8.1 Photosynthesis uses light energy to make food

8.1 Photosynthesis uses light energy to make food

I. The Structure of Chloroplasts

A. Photosynthesis takes place in the chloroplast

B. Chloroplasts contain compounds called pigments that give leaves their color (chlorophyll).

C. Leaves contain the most chloroplasts. (fig. 8-2)

D. Stoma are tiny pores that allow carbon dioxide to enter and oxygen to leave the plant cell.

Structure of chloroplastE. Veins (xylem) carry CO2 and H2O from the

plants roots to the leaves and deliver (phloem) organic compounds to other parts of the plant.

F. The inner membrane of a chloroplast encloses a thick fluid called stroma.

G. Suspended in the stroma are many disk shaped sacs called thylakoids which are arranged in stacks called grana.

H. These stacks organize the series of reactions that make up photosynthesis.

Chloroplast

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1. In which part of a leaf are most chloroplasts located?

Cells containing chloroplasts are concentrated in the mesophyll.

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A granum is a stack of thylakoids within a chloroplast.

2. How is a thylakoid related to a granum?

II. Overview of PhotosynthesisA. In cellular respiration, electrons “fall” from

glucose to O2 to release energy.B. In photosynthesis, electrons from water are

boosted “uphill” (potential) by the energy of sunlight.

C. These excited electrons, along with carbon dioxide and hydrogen ions to produce C6H12O6 molecules

D. Photosynthesis occurs in two main steps: Light and Calvin Cycle (Dark Reaction).

III. The Light Reactions A. Light Reactions convert the energy in sunlight

to chemical energy.B. Chloroplasts use captured light energy to

remove electrons from H2O, splitting it into oxygen and hydrogen ions.

C. The electrons and hydrogen ions are used to make NADPH, which is an electron carrier.

D. Chloroplasts also use the captured light energy to generate ATP.

E. The overall result of the light reactions is the conversion of light energy to chemical energy stored in NADPH and ATP

IV. The Calvin Cycle

A. Calvin Cycle makes sugar from the atoms in carbon dioxide plus the hydrogen ions and high energy electrons carried in NADP

B. The ATP made in the light reactions provides the energy to make sugar.

C. The Calvin cycle is sometimes referred to as the “light-independent reactions” because it does not require light energy to begin.

See Overview fig. 8-4

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1. For each of the two main stages of photosynthesis, identify the inputs.

Inputs of the light reactions are light and water, and ADP, P, and NADP+ from the Calvin cycle. Inputs of the Calvin cycle are CO2, and ATP and NADPH from the light reactions.

Outputs of the light reactions are oxygen, which is released to the atmosphere, and ATP and NADPH, which go into the Calvin cycle. Outputs of the Calvin cycle are ADP, P, and NADP+, which go into the light reactions, and sugar, which is used by the plant.

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2. Identify the outputs for each stage, and tell how each is used.

8.2 The light reaction convert light energy to chemical

energy

I. Light Energy and Pigments

A. Light is a form of electromagnetic energy that travels in waves and the distance between adjacent waves is called a wavelength.

B. The range of wavelengths is called the electromagnetic spectrum. (fig. 8-5

C. Visible light only makes up a small portion of the electromagnetic spectrum.

II. Pigments and Color

A. A substances color is due to chemical compounds called pigments.

B. Waves of light shining on a material can be absorbed, transmitted or reflected

C. Leaves absorb blue-violet and red-orange light very well but either reflect or transmit green light and that is why leaves look green.

III. Identifying Chloroplast Pigments

A. Using a technique called chromatography different pigments in a leaf can be observed. (fig. 88-7)

B. Chlorophyll a absorbs mainly blue-violet light while chlorophyll b absorbs mainly red light.

IV. Harvesting Light Energy

A. Within the thykaloid membrane, chlorophyll and other molecules are arranged in clusters called photosystems. (fig. 8-8)

B. Each photosystem contains a few hundred pigment molecules, including chlorophyll a and b as well as carotenoids.

C. Each time a pigment molecule absorbs light energy electrons are raised from a “ground state” to an “excited state”.

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1. What does a photosystem consist of?

clusters of chlorophyll and other molecules embedded in the thylakoid membrane

Electrons become “excited”—that is, they gain energy when the photosystem absorbs sunlight.

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2. How are electrons in chlorophyll and other pigment molecules affected by light striking the photosystem?

Harvesting light energy

D. This electron “jumps” from molecule to molecule until it arrives at the reaction center.

E. The reaction center consists of chlorophyll a and a primary electron carrier. Other teams of molecules are also used to make ATP and NADPH

V. Chemical Products of Light Reactions

A. 2 photosystems are involved in the light reactions.

B. The first photosystem traps light energy and transfers the light-excited electrons to the electron transport chain, this can be referred to as the “water splitting photosystem”.

