Download Photosynthesis Notes

Photosynthesis Notes
1. WHY EAT ???
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ENERGY
o needed to do things such as play sports
o also needed for things we don’t see or know about such as building new cells and
materials (proteins & amino acids)
**Without energy, live would cease to exist
So, where does the energy we need come from??  Food
2. Do all living things eat ???  NO
So, where does there energy come from?  They make their own food
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So, organisms can be grouped into 2 types, depending on how they get energy:
o Heterotrophs – get energy from the foods they consume, not from the sun. They
DO NOT make their own energy
o Autotrophs – make their own food, primarily by using light energy and converting
it to usable energy
Fig. 1
3. Why do we need energy?  It allows work to be done
 energy is stored and energy is released
 Remember from physical science that energy is neither created nor destroyed, only
transferred or changes forms
 Storage – the molecule ADP (adenosine triphosphate) is a compound that has 2
phosphate groups. It can store energy by adding a third phosphate group. Then it
becomes ATP (adenosine TRIphosphate).
o ATP is like a fully charged battery
Fig. 2
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Releasing – how is the energy released?
o by breaking the bond between the 2nd and 3rd phosphate groups
o cells can subtract the third the 3rd phosphate group, so can release the energy as
needed
o ATP has enough energy to power many cellular activities such as muscle
contraction and ACTIVE TRANSPORT (which we just talked about in the last
chapter)
Fig. 3
Fig. 4
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Since ATP can store so much energy, you would expect an organism to have tons of
ATP. However, organisms usually only have a few ATP on hand at a time.
Even though ATP is a great molecule for transferring energy, it is not good for storing
large amounts of energy over the long term
1 molecule of glucose stores 90 times more chemical energy than ATP
Cells can make ATP from ADP as needed by using the energy in foods like glucose
PHOTOSYNTHESIS
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when plants (autotrophs) use sunlight, carbon dioxide, and water to make sugar
(glucose) and oxygen
reactants
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products
Photosynthesis takes place inside the CHOLOROPLAST in a plant cell, specifically
on the thylakoid membrane, where chlorophyll is found
Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems
Chloroplast – organelle where photosynthesis takes place
Fig. 5
o Stroma – fluid that fills chloroplast
o grana – stack of thylakaloids
o thylakaloids – contains chlorophyll pigment & site of light dependent
reaction of photosynthesis
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The key to photosynthesis is the excitement of chlorophyll; this kicks off the process
***DID YOU KNOW??? the highest rate of photosynthesis on Earth occurs in the ocean
Plants Need (reactants)
Plants Produce (products)
sunlight
glucose sugar
water
oxygen
carbon dioxide
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glucose is stored energy
ATP is usable energy
**Due to factories, overpopulation, deforestation, SUV’s, etc., there is a huge imbalance of carbon and
oxygen. “Green” solutions are being tried to try to restore the balance (alternative energy sources that
don’t give off carbon, less transport, recycling)
Global Warming: when greenhouse gases, like CO2 trap heat from sun in the atmosphere instead of reflecting it
back into space
Info about pigments, color, and chlorophyll
a. a pigment is a light absorbing molecule that gather the energy from the sun, chlorophyll is a
plants main pigment
b. colors are based on wavelengths: On the visible spectrum of light, we have sunlight, which
is white b/c it has all wavelengths of colors; we have infrared, which has the largest wavelength
and lowest energy & frequency, green is in the middle w/shorter wavelength and higher
energy/frequency, and UV has very short wavelength and highest energy/frequency
c. the color that a pigment appears is actually the color light it is reflecting. All other colors are
absorbed. Chlorophyll appears green, so it is reflecting green light and absorbing the other
colors of other wavelengths.
d. red color wavelength and blue-violet and UV wavelengths are ideal for photosynthesis, so
rate of photosynthesis is highest under these colored lights
e. plants principal pigment is chlorophyll; there are 2 types: chlorophyll a and b
f. when chlorophyll absorbs light, a lot of the energy is transferred directly to electrons in the
chlorophyll molecule, raising the energy level of the electron (also called exciting the
electrons/chlorophyll)
g. the high energy electrons are what makes photosynthesis work
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carbon & oxygen in sugar comes from the air and hydrogen in sugar comes from
water in the soil
energy to build sugar comes from the sun
Thus, organisms that do photosynthesis (autotrophs) are called PRIMARY
PRODUCERS
Primary Producers: the only living organisms that can convert sunlight into food
Ex: algae, kelp (in oceans), flowers, trees (on land), photosynthetic bacteria
(cyanobacteria)
The Process of Photosynthesis
There are two parts to photosynthesis:
1. The light reaction happens in the thylakoid membrane and converts light energy to
chemical energy.
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This chemical reaction must, therefore, take place in the light.
Chlorophyll is organized in clusters in the thylakoid membrane and is involved in the
light reaction.
The energy harvested via the light reaction is stored by forming ATP
Remember that this chemical is made of adenosine bonded to a ribose sugar, and
that is bonded to three phosphate groups. This molecule is very similar to the
building blocks for our DNA.
2. The dark reaction takes place in the stroma within the chloroplast, and converts CO2 to
sugar.
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This reaction doesn't directly need light in order to occur, but it does need the products
of the light reaction (ATP and another chemical called NADPH).
The dark reaction involves a cycle called the Calvin cycle in which CO2 and energy
from ATP are used to form sugar.