Transcript The Green World’s Gift: Photosynthesis Objectives: 1. Explain why organisms need a supply of energy. 2.

The Green World’s Gift:
Photosynthesis
Objectives:
1. Explain why organisms need a supply of energy.
2. Explain how energy is stored in/or released from ATP.
3. Explain the role of chlorophyll in photosynthesis.
4. Explain how the light dependent and the Calvin Cycle are
related.
5. Identify the reactants and the products of photosynthesis.
6. Discuss the importance of photosynthesis to life on Earth!!
Photosynthesis and Energy
1. Try to name something you eat that isn’t from a
plant or from an animal that ate a plant.
2. All food comes from plants.
Molecules of our bodies are made from food
we eat, but plants make their own food from sunlight.
Food made by plants and eaten by animals is used for:
a) Creating macromolecules from monomers like glucose and amino
acids. Making all the organic molecules found in living things!
b) More importantly, food is used in cells generate cellular energy, ATP.
Therefore:
Plants are the nearly
universal source of
energy for all living
things.
ATP is the most important temporary energy
storage molecule:
1. Biological work takes energy
2. Energy locked up in molecules is potential energy,
however it is not available for work.
3. The potential energy from food breakdown is used to drive
the synthesis of ATP (like recharging a battery).
4. This high energy ATP has stored energy that can be used by
cells to do a variety of actions.
5. ATP energy can be released at any time by breaking off the
third phosphate
Plants take energy-poor reactants (water and carbon dioxide)
and use solar energy to drive the uphill reaction of trapping
those reactants in complex, ordered bonds of glucose.
Photosynthesis
• The goal of photosynthesis :_________________
________________________________________
• Photosynthesis is necessary because glucose is
needed for ___________________.
• The energy required to synthesize (make) glucose
comes from ___________________________.
which does not have mass (weight);
• The materials needed to synthesize glucose come
from ______and _______.
Photosynthesis Equation:
•6CO2 + 6H2O + light energy  C6H12O6 + 6O2
CO2 is from ________
H2O is from ________
A. Nature of Light
1. Energetic rays have different wavelengths in a spectrum from
gamma rays to radio waves, only a portion of which is visible
light:
PLANT PIGMENTS:
• When we see a green plant: ______________- light is
absorbed while _______________light is reflected.
3. Why is a black car is hotter on a sunny day than a white
car?
4. Chlorophyll is a pigment molecule in plants (in
chloroplasts), that absorbs light. What color(s) do you
think chlorophyll absorbs??
5. Plants have other pigments too– each with their own
specific wavelength of absorption. The other pigments
increase the wavelengths, (colors), of light that the leaf can use for
photosynthesis!
Plant Pigments
• Chlorophyll is a pigment molecule in plants (in
chloroplasts), that absorbs light
• Plants have other pigments too– each with their
own specific wavelength of absorption. The other
pigments increase the wavelengths, (colors), of light that the
leaf can use for photosynthesis!
Photosynthesis is driven by only part of the visible spectrum (blue
and red); plant pigments in the green plant reflects green and
absorbs blue and red.
Note: The higher the peak, the stronger the absorption of that
wavelength of light.
Tour of a leaf, where plants absorb light:
Blade
Leaf section, epidermis,
stomata, mesophyll
Chloroplasts, inner
and outer membranes,
Grana and stroma
Thylakoid membrane,
and compartment
Stomata…
are pores in the leaf surface
that allow gases in or out.
What gases pass in and out of
stomata?
(Singular = stomate)
Leaf cross section
Photosynthesis mostly occurs in the mesophyll cells.
A. Photosynthesis occurs in two essential phases.
1.
Light-dependent Reactions =“photo” of photosynthesis.
a) Power of sunlight excites electrons in pigment
molecules.
b) Excited electrons are carried down transport
chain to provide energy for the second phase .
c) Pigment electrons are replaced by electrons
stripped from water, making O2 gas.
((This is where the water is used and the
oxygen is produced!))
d) Photosystems are the working units that absorb solar energy.
1. Clusters of hundreds of pigment molecules serve as antenna to
absorb solar energy.
