PHOTOSYNTHESIS

The development of ideas

Hales 1727 Plants took their nourishment in part from the atmosphereLight 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

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Ingenhousz 1779

Light is necessary for the production of O2 by plantsSenebier 1782 Plants breathe like animals in the darkDe 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

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 (CH2O) + O2 Carbohydrate

© 2010 Paul Billiet ODWS

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.

Think!1. Why is the carbohydrate molecule considered “chemical

energy”?

2. 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

Visible spectrum

Cladophora cells

Motile bacteria

Chloroplasts which practically fill each cell

Red

Orange

Yellow

Green

Blue

Indigo

Violet© 2010 Paul Billiet ODWS

3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll.

ObservationMotile bacteria sensitive to oxygen accumulate in the areas illuminated by red and blue light

ConclusionPhotosynthesis, which produces oxygen, takes place in the parts illuminated by red and blue lightThis 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

3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll.

WHITE

LIGHT

Oxygen sensitive bacteria

Chloroplast

© 2010 Paul Billiet ODWS

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

3.8.4: Outline the differences in absorption of red, blue and green light by chlorophyll.

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 PhotosynthesisPredict 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