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Title: Biology 108 Chapter 7
Description: Non-major biology course Christine Yates University of Alabama
Description: Non-major biology course Christine Yates University of Alabama
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Photosynthesis
● The basics
○ Almost all plants are photosynthetic autotrophs, as are some bacteria and
protists
■ They generate their own organic matter through photosynthesis
● Chloroplasts: The site of photosynthesis
○ Photosynthesis
■ Occurs in chloroplasts
○ Chloroplasts
■ Are found in the cells of the mesophyll
■ Contain stroma, a thick fluid
■ Contain thylakoids, membranous sacs
● The overall Equation for Photosynthesis
○ 6CO
+ 6H
O → C 12 6
H
2
2
6 O
○ In photosynthesis
■ Energized electrons are added to carbon dioxide to make sugar
■ Sunlight provides the energy
● A photosynthesis road map
○ A 2 step process
■ The light reactions convert solar energy to chemical energy
■ The calvin cycle makes sugar from CO
2
● The light reactions: Converting solar energy to chemical energy
○ Sunlight is a type of energy called radiation, or electromagnetic energy
○ The full range of radiation is called the electromagnetic spectrum
○ Chloroplasts absorb light energy and convert it to chemical energy
○ Chloroplasts contain several pigments
■ Chlorophyll A→ Green
■ Chlorophyll B→ Green
■ Carotenoids→ Orange and browns
● How photosystems Harvest Light Energy
○ Light behaves as photons, discrete packets of energy
○ Chlorophyll molecules absorb photons
■ Electrons in the pigment gain energy
■ As the electrons fall back to their ground state, energy is released as heat
or light
○ A
photosystem
is a group of chlorophyll and other molecules that function as a
lightgathering antenna
● How the Light Reactions Generate ATP and NADPH
○ Two types of photosystems cooperate in the light reactions:
■ The watersplitting photosystem
■ The NADPHproducing photosystem
○ An electron transport chain
■ Connects the two photosystems
●
●
●
■ Releases energy that the chloroplast uses to make ATP
The Calvin cycle
○ Making sugar from CO
2
○ The Calvin cycle
■ Functions like a sugar factory within a chloroplast
■ Regenerates the starting material with each turn
WaterSaving Adaptations of C
and CAM Plants
4
○ C
plants
3
■ Use CO
directly from the air
2
■ Are very common and widely distributed
○ C
plants
4
■ Close their stomata to save water during hot and dry weather
■ Can still carry out photosynthesis
○ CAM plants
■ Open their stomata only at night to conserve water
How Photosynthesis Moderates the Greenhouse effect
○ Old growth forests
■ Are important for lumber
■ Are important for moderating world climates
○ The greenhouse effect
■ Warms the atmosphere
■ Is caused by atmospheric CO
2
○ Greenhouse gases are the most likely cause of global warming, a slow but
steady rise in the earth’s surface temperature
■ Destruction of forests may be increasing this effect
Title: Biology 108 Chapter 7
Description: Non-major biology course Christine Yates University of Alabama
Description: Non-major biology course Christine Yates University of Alabama