2. Reaction center of aggregate contains pair of chlorophyll
molecules with electrons that absorb the energy and jump to
electron carrier molecules:
e)
Energy transfer is possible using redox reactions.
1. One substance loses electrons (oxidized) while another gains
electrons (reduced). = ‘Redox’
2. Electrons move down the energy hill, losing energy as they go
(Analogy: the passing of a hot potato warming each hand as it drops,
giving off some heat as it goes. The last person to get the potato
gets some heat and food as well.)
…until the final recipient of the electrons, in this case is
+
NADP
which becomes NADPH
+
Follow the pathway of the Light Reactions:
1. Photosystem II absorbs solar energy.
2. Electron jumps to the primary electron acceptor.
3. Chlorophyll is left without an electron, but it is replaced by the
splitting of water into H+ ions, electrons and O2.
4. Ejected electron falls back down the energy hill
through a series of electron transfer molecules
called an ‘electron transport chain, until it
reaches Photosystem I (another reaction center also
receiving solar energy that excites its electrons).
**In the process some ATP is made**
5. Again, energized electrons from Photosystem I are
transferred back down another energy hill (electron
transport chain), until they are received by NADP+,
an electron carrier that ferries electrons to the
second stage, the light-independent stage of
photosynthesis.
B.
Importance of the light-dependent
phase
1. Oxygen formation
O2
2. Energized electrons being transferred, (not just
giving off heat or fluorescing), and ferried by
NADPH for stage 2.
NADPH
3. Formation of ATP, which is also used to power
the second stage, the light-independent reactions,
stage 2.
ATP
ATP NADPH
O2
B. Light-independent Reactions-Synthesis
Phase = The Calvin Cycle
a) ATP and NADPH are not good permanent storage
molecules but are good carriers.
b) Plants covert the energy in ATP and NADPH into the
bonds in a glucose molecule. Electrons from carriers are
brought together with CO2 and H2O to make this glucose.
Simplified:
1.
Carbon Fixation = the process of taking CO2 from the
atmosphere and creating an organic compound from it.
2.
Enzyme called rubisco is responsible for this process: it brings
together CO2 and a five carbon sugar.
More Detail:
Importance of Light Independent
Reactions:
**Carbon is fixed into
organic compounds!!
The glucose can be converted into the other
organic substances in the plant AND it supplies
animals with food.
A. Glitch in the system—Photorespiration
1. Rusbisco often combines O2 instead of CO2 with RuBP,
unproductively.
2. Occurs one O2 for every three CO2.
3. Undercuts food production in crops that use C3 cycle.
4. Especially problematic in hot weather because of evaporation of
water. Plant closes stomata in leaves to prevent evaporation, but as
water is kept in, CO2 is kept out. As the light-dependent reactions
continue, O2 builds up, combining with RuBP unproductively.
1. Grasses, corn, sugarcane, and sorghum
2. Use a different enzyme located in bundle-sheath cells: Figure 8.10
3. Costs ATP to shuttle CO2 to bundle-sheath cells; in sunny climates this
is not an issue, because with abundant sunlight, ATP is plentiful.
4. In northern climates, C4 plants are not as well adapted.
Video C-4 Pathway
• file:///D:/bc_campbell_biology_7/0,7052,31
17218-,00.html
CAM Plants—another adaptation that saves
water in hot climates (Section 8.8)
A. Cactus, pineapple, mint, and orchid
B. Close stomata during the day, open at night
C. Start C4 metabolism at night by fixing CO2 but wait for
day to use abundant ATP to finish.
D. Comparison of three strategies: Figure 8.12
Summary of Photosynthesis in
most kinds of plants
Review The Process in a leaf:
Review the Process in a Chloroplast
Some autotrophic bacteria can survive without
light
Instead they use the energy in inorganic
compounds like Hydrogen sulfide or ammonia
to make organic compounds
Such organisms are called
Chemosynthetic autotrophs
Today these organisms are found in
extreme environments like deep sea
vents and sulfur springs
How do organisms use the food made by
photosynthesis??.
3. Oxygen needed for respiration is produced as a byproduct of photosynthesis.
The End