Name: _____________________ Date: __________ Period: ____
Chapter 5 Section 2
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Photosynthesis
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Energy from the Sun
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When you eat a hamburger, you get energy from the sun!
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Energy from the Sun
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With few exceptions, you end up with energy from plants whenever you
trace your food back to its origin.
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Photosynthesis
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Its the process that provides energy for almost all life.
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We represent photosynthesis by:
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6CO2 + 6 H20 → C6H12O6 + O2
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Photosynthesis
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Plants use pigments to capture light from the sun to produce
carbohydrates.
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Sunlight contains a mixture of all wavelengths (colors) of visible light.
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Three Kinds of Pigments & Colors absorbed
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Chlorophyll a - Indigo, red, violet, orange
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Chlorophyll b – Blue, indigo, violet, orange
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Carotenoids - Blue, dark green
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Why all the different pigments?
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The reason that there are so many pigments is that each absorbs light
more efficiently in a different part of the spectrum.
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Where are pigments found?
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Pigments involved in plant photosynthesis are located in the chloroplasts
of leaf cells.
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Within the chloroplasts, pigments are embedded in disk-shaped
structures called thylakoid.
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How do pigments work?
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Pigments attract light.
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In the pigments, electrons freely float around until light strikes it.
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When light strikes the electrons, the electrons capture the energy.
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How do pigments work?
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The electrons then use the captured energy in the photosynthetic
process.
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Why is water used in photosynthesis?
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Water is absorbed by the plants to be broken down and used in the
photosynthetic process.
Uses of H2O in photosynthesis:
 When water splits, the electrons are taken from the hydrogen atoms.
 Electrons replace those lost from the pigment when light is
absorbed.
 The hydrogen ions is used to produce NADPH – used in producing
glucose.
 The oxygen atom combines with another oxygen atom and is
released as a by-product (waste).
Why is carbon dioxide used in photosynthesis?
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The carbon in carbon dioxide is used to build the glucose molecule
(C6H12O6).
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The two oxygen atoms are released as a by-product.
2 Phases of Photosynthesis
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Light cycle
– Light energy is captured
– Water molecules are split
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Dark cycle (Calvin cycle)
– Carbon dioxide is split
– Captured light energy is converted into stored energy with the
carbon from CO2 to make glucose.
3 Factors that Affect Photosynthesis
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Amount of Light – Increases until all the pigments are used.
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Amount of Carbon Dioxide
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Temperature