1. Photosynthesis: An Overview
Chapter 8 Section 2
Photosynthesis:
An Overview

2. Photosynthesis Plants use the energy of sunlight
to convert water and carbon dioxide
into oxygen and high-energy carbohydrates (sugars and starches)

3. Investigating photosynthesis
Voan Helmont’s experiments -

4. Investigating photosynthesis
Voan Helmont’s experiments –
In 1600’s, he devised a way to find out if plants grew by taking material out of the soil

5. Investigating photosynthesis
Voan Helmont’s experiments –
In 1600’s, he devised a way to find out if plants grew by taking material out of the soil
Determined the mass of a pot of dry soil and a small seedling
Planted the seedling in the pot of dry soil
Watered the plant regularly

6. Investigating photosynthesis
Voan Helmont’s experiments –
Results –

7. Investigating photosynthesis
Voan Helmont’s experiments –
Results –
At the end of 5 years
the seedling had gained about 75 kg.
the mass of the soil was almost unchanged

8. Investigating photosynthesis
Voan Helmont’s experiments –
Results –
At the end of 5 years
the seedling had gained about 75 kg.
the mass of the soil was almost unchanged
Conclusions –

9. Investigating photosynthesis
Voan Helmont’s experiments –
Results –
At the end of 5 years
the seedling had gained about 75 kg.
the mass of the soil was almost unchanged
Conclusions –
Most of the mass gained had come from water

10. Investigating photosynthesis
Voan Helmont’s experiments –
Conclusions told part of the story of the growth. What was missing?

11. Investigating photosynthesis
Voan Helmont’s experiments –
Conclusions told part of the story of the growth. What was missing?
Carbohydrate –
‘hydrate’ – water
‘carbo’ – from carbon dioxide

12. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up

13. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up
Placed a candle under a glass jar

14. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up
Placed a candle under a glass jar
Results

15. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up
Placed a candle under a glass jar
Results
Flame of candle eventually goes out

16. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up
Placed a candle under a glass jar
Results
Flame of candle eventually goes out
Conclusions

17. Investigating photosynthesis
Priestley’s experiments –
100 years after Helmont’s experiments
Experiment set-up
Placed a candle under a glass jar
Results
Flame of candle eventually goes out
Conclusions
Something in air was necessary to keep flame burning

18. Investigating photosynthesis
Priestley’s experiments –
Additional experiments

19. Investigating photosynthesis
Priestley’s experiments –
Additional experiments
If placed a live sprig of mint under the jar and allowed a few days to pass, the candle could be relighted and remain lighted for a while

20. Investigating photosynthesis
Priestley’s experiments –
Additional experiments
If placed a live sprig of mint under the jar and allowed a few days to pass, the candle could be relighted and remain lighted for a while
Conclusions

21. Investigating photosynthesis
Priestley’s experiments –
Additional experiments
If placed a live sprig of mint under the jar and allowed a few days to pass, the candle could be relighted and remain lighted for a while
Conclusions
The mint plant had produced the substance required for burning - oxygen

22. Investigating photosynthesis
Ingenhousz experiments –

23. Investigating photosynthesis
Ingenhousz experiments –
Dutch scientist who later showed that the effect observed by Priestley occurred only when the plant was exposed to light

24. Investigating photosynthesis
Ingenhousz experiments –
Dutch scientist who later showed that the effect observed by Priestley occurred only when the plant was exposed to light
Conclusion?

25. Investigating photosynthesis
Ingenhousz experiments –
Dutch scientist who later showed that the effect observed by Priestley occurred only when the plant was exposed to light
Conclusion –
Light is necessary for plants to produce oxygen

26. Investigating photosynthesis
The experiments performed by these and other scientists reveal that
In the presence of light

27. Light energy
chloroplast

28. Investigating photosynthesis
The experiments performed by these and other scientists reveal that
In the presence of light
Plants transform carbon dioxide and water

29. Light energy
chloroplast
Carbon dioxide + water

30. Investigating photosynthesis
The experiments performed by these and other scientists reveal that
In the presence of light
Plants transform carbon dioxide and water
Into carbohydrates and release oxygen

31. Light energy
chloroplast
Carbon dioxide + water
Sugars + oxygen

32. The Photosynthesis Equation
light
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugar + oxygen

33. Light and Pigments
In addition to water and carbon dioxide, photosynthesis requires?

34. Light and Pigments
In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.

35. Light and Pigments
Energy from the sun travels to the Earth in many forms.
One of these forms is light (sunlight) which your eyes perceive as ‘white light’
It is actually a mixture of different wavelengths of light
Many of these wavelengths are visible to your eyes and are referred to as the visible spectrum
R O Y G B I V

36. Light and Pigments
Plants gather the sun’s energy with light-absorbing molecules called pigments.

37. Light and Pigments
Plants gather the sun’s energy with light-absorbing molecules called pigments.
The plants principal pigment is chlorophyll

38. Light and Pigments
Plants gather the sun’s energy with light-absorbing molecules called pigments.
The plants principal pigment is chlorophyll
There are 2 main types of chlorophyll
chlorophyll a and chlorophyll b

39. Chlorophyll absorbs light very well in the blue and red regions
Absorption of light by
Chlorophyll a and chlorophyll b
Chlorophyll b
Chlorophyll a
Chlorophyll absorbs light very well in the blue and red regions
However, it does not absorb it very well in
the green and yellow regions

40. Light and Pigment
Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light.

41. Light and Pigment
Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light.
When chlorophyll absorbs light much of the energy is transferred directly to electrons in the chlorophyll molecules, raising the energy levels of these electrons

42. Light and Pigment
Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light.
When chlorophyll absorbs light much of the energy is transferred directly to electrons in the chlorophyll molecules, raising the energy levels of these electrons
These high energy electrons make photosynthesis work