Download Photosynthesis Notes Gresham

Photosynthesis Notes Gresham
Photosynthesis
The Equation for Photosynthesis: 6 molecules of carbon dioxide and 6 water molecules are converted by plants in
the prescence of light to 1 molecule of glucose (sugar) and 6 molecules of oxygen.
Reactants: CO2 + H2O
Products: Sugar + oxygen
ATP (Adenosine Triphosphate)
ATP: Adenosine TriPhosphate - Energy carrying molecule. Carries measured doses of energy. Used to facillitate many
cell reactions.
Oxidation/ Reduction Reactions
Oxidation: Loses e- & energy. (Gains Oxygen.)
Reduction: Gains e- & energy. (Loses Oxygen.)
Comparing Oxidation & Reduction Reactions
Oxidation Reactions
Adding oxygen atoms to a substance.
Reduction Reactions
Removing oxygen atoms from a substance.
Loss of electrons from a substance.
Adding electrons to a substance.
Loss of hydrogen atoms from a substance.
Addition of hydrogen atoms to a substance.
The substance loses energy when it loses electrons & hydrogen
atoms.
The substance gaining electrons or hydrogen atoms gains
energy.
As a result of oxidation reactions in living cells, hydrogen atoms tend to carry electrons and energy to the substance to be reduced.
Example #1:
Reduction: Carbon dioxide gains electrons and hydrogen to become glucose. It is reduced.
Oxidation: Water loses electrons and loses hydrogens to become oxygen. It is oxidized.
Measuring Rates of Photosynthesis
The rate of photosynthesis may be measured by the quantity of carbon dioxide consumed per unit time, or by measuring the quantity
of oxygen produced per unit time. In addition, the increase in biomass of a pre-determined area of plants may be measured per unit
time. Biomass is the total dry mass of organic matter in organisms or ecosystems.
1. Measure uptake of carbon dioxide
2. Measure production of oxygen
3. Measure increase of plant biomass (Biomass is the total dry mass of organic matter in organisms or
ecosystems.)
Factors Affecting Photosynthetic Rate
The rate of photosynthesis may be measured by the quantity of carbon dioxide consumed per unit time, or by measuring the quantity
of oxygen consumed per unit time. Since photosynthesis is a very complex process, the rate at which photosynthesis occurs is
determined by the step that is occuring the most slowly. This step is then known as the rate-limiting step. Factors which affect the
rate of photosynthesis include, light intensity, temperature and carbon dioxide concentration. Each factor affects a different ratelimiting step.
Light Intensity
How Light Intensity Affects Photosynthetic Rate
As light intensity increases, the photosynthetic rate increases until a point is reached where the rate begins to level off. At low light
intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions.
As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate. At high light intensity,
photosynthetic rate levels out, not due to light intensity but due to other limiting factors, including competition between oxygen and
carbon dioxide for the active site on RUBP carboxylase.
How Carbon Dioxide Concentration Affects Photosynthetic Rate
As carbon dioxide concentration increases, the rate of photosynthesis increases. At high concentrations, the rate of photosynthesis
begins to level out due to factors not related to carbon dioxide concentration. One reason might be that some of the enzymes of
photosynthesis are working at their maximum rate.
In general, carbon dioxide is found in low concentration in the atmosphere, and so atmospheric carbon dioxide levels may be a major
limiting factor on photosynthesis when at low levels.
How Temperature Affects Photosynthetic Rate
As temperature increases above freezing, the rate of photosynthesis increases. This ocurs because molecules are moving more quickly
and there is a greater chance of a collision resulting in a chemical reaction. At some point, a temperature is reached that is an optimum
temperature. The photosynthetic reaction rate is at its quickest rate at this point. Above that temperature, the enzymes begin to
denature (as in RUBP carboxylase), slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not
occur at all.
The Chloroplast
Chloroplast: Site of photosynthesis in eukaryotic cells.
Thylakoids: Disk shaped membranes containing photosynthetic pigments. Site of light dependent reactions.
Grana: Stacks of thylakoids.
Stroma: Fluid filled space surrounding grana. Site of light independent reactions.
Properties of Light
Sunlight is a form of electromagnetic radiation, transmitted as waves or photons.
Sunlight is a mixture of all colors of light. Each color of light has a different wavelength, and thus a different
amount of energy.
Plants only use visible wavelengths of light.
Blue light has more energy than red light (its faster for a small wave to move than a long wave----think of
jumping rope!)
When an object reflects a color, that is the color it appears.
Blue book reflects blue. All other colors are absorbed.
Green leaf reflects ____?____. All other colors absorbed.
Photosynthetic Pigments
Natural sunlight is a mixture of all the colors of light.
Photosynthetic plant pigments have the capability to absorb certain wavelengths (colors) of light & change the
light energy to chemical energy.
The plant pigments are found in chloroplasts on the thylakoids.
4 Plant Pigments
1. Chlorophyll a: Light to medium green. Main photosynthetic pigment.
2. Chlorophyll b: Blue-green. Accessory Pigment.
3. Carotene: Orange. Accessory Pigment.
4. Xanthophyll: Yellow. Accessory Pigment.
Accessory pigments absorb other colors of light (green) that chlorophyll a can't absorb. They help boost energy
absorption.
Think of plant pigments as being like TV antennas. Each type of pigment absorbs and uses a different
wavelength of light (just as antennas pick up different stations). All the pigments are linked together, to give the
energy they pick up to then energize electrons.
Photosystems: Groups of accessory pigments surrounding a central chlorophyll a. They collect light energy, and send
energized electrons to the central chlorophyll a to be used in the light dependent reactions.
Chromatography Lab
The Light Dependent Reactions of Photosynthesis
All the reactions of photosynthesis that are directly dependent upon light are known as the light dependent reactions. The light
dependent reactions occur in the part of the cell known as the thylakoids (Stacks of thylakoids are known as grana.). Many
chlorophyll molecules are found embedded into the membranes of the thylakoids.
The purpose of the light reactions is to convert light energy into chemical energy in the form of ATP & NADPH.
ATP & NADPH are energy carriers. They carry energy to the 2nd part of photosynthesis, known as the dark reactions.
The light dependent reactions can be split into the following specific steps:
1. Light absorption & splitting of water.
2. Production of ATP.
3. Movement of electrons through electron acceptors to power a hydrogen pump.
4. Re-energizing electrons so they can produce NADPH.
The Light Independent Reactions of Photosynthesis
Also known as the Calvin Cycle or Dark Reactions
All reactions of photosynthesis not directly dependent upon light are known as the light independent reactions.
They occur whether there is light present or not. They only depend on the presence of the energy carriers ATP
and NADPH made during the light dependent reactions.
The light independent reactions occur in the part of the chloroplast known as the stroma.
The purpose of the light independent reactions is to take the energy from ATP and energized electrons and
hydrogen ions from NADPH and add them to CO2 to make glucose or sugar.
The LIR reduce CO2 by adding energized electrons & protons (H+) to it and removing one oxygen atom. This
effectively converts the CO2 to CH2O.
Light Independent Reactions (more advanced version!)
Carbon Dioxide Concentration
Temperature
ATP, and Oxidation/Reduction Reactions
Measuring Rates of Photosynthesis
Factors Which Affect the Rate of Photosynthesis
Structure of Chloroplasts
Properties of Light
Photosynthetic Pigments
Chromatography Lab
Photosystems & Photoactivation
Light Dependent Reactions of Photosynthesis
Light Dependent Reactions of Photosynthesis (More Advanced)
Cyclic Photophosphorylation
Noncyclic Photophosphorylation
Light Independent Reactions of Photosynthesis: Calvin Cycle