Chapter 10:
Plant Metabolism
In this chapter you will learn about
photosynthesis and
respiration at three different levels: the essence of the
process, the major steps, and the processes. The chapter discusses the
importance of the main features of each process and summarizes the light
reactions, the dark reactions, glycolysis, the Krebs cycle, and the electron
transport system. It concludes with a tabular comparison between photosynthesis
and respiration, and makes a few brief observations on assimilation and digestion.
At the end of this chapter the successful student will be able to
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Will the "capacity" of plants, which are autotrophs, to satisfy humanity's
energy needs determine the ultimate size of human populations. For
example
there is starvation/overpopulation in many areas of the world. Will our
population exceed the capacity of plants to sustain us? 50% of the oxygen
is in ocean and lakes. What happens when air pollution drives down the
amount of oxygen in the air?
The sun, the star that provides the earth with energy, is 150 million
Kilometers from earth. It takes 8.3 minutes for energy in the from of
light to travel from the sun to the earth even though it travels at the rate of
186 thousand mile/second.
What happens to this light when it reaches the earth? Plants absorb it
in Cloroplasts. Why do plants need this light? There are "autotropic"
and sustain themselves without eating other organisms or organic molecules.
Look closely at this illustration of the energy cycle. Will it continue
forever? What points of this cycle seem "at risk" to you? Why?
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Sunlight through a prism produces a spectrum of light.
Certain wavelengths of the light are absorbed by the plants.
These animations will help you understand the way light and plants work.
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Review the spectrum of visible light and parts used
by plants on page 178 of your text. The graphs below show the Effects
of Light and Temperature on Photosynthesis
- Carbon dioxide combines with RuBP and then the combined molecules are
converted to sugars (Glucose).
- Energy for these chemical reactions is furnished by ATP and NADPH from
Light-Dependent Reactions
Interact with this animation to gain
understanding of photosynthetic pigments.
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Note the role of the cholorpolasts.
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Photosynthesis:
- Energy for most cellular activity involves adenosine triphosphate (ATP).
- Plants make ATP using light as an energy source.
- Take place in cholorpolasts and other green parts of the organisms.
Click here to see an animation of leaf
photosynthesis converting light to energy
- reactants
- Carbon Dioxide
- Carbon dioxide reaches cholorplasts in the mesophyll cells by diffusing
through the stomata into the leaf interior.
- Use of fossil fuels, deforestation, and other human activities have added
excess carbon dioxide to the atmosphere.
- May enhance photosynthesis.
- Plants may counter-balance by developing fewer stomata
- water
- Less than 1% of all the water absorbed by plants is used in
photosynthesis.
- Most of the remainder is transpired or incorporated into plant materials.
- If water is in short supply, stomata usually close and thus reduce the
supply of carbon dioxide available for photosynthesis.
- light
- About 40% of the radiant energy received on earth is in the form of
visible light.
- Leaves commonly absorb about 80% of the visible light reaching them.
- Light intensity varies with time of day, season, altitude, latitude, and
atmospheric composition.
- Considerable variation in the light intensities necessary for optimal
photosynthetic rates.
- products
- glucose
- oxygen
- water
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- Water molecules split apart.
- Electrons passed along electron transport.
- ATP produced.
- NADPH produced.
Details of Light-Dependent Reactions
- Calvin Cycle
- Carbon dioxide combined with RuBP and then combined molecules are
converted to sugars (Glucose).
- Energy furnished by ATP and NADPH from Light-Dependent Reactions.
Light Independent Reactions - In Depth
- Calvin Cycle
- Six molecules of CO2 combine with six molecules of RuBP with the aid of
rubisco.
- Resulting complexes split into twelve 3PGA molecules.
- NADPH and ATP supply energy and electrons that reduce 3PGA to 12 GA3P.
- Ten of the twelve GA3P molecules are restructured into six RuBP
molecules
Click here to learn more about the Calvin Cycle
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- For extra learning about the C3, C4 and CAM, look at
- For extra learning about photosynthesis in C3, C4, and CAM, you can look
at:
- Here is a reasonable comparison of C3, C4, and CAM as well as other
aspects of photosynthesis:
- Similar to C4 photosynthesis in that 4-carbon compounds are produced
during the light-independent reactions.
- However, in CAM, the organic acids accumulate at night and break down
during the day, releasing carbon dioxide.
- Allows plants to function well under limited water supplies, as well
as high light intensity.
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Last modified:
October 08, 2004 by
Cynthia Herbrandson 
© Copyright 1999, Kellogg Community College.
All rights reserved.