Outline
•
•
Overview
Photosynthesis
I.
II.
III.
IV.
V.
•
Properties of light and pigments
Chloroplast structure and function
Light reactions
“Dark” or Carbon reactions
Summary and conclusions
Respiration
I. Processes
II. Energy and food chains
III. Carbon Cycle
Photosynthesis and Cellular
Respiration
Photosynthesis and respiration are complementary
processes in the living world. Photosynthesis uses
the energy of sunlight to produce sugars and other
organic molecules.
These molecules in turn serve as food for other
organisms that carry out respiration to obtain the
chemical bond, a process that uses O2 to form CO2
from the same carbon atoms that had been taken
up as CO2 and converted into sugars by
photosynthesis.
PHOTOSYNTHESIS
6 CO2 +
6 H2O
SUNLIGHT
6 O2 +
CHLOROPLASTS
1 C6H12O6
RESPIRATION
1 C6H12O6 + 6 O2
6H2O + 6 CO2 + ATP
MITOCHONDRIA
What came first, photosynthesis
or respiration?
The first cells on the earth are thought to have been
capable of neither photosynthesis nor respiration.
However, photosynthesis must have preceded
respiration on the earth, since there is strong
evidence that billions of years of photosynthesis
were required before O2 had been released in
sufficient quantity to create an atmosphere rich in
this gas. (The earth's atmosphere presently
contains 20% O2.)
Introduction to photosynthesis
• From the Greek
PHOTO = produced by light
SYNTHESIS = a whole made of parts put
together.
Definition: PHOTOSYNTHESIS is the process
whereby plants, algae, some bacteria,
use the energy of the sun to synthesize organic
compounds (sugars) from inorganic compounds
(CO2 and water).
WHY IS PHOTOSYNTHESIS
SO IMPORTANT?
PHOTOSYNTHESIS is one of the most
important biological process on earth!
• Provides the oxygen we breathe
• Consumes much of the CO2
• Food
• Energy
• Fibers and materials
GENERAL FORMULA FOR
PHOTOSYNTHESIS
light
*
*
6 CO2 + 12 H2O ---------> C6H12O6 + 6 O2 + 6 H2O
pigments, enzymes
• Oxygen on earth allowed for the evolution of aerobic
respiration and higher life-forms.
• Respiration: extracting energy from compounds (sugars)
C6H12O6 + O2  6 CO2 + ATP
PROPERTIES OF LIGHT
Virtually all life depends on it!
• Light moves in waves, in energy units
called PHOTONS
• Energy of a PHOTON inversely proportional
to its wavelength
• Visible light (between UV and IR) occurs in
a spectrum of colors
Visible light contains just the right amount of
energy for biological reactions
Light is absorbed by pigments
• The primary pigment for photosynthesis is
chlorophyll a
• It absorbs blue and red light, not green (green
light is reflected back!)
Absorption spectrum
of chlorophyll a
Chlorophyll a is the primary
photosynthetic pigment that drives
photosynthesis.
Accessory pigments absorb at
different wavelengths,
extending the range of light
useful for photosynthesis.
• Absorption spectrum of chlorophyll a:
BLUE & RED
• Action spectrum of photosynthesis closely
matches absorption spectrum of
chlorophyll a, but not perfectly (due to
accessory pigments)
Chloroplast structure
•
•
•
•
Football shaped
Double membrane
Stroma
Thylakoid
membrane
• Grana (stacks)
• Lumen
(inside thylakoid)
stroma
Grana
lumen
thylakoids
Chloroplast structure and function:
solar chemical factory
Chloroplast Membrane Structure
• The thylakoid is the structural unit of
photosynthesis containing photosynthetic
chemicals.
• Thylakoids are stacked like pancakes in
stacks known collectively as grana. The
areas between grana are referred to as
stroma.
• While the mitochondrion has two
membrane systems, the chloroplast has
three, forming three compartments.
Chloroplast Structure & Function
• The chloroplast has three membranes: inner,
outer, and thylakoid . It has three
compartments: stroma, thylakoid space, and
inter-membrane space.
• These compartments and the membranes
that separate them serve to isolate different
aspects of photosynthesis.
– Dark reactions take place in the stroma.
– Light reactions take place on the thylakoid
membranes.
Inside a Chloroplast
• Remember: Structure correlates to function!
Overview of photosynthesis:
Note: The Light and “Dark”or Carbon
reactions happen at different sites in the
chloroplast
H2O
light
CO2
LIGHT
REACTIONS
(Thylakoids)
ATP
“DARK” or CARBON
REACTIONS
NADPH
(Stroma)
(ENERGY)
O2
C6H12O6
(OXYGEN GAS)
(GLUCOSE)
The Light Reactions
1. Light dependent
2. Occur in the thylakoid membrane of
chloroplast
3. Water is split into oxygen gas (O2) and H+
4. Use light energy (photons) to generate two
chemical energy compounds: ATP &
NADPH
The“Dark” or Carbon Reactions
1. Light independent (can occur in light or dark;
some enzymes require activation by light)
2. Occur in the stroma of chloroplasts
3. Use the chemical energy produced in Light
Reactions (ATP; NADPH) to reduce CO2 to
carbohydrate (sugar).
4. CO2 is converted to sugar by entering the
Calvin Cycle
Efficiency & Photosynthesis
• Photosynthesis is not perfect.
• Depending upon the plant type, it ranges
from being only 1 - 4 % efficient to having
7% efficiency
Summary of Photosynthesis:
1. Light energy absorbed by chlorophyll a
drives the reactions of photosynthesis.