(figs.8-10,11)

Light reaction products

C. The second photosystem can be thought of as the “NADPH- producing photosystem” This system produces NADPH by transferring excited electrons and hydrogen ions to NAD+

D. The light reactions convert light energy to the chemical energy of ATP and NADPH, NO SUGAR has been produced, which is the job of the CALVIN CYCLE.

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1. What happens to water molecules in the first photosystem?

Water molecules are split into H+ ions, electrons, and oxygen.

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2. What is the overall result of the light reactions?

Energy in sunlight is converted to chemical energy in the form of ATP and NADPH.

8.3 Calvin Cycle makes sugar from carbon dioxide

I. A Trip Around the Calvin Cycle

A. The Calvin Cycle is the sugar factory within the chloroplasts.

B. The starting material for the Calvin cycle is regenerated each time the process occurs, the starting material is called RuBP, (a sugar with five carbons).

Calvin cycle

C. The inputs for the Calvin cycle are ATP, CO2 and NADPH. (from light reaction and air thus no light)

D. The cycles output is an energy rich sugar molecule called G3P which is not quite glucose but is used as the raw material to make glucose as the plant needs to.

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does carbon enter and exit the Calvin cycle?

Carbon enters the cycle in the form of three CO2 molecules and exits as one molecule of G3P.

Transparency 8D-9 2. What is the source of the energy-rich ATP and NADPH molecules used in

the cycle?

ATP and NADPH are produced during the light reactions.

II. Summary of Photosynthesis

A. The equation (unbalanced) for photosynthesis is

Carbon Dioxide + Water --> Glucose + OxygenCO2 + H2O --> C6H12O6 + O2

B. The light reactions take place in the thylakoid membranes and convert light energy into chemical energy in the form of ATP and NADPH. (fig. 8-14)

C. The light reactions use the reactant H2O and release the product O2.

Summary of photosynthesis

D.The Calvin cycle takes place in the stroma uses ATP and NADPH to convert CO2 to C6H12O6.

E. Photosynthesis is the first step in the flow of energy through an ecosystem

F. Photosynthesis is the ultimate source of all the food that you eat and all the oxygen that you breathe

8.4 Photosynthesis has a global impact

I. The Carbon Cycle

A. The C cycle is the process by which carbon moves from inorganic to organic compounds and back.

B. Through photosynthesis, producers convert inorganic CO2 to organic compounds (ie sugar).

C. Cellular Respiration by both producers and consumers return the CO2 to the atmosphere.

Carbon Cycle

D. No other chemical process matches the output of photosynthesis.

E. Earth’s plants and other photosynthetic organisms make up about 160 billion metric tons of organic material per year.

II. Photosynthesis and Climate

A. One organism may either produce or use a relatively small amount of CO2, the total effect of all the organisms on Earth is very large.

B. CO2 only makes up 0.03 percent of the Earth’s atmosphere before this century

C. CO2 is one of many gases that traps heat from the sun that would have otherwise escape back into space, this is the greenhouse effect.

Global climate

D. The greenhouse effect keeps the average temperature on Earth about 10 degrees C warmer than it would be otherwise

E. The amount of CO2 in the atmosphere is rising.

Climate Change - 1896

Greenhouse effect: Swedish scientist Svante Arrhenius theorizes that doubling the amount of carbon dioxide in the atmosphere might raise the Earth's temperature by 5 or 6 degrees Celsius. Arrhenius suspects that coal and fossil fuels burned by industrialized countries are adding to the levels of carbon dioxide in the atmosphere. The greenhouse effect is a natural phenomenon in which gasses such as carbon dioxide trap the sun's warmth.


Ice insight: Ice cores from the Greenland ice sheet show dramatic temperature oscillations in a single century from the past, an extremely short period for climate change. Scientists also report strong evidence for global warming and call 1981 the warmest year on record.

Climate Change - 1990Sign here: The IPCC presents its First

Assessment Report, stating that human activities are substantially increasing the concentrations of greenhouse gases in the atmosphere. Two years later, the United States, along with more than 100 other countries, sign the United Nations Framework Convention on Climate Change in Rio de Janeiro, Brazil. It recognizes the climate system as a shared resource and launches efforts to curb climate change.


Kyoto: The Kyoto Protocol is negotiated to reduce greenhouse gas emissions 5.2 percent below 1990 levels by 2012. The United States signs the treaty, but never becomes a full-fledged participant as the U.S. Senate agrees in advance not to ratify the treaty, citing economic concerns. President Bush will withdraw the United States from the treaty in 2001.


Mercury rising: The U.S. National Academy of Sciences publishes a report requested by President Bush on the human role in climate change. The panel declares "temperatures are, in fact, rising" and human activity is the likely culprit, although it does not define the influence of natural climate variability. Predictions of a 3 degree Celsius warming are called "consistent" with climate science.


Kyoto: The Kyoto Protocol enters into force on February 16. The treaty was ratified by more than 140 countries. Concentration of carbon dioxide now stands at 372 parts per million, higher than at any time in at least the past 420,000 years, according to David King, chief science adviser to the British government.

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8.1 Photosynthesis uses light energy to make food