PHOTOSYNTHESIS
Chapter 10
Biological systems utilize free energy and
molecular building blocks to grow, to reproduce
and to maintain dynamic homeostasis.
Sunbeams- photons provide the energy to drive photosynthesis.
Without photosynthesis almost all organisms would die. They would have no energy.
To begin…
the why of photosynthesis.
Growth, reproduction and maintenance of
the organization of living systems require
free energy and matter.
Organisms must exchange matter with
the environment to grow, reproduce and
maintain organization.
a. Molecules and atoms from the environment
are necessary to build new molecules.
(BIOGEOCHEMICAL CYCLES)
1.
2.
3.
4.
Carbon moves from the environment to organisms
where it is used to build carbohydrates, proteins, lipids
or nucleic acids. Carbon is used in storage compounds
and cell formation in all organisms. (atmospheric)
Nitrogen moves from the environment to organisms
where it is used in building proteins and nucleic acids.
Phosphorus moves from the environment to organisms
where it is used in nucleic acids and certain lipids.
Water. Living systems depend on properties of water
that result from its polarity and hydrogen bonding.
(Nitrogen & Phosphorus in water- roots)
W
Biogeochemical Cycles
Organisms capture and store free
energy for use in biological
processes.
a. Life requires a highly ordered system
b. Living systems do not violate the second law of thermodynamics,
which states that entropy increases over time.
c. Energy-related pathways in biological systems are sequential and
may be entered at multiple points in the pathway.
d. Organisms use free energy to maintain organization, grow and
reproduce.
e. Changes in free energy availability can result in changes in
population size.
f. Changes in free energy availability can result in disruptions to an
ecosystem.
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
Organisms capture and store free energy for use in biological processes.
____________________________________________________________________
a. Life requires a highly ordered system
1. Order is maintained by constant free energy input into the system.
OPEN SYSTEM NOT CLOSED
2. Loss of order or free energy flow results in death.
WITHOUT
ATP THE ORGANISM WILL DIE
3. Increased disorder and entropy are offset by biological processes
that maintain or increase order. PHOTOSYNTHESIS AND CELL
RESPIRATION STORE AND CONVERT ENERGY INTO ATP
WHICH CAN MAINTAIN ORDER AND INCREASE IT WHEN
NEW PROTEINS AND CELLS ARE BUILT.
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
Organisms capture and store free energy for use in biological processes.
__________________________________________________________
b. Living systems do not violate the second law of thermodynamics,
which states that entropy increases over time.
1. Order is maintained by coupling cellular processes that increase
entropy (and so have negative changes in free energy) with those that
decrease entropy (and so have positive changes in free energy).
2. Energy input must exceed free energy lost to entropy to maintain
order and power cellular processes. (lost as heat)
3. Energetically favorable exergonic reactions, such as ATP→ADP, that
have a negative change in free energy can be used to maintain or
increase order in a system by being coupled with reactions that have a
positive free energy change.
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
Organisms capture and store free energy for use in biological processes.
____________________________________________________________________
c. Energy-related pathways in biological systems are sequential
and may be entered at multiple points in the pathway.
Illustrative examples:
• Krebs cycle
• Glycolysis
• Calvin cycle
• Fermentation
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
d. Organisms use free energy to maintain organization, grow
and reproduce.
1. Organisms use various strategies to regulate body temperature
and metabolism.
Illustrative examples:
– Endothermy (the use of thermal energy generated by
metabolism to maintain homeostatic body temperatures)
REQUIRES GREATER AMOUNTS OF FUEL/FOOD
– Ectothermy (the use of external thermal energy to help
regulate and maintain body temperature)
REQUIRES LESS FUEL/FOOD
– Elevated floral temperatures in some plant species
RESEARCH WHY FOR EXTRA CREDIT
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
d. Organisms use free energy to maintain organization, grow
and reproduce.
2. Reproduction and rearing of offspring require free energy beyond
that used for maintenance and growth. Different organisms use
various reproductive strategies in response to energy availability.
Illustrative examples:
– Seasonal reproduction in animals and plants
– Life-history strategy (biennial plants, reproductive diapause)
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
d. Organisms use free energy to maintain organization, grow and
reproduce.
3. There is a relationship between metabolic rate per unit body mass and
the size of multicellular organisms — generally, the smaller the
organism, the higher the metabolic rate. HUMMINGBIRD vs. ME
4. Excess acquired free energy versus required free energy expenditure
results in energy storage or growth. IF YOU EAT MORE THAN
YOU BURN YOU WILL GAIN WEIGHT/GROW.
5. Insufficient acquired free energy versus required free energy
expenditure results in loss of mass and, ultimately, the death of an
organism. IF YOU DON’T EAT ENOUGH YOUR CELLS WILL
TAKE ENERGY FROM APOPTOSIS OF CRUCIAL CELLSLIKE CARDIAC MUSCLE. PLEASE EAT ENOUGH FOODHAVE ENOUGH STORED ENERGY AS MUSCLE & FAT.
