOES:
SPLITS H2O
Creates ATP and NADPH
For Calvin Cycle
Forms O2 as a byproduct
WHERE IT HAPPENS:
Leaf
Chloroplasts
Inside Thylakoids
Light-Independent Reactions
• The light-independent reactions do not need light
• Reactions make up the Calvin cycle.
• Carbon dioxide (CO2) is taken up by the plant
(from the atmosphere)
• ATP and NADPH (made from the light dependant
reactions) add phosphates and electrons to CO2,
and convert it to glyceraldehyde 3- phosphate, or
G3P
• G3P is a type of sugar which a plant can easily
convert to glucose. This glucose can then be used
as a source of stored energy for the plant
The Calvin Cycle
DARK REACTION
Requires ATP, NADPH,
and CO2
WHAT IT DOES:
Produces High
Energy Sugars
Combines CO2, ATP
and NADPH
Forms a 6 carbon sugar
(Glucose)
WHERE IT HAPPENS:
Leaf
Chloroplasts
In the Stroma
(Thick Fluid inside Chloroplast)
Overview of Photosynthesis
Photosynthesis Vs. Cellular Respiration
Overall equation for photosynthesis is:
Overall equation for cellular respiration is:
Photosynthesis Vs. Cellular Respiration
Photosynthesis
Occurs in plants,
algae, & some
bacteria
Occurs in
chloroplasts
Glucose is
produced
Cellular
Respiration
Occurs in all
organisms
Occurs in
mitochondria
Glucose is
broken down
Photosynthesis Vs. Cellular Respiration
(cont’d)
Photosynthesis
Occurs in plant
cells during day
Cellular
Respiration
Occurs in plant
cells day AND
night
Uses electron
Uses electron
transport system transport system
Uses NADP+ and Uses NAD+ and
NADPH
NADH
Photosynthesis versus cellular
respiration
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter10/animations.ht
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