Download Photosynthesis - Crestwood Local Schools

Energy in living systems
C-9-1
Photosynthesis is how plants obtain energy!
~ done by autotrophs
They take CO2 and H2O and convert it to glucose
and O2.
The heterotrophs then take those products
(glucose and O2) and use them for energy in
cellular respiration
Ex:
There are several energy transferring reaction
within photosynthesis:
1.) Using or making ATP – when ATP is split, it
releases energy
2.) ATP synthetase – enzyme that makes ATP
3.) H+ pumps – actively pump in H+ ions to build up
a concentration gradient
~ those will slip back through the synthetase
and make ATP!
Photosynthesis
C-9-2
Factors that can affect photosynthesis are :
Amount of CO2, temperature, and light
intensity
3 steps:
1.) Plants harvest energy from the sun
~ thylakoids – contain chlorophyll - within the
chloroplast
Ex:
Chlorophyll is a pigment that absorbs red and blue
but reflects green and yellow
~2 types: chlorophyll a and chlorophyll b
Also have carotenoids – absorb green and blue
reflect red, orange and yellow
~ where we get the fall leaf colors!
2.) Light reactions produce energy
~ light comes in different wavelengths and
energies: the longer the wavelength, the less
energy it has
Energy from these photons zaps the e- and gives it
more energy
*this energy is used in 2 different processes
in the light reactions:
a.) Making ATP:
~ excited e- get replaced by splitting H2O
molecules - H donates its e- and is left
with H+
- O isn't used anymore so it leaves as O2 gas
~ excited e- then goes down the e- transport
chain to power a proton pump which
brings in H+
~ H+ creates a concentration gradient and it
wants to slip out again - does this through
the ATP synthetase!
~ATP is made from ADP
b.) Making NADPH:
~ less excited e- continues down the etransport chain to the next chlorophyll
molecule
~ gets zapped again - excited e- go down the
second e- transp. chain to an e- acceptor
call NADP+
~ combines with H+ to make NADPH
3.) Dark reaction produces sugars
Called the Calvin Cycle…
a.) 6 CO2 are added to 6 5C molecules – yields
12 3C mol
b.) use ATP and NADPH to power conversion to
split the 12 3C into 2 3C mol. to go to sugar
c.) other 10 3C use ATP to rearrange and
regenerate the 6 5C at the start
Like this:
Cellular Respiration
C-9-3
Energy that was made in photosynthesis can be used in cellular
respiration by stripping the e- from the molecules built in
photosynthesis. The e- have extra energy from the photon that
hit it.
Has 2 stages:
1. Glucose converted to pyruvate - produces small amount of ATP
*occurs in the cytosol
2. O2 present = pyruvate and NADH used to produce lots of ATP :
aerobic - needs O2
*occurs in mitochondria (eukaryotic cells); cell
membrane in cells w/o mitochondria
O2 not present = pyruvate converted to lactic acid or ethyl
alcohol : anaerobic - w/o O2
Here's the flow chart:
And the chemical reaction:
C6H12O6
+
O2
----------
CO2
+
H2O
+ 36ATP
Glycolysis:
*Sequence of enzyme-catalyzed rxns that converts a 6C
glucose molecule into 2, 3C molecules of pyruvate.
*This is an anaerobic reaction!!
Here's how the flow chart works:
*So at the end, we have 2- 3C pyruvates and 2ATP's
After glycolysis, the pyruvate molecules are converted into a 2C
fragment and a CO2 and H+ are also extracted. CO2 leaves the
cell; H+ goes to a NAD+ molecule to be used later.
The remaining 2C fragment (called an acetyl group) is attached to a
coenzyme (coenzyme A) and forms acetyl-CoA.
The acetyl-CoA gets either used in fat synthesis if there is enough
ATP or it goes to be used in the Krebs Cycle to make more ATP.
The Krebs Cycle:
This is a repeating series of rxns that produces ATP, e- carriers,
and CO2
Let's see how the cycle works!
The Krebs Cycle must turn 2x for every glucose that is converted
to pyruvate.
Electron transport chains:
*in the inner membrane of the mitochondria
*as e- pass through an e- transport chain, p+ are
pumped out of the inner chamber, the p+ build up outside
and then rush back in via ATP synthetase thus making ATP
**32 ATP's are made!!!
*at the end of each e- transport chain, H+ are added to
O forming H2O
Without O2, Fermentation occurs!
*instead of the e- getting carried away by NAD+, the
e- remain attached to NADH
*this takes up all available NAD+ and then glycolysis
can't continue
*SO the H+ must be attached to something else…
- in animals = H+ gets attached back to pyruvate to
form lactic acid
*this is what causes your muscles to hurt when
you work out!
- in plants = H+ gets attached to CO2 from
glycolysis to form ethyl alcohol
*this is what causes bread to rise (CO2) and beer
to become alcoholic (ethyl alcohol)
*Yeast is the microorganism that performs this task!