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PHOTOSYNTHESIS. The development of ideas. Hales 1727 Plants took their nourishment in part from the atmosphere Light energy participated in this process. Preistly 1771

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the development of ideas
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
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

slide4
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

slide5
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 producedIn the covered parts starch is absent

© 2010 Paul Billiet ODWS

by the end of c19 th
By the end of C19th

Sunlight

CO2 + H2O

(CH2O) + O2

Carbohydrate

© 2010 Paul Billiet ODWS

light chlorophyll and photosynthesis

Image Credit: Cladophora

Light, Chlorophyll and Photosynthesis

Engelmann 1894

Experiment 1 Using Cladophora, a filamentous alga, and motile oxygen sensitive bacteria

© 2010 Paul Billiet ODWS

slide8

Red

Orange

Yellow

Green

Blue

Indigo

Violet

Cladophora cells

Chloroplasts which practically fill each cell

Visible spectrum

Motile bacteria

© 2010 Paul Billiet ODWS

slide9
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

experiment 2 using spirogyra a filamentous alga motile oxygen sensitive bacteria
Experiment 2 Using Spirogyra, a filamentous alga + motile oxygen sensitive bacteria

© 2010 Paul Billiet ODWS

slide11

WHITE

  • LIGHT

Oxygen sensitive bacteria

Chloroplast

© 2010 Paul Billiet ODWS

slide12
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

light intensity v temperature

Rate of photosynthesis

T + 10°C

T°C

Light intensity

Light Intensity v Temperature

Blackman 1920sExperiment 1

© 2010 Paul Billiet ODWS

slide14
Observations

At low light intensities – when light is a limiting factor – temperature has no effect upon photosynthesis.

Therefore Q10 = 1

At high light intensities – when light is not limiting – temperature has an effect upon photosynthesis. The rate doubles for every 10°C rise in temperature

Therefore Q10 = 2

Rate of photosynthesis

T + 10°C

T°C

Light intensity

© 2010 Paul Billiet ODWS

conclusion
Conclusion

Photosynthesis consists of two reactions

I The Light Dependent Reaction

Photochemical and unaffected by the temperature (Q10 = 1)

II The Light Independent Reaction

Enzyme controlled as it has a Q10 2

© 2010 Paul Billiet ODWS

experiment 2 light intensity and co 2 concentration

Rate of photosynthesis

Light intensity

Experiment 2:Light Intensity and CO2 Concentration

0.13% CO2

0.03% CO2

© 2010 Paul Billiet ODWS

carbon fixation is light independent
Carbon fixation is light independent

Observation

CO2 limits the rate of photosynthesis at high light intensities i.e. when light is not a limiting factor

Conclusion

Carbon fixation takes place in the Light Independent Reaction

It is an enzyme controlled process

© 2010 Paul Billiet ODWS