PHOTOSYNTHESIS

The development of ideas Hales 1727 Plants took their nourishment in part from the atmosphere Light energy participated in this process. Preistly 1771 Green plants “renewed” air was made “bad” by breathing animals or burning candles “Renewed” air = Oxygen “Bad” air = Carbon Dioxide © 2010 Paul Billiet ODWS

The composition of the atmosphere O2 Scheele 1773 and Preistly 1774 CO2 Black 1777 N2 Rutherford 1772 The composition of air Lavoisier 1774 © 2010 Paul Billiet ODWS

The difference was attributed to water Ingenhousz 1779 Light is necessary for the production of O2 by plants Senebier 1782 Plants breathe like animals in the dark De Saussure 1804 Quantitative measurements of photosynthesis. Mass gain by plants through growth > Mass of CO2 absorbed – Mass of O2 released The difference was attributed to water © 2010 Paul Billiet ODWS

Observed the growth of starch grains in illuminated chloroplasts Sachs 1864 Observed the growth of starch grains in illuminated chloroplasts Classic experiment: Leaf exposed to light with certain parts covered In the exposed parts starch is produced In the covered parts starch is absent © 2010 Paul Billiet ODWS

By the end of C19th Sunlight CO2 + H2O Carbohydrate (CH2O) + O2  Photosynthesis involves the conversion of light energy into chemical energy. 3.8.1: State that photosynthesis involves the conversion of light energy into chemical energy. © 2010 Paul Billiet ODWS

Think! Why is the carbohydrate molecule considered “chemical energy”? How does the plant receive the building blocks for the “chemical energy”?

The Nature of Light White light from the sun is composed of a range of wavelengths (colors). 3.8.2: State that light from the sun is composed of a range of wavelengths (colours).

The Nature of Light Different colors are actually different wavelengths; violet is the shortest wavelength (and most energy) and red is the longest (and least energy)

Think!! What is colour?

Chlorophyll and Light Chlorophyll is the main photosynthetic pigment. Plants are green because of the presence of this pigment; the pigment REFLECTS green light and absorbs all others. There are several kinds of chlorophyll with slightly different spectrums 3.8.3: State that chlorophyll is the main photosynthetic pigment.

Light, Chlorophyll and Photosynthesis Engelmann 1894 Experiment 1 Using Cladophora, a filamentous alga, and motile oxygen sensitive bacteria Image Credit: Cladophora © 2010 Paul Billiet ODWS

Chloroplasts which practically fill each cell Visible spectrum 3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll. Red Orange Yellow Green Blue Indigo Violet Cladophora cells Chloroplasts which practically fill each cell Visible spectrum Motile bacteria © 2010 Paul Billiet ODWS

This is the action spectrum of photosynthesis 3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll. Observation Motile bacteria sensitive to oxygen accumulate in the areas illuminated by red and blue light Conclusion Photosynthesis, which produces oxygen, takes place in the parts illuminated by red and blue light This is the action spectrum of photosynthesis © 2010 Paul Billiet ODWS

3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll. Experiment 2 Using Spirogyra, a filamentous alga + motile oxygen sensitive bacteria © 2010 Paul Billiet ODWS

WHITE LIGHT Oxygen sensitive bacteria Chloroplast 3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll. © 2010 Paul Billiet ODWS

The bacteria accumulate in the regions nearest the chloroplasts 3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll. Observation The bacteria accumulate in the regions nearest the chloroplasts Conclusion O2 is produced by the chloroplast This is the site of photosynthesis © 2010 Paul Billiet ODWS

Think!!! There are some photosynthetic plants and bacteria that are colours other than green. Would you expect them to utilize the same spectrum of light for photosynthesis? Can you give an example?

Light Reactions Light strikes chlorophyll and excites an electron to a higher energy state That energy is converted into ATP and NADPH (energy carrier molecules) through an electron transport process Water is split (photolysis) in the reaction releasing O2 as a by-product ATP and NADPH are used to make covalent C-C bonds in the dark reactions 3.8.5: State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

Light Independent Reactions H+ and ATP drive the formation of glucose from CO2. These are known as carbon-fixing reactions and occur in the stroma of the chloroplast 6 CO2 molecules enter the Calvin Cycle to produce one glucose 3.8.6: State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.

Think! Create a flow map outlining the general process of photosynthesis.

Rate of Photosynthesis Photosynthesis requires chlorophyll, light, carbon dioxide and water in order to proceed. Factors such as temperature, light intensity and concentration of CO2 affect the rate of photosynthesis A factor that can affect the rate is called a limiting factor – greenhouses maximize by adding heat, water, light and sometimes CO2.

How can we measure the rate of photosynthesis? 3.8.7: State that the rate of photosynthesis can be measured directly by the production of ____________, or the uptake of __________, or indirectly by an increase in ___________.

Rate of Photosynthesis Predict how temperature, light intensity, and CO2 concentration effect the rate of photosynthesis. 3.8.8: Outline the effects of temperature, light intensity, and carbon dioxide concentration on the rate of photosynthesis.

GIZMO!!!! Complete the gizmo on photosynthesis