Where does the energy for living things come from?  Autotrophs – make their own food Plants and other organisms (like algae) can use light energy from the sun to produce their own food  Heterotrophs – get energy from the foods they consume Impalas eat grasses (which are autotrophs) Leopards eat other animals (get their energy indirectly from autotrophs by feeding on animals that eat autotrophs) Mushrooms and other fungi obtain food by decomposing other organisms

Chemical Energy and ATP  Energy comes in many forms: light, heat, electrical, chemical  Adenosine triphosphate (ATP) is the primary chemical compound cells use to store and release energy. Consists of adenine, 5-carbon sugar (ribose), and three phosphates ○ Phosphates are necessary for ATP to store and release energy.  ATP enables active transport, synthesis of proteins and nucleic acids, muscle contraction, etc.

ATP – Adenosine Triphosphate

Photosynthesis  Photosynthesis – plants use the energy from the sun to convert water and carbon dioxide into high-energy carbohydrates (sugars). Oxygen is the waste product. (light) 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 (light) carbon dioxide + water  glucose + oxygen

Investigating Photosynthesis  1643 – Jan van Helmont Do plants grow by taking material out of the soil? ○ Determined the mass of soil and willow seedling. Watered for five years. Seedling gained 165lbs; soil unchanged. ○ Conclusion: Gain in mass from the water not the soil. This accounts for the hydrogen in the glucose production.  1771 – Joseph Priestley What in the air makes a flame die out in a jar? ○ Determined when the substance from the air was used up, the candle would burn out. If a sprig of mint was placed in the jar, the candle could be relit after several days. ○ The mint produced a substance that was required for combustion. That substance was oxygen.

Investigating Photosynthesis  1779 – Jan Ingenhousz Do aquatic plants produce oxygen in the dark? ○ Determined that aquatic plants would only produce oxygen bubbles in the light. ○ Concluded that plants need sunlight to produce oxygen.  These experiments led to work by other scientists who discovered that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen.  Photosynthesis explained (4:09) Photosynthesis explained (4:09)

Investigating Photosynthesis  1845 – Julius Robert Mayer Proposed that plants convert light energy into chemical energy  1948 – Melvin Calvin Traced the chemical path that carbon follows to form glucose; steps called the Calvin cycle; awarded Nobel Prize in Chemistry in 1961  1992 – Rudolph Marcus Described the process by which electrons are transferred from one molecule to another in the electron transport chain; awarded Nobel Prize in Chemistry in 1992

How do plants capture sunlight?  Sunlight – a mixture of different wavelengths of light. Different wavelengths are visible as different colors.  Plants gather the sun’s energy with light absorbing molecules called pigments.  Chlorophyll is the main pigment in plants. Two types: chlorophyll a and chlorophyll b Light is a form of energy, so when pigments absorb light they also absorb the energy from that light. Much of the energy is transferred directly to electrons in the chlorophyll molecule, raising the energy levels of these electrons. These energetic electrons power photosynthesis.

Chlorophyll  Absorbs light in violet, blue, and red regions of the visible spectrum  Doesn’t absorb well in the green region. Green light is reflected by chlorophyll, so plants appear green.  Other pigments absorb light in other regions.

Photosynthesis takes place inside Chloroplasts  Thylakoids – sac-like photosynthetic membranes, where light-dependent reactions occur  Grana – stacks of thylakoids  Photosystems – clusters of chlorophyll and other pigments in the thylakoid membrane  Stroma – region outside the thylakoids where Calvin cycle occurs  Chloroplast Cyclosis (:30) Chloroplast Cyclosis (:30)

● When the sunlight excites electrons in chlorophyll, the electrons gain a great deal of energy. ● They need a special electron carrier to move them from chlorophyll to other molecules. ● NADP + is a carrier molecule that holds 2 high energy electrons and an H + ion and becomes NADPH. ● NADPH can then carry the high- energy electrons to the Calvin cycle. Overview of Photosynthesis

Light-Dependent Reactions Take place in the _____ _____ A. Begin when pigments in PS II absorb light. Light energy is absorbed by electrons in chlorophyll, increasing their energy level. They then move down the ETC.  Additional electrons are provided by water. Oxygen is released into the air. The unused H + ions are released into the ITS.

Light-Dependent Reactions B. Electrons pass through the ETC from PS II to PS I. The energy from the electrons is used to actively transport H + ions from the stroma into the ITS. C. The electrons are reenergized in PS I. NADP + picks up these electrons, along with H + ions, to become NADPH.

Light-Dependent Reactions D. Eventually, the ITS fills up with H + ions. The outside of the thylakoid membrane is – while the inside is +. This provides energy to make ATP. E. ATP synthase – an enzyme that allows H + ions to pass through it causing it to rotate and bind ADP and a phosphate to produce ATP. The ATP and NADPH get sent to the Calvin cycle.

Calvin Cycle Calvin cycle uses energy from ATP and NADPH (both from the LDR) to produce sugars. It uses 18 molecules of ATP and 12 molecules of NADPH to complete one cycle. PGA PGAL RuBP

Calvin Cycle  The two reactions work together perfectly – LDR trap the energy of sunlight in chemical form (ATP and NADPH) and the Calvin cycle uses that energy to produce sugars from CO 2 and H 2 O. Photosynthesis Summary Photosynthesis Summary (7:30) PGA PGAL RuBP

Factors that Affect Photosynthesis  Water – shortage can slow or stop photosynthesis because it’s a raw material  Temperature – photosynthesis depends on enzymes. Temperature extremes will denature enzymes and slow the rate of photosynthesis  Intensity of light – increasing intensity increases rate of photosynthesis, but only up to a point Photosynthesis SongPhotosynthesis Song (1:52)

Review!  Scientists: Traced path carbon follows through chloroplast Stated that mass of plants comes from H 2 O Discovered oxygen Proved that plants transform light energy into chem energy ETC Discovered that plants produce O 2 in light but not in dark

Review!  H 2 O is broken up into what three components in PSII?  What is an autotroph?  Name at least three factors that affect rate of photosynthesis.  The LDR take place in the...  What is located between PSII and PSI?  Purpose of the electrons as they move down the ETC?

Review!  The two predominant pigments found in chloroplasts?  Pigments can be found in the...  Organisms that must eat other organisms for energy?  The LDR produce ___ and ___ which are required for Calvin.  Raw material for LDR?  Raw material for Calvin?

Review!  Where does Calvin take place?  Stack of thylakoids?  What is actively transported into the ITS?  What provides the energy?  Primary energy compound for all cells?  Product of LDR?  Product of Calvin?