8.3 The Process of Photosynthesis - WordPress.com...2016/11/08 · 8.3 The Process of...
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8.3 The Process of Photosynthesis
8.3 The Process of Photosynthesis
Review
Phototrophs: obtain energy from light
Chemotrophs: obtain energy from
chemicals
Autotrophs: obtain carbon from CO2
Heterotrophs: obtain carbon from organic
sources
Light-Dependent Reactions: ATP and NADPH
The light-dependent reactions occur in the thylakoids of
chloroplasts.
Photosystems - groups of chlorophyll and proteins in the
thylakoid. Absorb sunlight and generate high energy electrons that
are used to make sugars.
Photosystem II
Water molecules provide new
electrons to chlorophyll.
Enzymes break up the water
molecules into 2 electrons, 2
Hydrogen atoms, and 1
oxygen atom.
Oxygen is released into the air.
The H+ ions are released inside
the thylakoid.
Electron Transport Chain
Electron transport chain - a
system that carries high-
energy electrons during ATP-
generating reactions.
Electron transport chain
takes energy from the
electrons and uses it to pump
H+ ions from the stroma into
the thylakoid space.
Electron Transport Chain
At the end of the electron
transport chain, the
electrons pass to
photosystem I.
Photosystem I - pigments
use energy from light to
re-energize the electrons
At the end of a short second electron transport chain, NADP+
molecules in the stroma pick up the high-energy electrons and H+
ions at the outer surface of the thylakoid membrane to become
NADPH.
The difference in both charge and H+ ion concentration across
the membrane creates a gradient, or build up, of hydrogen
inside the thylakoid. The H+ now wants to diffuse out of the
thylakoid.
ATP synthase spans the thylakoid membrane and allows H+ ions
to pass through it, while creating ATP as result. This is called
chemiosmosis.
Light-Independent Reactions: Producing
Sugars
Light-independent reactions aka the Calvin cycle - plants use the energy
that ATP and NADPH contains to build stable high-energy carbohydrate
compounds that can be stored for a long time.
Summary of the Calvin Cycle
Calvin cycle - 6 CO2 → 1 6
carbon sugar.
The energy for the reactions
is supplied by compounds
produced in the light-
dependent reactions.
Temperature, Light, and WaterThe reactions of photosynthesis are made possible by enzymes that function best
between 0°C and 35°C.
High light intensity increases the rate of photosynthesis.
After the light intensity reaches a certain level, however, the plant reaches its
maximum rate of photosynthesis, as is seen in the graph.
Photosynthesis Under Extreme Conditions
In order to conserve water, most
plants under bright, hot
conditions close the small
openings in their leaves that
normally admit carbon dioxide.
This causes carbon dioxide within
the leaves to fall to very low
levels, slowing down or even
stopping photosynthesis.
C3 Plants, like soy, oats, wheat
and rice, when the climate is
hot and dry, these plants close
their stomata. This prevents
CO2 from entering the plant
cells.
Photorespiration is where no
ATP and no sugar is made in
the plant cell due to the fact
that carbon dioxide is depleted
and oxygen is building up.
C4 Plants, like corn and
sugarcane keep their
stomata closed most of the
time to conserve water.
They are able to prevent
photorespiration by using
special enzymes that
continue photosynthesis
even when carbon dioxide
levels are low.
CAM plants, like cacti and
pineapples, conserve water by
opening their stomata and
admitting CO2 only at night.
The plant is then able to bank a
large amount of CO2 to
continue photosynthesis during
the day.
Video ReviewCrash course: http://youtu.be/sQK3Yr4Sc_k
TED-Ed Calvin Cycle: http://youtu.be/0UzMaoaXKaM