Two guard cells form the 'stomata' or 'stoma'. These cells allow for the transport of H2O, CO2 and O2 into the leaf – and through the cuticle. Note the 'green' cells. Anything that is green contains chlorophyll, which is located in the cell oranelles – chloroplasts.
Light is part of the electromagnetic spectrum. 'Wavelength' is the distance between the crests (or nadirs) of the wave. Light is made up of photons, which have properties of both waves AND particles!! (see Einstein... )
When molecules absorb photons of light, they absorb energy. Chlorophyll enters an excited, unstable state; to return to ground state, chlorophyll gives off heat and some photons (in the form of fluroescent light).
Photosystem I was so-named because it was discovered FIRST, not the order in which the systems operate, and were never renamed...
The enzymes in the Calvin cycle are functionally equivalent to many enzymes used in other metabolic pathways but are found in the chloroplast stroma instead of the cell cytoplasm, separating the reactions. They are activated in the light (which is why the name &quot;dark reaction&quot; is misleading), and also by products of the light-dependent reaction. It should be noted that hexose (six-carbon) sugars are not a product of the Calvin cycle. Although many texts list a product of photosynthesis as C 6 H 12 O 6 , this is mainly a convenience to counter the equation of respiration, where six-carbon sugars are oxidized in mitochondria. The carbohydrate products of the Calvin Cycle are three-carbon sugar phosphate molecules, or &quot;triose phosphates,&quot; to be specific, glyceraldehyde-3-phosphate Two G3P molecules (or one F6P molecule) that have exited the cycle are used to make larger carbohydrates. In simplified versions of the Calvin cycle, they may be converted to F6P or F5P after exit, but this conversion is also part of the cycle. Hexose isomerase converts about half of the F6P molecules in to glucose-6-phosphate. These are dephosphorylated and the glucose can be used to form starch, which is stored in, for example, potatoes, or cellulose used to build up cell walls. Glucose, with fructose, forms sucrose, a non-reducing sugar that, unlike glucose, is a stable storage sugar.
Biol161 08 Bw
Ocean County College BIOL 161 Lectures Photosynthesis ... Not like Chinese food, where you eat it and then you feel hungry an hour later. – Ray Liotta BIOL161_08 G. F. Barbato
Once upon a time … <ul><li>In 1649, A Belgian physician, Jan Baptista van Helmont, planted a willow sapling in a large bucket with a known amount of soil.
After 5 years, the tree had gained 74kg in weight but the soil had lost only 57g.
Van Helmont concluded that the tree had made 74kg of new growth from water alone. </li></ul>
… long, long ago ... <ul><li>In the late 1600's, John Woodward (at Cambridge University) designed an experiment to test Van Helmont's hypothesis that water was the source of the extra plant mass.
In a series of experiments Woodward measured the water consumed by plants. He observed that most of the water was “drawn off and conveyed through the pores of the leaves and exhaled into the atmosphere”.
The hypothesis that water is the nutrient used by plants was rejected. </li><ul><li>Woodward is considered to be the 'father' of contemporary experimental plant physiology! </li></ul></ul>
… in a land far, far away ... <ul><li>Joseph Preistly, the British man who is credited with the discovery of oxygen, put a sprig of mint into a transparent closed space with a candle that burned out after combusting all the air.
After 27 days, he relit the extinguished candle again and it burned perfectly well in the air that previously would not support it. </li><ul><li>Priestley relit the candle by focusing sun light with a mirror onto the candle wick </li></ul><li>So priestly proved that plants somehow change the composition of the air.
In 1772, Priestley kept a mouse in a jar of air until it collapsed. He found that a mouse kept with a plant would survive. </li><ul><li>However, I do not recommend repeating this experiment at home unless you have spare cat. </li></ul></ul>
… stuff happened. <ul><li>In 1779, a Dutch physician, Jan Ingenhousz, put a plant and a candle into a transparent closed space. </li><ul><li>He allowed the system to stand in sunlight for two or three days. This assured that the air inside was pure enough to support a candle flame.
Instead, he covered the closed space with a black cloth for several days.
When he tried to light the candle it would not light. </li></ul><li>Ingenhousz concluded that the plant must function like an animal while in the dark. Hypothesizing that the plant must have breathed, fouling the air. In order to purify the air plants need light.
