Chapter 8: The Working Cell: Energy from Sunlight
Concept 8.1: Photosynthesis Uses Light Energy to Food
I. The Structure of Chloroplasts
A. Photosynthesis takes place in the chloroplast
B. Chloroplasts contain compounds called pigments that give
leaves their color (chlorophyll).
C. Leaves contain the most chloroplasts. (fig. 8-2)
D. Stoma are tiny pores that allow carbon dioxide to enter and
oxygen to leave the plant cell.
E. Veins (xylem) carry CO2 and H2O from the plants roots to
the leaves and deliver(phloem) organic compounds to other
parts of the plant.
F. The inner membrane of a chloroplast encloses a thick fluid
called stroma.
G. Suspended in the stroma are many disk shaped sacs called
thylakoids which are arranged in stacks called grana.
H. These stacks organize the series of reactions that make up
photosynthesis.
II. Overview of Photosynthesis
A. In cellular respiration, electrons “fall” from glucose to O2 to release energy.
B. In photosynthesis, electrons from water are boosted “uphill”
(potential) by the energy of sunlight.
C. These excited electrons, along with carbon dioxide
and
hydrogen ions to produce C6H12O6 molecules
D. Photosynthesis occurs in two main steps: Light and Calvin
Cycle (Dark Reaction).
III. The Light Reactions
A. Light Reactions convert the energy in sunlight to
chemical energy.
B. Chloroplasts use captured light energy to remove electrons
from H2O, splitting it into oxygen and hydrogen ions.
C. The electrons and hydrogen ions are used to make NADPH,
which is an electron carrier.
D. Chloroplasts also use the captured light energy to generate
ATP.
E. The overall result of the light reactions is the conversion of
light energy to chemical energy stored in NADPH and ATP
IV. The Calvin Cycle
A. Calvin Cycle makes sugar from the atoms in carbon dioxide plus the
hydrogen ions and high energy electrons carried in NADPH
B. The ATP made in the light reactions provides the energy to make sugar.
C. The Calvin cycle is sometimes referred to as the “lightindependent reactions” because it does not require light
energy to begin.
Overview fig. 8-4
Concept 8.2: Light Energy to Chemical Energy
I. Light Energy and Pigments
A. Light is a form of electromagnetic energy that travels in
waves and the distance between adjacent waves is called a
wavelength.
B. The range of wavelengths is called the electromagnetic
spectrum. (fig. 8-5)
C. Visible light only makes up a small portion of the
electromagnetic spectrum.
II. Pigments and Color
A. A substances color is due to chemical compounds called
pigments.
B. Waves of light shining on a material can be absorbed,
transmitted or reflected.
C.Leaves absorb blue-violet and red-orange light very well but either reflect or
transmit green light and that is why leaves look green.
III. Identifying Chloroplast Pigments
A. Using a technique called chromatography different pigments
in a leaf can be observed. (fig. 8-7)
B. Chlorophyll a absorbs mainly blue-violet light while
chlorophyll b absorbs mainly red light.
IV. Harvesting Light Energy
A. Within the thykaloid membrane, chlorophyll and other
molecules are arranged in clusters called photosystems.
(fig. 8-8)
B. Each photosystem contains a few hundred pigment
molecules, including chlorophyll a and b as well as
carotenoids.
C. Each time a pigment molecule absorbs light energy
electrons are raised from a “ground state” to an “excited
state”.
D. This electron “jumps” from molecule to molecule until it
arrives at the reaction center.
E. The reaction center consists of chlorophyll a and a
primary
electron carrier. Other teams of molecules are also used to
make ATP and NADPH.
V. Chemical Products of Light Reactions
A. 2 photosystems are involved in the light reactions.
B. The first photosystem traps light energy and transfers the
light-excited electrons to the electron transport chain, this
can be referred to as the “water splitting photosystem”.
(figs.8-10,11)
C. The second photosystem can be thought of as the “NADPHproducing photosystem” This system produces NADPH by
transferring excited electrons and hydrogen ions to NAD+
D.The light reactions convert light energy to the chemical energy of ATP and
NADPH, NO SUGAR has been produced, which is the job of the CALVIN
CYCLE.
Concept 8.3: Calvin Cycle: Sugar from Carbon Dioxide
I. A Trip Around the Calvin Cycle (fig.8-13)
A. The Calvin Cycle is the sugar factory within the chloroplasts.
B. The starting material for the Calvin cycle is regenerated
each time the process occurs, the starting material is called
RuBP, (a sugar with five carbons).
C. The inputs for the Calvin cycle are ATP, CO2 and NADPH.
(from light reaction and air thus no light)
D. The cycles output is an energy rich sugar molecule called
G3P which is not quite glucose but is used as the raw
material to make glucose as the plant needs to.
II. Summary of Photosynthesis
A. The equation (unbalanced) for photosynthesis is
Carbon Dioxide + Water --> Glucose + Oxygen
CO2 +
H2O
--> C6H12O6 + O2
B. The light reactions take place in the thylakoid
membranes and convert light energy into chemical energy
in the form of ATP and NADPH. (fig. 8-14)
C. The light reactions use the reactant H2O and release the
product O2.
D.The Calvin cycle takes place in the stroma uses ATP and
NADPH to convert CO2 to C6H12O6.
E. Photosynthesis is the first step in the flow of energy
through an ecosystem
E. Photosynthesis is the ultimate source of all the food that you
eat and all the oxygen that you breathe
Concept 8.4: Photosynthesis has a Global Impact
I. The Carbon Cycle (fig 8-15)
A. The C cycle is the process by which carbon moves from
inorganic to organic compounds and back.
B. Through photosynthesis, producers convert inorganic CO2
to organic compounds (ie sugar).
C. Cellular Respiration by both producers and consumers
return the CO2 to the atmosphere.
D. No other chemical process matches the output of
photosynthesis.
F. Earth’s plants and other photosynthetic organisms make up
about 160 billion metric tons of organic material per year.
II. Photosynthesis and Global Climate
A. One organism may either produce or use a relatively small
amount of CO2, the total effect of all the organisms on Earth
is very large.
B. CO2 only makes up 0.03 percent of the Earth’s atmosphere
before this century
C. CO2 is one of many gases that traps heat from the
sun that
would have otherwise escape back into space, this is the
greenhouse effect.
D. The greenhouse effect keeps the average temperature on
Earth about 10 degrees C warmer than it would be otherwise
E. The amount of CO2 in the atmosphere is rising.