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
e. Changes in free energy availability can result in changes in
population size. (BOOM BUST CYCLES)
Big Idea 2: Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
f. Changes in free energy
availability can result in
disruptions to an ecosystem.
Illustrative Examples:
– Change in the producer level
can affect the number and
size of other trophic levels.
– Change in energy resources
levels such as sunlight can
affect the number and size of
the trophic levels.
Rainforest- diverse
Tundra-not
Desert-not
What organisms can do
photosynthesis???
Photoautotrophs- plants, kelp, protists, fillametousous algae, cyanobacteria
KELP
PLANT
UNICELLULAR
PROTIST
ALGAE
CYANOBACTERIA
In plants, where does
photosynthesis occur?
Photosynthesis
occurs within the :
leaves of plants
within
mesophyll cells
within
chloroplasts
LEAF IN
CROSS SECTION
(MESOPHYLL CELLS)
CHLOROPLAST
Mesophyll cells filled with
chlorplasts…
How is the chloroplast
organized? (draw it)
a) Double membrane
b) Stroma
c) Thylakoid
What is the overall reaction for
photosynthesis???
What is the overall reaction for
photosynthesis???
6 CO2 + 12 H20 + photons --> C6H12O6 + 6 H2O + 6 O2
PHOTOSYNTHESIS: A 2 PART BIOCHEMICAL PATHWAY
LIGHT RXNS
thylakoid membrane
CALVIN CYCLE
stroma
#1: LIGHT REACTIONS
• Occur on/through thylakoid
membrane
• Chlorophyll is the light
absorbing pigment
• Produces: ATP and NADPH
and O2 gas from H2O and
light.
#2: LIGHT INDEPENDENT
REACTIONS a.k.a. Dark
reactions or Calvin Cycle
• Occur in the stroma
• Produces C6H12O6 from CO2 &
forms H2O (condensation rxn)
using energy supplied by NADPH
and ATP
The Light Reactions
Photons of light
absorbed by chlorophylls in
PHOTOSYSTEM II & I
Energized electrons travel ETC
e’s PS II  PS I
power a proton pump
pump H+ into thylakoid space
Chemiosmosis  ATP
e’s PS I  NADP+  NADPH
(NADP+ is final electron acceptor)
PS II’s replacement e’s from H20
The Calvin-Benson Cycle
C3 cycle/ dark rxns/ light independent rxns
OCCURS IN 3 STEPS:
1) Carbon Fixation
6 CO2
2) Reduction
12 ATP & 12 NADPH
3) Regeneration of RuBP
(the CO2 acceptor)
6 ATP
* 1 GLUCOSE
THE DETAILS
During photosynthesis, chlorophylls absorb
free energy from light, boosting electrons to a
higher energy level in Photosystems I and II.
Photosystems I and II are embedded in the
internal membranes of chloroplasts
(thylakoids) and are connected by the transfer
of higher free energy electrons through an
electron transport chain (ETC).
In photosynthesis,
H2O is the electron donor and
NADP+ is the electron acceptor
O2, H+, and NADPH are produced.
When electrons are transferred between
molecules in a sequence of reactions as they
pass through the ETC, an electrochemical
gradient of hydrogen ions (protons) across the
thykaloid membrane is established.
In prokaryotes, the passage of electrons is
accompanied by the outward movement of protons
across the plasma membrane.
The formation of the proton gradient is a
separate process, but it is linked (through
chemiosmosis) to the synthesis of ATP from
ADP and inorganic phosphate via ATP synthase.
The energy captured in the light reactions as ATP
and NADPH powers the production of
carbohydrates from carbon dioxide in the Calvin
cycle, which occurs in the stroma of the chloroplast.
QUIZ
What are autotrophs?
Heterotrophs?
What are autotrophs?
• “self-feeders”/ producers
• Create chemical energy for self that is later
converted to ATP via cellular respiration.
• The amount of sunlight and water available to the
ecosystem determines the amount of energy.
• Compare and contrast a tropical rainforest with a
desert with tundra biomes.
What are heterotrophs?
• “other-feeders”/ Consumers
• Consumes energy trapped in the chemical bonds of
autotrophs or other heterotrophs.
• RAINFORESTS exhibit the greatest biodiversity
(large #s and large #s of species)
• H20, sunlight, CO2 is abundant.
• Tundra lacks light and liquid water- low biodiversity
• Desert lacks water- low biodiversity
Where does the oxygen produced
by plants come from?
Where does the oxygen produced
by plants come from?
• The oxygen plants release comes from
breaking water (by the water splitting
enzyme) into 2 e-, 2 H+, and 1/2 O2 gas…
is called PHOTOLYSIS.
Why does water appear on both
sides of the reaction?
Why does water appear on both
sides of the reaction?
