What Photosynthesis Means to You:
Source of all our oxygen.
Absorbs toxic carbon dioxide released by animals, cars and industry.
(natural gas, oil, and coal)
Transfer of energy
Light Energy
(sunlight)
ä N lost as heat
Kinetic Energy
(excited electrons)
ä N lost as heat
Potential Energy
(glucose)
ä N lost as heat
Chemical Energy
(ATP)
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I). Autotrophs & Heterotrophs
A). Autotrophs make their own nutrients.
Sometime called producers.
(i.e. produce)
1). Phototrophs: make glucose from sunlight.
2). Chemotrophs: make nutrients without light in a complex chemical process. (some bacteria)
B). Heterotrophs cannot make their own nutrients.
They receive nutrients by eating other organisms.
Sometimes called consumers.
Either they eat autotrophs or
they eat the organism that ate the autotrophs.
This is the food pyramid (or food chain)
II). Summary of Photosynthesis
A). Photosynthesis is only carried out by autotrophs.
B). It involves:
sunlight + 6CO2 + 6H2O Þ C6H12O6 +6O2
carbon dioxide + water -> glucose (sugar) + oxygen
It involves the conversion of sunlight, carbon dioxide and water into glucose and oxygen.
C). Stages:
1). Light conversion
2). CO2 conversion
(dark cycle or light independent cycle
Oxygen is a waste product of photosynthesis and carbon dioxide is a waste product of cellular respiration.
Autotrophs do not give of oxygen for the sole use of animals. Autotrophs create glucose and oxygen for their own use: growth, reproduction etc. They create more than they use.
A build up of oxygen or carbon dioxide is toxic to a cell.
Carbon dioxide travels through the blood stream of many animals and is released through the respiratory system. Some animals release it through their skin.
Plants release built up oxygen through openings in their leaves called stomas.
Autotrophs and heterotrophs can take in needed gases that way too.
III). Materials needed
A). Adenosine Triphosphate (ATP)
1). Adenosine with 3 high energy phosphate bonds
(ADP: adenosine diphosphate)
(AMP: adenosine monophosphate)
2). A cell utilizes energy that is released when the phosphates are removed from ATP
Some of the energy is lost as heat.
3). It takes energy to put the phosphates back
This is called phosphorylation.
4). The adenosine phosphate molecule can be recycled.
B). Coenzymes Involved in Photosynthesis & Respiration
coenzyme: enzyme + vitamin
1). NADP+ :
(nicotinamide adenine dinucleotide phosphate)
An electron acceptor and hydrogen carrier in photosynthesis.
It picks up and carries hydrogen and becomes NADPH. It takes the hydrogen to CO2 to form glucose and returns to NADP+
2). NAD+ :
(nicotinamide adenine dinucleotide)
An electron acceptor and hydrogen carrier used in respiration.
It will become NADH and transfer the hydrogen to the electron transfer chain.
3). FAD:
(flavin adenine dinucleotide)
A hydrogen carrier used in respiration. It will become FADH2
C). Properties of light
Light travels as waves of energy.
Each wavelength has a different color and amount of energy.
Some (wavelength) colors are absorbed by objects and other (wavelengths) colors are reflected back. We see the colors that are reflected back.
The colors that provide the energy for photosynthesis are correlated with different kinds of energy absorbing pigment.
D). Plastids
1). Plants contain a variety of plastids that absorb various wavelengths of light.
chlorophyll a: absorbs red & blue & reflects green
chlorophyll b: absorbs red & blue & reflects green
carotenoids: absorb blue green &
reflect yellow and orange
2). Chloroplasts
Chloroplasts are double membrane organelle that contains its own DNA and ribosomes.
A). Inside of the chloroplasts there are discs that are called thylakoids.
Contain the pigments chlorophyll a & b
B). Each stack of 10 discs is called grana
C). The regions outside the discs are called stroma.
Photosynthesis is carried out in the grana & stoma
IV). Structure of chloroplasts
A). Chloroplasts are double membrane organelle that contains its own DNA and ribosomes.
B). Inside of the chloroplasts there are discs that are called thylakoids.
C). Each stack of 10 discs is called a stroma.
D). The green color comes from the pigment
chlorophyll a & b.
There are other pigments called carotenes and xanthophylls. (Chlorophyll a hides the presence of the carotenes and xanthophylls until fall when the chlorophyll a breakdown)
Chlorophyll
The most common pigments are called chlorophyll.
