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CHAPTER 6
PHOTOSYNTHESIS
BIOLOGY LECTURE
ENERGY FOR LIFE PROCESS
1. All organisms
require a constant supply
of energy
2. Energy does not recycle;
almost all energy is from
the sun
3. Organisms capture the energy of light and
store it in organic compounds
ENERGY FOR LIFE PROCESS
• Classifying Organisms By How They
Get Their Energy:
– Autotrophs – manufacture their
own food from inorganic
substances and energy
– Heterotrophs – cannot
manufacture their own
organic compounds from
inorganic substances
AUTOTROPHS
MAKE FOOD:
Use photosynthesis to convert
light energy from the sun into
chemical energy
They store the chemical energy
in organic compounds
(carbohydrates)
Examples are plants, algae, and
cyanobacteria
HETEROTROPHS
• Take in food
• They eat autotrophs or
other heterotrophs
– A caterpillar (H) feeds
on grass (A)
– A bird (H) feeds on the
caterpillar (H)
• Examples are animals,
most bacteria, fungi,
and protozoa
All fuel originates
with
the Autotrophs
Energy Transfer Compounds
Photosynthesis – a biochemical pathway that
converts solar energy to chemical energy
(STORE ENERGY = FOOD)
Autotrophs manufacture organic
compounds from carbon dioxide and
water and oxygen is released
6CO2 + 6H2O + LIGHT = C6H12O6 + 6O2
How Do We Get Energy?
Cellular Respiration – A biochemical pathway
that breaks down chemical energy for use by
the cell (RELEASE ENERGY)
In both autotrophs and heterotrophs,
organic compounds are combined with
oxygen to produce ATP, carbon dioxide
and water
C6H12O6 + 6O2 = 6CO2 + 6H2O + ENERGY
(ATP)
Energy Transfer Compounds
Adenosine Triphosphate – molecule of
stored energy
Energy stored in bonds between
phosphate (A M P ~ P ~ P)
AMP, ADP, ATP
Nicotinamide Adenine Dinucleotide
Phosphate - molecule that transports
energy
NADP+ to NADPH
Do Now
• 1. What is the difference between
autotrophs and heterotrophs?
• 2. What is photosynthesis?
• 3. What is cellular respiration?
• 4. What are the 2 energy transfer
compounds we talked about?
LIGHT ABSORPTION IN
CHLOROPLASTS
Chloroplasts - membrane bound organelles
that contain:
1. the pigment chlorophyll
2. enzymes for photosynthesis
*Both light and dark reactions take place here
Chloroplasts
• Inner/outer membrane
• Thylakoids: flattened sacs where photosynthesis takes
place
• Granum (pl. grana): stack of thylakoids
• Stroma: liquid solution that surrounds the thylakoids
CHLOROPLASTS IN PLANT
CELL
Light
A. White light composed of
visible spectrum
– ROY G BIV
B. Light travels in energy waves
C. Wavelength (λ) determines
color of light
D. UV → violet → red
Short λ
→ Long λ
E. Pigment: compound that
absorbs light
F. Ex. Green pigment absorbs
colors other than green &
reflects/transmits green
Chloroplast Pigments
•
•
•
There are several different
pigments in the thylakoid
membranes
Chlorophyll is a pigment
that absorbs red and blue
light and reflects green light
Chlorophyll a is directly involved with the
light reaction
Chloroplast Pigments
• Accessory pigments trap wavelengths of
light that can not be absorbed by
chlorophyll a (help capture more light)
a. Chlorophyll b – also reflects green,
but absorbs more blue than red
b. Carotenoids – reflect orange, yellow,
and brown and absorbs green and blue
c. Phycobilins – reflect violet & blue
and absorb orange, brown and green
Do Now
• 1. What important process occurs in
chloroplasts?
• 2. What are the flattened sacs in
chloroplasts called?
• 3. What is a pigment and what important
pigment is found in the chloroplast?
