Chapter 8 Section 2 Photosynthesis: An Overview. Photosynthesis Plants use the energy of sunlight to...

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