Chlorophyll a absorbs red light
Chlorophyll b absorbs blue-green light.
sunlight + H2O + NADP+ + chlorophyll Þ
(water) (hydrogen carrier)
White light or visible light is composed of many different wavelengths of light that can be seen as different colors.
(Rainbows occur because light is bent and refracted so that the wavelength separate and can be seen individually.)
Black is the absence of all colors or wavelength of light.
When light hits an object some of the wavelengths are absorbed the rest bounce back and are reflected.
What we perceive as color is made up of the light waves that bounce back.
Chloroplasts absorb all of the wavelengths except green, which is reflected back.
When the day shortens in the fall the trees change colors.
The chlorophyll a & b are the first plastids to be destroyed.
That is when we see the colors reflected from the other plastids (red, yellow, orange).
Those plastids and colors were there all of the time.
The green "overpowered" the other plastids.
V). Photosynthesis
A). Light-energy conservation stage
Light energy +H2O +NADP+ ADP + P + chlorophyll–
sunlight + water + coenzyme+ ADP + Phosphate + chlorophyll electrons
ATP + NADPH + O2
ATP + coenzyme with hydrogen + oxygen
*NADPH will return to NADP in the next stage
In the grana (stacked thylakoids)
1). Sunlight is absorbed by the electrons of the pigments. Converting it to kinetic energy
Pigments other than chlorophyll a will absorb other parts of the spectrum and pass their charged electrons to chlorophyll a
2). The charged electrons attach to NADP+.
NADP+ holds 2 electrons becoming NADP-
3). NADP- attracts the Hydrogen from water becoming NADPH.
4). Water splits losing its Hydrogen to NADP- releasing the Oxygen as O2.
5). The charged electron than converts ADP to ATP by attaching a phosphorous.
B). Carbon Dioxide Conversion Stage
It does not require light so sometimes it is called the Dark Cycle or Light Independent Cycle (or Calvin Cycle)
*Occurs in the stroma
*It is cyclic which means at the end it produces a product that can be used as an original reactant.
a 5 carbon sugarRuBP: ribulose biphosphate
PGA: phosphoglyceric acid 3 carbon compound
PGAL: phospoglyceradlehyde 3 carbon
12 NADPH convert back to 12 NADP
18 ATP become 18 ADP and 18 Phosphorous
Pathway
Step 1: Carbon dioxide reacts with
ribulose biphosphate producing phosphoglyceric acid
6CO2 + 6RuBP à 12PGA
follow the carbons: (6 C) (6 x 5 = 30 C) (12 x 3 = 36C)
Step 2: PGA becomes
PGAL (phosphoglyceraldehyde)
Hydrogen comes form NADPH
Energy comes from 12 ATP becoming
12ADP + 12 P.
12 PGA+ 12 NADPH + 12 ATP–
(36 C) (12 H)
3 –carbon sugar coenzyme high energy source
– 12PGAL + 12 NADP + 12 ADP + 12 P
(36C) coenzyme low energy
3-carbon sugar
Step 3: Split the 12 PGAL (phosphoglyceraldehyde)
into groups of 2PGAL & 10PGAL
12 PGAL Ì 2 PGAL
Ê 10 PGAL
follow the carbons: ( 36 C) Ì (6C)
Ê (30C)
Step 4: 2 PGAL convert into 1 glucose.
2 PGAL – C6H12O6
(6C) (6C)
3 –carbon sugar glucose
Step 5: 10 PGAL become 6RuBP (5 carbon sugars)
Energy comes from 6 ATP becoming 6 ADP + 6 P.
10 PGAL + 6 ATP – 6 RuBP + 6 ADP + 6 P
(30 C) (30 C)
3 –carbon sugar energy source 5–carbon sugar
Step 6: RuBP can combine with CO2 and start the cycle again.
* C6H12O6 is only one possible final product.
The actual product is 2-PGAL
(3-carbon phosphoglyceraldehyde)
It can be converted to
Summary of Carbon Dioxide Conversion Cycle
6CO2 + 6RuBP
Ü
12PGA
12 NADPH 12 ATP
O Ü N
12 NADP+ 12 ADP + 12 P12PGAL
ß à
2PGAL 10PGAL
6 ATP
Ü Ü N
6 ADP + 6 P
1 Glucose 6 RuBP
Ü
Ü + 6 CO2
ß
12PGA