chapter 8 section 2 photosynthesis: an overview. photosynthesis plants use the energy of sunlight to...
TRANSCRIPT
Chapter 8 Section 2
Photosynthesis:
An Overview
Photosynthesis
• Plants use the energy of sunlight
to convert water and carbon dioxide
into oxygen and high-energy carbohydrates (sugars and starches)
Investigating photosynthesis
• Voan Helmont’s experiments -
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
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
Investigating photosynthesis
• Voan Helmont’s experiments –– Results –
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
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 –
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
Investigating photosynthesis
• Voan Helmont’s experiments –Conclusions told part of the story of the
growth. What was missing?
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
Investigating photosynthesis
• Priestley’s experiments –– 100 years after Helmont’s experiments– Experiment set-up
Investigating photosynthesis
• Priestley’s experiments –– 100 years after Helmont’s experiments– Experiment set-up
• Placed a candle under a glass jar
Investigating photosynthesis
• Priestley’s experiments –– 100 years after Helmont’s experiments– Experiment set-up
• Placed a candle under a glass jar
- Results
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
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
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
Investigating photosynthesis
• Priestley’s experiments –- Additional experiments
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
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
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
Investigating photosynthesis
• Ingenhousz experiments –
Investigating photosynthesis
• Ingenhousz experiments –- Dutch scientist who later showed that the
effect observed by Priestley occurred only when the plant was exposed to light
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?
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
Investigating photosynthesis
• The experiments performed by these and other scientists reveal that– In the presence of light
Light energy
chloroplast
Investigating photosynthesis
• The experiments performed by these and other scientists reveal that– In the presence of light
• Plants transform carbon dioxide and water
Light energy
chloroplast
Carbon dioxide + water
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
Light energy
chloroplast
Carbon dioxide + water Sugars + oxygen
The Photosynthesis Equation
light
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water sugar + oxygen
Light and Pigments
• In addition to water and carbon dioxide, photosynthesis requires?
Light and Pigments
• In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll, a molecule in chloroplasts.
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
Light and Pigments
• Plants gather the sun’s energy with light-absorbing molecules called pigments.
Light and Pigments
• Plants gather the sun’s energy with light-absorbing molecules called pigments.
• The plants principal pigment is chlorophyll
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
Absorption of light byChlorophyll a and chlorophyll b
Chlorophyll b
Chlorophyll a
Chlorophyll absorbs light very well in the blue and red regionsHowever, it does not absorb it very well in
the green and yellow regions
Light and Pigment
• Because light is a form of energy, any compound that absorbs light also absorbs the energy from that light.
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
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