Photosynthesis & Cellular Respiration

Photosynthesis & Cellular RespirationChapters 8 and 9

Remember...

Autotrophs:can generate their own foodare the base of many food chainsinclude plants, bacteria, etc.8-1 Energy and Life Autotrophs are any organism that can make their own energy. Photoautotrophs undergo photosynthesis which changes light energy to chemical energy. Ex. Plants and cyanobacteria Chemoautotrophs undergo chemosynthesis which changes inorganic chemicals such as hydrogen sulfate into chemical energy. Ex. NitrobacteriaChemical EnergyWe use Adenosine Triphosphate (ATP)Contains adenine, ribose, and 3 phosphate groups.

When ATP loses a phosphate, it becomes ADP (only has 2 phosphates) and energy is released

What does ATP do?Movement in the cell (organelles)Moves ions across membranes (sodium and potassium for many reactions)

EnergyMost cells only contain small amounts of ATP, they cant store large amounts

Get new ATP from carbohydrates

Where do the carbohydratesget the stored energy?Properties of Light

White light from the sun is composed of a range of wavelengths.Only 1-3% of light energy is harvested by plants = not very efficientJames Clerk Maxwell- 1st person to recognize electromagnetic spectrum

Photosynthesis & Plant partsChloroplast: 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.

Light CollectionUse antenna complexes found in the thylakoid membranesChlorophyll is the main pigment that absorbs sunlight. Chlorophyll absorbs blue light and red light. It doesnt absorb green light hence its intense green color.Accessory Pigments (mop up)Ex: carotenoids (red, blue, black)xanthrophyll (yellow, red)beta carotene (reddish-yellow)*animals dont make, but can absorbex: flamingos from shrimp

Photosynthesis Occurs in two stages. The light-dependent reactions require light to work = Light Reaction The light-independent reactions do not require light = Dark Reaction

Two Main Parts of the Light Dependent Reactions:

Cyclic Photophosphorylation: Excited electrons are cycled through a series of electron acceptors to make ATP.Noncyclic Photophosphorylation:Light energizes chlorophyll, which splits H2O (photolysis). The O2 is released to air.More light energizes another chlorophyll which releases energy to make 2 ATP.A different wavelength of light energizes another chlorophyll, which then releases energy to make 2 NADPH.Light Dependent ReactionsThylakoid membranePlant pigments are organized as photosystems (Pigments surrounding a central chlorophyll a molecule....the reaction center).Each pigment absorbs a different wavelength of light & transfers its energy to the reaction center which in turn energizes an electron.The energized electron is then used elsewhere to make ATP or NADPH.E- that are moving must be replaced by splitting H2O moleculesElectron Transport Chain

Light Independent ReactionsStroma of Chloroplast

Also known as the Calvin Cycle

They occur whether or not light is present.

The purpose of the reactions is to take the energy from ATP and energized ions from NADPH and add them to carbon dioxide to make glucose or sugar.

uses 6 carbon dioxide molecules to make a single 6-carbon sugar

Photosynthesis

PhotorespirationDark Reaction cant tell difference between oxygen and carbon dioxide. If it uses Oxygen = wasteIt is only 30% efficientFactors that Affect Rates- light

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.

Factors that Affect Rates- carbon dioxide

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.

Factors that Affect Rates- temperature

As temperature increases above freezing, the rate of photosynthesis increases. This occurs 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, slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not occur at all.

Cellular Respiration and Glycolysis

Energy arrives from the sun and is captured by green photosynthetic plants, and stored in the chemical bonds of glucose.Nonphotosynthetic organisms must obtain their energy by the breakdown of these energy rich storage molecules in order to release the energy for their use.Photosynthesis stores this energy in glucose; glycolysis and cellular respiration release it.These are the processes by which cells can "burn" or breakdown glucose into CO2 and H2O and transfer most of the energy to the phosphate bonds of ATP.Cellular RespirationGlucose > ATPAnaerobic- w/o O2Aerobic- w O2

C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP

Cellular RespirationStepWhere?summationATPGlycolysisAnaerobiccytoplasmUses glucose to make 2 3C pyruvic acidsUses 2ATPMakes 4ATPNet = +2ATPKrebs CycleAerobicMitochondriaMakes 3 NADH & 1FADH2 (electron carriers that temporarily store energy) for each pyruvateMakes 2 ATPElectron Transport ChainAerobicMitochondria membranesElectrons from NADH & FADH2 pass through membranes of mitochondriaChange ADP >ATPMake 34 ATPNet = 38 ATPFermentation- anaerobic1. Lactic Acid- muscles dont have enough O2Turns pyruvate into lactic acid2. alcoholic Fermentation- pyruvate into ethanol & CO2