P HOTOSYNTHESIS

8-1 E NERGY AND L IFE Copyright Pearson Prentice Hall

A UTOTROPHS AND H ETEROTROPHS Living things need energy to survive. This energy comes from food. The energy in most food comes from the sun. Where do plants get the energy they need to produce food? Copyright Pearson Prentice Hall

A UTOTROPHS AND H ETEROTROPHS Autotrophs and Heterotrophs Plants and some other types of organisms are able to use light energy from the sun to produce food. Copyright Pearson Prentice Hall

Energy: Energy for living things comes from food. Originally, the energy in food came from the sun.

Organisms that use light energy from the sun to produce food—autotrophs (auto = self) Ex: plants and some microorganisms (some bacteria and protists)

Organisms that CANNOT use the sun’s energy to make food—heterotrophs Ex: animals and most microorganisms

S OME THOUGHTS ABOUT ENERGY Energy can not be created or destroyed It is only converted from one form to another Plants take light energy and covert it to chemical energy (sugar)-photosynthesis Other organisms change this chemical energy into another form (ATP) so that the cell can use it a the cellular level- cell respiration

C HEMICAL E NERGY AND ATP Chemical Energy and ATP Energy comes in many forms What are some different forms of energy? Energy can be stored in chemical compounds, too. Copyright Pearson Prentice Hall

C HEMICAL E NERGY AND ATP An important chemical compound that cells use to store and release energy is adenosine triphosphate, abbreviated ATP. ATP is used by all types of cells as their basic energy source. Copyright Pearson Prentice Hall

C HEMICAL E NERGY AND ATP ATP consists of: adenine ribose (a 5-carbon sugar) 3 phosphate groups Copyright Pearson Prentice Hall Adenine ATP Ribose 3 Phosphate groups

Storing Energy ADP has two phosphate groups instead of three. A cell can store small amounts of energy by adding a phosphate group to ADP. Copyright Pearson Prentice Hall ADP ATP Energy Partially charged battery Fully charged battery + Adenosine Diphosphate (ADP) + Phosphate Adenosine Triphosphate (ATP)

C HEMICAL E NERGY AND ATP Releasing Energy Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. Copyright Pearson Prentice Hall P ADP 2 Phosphate groups

phosphate removed ATP – ADP Cycle

C HEMICAL E NERGY AND ATP What is the role of ATP in cellular activities? Copyright Pearson Prentice Hall

C HEMICAL E NERGY AND ATP The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction. ATP’s characteristics make it exceptionally useful as the basic energy source of all cells. Copyright Pearson Prentice Hall

U SING B IOCHEMICAL E NERGY Using Biochemical Energy Most cells have only a small amount of ATP, because it is not a good way to store large amounts of energy. Cells can regenerate ATP from ADP as needed by using the energy in foods like glucose. Copyright Pearson Prentice Hall

Carbohydrates – most commonly broken down to make ATP. – not stored in large amounts – up to 36 ATP from one glucose molecule Lipids – store the most energy. – 80% of energy in your body – About 146 ATP from a triglyceride Proteins – least likely to be broken down to make ATP. – amino acids not usually needed for energy – about the same amount of energy as a carb.

E NERGY ??

Using Biochemical Energy 1) Movement in cell 2) Protein synthesis 3) Active Transport (Low to high concentration across membrane)

8-2 P HOTOSYNTHESIS : A N O VERVIEW Copyright Pearson Prentice Hall

8-2 P HOTOSYNTHESIS : A N O VERVIEW The key cellular process identified with energy production is photosynthesis. Photosynthesis is the process in which green plants use the energy of sunlight to convert water and carbon dioxide into high-energy carbohydrates and oxygen. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS What did the experiments of van Helmont, Priestley, and Ingenhousz reveal about how plants grow? Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Investigating Photosynthesis Research into photosynthesis began centuries ago. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Van Helmont’s Experiment In the 1600s, Jan van Helmont wanted to find out if plants grew by taking material out of the soil. He determined the mass of a pot of dry soil and a small seedling, planted the seedling in the pot, and watered it regularly. After five years, the seedling was a small tree and had gained 75 kg, but the soil’s mass was almost unchanged. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Van Helmont concluded that the gain in mass came from water because water was the only thing he had added. His experiment accounts for the “hydrate,” or water, portion of the carbohydrate produced by photosynthesis. But where does the carbon of the “carbo-” portion come from? Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Although van Helmont did not realize it, carbon dioxide in the air made a major contribution to the mass of his tree. In photosynthesis, the carbon in carbon dioxide is used to make sugars and other carbohydrates. Van Helmont had only part of the story, but he had made a major contribution to science. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Priestley’s Experiment More than 100 years after van Helmont’s experiment, Joseph Priestley provided another insight into the process of photosynthesis. Priestley took a candle, placed a glass jar over it, and watched as the flame gradually died out. He reasoned that the flame needed something in the air to keep burning and when it was used up, the flame went out. That substance was oxygen. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Priestley then placed a live sprig of mint under the jar and allowed a few days to pass. He found that the candle could be relighted and would remain lighted for a while. The mint plant had produced the substance required for burning. In other words, it had released oxygen. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS Jan Ingenhousz Later, Jan Ingenhousz showed that the effect observed by Priestley occurred only when the plant was exposed to light. The results of both Priestley’s and Ingenhousz’s experiments showed that light is necessary for plants to produce oxygen. Copyright Pearson Prentice Hall

