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Chapter 5

BIOL 1500 Chapter 5: Chapter 5


Department
Biology
Course Code
BIOL 1500
Professor
Tanya Da Sylva
Chapter
5

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Chapter 5: Photosynthesis
5.1 Life Depends on Photosynthesis
Autotroph - “self-feeder” uses inorganic substances
Heterotroph obtains carbon consuming preexisting organic molecules
o Energy, raw materials and Oxygen support most heterotrophs
6CO2 + 6H20 ---------------- C6H12O6 + 6O2
More than half of the world’s photosynthesis occurs in the vast oceans (algae and bacteria)
5.2 Photosynthesis Pigments Capture Sunlight
Sun releases energy in all directions in the form of waves of electromagnetic radiation
1% used for photosynthesis
Electromagnetic spectrum range of frequencies of radiation
Photons packets of kinetic energy
Wavelength distance it moves during a complete vibration
o Shorter the photon’s wavelength = more energy it contains
Sunlight on earth has 3 components:
o Ultraviolet Radiation
Shortest wavelengths
Damage DNA
o Visible Light
Powers photosynthesis
o Infrared Radiation
Too little energy to be useful to organisms
Most energy converted to heat
Plant cells have pigment molecules
o Chlorophyll a
Most abundant
In plants, algae, cyanobacteria
o Accessory Pigments
Energy-capturing pigments (other than Chlorophyll a)
Extend the range of light wavelengths that a cell can harness
o Chlorophyll b and carotenoids
Accessory pigments n plants
Photosynthesis pigments have distinct colors because they absorb some wavelengths of visible
light while reflecting others
Only absorb light is useful in photosynthesis
5.3 Chloroplasts Are the Sites of Photosynthesis
Glossary: Leaf Anatomy
Stoma
Opening through which a leaf exchanges gases
with the atmosphere

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Mesophyll Cell
Leaf cell where photosynthesis occurs
Chloroplast
Organelle of photosynthesis in a plant cell. It
have lots of surface area.
Granum
A stack of thylakoids suspended in a chloroplast
Thylakoid
A pancake-shaped compartment within a
chloroplast; site of the light reactions
Thylakoid membrane
The lipid bilayer in which photosystems are
embedded
Photosystem
Cluster of pigments and proteins that participate
in the light reactions of photosynthesis
Thylakoid space
The compartment enclosed by the thylakoid
membrane
Stroma
The fluid inside the chloroplast; site of the
carbon reactions
Photosynthesis
1. Water
Roots absorb ingredients which then go up the stem and into the leaves
2. Exchange CO2 and O2
Through stromata of a leaf or stem
o Occurs in the Mesophyll cell which contain an abundant amount of chloroplast
o Stroma contains ribosomes DNA, and enzymes
o Thylakoid stacked to make grana
o Photosystems imbedded in Thylakoid membrane
o Consist of reaction center (which also includes):
Chlorophyll a
Use the energy in photosynthetic reactions
But only absorbs small amounts of light energy at a time
Other Pigments
Makes up the light-harvesting complex that surrounds reaction center
Antenna Pigments
Capture photos energy and funnel it to the reaction center
Passes light energy quickly
5.4 Photosynthesis Occurs in Two Stages
Photosynthesis occurs in two stages:
o Light Reactions
Solar energy to chemical energy
Pigment molecules capture photons and store potential energy as:
ATP
NADPH
NADPH carries pairs of energized electrons that come from one of the two
reaction center chlorophyll molecules
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