General Biology

Marianne Cathleen_12Democritus

PHOTOSYNTHESIS
The Basics of Photosynthesis
 Almost all plants are photosynthetic The thylakoid membrane of the chloroplast is
autotrophs, as are some bacteria and impregnated with photosynthetic pigments
protists. (i.e., chlorophylls, carotenoids).
 Autotrophs generate their own
organic matter through
photosynthesis
 Sunlight energy is transformed to
energy stored in the form of chemical
bonds

 Energy can be transformed from one from to

another.

Free Energy(available for work) vs.

Heat(not available for work)
Photosynthetic Pigments: The Light Receptors
• Pigments are substances that absorb
visible light
• Different pigments absorb different
wavelengths
• Wavelengths that are not absorbed
are reflected or transmitted
• Leaves appear green because
chlorophyll reflects and transmits
Types of Consumers
green light

Chlorophyll
 A light absorbing Pigment The Solar
Panel Chemical

Light Energy Harvested by Plants & Other

Photosynthetic Autotrophs

THE SUN: MAIN SOURCE OF ENERGY FOR LIFE Two Major Pigments involved in Photo
ON EARTH synthesis
1. Chlorophyll A
WHY ARE PLANTS GREEN? 2. Chlorophyll B
General Biology
Marianne Cathleen_12Democritus

1. Chlorophyll A CHLOROPLAST
 Appears green = absorb “blue”  absorb light energy and convert it
and “red” light to chemical energy
 Most abundant type of pigment
 Most important
 Store most of the energy
 primary pigment of
photosynthesis, trapping the light
energy and emitting high energy
electrons into the two
photosystems P680 and P700
 present in all the photosynthetic
organisms on earth, giving a
bluish green color to those
organisms.

2. Chlorophyll B
• Absorb “blue” light PHOTOSYNTHESIS
• accessory pigment, passing the  process by which autotrophic
trapped energy into chlorophyll A organisms use light energy to make
• gives a yellowish green color to sugar and oxygen gas from carbon
organisms. dioxide and water
• Less abundant  turns light to chemical energy
• Absorbed wider wavelength energy  process are capable of producing
Main difference between chlorophyll A their own food
and B is their functions in photosynthesis.  Anabolic (small molecules and
combined)
 Needed: Carbon dioxide, sunlight,
Water
 An Endergonic Process: Low energy
compound to high energy compound
 Endergonic (stores energy)
 Occurs in plants, algae and some
SIMILARITIES of Chlorophyll A and B prokaryotes
• The most absorbing wavelengths of  Organic Compound that are produced
chlorophyll A and B are 439 nm and light to energy: Glucose,
455 nm respectively. Carbohydrates, Proteins, Lipids,
3. Carotenoids Nucleic acid
• Accessory pigments
• absorb excessive light that would FORMULA FOR PHOTOSYNTHESIS
damage chlorophyll. 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
• Absorb “violet” and “blue-green”
light
• Absorbs all excess light energy
6 Carbon dioxide + 6water yields to glucose + 6oxygen

More pigments = more absorption = food IMPORTANCE OF PHOTOSYNTHESIS

will produce by plant
Photosynthesis and Sun Energy
General Biology
Marianne Cathleen_12Democritus

 Harnesses he sun’s energy into

utilizable form of energy on earth.
 A process that most biological
organisms are unable to perform.
 ATP is used to power these processes.
 Converts light energy into chemical
energy in the form of glucose.
 Then the process of cellular
respiration converts energy of glucose
to energy in the form of ATP which is
used to power biological process
Photosynthesis and Carbon Dioxide Removal
 Carbon dioxide releases in the
atmosphere and enters the plant and
leaves as oxygen
Relationship of plant and consumer Two Reactions
 Plant (needs Carbon dioxide) 1) Light Dependent Reaction
 Consumer (needs Oxygen) 2) Light Independent Reaction(Calvin Cycle)
 They are mutual because they’re both
beneficiated LIGHT REACTION
 A process which is ecologically and Light Dependent Reaction
environmentally important in nature  Light Reactions
 Happens in Thylakoid
Sites of Photosynthesis  Occurs in day light/day time
 A chloroplast contains:  Electron Flow (Linear)
o A chloroplast Stroma (a fluid)  Convert solar energy to chemical
o Grana (Stacks of thylakoid) energy
 Thylakoid contain chlorophyll  Pigments in the thylakoid membranes
o Chlorophyll is the green form protein complexes called
pigment that captures light Photosystem I and Photosystem II.
for photosynthesis  These photosystems harvest photons
Photosynthesis Overview to charge up energy carrying
Overall Purpose: molecules that will power the dark
 Photosynthesis->light->Chemical reactions.
energy Thylakoid Membrane
 Complements respiration  Pigments such chlorophyll are found
 Energy for all life on earth ultimately and is where light gets absorbed.
comes from photosynthesis  Photosystems
• Pigments arranged in clusters
Photosystem II
 When photosystem 2 absorbs light,
electrons in chlorophyll gain energy
(or get excited) from the light
 splits water molecules into two
protons (H+) and oxygen atoms are
expelled as O2 gas through the
stomata.
 General Biology
Marianne Cathleen_12Democritus

