Transcript light independent reactions

Drill – February 2012
Overview of Photosynthesis
1.) The process by which autotrophs convert sunlight energy into chemical
energy for use by their cells is called photosynthesis.
2.) How can it be said that photosynthesis “supports most life on Earth?”
With the exception of chemoautotrophs, organisms that make food
directly from sunlight (photoautotrophs) form the basis of all food chains
on Earth.
3.) Visible light or white light is made up of a spectrum of colors. Each color
has a different wavelength and each wavelength contains a different
amount of energy.
a. Which color (wavelength) contains the most energy? violet / blue
b. Which color contains the least energy? red
c. Which color is reflected by plants that appear green? green
Overview of Photosynthesis
4.) Photoautotrophs obtain energy from light wavelengths that they
__________,
absorb
but not from colors that they ________.
reflect
pigment is a molecule that absorbs certain wavelengths (colors) of
5.) A __________
light and reflects others.
Photosynthetic pigment
Colors/Wavelengths of
Light Absorbed
Colors/Wavelengths of
Light Reflected
chlorophyll a
violet / blue / red
green / yellow
chlorophyll b
blue / orange
green / yellow
carotenoids
blue
green / yellow / orange / red
Overview of Photosynthesis
6b.) What color(s)/
wavelength(s) of visible light
are absorbed by all three of
the photosynthetic pigments
in the chart? violet / blue
Why might this be so?
Violet/ blue light contains the
most energy, therefore plants
might have adapted pigments
that can capture this
energetic light.
6c.) What color(s)/
wavelength(s) of visible light
are reflected by all three of
these photosynthetic
pigments? green
Overview of Photosynthesis
7.) Which of the three photosynthetic pigments in the table is most
commonly found in plants? ____________
chlorophyll a
8.) Given the information from questions #6 and #7, why do most plants
appear green?
Most plants appear green because they contain chlorophyll a, a
pigment that reflects green light.
9.) Photosynthetic pigments are located in an organelle called a
____________.
chloroplast
Overview of Photosynthesis
10.) Below is a diagram of a chloroplast. Label the following parts:
inner membrane
intermembrane space
granum
lumen
interior of the
thylakoid
thylakoid
stroma
outer membrane
Overview of Photosynthesis
• Photosynthesis occurs in two phases:
1. Light dependent reactions
• Occur in the thylakoids
2. Light independent reactions / Calvin cycle
• Sometimes called dark reactions, but this is inaccurate
• Occur in the stroma
Light
dependent
reactions
Glucose
Typical
chloroplast
Calvin
cycle
Overview of Photosynthesis
Calvin Cycle
Overview of Photosynthesis
ADP + P
NADP+
Calvin Cycle
Light Dependent Reactions
Calvin Cycle
(a.k.a. dark reactions or light independent reactions)
STEP 1.
Carbon fixation: Six CO2 molecules combine with six 5-carbon compounds
and are rearranged into twelve 3-carbon compounds (PGA).
STEP 2.
ATP and NADPH from the LD rxn are used to convert twelve PGA
molecules into twelve G3P molecules.
STEP 3.
Two G3P molecules leave the cycle and are converted into
glucose or other compounds.
STEP 4.
An enzyme (Rubisco) converts the remaining ten G3P back into
six 5-carbon compounds.
Calvin cycle (recap)
Carbon accounting
1.
2.
3.
4.
Carbon fixation: Six CO2 molecules
combine with six 5-carbon compounds and
are rearranged into twelve 3-carbon
compounds (PGA).
ATP and NADPH from the LD rxn are used
to convert twelve PGA molecules into
twelve G3P molecules.
Two G3P molecules leave the cycle and are
converted into glucose or other
compounds.
An enzyme (rubisco) converts the
remaining ten G3P back into six 5-carbon
compounds.
(6*1) + (6*5) =
6 + 30 = 36
12 * 3 = 36
36 – (2 * 3) =
36 – 6 = 30
(10 * 3) = 30
(6 * 5) = 30
C4 pathway
• Fix carbon into 4-carbon compounds
instead of 3-carbon compounds.
• Keep the pores in their leaves (called
stomata) closed during hot days.
• Minimizes water loss while allowing
these 4-carbon compounds to enter
the Calvin cycle
• Occurs in sugar cane and corn.
CAM plants
• Crassulacean acid metabolism (CAM)
photosynthesis
• Allow CO2 to enter leaves only at night.
• CO2 is fixed into organic compounds.
• During the day CO2 can be released
from these compounds and used in the
Calvin cycle.
• Water-conserving plants that live in
harsh environments (salt marshes,
deserts, high altitude)
• Cacti, orchids, pineapple