2. Converts light energy into chemical
energy to make organic compounds.
3. CO2 and H2O used to produce
C6H12O6 (glucose) and O2 (gas).
4. Light Reactions occur in thylakoids of the
chloroplasts; ATP and NADPH are formed;
water is split to O2 (gas) and protons.
5. Carbon Reactions occur in stroma – Calvin
Cycle fixes CO2 to produce C6H12O6
(glucose).
6. Low efficiency, about 1- 7%
7. Nevertheless, PHOTOSYNTHESIS is still the
most important biological process on earth!
Without
photosynthesis,
virtually all
plants and
animals would
become extinct.
RESPIRATION
• Process of making energy of food available in
the cell…
• Involves breaking down
• Complicated molecules  into simple molecules
(C6H12O6, sugars)
(CO2, water)
Chloroplast –vs- Mitochondria
• Both are surrounded by a double membrane
with an intermembrane space.
• Both have their own DNA .
• Both are involved in energy metabolism.
• Both have membrane reticulations filling
their inner space to increase the surface area
on which reactions with membrane-bound
proteins can take place.
Mitochondria Structure
• The outer membrane to protect the organelle
• The intramembranous space of the
mitochondria (the space between the inner
and outer membranes)
• The inner membrane is folded into a series
cristae or long folds that greatly increase the
surface area of the inner membrane allowing
more area for energy production.
RESPIRATION
The energy held by complicated molecules is held
temporarily as ATP (energy currency)
C6H12O6 + 6 O2  6CO2 + 6 H2O + 36 ATP
(glucose)
(energy)
Respiration occurs mainly in
Mitochondria and Cytoplasm
Stages of Respiration
Cellular Respiration has three main stages:
• Glycolysis
• Krebs Cycle
• Electron transport system
3 Stages of cellular respiration
• Glycolysis: Splitting of glucose – 2 net ATP generated
• Krebs Cycle: Energy of glucose molecule is harvested
as ATP (2) – it occurs in the mitochondria (matrix)
• Electron Transport System: also happens in the
mitochondria, more ATP are generated (32).
• For each glucose molecule, total ATP = 36
• Only 39% efficient, rest is lost as heat.
Photosynthesis
• Reaction:
Respiration
CO2+H2O+sunC6H12O6+O2+H2O
C6H12O6+O2CO2+H2O+36ATP
• Reactants: Carbon dioxide, water, sun
Glucose, oxygen
•
•
•
•
Energy
Products: Glucose
By-products: Oxygen
Cellular location: Chloroplasts
Energetics: Requires energy
• Chemical paths: Light reactions &
Calvin cycle
• Summary: Sugar synthesized using
energy from the sun
Carbon dioxide, water
Cytoplasm, mitochondria
Releases energy
Glycolysis, Krebs cycle
& Electron Transport Syst.
Energy released from
sugar breakdown
Photosynthesis and respiration
• Photosynthesis and respiration are
complimentary reactions…
PHOTOSYNTHESIS
CO2 + H2O  O2 + SUGARS
O2
H2O
RESPIRATION
SUGARS + O2  H2O + CO2
CO2
CO2
PLANTS,
ALGAE,
BACTERIA
Sunlight
energy
SUGARS
O2
MOST LIVING
ORGANISMS
USEFUL CHEMICAL
ENERGY (ATP)
H2O
Respiration, Energy & Carbon Cycle
•
•
•
•
•
•
•
Energy
Virtually all organisms require energy of food for:
Making chemicals
(proteins, carbs, etc.)
Movement
Cell division
Heat, electricity and light production
The way living organisms obtain energy is through
Cell respiration
ENERGY: ability to do work
Newton’s First Law of Thermodynamics:
(1701)
“Energy cannot be created or destroyed, it
can only be transformed from one form
to another”
• Once a cell has used energy to do work, it cannot
be used again by any organism.
ENERGY
ENERGY FLOW IS LINEAR
Sun  Earth Producers 1o consumers  2o consum
heat
resp, heat
resp, heat
resp, heat
Energy flows into ecosystem from the sun
Energy travels in a straight line by way of
food chains.
ENERGY
However, much energy is lost as heat along the
way – as a result of respiration.
Approximately 90% energy is lost on each step!
• Newton’s Second Law of
Thermodynamics:
“In any transfer of energy there is always a
loss of useful energy to the system, usually in
the form of heat”
Food Chains
Food chains demonstrate linear nature of energy
• Producers are the base of the food chain, they
include photosynthetic organisms like:
• Plants
• Algae
• Certain bacteria
Food chains
• Primary
consumers –
all plant eaters
(herbivores).
Secondary
consumers –
Eat primary
consumers,
(carnivores)
Food chains
• Decomposers – obtain energy by breaking
down remaining organic material of the
other members of the food chain.
• Fungi and bacteria.
Matter
• All important elements move in cycles;
Environment
Organisms
Cycles called biogeochemical cycles:
Water cycle
Carbon cycle
Nitrogen cycle
The Carbon Cycle
• Carbon from the atmosphere (CO2) enters the
biosphere by way of plants!
– CO2 used in photosynthesis
– Carbon moves into food chain
• Carbon is released to the physical environment by
respiration
– Release CO2 during respiration
– Amount CO2 fixed in photosynthesis = the amount
released by respiration
Carbon Cycle
• Carbon moves from atmosphere to plants to
animals and back to atmosphere.
“Look deep into nature,
and then you will
understand everything
better.”
Albert Einstein
• http://www.biologie.uni-hamburg.de/bonline/library/falk/CellStructure/cellStructur
e.htm