• Water is used (reactant) to provide replacement
electrons to photosystem 2 at the beginning of the
electron transport chain.
• Water is released during the Calvin Cycle during
the “condensation reactions” that form the glucose
from CO2.
I. THE LIGHT REACTIONS
How is light used in the process of photosynthesis?
I. THE LIGHT REACTIONS
How is light used in the process of photosynthesis?
1. Photons drive electrons in ETC of the thylakoid
membrane and and are used to make NADPH from
NADP+.
2. Moving electrons power a proton pump which
creates a concentration gradient. ATP is formed by
chemiosmosis from the thylakoid space out into the
STROMA.
Figure 10.5 The electromagnetic spectrum
380-750 nm
Visible light spectrum
is the energy that
drives photosynthesis.
Figure 10.7 Determining an absorption spectrum
LIGHT CAPTURING PIGMENTS:
1) Chlorophyll a absorbs red & purple
2) Chlorophyll b absorbs blue & orange
3) Carotenoids absorb green & blue
Why do leaves change color in the fall?
Chlorophyll a
initiates the
light reactions
Chlorophyll b and
Carotenoids are
accessory pigments
Figure 10.x1 Melvin Calvin
II. THE CALVIN-BENSON CYCLE
GENERATE SUGAR!!!!
DON’T FORGET THAT
LAB #4 IS NEXT CLASS…
EXTRA CREDIT (1 QUIZ PT)
TO HELP SET UP TOMORROW
DURING 7TH PERIOD.
ALL YOU NEED TO KNOW IS THAT ATP & NADPH IS USED TO FORM GLUCOSE
FROM CO2 AND H2O IN THIS ENZYME MEDIATED SERIES OF REACTIONS
On a hot dry day…
plants reduce water loss (transpiration)
by closing their stomata = problem
PHOTORESPIRATION
•
•
•
•
Occurs in the light “photo”
Consumes Oxygen “respiration”
Problem: Rubisco binds oxygen as well as carbon dioxide.
Evolutionary relic from a time when the atmosphere lacked/was
low in Oxygen.
• On hot days when plants close their stomates to prevent water
loss, CO2 levels drop and O2 levels rise.
• Rubisco adds O2 to the Calvin Cycle… a two carbon product splits
and is transported to the peroxisomes where it is broken down into
CO2.
• Drains away as much as 50% of the carbon fixed by the Calvin
cycle.
EVOLUTIONARY
ADAPTATIONS TO PREVENT
PHOTORESPIRATION
1) C4 Plants- have stomates partially closed during the
day. They preface the Calvin Cycle with an
alternate form of carbon fixation that uses a
different enzyme to “fix” Carbon dioxide that is
more choosey… picks the few CO2 out like a
needle from a haystack. It creates a 4 carbon
compound (OAA) called the C4 pathway.
2) CAM Plants- use the C4 pathway then Calvin cycle;
but also are strict… they have their stomates closed
during the day and OPEN at night.
CRYPTS
Are pockets on the
Underside of the leaf
Creates a humid microclimate in an arid climate.
Biological systems utilize free energy and molecular building
blocks to grow, to reproduce and to maintain dynamic
homeostasis.
Organisms capture and store free energy for use in biological processes.
1. Different energy-capturing processes use different types of electron acceptors.
Cellular Respiration- Oxygen
Photosynthesis- NADP+
2. The light-dependent reactions of photosynthesis in eukaryotes involve a series
of coordinated reaction pathways that capture free energy present in light to
yield ATP and NADPH, which power the production of organic molecules.
light rxns = H20 + Light  ATP & NADPH + (O2) + CO2  glucose
3. Photosynthesis first evolved in prokaryotic organisms; scientific evidence
supports that prokaryotic (bacterial) photosynthesis was responsible for the
production of an oxygenated atmosphere; prokaryotic photosynthetic pathways
were the foundation of eukaryotic photosynthesis.
PHOTOSYNTHESIS OUTLINE QUESTIONS:
Biological systems utilize free energy and molecular building
blocks to grow, to reproduce and to maintain dynamic
homeostasis.
Organisms capture and store free energy for use in biological processes.
a. Autotrophs capture free energy from physical sources in the environment.
b. Heterotrophs capture free energy present in carbon compounds produced by other
organisms.
c. Different energy-capturing processes use different types of electron acceptors.
d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of
coordinated reaction pathways that capture free energy present in light to yield ATP
and NADPH, which power the production of organic molecules.
e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports
that prokaryotic (bacterial) photosynthesis was responsible for the production of an
oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation
of eukaryotic photosynthesis.
f. Cellular respiration in eukaryotes involves a series of coordinated enzyme-catalyzed
reactions that harvest free energy from simple carbohydrates.
g. The electron transport chain captures free energy from electrons in a series of
coupled reactions that establish an electrochemical gradient across membranes.