Download Light reactions

DO NOW:
Answer the following question:
A plant was planted six months ago
that weighed 12 oz (including the soil)
in the window. Now the plant and soil
weigh 22 oz!!! How is this possible?
(No soil was added, and wet soil does
not account for the answer).
Plants and Light
How do plants get their energy?
Photosynthesis!!! which means?
Using light to make energy.
Photo= light
Synthesis= to make
2 Types of organisms…
Autotrophs make their own food
Heterotrophs must obtain food
from environment (eat)
What are plants?
Autotrophs!!!
2 Types of Autotrophs…
1)Photoautotrophs- organisms that use
light to make food
plants
bacteria
2)Chemoautotrophs- organisms that use
chemicals to make
food.
Photosynthesis in brief…
Plants are autotrophs, relying on
photosynthesis to make food
(glucose).
What’s required for photosynthesis?
Light, CO2, and water…
…sugar and oxygen are given off
Light Energy!!!
Light is a form of radiation, which
travels in what are called waves…
Let’s see some examples…
wavelength
Smaller wavelength, but greater
frequency…
So…
Sunlight is a mixture of all visible
wavelengths…what color is it?
White!!!
White light can be broken down into
different colors using a prism, which
diffracts the light to form a spectrum.
Spectrum?
A spectrum is simply a distribution
of light, arranged in order according
to its energy…
Good Ole Roy!!!
How can you remember the colors?
Listed backwards, they spell:
ROY G. BIV
Why are they arranged this way?
It’s due to wavelength…
380 430
500
560 600
750
Why do we see colors?
When we see color, it is due to
reflected light.
This dot, absorbs all light, but
that in the red end of the
spectrum.
Umm Hmm…
Substances that absorb light are
called pigments.
Umm, what doesn’t absorb light?
Anything that’s white!!!
Photosynthetic Pigments
By far, the most important pigment
in plants, is chlorophyll.
All plants have 2 types of
chlorophyll:
chlorophyll a and
chlorophyll b
green
Other Pigments
Besides chlorophyll, plants have
other pigments:
carotene (orange) and
xanthophyll (yellow)
Pigments continued…
Why don’t we see the other
pigments?
They’re masked by chlorophyll,
which is present in great quantities.
Why are the other pigments there?
They absorb light at different
wavelengths than chlorophyll.
Light
Reflected
Light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Figure 10.7
Photosynthesis again…
Where does photosynthesis occur?
Plants!!!
More specifically?
Chloroplasts!!!
Anatomy of a Chloroplast:
Chloroplasts contain flattened sacs
of photosynthetic membranes
called thylakoids.
A bunch of thylakoids make up
grana.
The fluid surrounding the grana is
called stroma.
Why are chloroplasts necessary?
Chlorophyll is contained within the
grana…
Chlorophyll can absorb energy
without stroma present, but it
immediately gives off the energy
as heat or light.
Necessity of chloroplasts continued.
For chlorophyll to produce food for
the plant, all of the enzymes
contained within the stroma are
necessary.
thylakoid
stroma
grana
Photosynthesis
Overall reaction
6CO2 + 12H2O Light
C6H12O6 + 6O2 + 6H2O
Takes place over many steps…
Photosynthesis Dissected:
Divided into 2 types of reactions:
1)Light-dependent reactions
2)Light-independent reactions
Light-dependent reactions
Requires light
Take place in the grana of chloroplast
Store energy in high energy molecules
– ATP
– NADPH
Light Dependent Reactions
Chlorophyll a and b absorb blue-violet and
red-orange light from sun and excite
electrons
Transfer excited electrons to NADP (carrier)
and convert ADP to ATP
Some electrons split water called
photolysis
Oxygen is released
NADP+ + H+ + 2e-
ADP
ATP
2ephotosystem I
2ephotosystem II
2eH2O
2H+ + ½ O2
NADPH
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Figure 10.11 A
Chlorophyll
molecule
Ground
state
gure 10.14
e–
ATP
e–
e–
NADPH
e–
e–
e–
Mill
makes
ATP
e–
Photosystem II
Photosystem I
Light-independent Reactions
Energy from the light dependent
reactions is used to power the
light-independent reactions.
Do not necessarily occur in the
dark, but they don’t require
light.
Light-independent continued…
Occur in the stroma of the
chloroplast
Series of enzyme controlled steps
to convert CO2 and H into
glucose.
The reaction:
CO2 goes through a process
known as carbon fixation.
CO2 reacts with a 5 carbon sugar
called ribulose bisphosphate
(RuBP), and then enters the
Calvin Cycle
Light Independent Reactions
H from NAPH2 from light reactions
Carbon dioxide from environment
Require products from light reactions so
stop shortly after light reactions end
Water is also a by-product
Light reaction
Calvin cycle
H2O
CO2
Light
NADP+
ADP
+P1
RuBP 3-Phosphoglycerate
Photosystem II
Electron transport chain
Photosystem I
ATP
NADPH
Figure 10.21
G3P
Starch
(storage)
Amino acids
Fatty acids
Chloroplast
O2
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light energy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
Sucrose (export)
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic
phosphate, and
NADP+ to the light reactions
Factors influencing photosynthesis:
There are 3 main factors
influencing the rate:
1)Light intensity
2)Temperature
3)Water and mineral availability
4)Carbon dioxide level
Photosynthesis vs Cellular
Respiration
In brief, they are exact
opposites: photosynthesis stores
energy in glucose, respiration
releases energy.
Photosynthesis vs Cellular
Respiration
Photosynthesis:
6CO2 + 12H2O Light
C6H12O6 + 6O2 + 6H2O
Photosynthesis vs Cellular
Respiration
Photosynthesis:
6CO2 + 12H2O Light
C6H12O6 + 6O2 + 6H2O
Respiration:
C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O
Leaf cross section
Vein
Mesophyll
Stomata
Figure 10.3
CO2
O2