Photosynthesis

Energy and Life Autotrophs – make own energy Plants Photosynthesis, chemosynthesis Heterotrophs – obtain energy from food Animals Respiration

Chemical Energy and ATP Principle chemical compounds – ATP – Adenosine Triphosphate Adenine 5-carbon sugar (ribose) 3 phosphates ADP – Adenosine Diphosphate 2 phosphates

Chemical Energy and ATP When a cell has energy available it is stored by adding a phosphate group to ADP to make ATP To release energy, the bond between the 2nd and 3rd phosphates is broken ATP provides the power for many cellular functions such as active transport, protein synthesis, and muscle contractions. The characteristics of ATP make it exceptionally useful as the basic energy source for all cells!!!

ADP ATP

Investigating P.S. – The Dudes Jan Van Helmont’s Experiment Devised an experiment to see if plants grew by taking material out of the soil. Determined the mass of a pot of dry soil and a small seedling, then planted the seedling in the pot of soil. He watered it regularly. At the end of 5 years, the seedling had grown into a small tree and had gained about 75 kg. The mass of the soil was unchanged. He concluded the mass must have come from the water. The accounts for the “hydrate” portion of the carbohydrate produced by PS. Helmont didn’t realize that carbon dioxide also played a major role in PS.

Investigating P.S. – The Dudes Joseph Priestly’s Experiment Priestly took a candle, placed a glass jar over it, and watched as the flame died out. This lead him to believe that something in the air was necessary for the candle to continue burning. He then found that if he placed a live sprig of mint under the jar and allowed a few days to pass, the candle could be relit and would remain lit for a while. He concluded that the mint plant produced the substance required for the burning of the candle. He didn’t know it at the time, but what is being released is oxygen.

Investigating P.S. – The Dudes Jan Ingenhousz Showed the effect observed by Priestly occurred only when the plant was exposed to light. These experiments, along with others, led to the discovery that plants transform carbon dioxide and water into carbohydrates and oxygen in the presence of light.

The Photosynthesis Equation YOU MUST MEMORIZE THIS!!!!! sun Carbon dioxide + water  glucose + oxygen 6 CO2 + 6 H2O  C6H12O6 + 6 O2

Light and Pigments In addition to water and carbon dioxide, PS requires light and chlorophyll (a molecule in chloroplasts). Energy from the sun travels to Earth in the form of light. Sunlight is a mixture of different wavelengths of light, many of which are visible and make up the visible spectrum. Different wavelengths are seen as different colors.

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

Light and Pigments Chlorophyll absorbs light very well in the blue-violet and red regions of the visible spectrum. However it does not absorb light well in the green region of the spectrum. Green light is reflected by leaves, which is why plants look green. Plants also contain red and orange pigments such as carotene that absorb light in other regions of the spectrum.

Inside the Chloroplast Location of PS Contains thylakoids, which are sac-like photosynthetic membranes. Thylakoids are arranged in stacks called grana. Proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters known as photosystems, which are light collecting units of the chloroplast. Two types of reactions in the photosystems: Light-dependent reactions Light-independent reactions (aka Calvin Cycle)

Chloroplast

Electron Carriers When sunlight excites the e- in chlorophyll, e- gain a great deal of energy. High-energy e- require a special carrier to move them from chlorophyll to other molecules. Carrier molecule is a compound that can accept a pair of high-energy e- and transfer them along with most of their energy to another molecule. Called electron transport Carriers are called the electron transport chain (ETC)

Electron Carriers – NADP+ NADP+ : Nicotinamide adenine dinucleotide phospate Accepts and hold 2 e- along with H+ ion This converts NADP+ into NADPH NADPH then carries e- to other locations in cell Can be used to create glucose

Light-Dependent Reactions Use energy from light to produce O2 and converts ADP and NADP+ into ATP and NADPH Photosystem II (PS II) Chlorophyll a in PS II absorbs sunlight. This excites an e-. This e- is captures by the primary e- acceptor. An enzyme in the thylakoid splits water into 2 e-, 2 H+ ions, and an O atom. These e- replace the e- lost to the primary e- acceptor. Two O atoms combine to form O2. e- are passed to the ETC.

Light-Dependent Reactions ETC High energy e- move through the ETC from PS II to PS I. Energy from e- is used by molecules in ETC to transport H+ ions from stroma into inner thylakoid space. Photosystem I (PS I) Pigments in PS I use energy from light to reenergize e-. NADP+ picks up an e- with an H+ to become NADPH.

Light-Dependent Reactions Hydrogen Ion Movement As e- are passed from chlorophyll at NADP+, more H+ ions are pumped across membrane. Inside of the membrane fills with positively charged H+. Difference in charges provides energy to make ATP.

Light-Dependent Reactions ATP Formation H+ ions can’t cross membrane directly. ATP Synthase allows H+ to pass through it. As H+ passes through ATP Synthase, the protein rotates. As it rotates, ATP Synthase binds ADP and a phosphate group to produce ATP. http://www.youtube.com/watch?v=eY1ReqiYwYs

Light-Independent Reactions (aka Calvin Cycle) Plants use energy that ATP and NADPH contain to build high energy compounds that can be stored for a long time. The ATP and NADPH comes from light-dependent reactions.

Light-Independent Reactions (aka Calvin Cycle) 6 CO2 enter cycle from atmosphere. These 6 CO2 molecules combine with 6 5-carbon molecules. This results in 12 3-carbon molecules. The 12 3-carbon molecules are converted into high-energy forms. The energy comes from ATP and high-energy e- from NADPH.

Light-Independent Reactions (aka Calvin Cycle) 2 of the 12 3-carbon molecules are removed from cycle. These two molecules are used to produce sugars, lipids, amino acids, and other compounds. The remaining 3-carbon molecules are converted back into 6 5-carbon molecules. They combine with 6 new CO2 molecules to begin a new cycle. Uses 6 CO2 to produce a single 6-C sugar

Photosynthesis Light-Dependent Light-Independent Includes Light-Dependent Light-Independent Takes place in uses Takes place in uses Water Energy from Sunlight ATP NADPH Carbon dioxide To produce Thylakoid Stroma To produce ATP Oxygen Of the Chloroplast High Energy Sugar NADPH