In 1796, Ingenhousz suggested that this process of photosynthesis causes carbon dioxide to split into carbon and oxygen, and that the oxygen is released as a gas. </li></ul>‘ Starch picture’ of Dr Jan Ingen-Housz on a geranium leaf (prepared by William Ruf and Howard Gest). The image of Ingen-Housz consists of photosynthetically-produced starch granules, which were ‘developed’ by staining with I2-KI. An engraving of Ingen-Housz (in Reed 1949) was photographed, and the negative placed in a slide projector. Light passing through the negative was focused on a geranium leaf (depleted of starch by prior incubation in darkness) for about one hour. After extraction of pigments from the leaf with boiling 80% alcohol, the blanched leaf was flooded with I2-KI solution to stain the starch granules. Within minutes, the details of the engraving dramatically appeared on the leaf. The inscription at the bottom refers to Dr Ingen-Housz’s fame as a ‘smallpox inoculator’. The ‘starch picture’ procedure was invented by Hans Molisch in 1914. (fromGest, Photosynthesis Research 53: 65–72, 1997)
Chloroplasts make oxygen <ul><li>This is a photo representing Ingenhousz's original experiments that illustrated the production of oxygen by water plants! </li></ul>
Photosynthesis <ul><li>Method of converting sun energy into chemical energy usable by cells
Autotrophs : self feeders, organisms capable of making their own food </li><ul><li>Photoautotrophs : use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from light
Chemoautotrophs : use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane </li></ul></ul>
Chlorophylls a and b Chlorophyll b Chlorophyll a <ul><li>Chl a has a methyl group </li></ul><ul><li>Chl b has a carbonyl group </li></ul>-CHO CH 3 Porphyrin ring delocalized e - Phytol tail
<ul><li>Chloroplasts absorb light energy and convert it to chemical energy
Remember that the color we see is the light REFLECTED by the object – NOT the color absorbed!! </li></ul>Why are leaves green (again)? Light Reflected light Absorbed light Transmitted light Chloroplast
Photosynthesis: A two-stage process <ul><li>Light-dependent reactions (Photosystem I and II) </li><ul><li>Requires light energy and H 2 O
Occurs on the thylakoid membrane </li></ul><li>Calvin cycle </li><ul><li>(yes, another cycle … )
aka, Carbon fixation </li><ul><li>Light is not essential; but, products of the light reactions are required.
Carbon (from CO 2 ) is 'fixed', i.e., synthesized into glucose. </li></ul><li>Occurs in the stroma </li></ul></ul>
Overview of the chemistry 6 · CO 2 + 12 · H 2 O + <light energy> -> C 6 H 12 O 6 + 6 · O 2 + 6 · H 2 O <ul><li>The carbohydrate is in the form of glucose </li><ul><li>This overview is an oversimplification to make 'life' easy, more on this to follow! </li></ul><li>Water appears on both sides because 12 H 2 O molecules are required and 6 new H 2 O molecules are made
Water is 'split' as a source of electrons from hydrogen atoms releasing O 2 .
Electrons increase potential energy when moved from water to sugar; therefore energy is required </li></ul>
Photosynthesis road map Chloroplast Light Stack of thylakoids ADP + P NADP Stroma Light reactions Calvin cycle Sugar used for Cellular respiration Cellulose Starch Other organic compounds
Light-dependent reactions <ul><li>A photon of light strikes the chlorophyll in the Photosystem II on the thylakoid membrane exciting it (oxidation; thereby losing electrons).
These electrons flow down an energy gradient and are picked up by chlorophyll in photosystem I – a reduction reaction.
The electrons lost from photosystem II are replaced by the splitting of water, forming electrons, H ions and releasing O 2 .
The H ion concentration builds in the thylakoid space and are used for ATP synthesis. </li></ul>
Light dependent reactions (cont) <ul><li>reduced chlorophyll inphotosystem I is now ready to absorb a photon of light </li><ul><li>Gets excited and loses electrons (oxidized)
Electrons travel down and energy gradient along the thylakoid membrane again and reduce a molecule of NADP+ </li><ul><li>Forming the 'energy carrier' NADPH (how many ATP's?) </li></ul></ul><li>The ATP from photosystem II and the NADPH from photosystem I are used in the stroma of the chloroplast for the dark reactions, or the Calvin cycle </li></ul>
How the Light Reactions Generate ATP and NADPH 2 H + 1 / 2 Water-splitting photosystem Reaction- center chlorophyll Light Primary electron acceptor Energy to make Electron transport chain Primary electron acceptor Primary electron acceptor NADPH-producing photosystem Light NADP 1 2 3
Production of ATP Thylakoid compartment (high H + ) Thylakoid membrane Stroma (low H + ) Light Antenna molecules Light ELECTRON TRANSPORT CHAIN PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
Calvin cycle: Light independent (Dark reactions) <ul><li>ATP and NADPH generated in light reactions used to fuel the reactions which take CO 2 and break it apart, then reassemble the carbons into glucose.
Carbon fixation </li><ul><li>taking carbon from an inorganic molecule (atmospheric CO 2 ) and making an organic molecule (glucose) </li></ul></ul>