I NVESTIGATING P HOTOSYNTHESIS The experiments performed by van Helmont, Priestley, and Ingenhousz led to work by other scientists who finally discovered that, in the presence of light, plants transform carbon dioxide and water into carbohydrates, and they also release oxygen. Copyright Pearson Prentice Hall

T HE P HOTOSYNTHESIS E QUATION What is the overall equation for photosynthesis? Copyright Pearson Prentice Hall

T HE P HOTOSYNTHESIS E QUATION The Photosynthesis Equation The equation for photosynthesis is: 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 carbon dioxide + water sugars + oxygen Copyright Pearson Prentice Hall Light

T HE P HOTOSYNTHESIS E QUATION Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high-energy sugars and oxygen. Copyright Pearson Prentice Hall

L IGHT AND P IGMENTS What is the role of light and chlorophyll in photosynthesis? Copyright Pearson Prentice Hall

Light and Pigments How do plants capture the energy of sunlight? In addition to water and carbon dioxide, photosynthesis requires light and chlorophyll. Copyright Pearson Prentice Hall

L IGHT AND P IGMENTS Plants gather the sun's energy with light-absorbing molecules called pigments. The main pigment in plants is chlorophyll. There are two main types of chlorophyll: chlorophyll a chlorophyll b Copyright Pearson Prentice Hall

L IGHT AND P IGMENTS Chlorophyll absorbs light well in the blue-violet and red regions of the visible spectrum. Copyright Pearson Prentice Hall Wavelength (nm) Estimated Absorption (%) Chlorophyll b Chlorophyll a Wavelength (nm)

L IGHT AND P IGMENTS Chlorophyll does not absorb light will in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. Copyright Pearson Prentice Hall Estimated Absorption (%) Chlorophyll b Chlorophyll a Wavelength (nm)

L IGHT AND P IGMENTS Light is a form of energy, so any compound that absorbs light also absorbs energy from that light. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These high-energy electrons are what make photosynthesis work. Copyright Pearson Prentice Hall

8-3 T HE R EACTIONS OF P HOTOSYNTHESIS Copyright Pearson Prentice Hall

I NSIDE A C HLOROPLAST Inside a Chloroplast In plants, photosynthesis takes place inside chloroplasts. Copyright Pearson Prentice Hall Plant Plant cells Chloroplast

I NSIDE A C HLOROPLAST Chloroplasts contain thylakoids —saclike photosynthetic membranes. Copyright Pearson Prentice Hall Chloroplast Single thylakoid

I NSIDE A C HLOROPLAST Thylakoids are arranged in stacks known as grana. A singular stack is called a granum. Copyright Pearson Prentice Hall Granum Chloroplast

I NSIDE A C HLOROPLAST Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters called photosystems, which are the light-collecting units of the chloroplast. Copyright Pearson Prentice Hall Chloroplast Photosystems

Copyright Pearson Prentice Hall Chloroplast Light H2OH2O O2O2 CO 2 Sugars NADP + ADP + P Calvin Cycle Light- dependent reactions Calvin cycle

E LECTRON C ARRIERS Electron Carriers When electrons in chlorophyll absorb sunlight, the electrons gain a great deal of energy. Cells use electron carriers to transport these high-energy electrons from chlorophyll to other molecules. Copyright Pearson Prentice Hall

E LECTRON C ARRIERS One carrier molecule is NADP +. Electron carriers, such as NADP +, transport electrons. NADP + accepts and holds 2 high-energy electrons along with a hydrogen ion (H + ). This converts the NADP + into NADPH. Copyright Pearson Prentice Hall

L IGHT -D EPENDENT R EACTIONS Light-Dependent Reactions The light-dependent reactions require light. The light-dependent reactions produce oxygen gas and convert ADP and NADP + into the energy carriers ATP and NADPH. Copyright Pearson Prentice Hall