Electron Transport Chain  This creates a high concentration of

 exited electrons leave chlorophyll and hydrogen ions inside the thylakoid.
move to something
 Transport Electrons derived from “The protein ATP synthase attaches a
light energy phosphate group to ADP (D = di or two)
 Carrier electron making it ATP (T = tri or three).”
 series of protein complexes located in
ATP Production via ATP Synthase
the thylakoid membrane of
 Hydrogen ions diffuse back across the
chloroplasts.
membrane through ATP synthase.
 The flow of protons causes ATP
 Since Chlorophyll lost electrons, those electrons
synthase to spin, converting ADP and
need to be replaced.
inorganic phosphate (Pi) into ATP.
 To replace them, water is split and its electrons
 ATP is a key product of the light-
go to chlorophyll
dependent reactions.
Photosystem I and Electron Re-excitation
Water splits
 Electrons reach Photosystem I (PSI),
 Electrons, hydrogen ions and oxygen
where they are re-excited by light
are produced
energy.
Protons
 They then travel down a second,
 Positive charge in the remaining two
shorter electron transport chain.
hydrogen atoms when water
Formation of NADPH/NADP+
molecules break apart
(Nicotinamide Adenine Dinucleotide
 absorbed by the pigments to power
Phosphate)
photosystem I and photosystem II.
 can hold excited electrons (e-)
 Kept inside thylakoid by the thylakoid
charged from the light energy
membrane
harvested by chlorophyll to become
NADPH
NOTE:2 oxygen atoms are needed to make the
 Electrons are accepted by NADP+,
oxygen gas (O2.) that plants release into the
which also picks up hydrogen ions,
air.
forming NADPH.
 Freed oxygen atoms bind with each
 NADPH serves as an electron carrier
other to form the gas O2.
for subsequent reactions.
O2(dioxygen)
 NADPH passes the electron it’s
 product of photosynthesis not used by
holding to power the dark reactions
the plant so it is released through the
and reverts back to NADP+.
stomata of plants.
ATP
Stomata (Greek for mouth)
(Adenosine triphosphate)
 little pores in leaves that open and
 called the “cellular currency” because
close to let oxygen out and carbon
it is used to power all the reactions
dioxide in.
that take place in the cells of all living
Photolysis
things.
 Oxygen comes from
 When ATP’s third phosphate is broken
Proton Pumping
off it releases energy that the cell can
 Energy from electrons is used to
use.
pump hydrogen ions (protons) across
 is made when a third phosphate
the thylakoid membrane into the
group is added to ADP (diphosphate,
thylakoid lumen.
di = two).
General Biology
Marianne Cathleen_12Democritus

 Starts at RuBP molecules and carbon

Importance of ATP and NADPH dioxide molecules.
 Both ATP and NADPH are essential  RuBP-Ribulose Bisphosphate
products of the light-dependent Rubisco
reactions.  Ribulose 5-Bisphosphate
 They provide energy and reducing carboxylase/oxygenase
power for the Calvin Cycle, where  An enzyme that combines the RuBP to
sugars are synthesized. make unstable intermediate
 Energy carrier molecules used in  Most abundant type of protein
photosynthesis and cellular needed by the plant
respiration. Unstable Intermediate
 Splits in half and forms 2 molecules of
Summary 3-PGA which are stable
 Protons are absorbed by the pigments  ATP and NADPH from the light
to power photosystem I and reactions provide the energy to
photosystem II. convert the two molecules of 3-PGA
 Photosystem II splits water molecules into their final form
into two protons (H+) and oxygen Carbon Fixation
atoms are expelled as O2 gas through  converts the carbon from carbon
the stomata. dioxide into glucose in the stroma
 Protons cross the thylakoid membrane  Carbon is fixed into another form.
and power protein complex ATP
synthase to make ATP. Phases of the Calvin Cycle
 NADP+ is powered up by photosystem I Phase 1: Carbon Fixation
to make NADPH to be used in the dark  Enzyme Rubisco catalyzes the addition
reactions. of CO2 to a 5-carbon compound,
RuBP.
Products of Light Dependent Reaction
 This forms a 6-carbon compound that
 Oxygen(O2)
splits into two molecules of 3-
 NADPH+ (Nicotinamide Adenine
phosphoglycerate (3-PGA).
Dinucleotide Phosphate)
 Carbon fixation occurs for three
 ATP (Adenosine triphosphate)
molecules of CO2.
Phase 2: Reduction
DARK REACTION
 ATP provides energy to convert 3-PGA
Light Independent Reaction
into a reactive intermediate.
 Calvin Cycle
 NADPH donates electrons and
 Happens in Stroma of chloroplast the
hydrogen to reduce this intermediate,
(space that surrounds thylakoids) and
forming Glyceraldehyde-3-phosphate
fix carbon dioxide into glucose.
(G3P).
 Can occur day or night
 For every three CO2 molecules fixed,
 Electron Flow (Cycle)
one G3P molecule is produced.
 Makes sugar from carbon dioxide
Phase 3: Regeneration
 Discovered by three scientists, the
 One G3P is removed from the cycle,
dark reactions are also called the
while five remain.
Calvin-Bensen-Bassham cycle or just
 The five G3P molecules (15 carbons
Calvin Cycle.
total) are converted back to three
RuBP molecules (5 carbons each).
General Biology
Marianne Cathleen_12Democritus

 This regeneration requires ATP.

Production of Glucose
 Two G3P molecules are needed to
synthesize one glucose molecule (6
carbons).
 The overall photosynthesis equation
involves six CO2 molecules being used
to produce one glucose molecule.
 The left overs are reused in the light
reactions to remake ATP and NADPH.
Significance
 The products of the Calvin Cycle
contribute to plant growth and
support life on Earth by providing
organic compounds.

Product of Calvin Cycle

 Glucose
 ADP (Adenosine Diphosphate)
 NADP+ (nicotinamide adenine
dinucleotide phosphate)

“Photosynthesis is carried out in two steps.

First, in two light dependent photosystems.
Second, in a light independent carbon fixation
cycle called the Calvin Cycle.
Through this process, the plant is able to
convert sunlight, water, and CO2 into glucose
(or sugar) and ATP.
As a byproduct of this process, O2 is
released.”