1) Photosynthesis: process that provides energy for almost all life
a) Photosynthetic organisms (algae, plants, and cyanobacteria) transform solar energy into carbohydrates.
i) Photosynthetic organisms (plants, algae, cyanobacteria) are called autotrophs because they produce their own food.
ii) Organisms that must take in preformed organic molecules are called heterotrophs.
iii) Both autotrophs and heterotrophs use organic molecules produced by photosynthesis as chemical building blocks and as a source of energy.
2) Stages of Photosynthesis
a) 3 Stages
i) Stage 1: E is captured from sunlight
ii) Stage 2: Light E is coverted to chemical E. This E is temporarily stored in the form of ATP and NADPH.
iii) Stage 3: Chemical E of ATP and NADPH powers the formation of organic compounds using Carbon Dioxide.
b) Occurs in chloroplasts of plants and algae and in the cell membranes of certain bacteria
3) Stage One
a) Light is absorbed via pigments
i) Chlorophyll is the primary pigment involved in photosynthesis.
(1) Absorbs mostly blue and red light and reflects yellow and green
ii) Carotenoids absorb wavelengths of light different from chlorophyll which enables a greater spectrum of light to be absorbed for photosynthesis.
iii) Pigments located in chloroplasts.
b) Chloroplast and pigment
i) Thylakoids: disk-shaped structures in chloroplasts. Pigments are located in the membranes of these structures
(1) When light strikes a thylakoid, E is transferred to electrons in chlorophyll and other pigments
(a) This allows the electrons to jump to a higher energy level. They are now termed as “excited” electrons
(b) This is how plants first capture E from sunlight
4) Stage Two: Light Reactions
a) Excited electrons leave chlorophyll molecules and are used to produce ATP.
i) Excited electrons jump to a nearby molecule in the thylakoid membrane
ii) Electron Transport Chain: The electron is passed through a series of molecules in the thylakoid membrane like a ball passed down a line of people. This series of molecules is called the electron transport chain.
iii) This energy is captured and later used for ATP production. It also reduces NADP (an electron carrier) to NADPH.
5) Stage Three: Calvin Cycle Reactions
a) The first step in this portion of the process is carbon fixation. CO2 from atmosphere is added to RuBP (a 5 carbon molecule) mediated by the enzyme: RuBP carboxylase .
i) Result is a 6 carbon molecule that will split into 2- 3 carbon molecules.
b) Carbon dioxide is taken up and reduced to a carbohydrate (G3P)
i) The ATP and NADPH formed during the light reactions are used to reduce carbon dioxide b/c both energy and electrons are needed for this reduction.
c) The last step is the regeneration of RuBP
d) The Importance of the Calvin Cycle
i) G3P (glyceraldehydes-3-phosphate), the product of the Calvin Cycle can be converted into many other molecules.
(1) Glucose phosphate is one result of G3P metabolism; it is a common energy molecule.
(a) Glucose phosphate can bond with fructose to form sucrose.
(b) Glucose phosphate is the starting point for synthesis of starch and cellulose.
(2) The hydrocarbon skeleton of G3P is used to form fatty acids and glycerol; the addition of nitrogen forms various amino acids.
6) Factors that affect Photosynthesis
a) Light
b) Temperature
c) Carbon Dioxide Concentration
7) Other Types of Photosynthesis
a) There are other methods of photosynthesis that have been adapted by plants
b) Each method of photosynthesis has its advantages, depending on the environment.
1. C3 plants undergo what we have been describing as photosynthesis
i) C4 plants are adapted to areas of high light intensities, high temperatures, and limited rainfall. Ex. Sugarcane, Bermuda grass
2. C3 plants do better in cooler climates. Ex. Wheat, rice, and oats
3. CAM plants do well in an arid environment. Ex. Pineapple