Electron Transport Chain (ETC)
• Photosystem: a cluster of pigment
molecules found in the thylakoid membrane
• 2 Photosystems – each has different roles in
photosynthesis
– Photosystem I
– Photosystem II
Electron Transport Chain (ETC)
• Light Reaction – Photosystem II
1. Light energy absorbed by pigments and
transferred to chlorophyl a . Electron from
chlorophyl a gets “excited” & enters a
higher energy level
2. Electron leaves chlorophyl a & enters
primary e- acceptor
3. Primary e- acceptor transfers e- to series of
molecules (electron transport chain) & loses
Energy (E used to move p+ into thylakoid)
Electron Transport Chain (ETC)
• Light Reaction – Photosystem I
– 4. Light is absorbed by photosystem I, electrons
move from chlorophyll a molecules to another
primary electron acceptor. These e- are
replaced with those from photosystem II
– 5. e- used to make NADPH from NADP+
(NADP+ & H+ NADPH)
Water’s role
• e- from splitting of H2O replaces lost e- in
photosystem II
– 2 H2O → 4 H+ + 4 e- + O2
– O2 leaves plant or used for cellular respiration
– H+ stays in thylakoid → concentration gradient
Electron Transport Chain
E. Biochemical pathways – series of
biochemical reactions
Chemiosmosis - Make ATP
• Concentration gradient causes protons (H+) to
move from thylakoid (high conc) to stroma (low
conc)
• ATP synthase uses movement of protons/change
in potential energy to make ATP
– Converts potential E to chemical E
• ATP synthase (multifunctional protein)
– Carrier protein – carries protons across thylakoid
membrane
– Enzyme – catalyzes synthesis of ATP from ADP
Calvin cycle
• Uses ATP & NADPH from the light
reaction as energy to make organic
compounds
• Carbon from CO2 “fixed” into organic
compounds
• Each cycle uses 3 ATP & 2 NADPH
• Occurs in stroma of chloroplast
• Called the Dark Reaction
Photosynthesis Balance Sheet
• 3 turns of the Calvin Cycle are required to produce
each molecule of PGAL
• This uses up 9 molecules of ATP and 6 molecules
of NADPH
• Most of the molecules made in the Calvin Cycle
are built up into:
– Amino Acids
– Lipids
– Carbohydrates
• Heterotrophs use the energy in these organic
compounds for living
Photosynthesis Equation
6CO2 + 6H2O + Light Energy = C6H12O6 + 6O2
Do Now
•
•
•
•
1. What is a photosystem?
2. What is the electron transport chain?
3. What is the purpose of the Calvin cycle?
4. What is the equation for photosynthesis?
C3 Plants & Alternative Pathways
•Plants that use Calvin cycle are called C3 plants because
they fix CO2 into a 3C compound PGA
•Stomata (pl.) - small pores on the underside of a leaf
where water, CO2, and O2 pass through
•Plants can partially close stomata to minimize water loss
•Plants open stomata during day & close @ night
C3 Plants & Alternative Pathways
• When stomata close up, CO2 can’t get into
the plant and O2 can’t get out of the plant
• This inhibits carbon fixation by the Calvin
Cycle in the plant
• Plants have to find other ways
to fix carbon and make food
C4 Plants
• Partially close stomata during hottest part of
day
• Certain cells have enzymes that can fix CO2
into 4C compound even when CO2↓, O2↑
• Lose ½ the amount of water as C3 plants
but produce the same amount of carbs
• Ex. Corn, sugar cane, crab grass
CAM Plants
• Open stomata @ night &
close during day
• B/C of this CO2 enters when colder →
slower growth, less water loss
• Fix CO2 into a variety of diff. C comp.
at night, use for Calvin Cycle during day
• Cactuses, pineapple, and others with
different adaptations to hot climate
Rate of Photosynthesis
• Effected by the Environment:
– Light Intensity – as light increases – rate of
photosynthesis increases and then levels off
when available electrons are already excited
– CO2 – as CO2 levels increase – rate of
photosynthesis increases and then levels off
– Temperature – raising the temp. speeds up
chemical reactions and increases the rate of
photosynthesis, but soon the temp gets too high
and photosynthesis rate decreases
Rate of photosynthesis
1. Light, CO2: eventually level off @ maximum
2. Temperature: reach a maximum & decrease
– Enzymes begin to become unstable & ineffective
– Stomata close & limit water loss & CO2 entry
Cellular Respiration
Chapter 7
Cellular Respiration
Overview
A. Releases energy from organic molecules
(sugars) to make ATP (available cell energy)
B. Done by autotrophs and heterotrophs
C. Aerobic respiration – organic molecules
broken down with oxygen – yields a lot of
ATP
D. Anaerobic respiration – organic molecules
broken down without oxygen – little or no
ATP.
E. Living organisms could specialize in one, or
switch depending on available oxygen.
Glycolysis
A. All organisms begin respiration with glycolysis (to break glucose) = small amount of energy
(net 2 ATP produced), but makes energy carrying (electron) molecule NADH and pyruvic acid
(organic product)
B. Anaerobic in nature
C.
Products can either be fermented (recycle NADH) or aerobically broken (lots of ATP)
D. Takes place in cytoplasm
E. Reactions in the biochemical pathway:
Glycolysis
1. 2 phos. groups attach to glucose
from 2 ATPs to form a new 6 C
compound
2. 6 C comp. splits into 2 PGAL
molecules (3 C)
3. 2 phos. groups attach to PGALs
and PGALs oxidized. NAD+
reduced to NADH.