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall

L IGHT -D EPENDENT R EACTIONS Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Copyright Pearson Prentice Hall Photosystem II

L IGHT -D EPENDENT R EACTIONS These high-energy electrons are passed on to the electron transport chain. Copyright Pearson Prentice Hall Photosystem II Electron carriers High-energy electron

L IGHT -D EPENDENT R EACTIONS Enzymes on the thylakoid membrane break water molecules into: Copyright Pearson Prentice Hall Photosystem II 2H 2 O Electron carriers High-energy electron

L IGHT -D EPENDENT R EACTIONS hydrogen ions oxygen atoms energized electrons Copyright Pearson Prentice Hall Photosystem II 2H 2 O + O 2 Electron carriers High-energy electron

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall Photosystem II 2H 2 O + O 2 The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. High-energy electron

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall Photosystem II 2H 2 O As plants remove electrons from water, oxygen is left behind and is released into the air. + O 2 High-energy electron

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall Photosystem II 2H 2 O The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. + O 2 High-energy electron

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall Photosystem II 2H 2 O Energy from the electrons is used to transport H + ions from the stroma into the inner thylakoid space. + O 2

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall Photosystem II 2H 2 O High-energy electrons move through the electron transport chain from photosystem II to photosystem I. + O 2 Photosystem I

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall 2H 2 O Pigments in photosystem I use energy from light to re-energize the electrons. + O 2 Photosystem I

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall 2H 2 O NADP + then picks up these high-energy electrons, along with H + ions, and becomes NADPH. + O 2 2 NADP + 2 NADPH 2

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall 2H 2 O As electrons are passed from chlorophyll to NADP +, more H + ions are pumped across the membrane. + O 2 2 NADP + 2 NADPH 2

Copyright Pearson Prentice Hall 2H 2 O Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O 2 2 NADP + 2 NADPH 2

Copyright Pearson Prentice Hall 2H 2 O The difference in charges across the membrane provides the energy to make ATP + O 2 2 NADP + 2 NADPH 2

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall 2H 2 O H + ions cannot cross the membrane directly. + O 2 ATP synthase 2 NADP + 2 NADPH 2

Copyright Pearson Prentice Hall 2H 2 O The cell membrane contains a protein called ATP synthase that allows H + ions to pass through it + O 2 ATP synthase 2 NADP + 2 NADPH 2

Copyright Pearson Prentice Hall 2H 2 O As H + ions pass through ATP synthase, the protein rotates. + O 2 ATP synthase 2 NADP + 2 NADPH 2

L IGHT -D EPENDENT R EACTIONS Copyright Pearson Prentice Hall 2H 2 O As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. + O 2 2 NADP + 2 NADPH 2 ATP synthase ADP

Copyright Pearson Prentice Hall 2H 2 O Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. + O 2 ATP synthase ADP 2 NADP + 2 NADPH 2

T HE C ALVIN C YCLE What is the Calvin cycle? Copyright Pearson Prentice Hall

T HE C ALVIN C YCLE The Calvin cycle uses ATP and NADPH from the light-dependent reactions to produce high-energy sugars. Because the Calvin cycle does not require light, these reactions are also called the light-independent reactions. Copyright Pearson Prentice Hall

Six carbon dioxide molecules enter the cycle from the atmosphere and combine with six 5-carbon molecules. Copyright Pearson Prentice Hall CO 2 Enters the Cycle

The result is twelve 3-carbon molecules, which are then converted into higher-energy forms. Copyright Pearson Prentice Hall

The energy for this conversion comes from ATP and high-energy electrons from NADPH. Copyright Pearson Prentice Hall 12 NADPH ADP 12 NADP + Energy Input

T HE C ALVIN C YCLE Two of twelve 3-carbon molecules are removed from the cycle. Copyright Pearson Prentice Hall Energy Input 12 NADPH ADP 12 NADP +

T HE C ALVIN C YCLE The molecules are used to produce sugars, lipids, amino acids and other compounds. Copyright Pearson Prentice Hall 12 NADPH ADP 12 NADP + 6-Carbon sugar produced Sugars and other compounds

T HE C ALVIN C YCLE The 10 remaining 3-carbon molecules are converted back into six 5- carbon molecules, which are used to begin the next cycle. Copyright Pearson Prentice Hall 12 NADPH ADP 12 NADP + 5-Carbon Molecules Regenerated Sugars and other compounds 6 6 ADP

T HE C ALVIN C YCLE The two sets of photosynthetic reactions work together. The light-dependent reactions trap sunlight energy in chemical form. The light-independent reactions use that chemical energy to produce stable, high-energy sugars from carbon dioxide and water. Copyright Pearson Prentice Hall