by mary reyes lauren dobry & haleigh rousseau basic information photosynthesis involves the...
TRANSCRIPT
By Mary ReyesLauren Dobry
& Haleigh Rousseau
Basic InformationPhotosynthesis involves the conversion of :
light energy chemical energy
Light from the sun is composed of a range of wavelengths (colors).
Chlorophyll is the main photosynthetic pigment.Light energy is used to produce ATP, and to split
water molecules (photolysis) to form oxygen and hydrogen.
ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.
Generally, cell respiration is a catabolic process whilst photosynthesis is an anabolic one
Absorption of RED, BLUE, and GREEN Light by Chlorophyll
When a plant leaf is hit by sunlight, the BLUE and RED wavelengths of light are absorbed by chlorophyll and used for photosynthesis. However, almost all the energy of the GREEN wavelengths is reflected and not absorbed. Therefore, photosynthesis cannot occur when the leaf is hit solely by a green wavelength.
A chart showing the Action and Absorption Spectrums. BLUE, VIOLET, and RED light are most effective during the process of photosynthesis, since chlorophyll is the predominant photosynthetic pigment. Notice the similarities between the Action and Absorption Spectrums. The most absorbed wavelengths are the most active during photosynthesis, while the most reflected wavelengths are the least active.
Effect of changing light intensityThere is a positive correlation between light
intensity and photosynthesis until the enzymes and other factors are already working at their maximum rate. When this occurs, the rate of photosynthesis plateaus.
Effect of changing temperatureAs the temperature increases, the rate of
photosynthesis and the incidence of molecular collisions also increases. However, at a certain temperature, the enzymes and other proteins become denatured and the rate of photosynthesis drops tremendously until it becomes non-existent.
Effect of changing CO² concentrationThere is a positive correlation between
carbon dioxide concentration and photosynthesis, but the rate of reaction reaches a plateau unless light or temperature is also increased. Aquatic plants can alter the pH of the water during photosynthesis, raising it, due to CO² absorption.
Structure of the ChloroplastUnlike respiration, where some of the steps occur outside of the mitochondrion, all of the photosynthetic process occurs within the chloroplast. The chloroplast contains a double membrane and is about the same size as a bacterial cell. Like the mitochondrion, it contains its own DNA and 70S ribosomes. The DNA of the chloroplast is in the form of a ring. Besides DNA and ribosomes, the interior of the chloroplasts includes the grana, thylakoids, and stroma.
A granum is made up of numerous thylakoids stacked like a pile of coins. The thylakoids are flattened membrane sacs with components necessary for the absorption of light, which is the first step in the process of photosynthesis. The fluid stroma is similar to the cytosol of the cell. It occurs outside the grana but within the double membrane. Stroma contains many enzymes and chemicals necessary to complete the process of photosynthesis. Like mitochondria, chloroplasts are capable of reproducing independently of the cell.
Chloroplast Structure
Function Allowed
Extensive membrane surface area of the
thylakoids
Allows greater absorption of light by
photosystems
Small space (lumen) within the thylakoids
Allows faster accumulation of protons to create a concentration
gradient
Stroma region similar to the cytosol of the cell
Allows an area for the enzymes necessary for
the Calvin cycle to work
Double membrane on the outside
Isolates the working parts and enzymes of the
chloroplast from the surrounding cytosol
The First Stage of PhotosynthesisThis stage is a set of reactions typically
referred to as the light-dependent reactions.
During this stage, chlorophyll (and other photosynthetic pigments) absorb light energy and convert it into a form of chemical energy, specifically ATP.
Light energy is also used to accomplish a reaction called photolysis, during which a water molecule is split into its component elements: hydrogen and oxygen.
The oxygen that is split away due to the photolysis of water is typically released from the plant as a waste product.
Here is an animation that explains the specifics of the light-dependent reactions: http://www.youtube.com/watch?v=eY1ReqiYwYs
Respiration Chemiosmosis
Photosynthesis Chemiosmosis
Electron Transport Chain in membranes of cristae
Electron Transport Chain in membranes of thylakoids
Energy released when electrons are exchanged from one carrier to another
Energy released when electrons are exchanged from one carrier to another
Released energy used to actively pump hydrogen ions to intermembrane space
Released energy used to actively pump hydrogen ions to thylakoid
space
Hydrogen ions come from matrix Hydrogen ions come from stroma
Hydrogen ions diffuse back into matrix through channels of ATP
synthase
Hydrogen ions diffuse back into stroma through channels of ATP
synthase
ATP synthase catalyses the oxidative phosphorylation of ADP to ATP
ATP synthase catalyses the phosphorylation of ADP to ATP
The Second Stage of Photosynthesis
The second stage is a series of reactions collectively known as the light-independent reactions or the Calvin Cycle.
ATP and hydrogen are used as forms of chemical energy to convert carbon dioxide and water into useful organic molecules for the plant.
Carbon dioxide is one of the few molecular forms of carbon that is considered to be inorganic.
Glucose, a typical product of photosynthesis, is an organic molecule. It requires six inorganic carbon dioxide molecules to form one glucose molecule.
This conversion of an inorganic form of an element to an organic form is known as fixation.
Therefore, photosynthesis can be described as a series of reactions in which carbon dioxide and water are fixed into glucose, and oxygen is produced as a by-product.
Fixation requires energy that comes directly from the ATP and hydrogen created in the first stage of photosynthesis.
Ultimately, the energy can be traced back to sunlight.
It is also important to note that glucose is only one of the many possible organic molecules that can form from photosynthesis.
Here is an animation that explains the specifics of the Calvin Cycle:
http://www.youtube.com/watch?v=mHU27qYJNU0&NR=1
Light-dependent Reaction
Light-independent
ReactionOccurs in the
thylakoidsOccurs in the stroma
Uses light energy to form ATP and
NADPH
Uses ATP and NADPH to form triose phosphate
Splits water in photolysis to provide
replacement electrons and H⁺,
and to release oxygen to the atmosphere
Returns ADP, inorganic phosphate
and NADP to the light-dependent
reaction
Includes two electron transport chains and photosystems I and II
Involves the Calvin cycle
• This is an alternate way creating ATP during the light-dependent reaction. It only occurs when light is not the limiting factor of photosynthesis, and when there are large amounts of NADPH in the chloroplasts.
• Light energized electrons from photosystemI go to the cytochrome complex and finish the last leg of the electron transport train.
• ATP is then created via chemiosmosis • NADPH is not created because the electrons
do not go through the second electron transport chain
Which two colors of light does chlorophyll absorb most?
The answer
was D
GOOD JOB
How is the proton gradient generated in chloroplasts during photosynthesis?
The answer
was A
GOOD JOB
Plants living in water can cause a pH change in the water when they carry out photosynthesis. What is the pH change and what causes it?
The answer
was B
GOOD JOB
Why is the action spectrum for photosynthesis similar to the absorption of photosynthetic pigments?
The answer
was C
GOOD JOB
What is the advantage of having a small volume inside the thylakoids of the chloroplast?
The answer
was A
GOOD JOB
Which diagram represents the process of cyclic photophosphorylation?
The answer
was B
GOOD JOB
Which graph shows the effect of increasing carbon dioxide concentration on the rate of photosynthesis?
The answer
was B
GOOD JOB
Which line shows an action spectrum of photosynthesis?
The answer
was A
GOOD JOB
What is occurring at X during the light-dependent reaction in photosynthesis?
The answer
was A
GOOD JOB