4. Phos. groups removed and
combine with ADPs → ATP. 2
pyruvic acid molecules formed.
Do Now
•
•
•
•
1. What is cellular respiration?
2. What is anaerobic respiration?
3. What is aerobic respiration?
4. What is glycolysis?
Fermentation
A. Performed in the absence of oxygen
B. Makes no ATP, occurs in cytoplasm
C. Regenerates NAD+ which can keep
glycolysis going
D. Types:
1. Lactic Acid
2. Ethyl alcohol
Lactic Acid Fermentation
• Enzyme converts pyruvic acid into lactic acid
• Some bacteria & fungi do this → yogurt,
cheese
• Animal cells (Muscle cells w/o oxygen)
Lactic Acid Fermentation
• Occurs when you are
exercising strenuously
• Muscle cells use up oxygen
faster than you can breathe it in
• Muscle cells switch from aerobic
respiration to lactic acid fermentation
• Can make muscles sore and cause
cramping
• Eventually the lactic acid gets turned
back into pyruvate in the liver
Alcoholic Fermentation
•
•
Plants and yeast
Pyruvic acid is broken down and a CO2 is
removed, the resulting 2C compound is ethyl
alcohol.
Alcoholic Fermentation
• The basis of the beer
and wine industry
• Yeast cells are added
to either crushed grapes
or grains
• They perform fermentation to produce
ethyl alcohol
– Regular wine – CO2 is released
– Beer and champagne – CO2 is retained
Anaerobic
Energy Yield
•
When glucose is broken down
anaerobically, only 2 ATPs are
produced during glycolysis
•
•
•
Most of the energy is still trapped in the
pyruvic acid
The efficiency of energy transfer is very
low at 3.5%
This is OK for small, unicellular
organisms, but larger organisms need
more energy!!
Do Now
• 1. Is fermentation done in the presence
or absence of oxygen?
• 2. What are the 2 types of fermentation
we talked about?
• 3. Is fermentation efficient for energy
transfer?
Aerobic Respiration
• If oxygen is present, pyruvic acid goes
from glycolysis to aerobic respiration
• Aerobic respiration produces ~ 20 X as
much ATP
• 2 major stages:
– 1. Kreb’s Cycle – small amount of ATP
– 2. Electron transport chain – large
amount of ATP
Aerobic Respiration
Occurs in mitochondria of eukaryotes
(cytoplasm in prokaryotes)
1. Outer membrane
2. Inner membrane (cristae – folds)
3. Matrix – inside inner membrane – contains
enzymes needed to catalyze the Kreb’s Cycle
Coenzyme A/Acetyl
CoA
1. As Pyruvic acid enters
the mitochondrial matrix it
bonds with Coenzyme A
(CoA) and produces CO2
& Acetyl CoA &
a.NAD+ → NADH
2. Acetyl CoA begins the
Kreb’s cycle
Kreb’s Cycle
Breaks down Acetyl CoA producing CO2,
H atoms, and ATP
1. Acetyl CoA rxts
w/ oxaloacetic
acid → CoA +
citric acid
2. 1 glucose does 2
cycles
3. Kreb’s cycle
produces 2 CO2,
3 NADH, 1
FADH2 and 1
ATP per cycle
(x2 b/c 2 cycles)
4. NADH & FADH2
used in ETC
Energy So Far
• Bulk of the energy released by the oxidation
of glucose is still not in form of ATP
• This will require the NADH and FADH2 that
we have made so far
– Glycolysis – 2 NADH
– Convert Pyruvic Acid to Acetyl CoA – 2 NADH
– Kreb’s Cycle – 6 NADH, and 2 FADH2
• These 10 NADH and 2 FADH2 molecules
will enter the electron transport chain and
make ATP
Electron Transport Chain
1. Electrons for the ETC are supplied by the
splitting of NADH and FADH2
2. Protons from NADH and FADH2 are pumped
through the inner mitochondrial membrane
away from the matrix by the ETC
3. The pumping of protons across the
membrane creates a conc. gradient which is
then used to make ATP by ATP synthase.
4. Final e- acceptor is O2. (H20 is produced)
Electron Transport
Chain
Energy
1. Converted in the ETC
a. 1 NADH = 3 ATP
b.1 FADH2 = 2 ATP
2.
a. 38 ATP (12
kcal)/Glucose (686 kcal)
b. Aerobic Efficiency =
66%
Respiration Equation
• C6H12O6 + 6O2 = 6CO2 + 6H2O +
Energy
• This equation is the opposite of the
equation for Photosynthesis!