PHOTOSYNTHESIS

Autotroph Heterotroph (Producers) (Consumers) Make their own food Photosynthesis Chemosynthesis - Plants - Some bacteria & protists Heterotroph (Consumers) Energy obtained by eating

Cellular Energy: ATP An important compound that cells use to store and release energy is Adenosine Triphosphate (ATP) ATP is used by all cells as their basic energy source Adenine 3 Phosphate groups Ribose

Releasing Energy From ATP Energy stored in ATP is released by breaking the chemical bond between the second and third phosphates. The energy from ATP is needed for many cellular activities, including active transport across cell membranes, protein synthesis and muscle contraction.

Photosynthesis 6H20 + 6CO2  C6H12O6 + 6O2

How can plants do it? Plants contain the green pigment chlorophyll, which takes in sunlight and captures it’s energy, in the chloroplasts. There are two main types of chlorophyll, “chlorophyll a” and “chlorophyll b” When chlorophyll absorbs light, energy is transferred to electrons in the chlorophyll molecule, raising their energy level. These high-energy electrons make photosynthesis work.

Interpreting Diagrams Which wavelengths/ color(s) are absorbed best? Which wavelengths/ color(s) are reflected? What is the relationship between reflection of light and the perception of color?

Not all plants have green leaves… They still have chlorophyll!! It is just hidden by other pigments.

Why do leaves change colors? Chlorophyll breaks down in cold weather as the strength of the sun’s rays weakens. The other colors, that were always there, show through.

How do we know? Chromatography Method of separating pigments The solvent moves past the spot that was applied The pigments will differ in solubility and in the strength of their adsorption to the adsorbent Some will be carried farther up the plate than others.

Location of Photosynthesis

The Chloroplast

Process Overview Two steps: Light Dependent (Light Reactions) -> thylakoid Light Independent (Calvin Cycle) -> stroma

Light- dependent reactions A closer look……. H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin cycle O2 Sugars

Light-Dependent Reactions Light is absorbed by chlorophyll in clusters called photosystems A flow of e- starts This provides energy to make ATP & NADPH Water is split to replace e- and allow the flow to continue & O2 is released ATP & NADPH go to the stroma to fuel the Calvin Cycle

NADPH When water is split to replace e- in PS-II, H+ are left over As free e- reach PS-I, two are picked up by NADP+, resulting in NADP- This negative charge attracts H+ ions resulting in NADPH NADP+ + 2e-  NADP- NADP- + H+  NADPH NADPH carries electrons (energy source) as well as hydrogen (to build sugars) to the stroma for the Calvin Cycle.

Chemiosmosis Mechanism that generates ATP Uses potential energy of an H+ concentration gradient H+ flow across the thylakoid membrane into the stroma through an enzyme membrane protein called ATP synthase This drives the (photo) phosphorylation of ATP

Self-Assessment – L.D. Reactions Where in the chloroplast do the light dependent reactions take place? What happens when a molecule of chlorophyll absorbs light? How is water used during the light dependent reactions? (2 uses) What is the bi-product of using water? What two things does NADPH supply for the Calvin Cycle? What is chemiosmosis? What enzyme is involved in this process? What supplies the energy for this process?

Calvin Cycle 1. CO2 enters the stroma 2. It combines with a 5-C sugar RuBP using the enzyme Rubisco to form a 3-C acid (carbon fixation) Using energy from ATP & NADPH high energy sugars (G3P) are made for the plant 4. ADP & NADP+ go back to the thylakoid to be “recharged” In order for the “cycle” to continue, RuBP must be regenerated. 3 “turns” of the Calvin Cycle are needed to generate one G3P molecule. In other words, 3 CO2 molecules are used to make 1 G3P and remake RuBP.

Self-Assessment – Calvin Cycle What is “waiting” in the stroma to combine with CO2? What enzyme catalyzes this combination? What is the direct result of this combination? What is the general name to describe this conversion of inorganic CO2 into a molecule plants can use for biosynthesis? Why is the Calvin Cycle called a “cycle”? How many “turns” are needed to provide the plants with a molecule of sugar?

Process Recap The two sets of photosynthetic reactions work together. The light-dependent reactions trap sunlight energy in chemical form (ATP and NADPH). The light-independent reactions use that chemical energy to produce stable, high-energy sugars.

Global Impact of Photosynthesis Carbon cycle Greenhouse effect Greenhouses gases in atm. prevent some heat from the sun from escaping CO2, methane, H2O vapor are the main GH gases Global warming Excessive levels of GH gases result in more heat being trapped This is not the same thing as ozone depletion

Food & Energy Food serves as a source of raw materials, or building blocks, for the cells in the body and also as a source of energy. Animal Cells Animal Mitochondrion Plant Plant Cells

Chemical Energy & Food Cells don't literally “burn” glucose. They release energy by breaking bonds of food molecules. Cellular (aerobic) respiration is the process of breaking down food to release energy. This process occurs in the mitochondria.

Structure of the Mitochondria

Cellular Respiration Oxygen + Glucose  Carbon Dioxide + Water + ATP (6O2 + C6H12O6  6CO2 + 6H2O + ATP) Cellular respiration is an aerobic process because it requires oxygen (aerobic respiration) There are three steps in cellular respiration Glycolysis Krebs Cycle (a.k.a. “Citric Acid Cycle”) Electron Transport Chain (ETC) In the absence of oxygen, glycolysis is followed by fermentation. This is called anaerobic respiration.

Overview of Cellular Respiration Mitochondrion Cytoplasm

Glycolysis Occurs in the cytoplasm One molecule of glucose (6-C) is split, producing two molecules of pyruvic acid (3-C) The cell uses two molecules of ATP to start the process and when glycolysis is complete 4 gross or 2 net ATP and 2 NADH are produced. 2 ATP 2 ADP 4 ADP 4 ATP

Fermentation Alcoholic Fermentation: Lactic Acid Fermentation: Performed by yeasts and a few other microorganisms pyruvic acid + NADH → alcohol + CO2 + NAD+ Lactic Acid Fermentation: - in cells, such as muscle cells, the pyruvic acid from glycolysis is converted to lactic acid - pyruvic acid + NADH → lactic acid + NAD+ **Fermentation regenerates NAD+ so that glycolysis can continue

Kreb’s Cycle Occurs in the matrix of the mitochondria In the presence of oxygen, pyruvate (pyruvic acid) enters the Kreb cycle and broken down, releasing carbon dioxide. As a result NADH, FADH2 and ATP are generated. The ATP is used for cellular energy and the electron carriers, NADH and FADH2 go to the E.T.C.

Electron Transport Chain (ETC) Occurs in the cristae (inner membrane) of the mitochondria. ATP is generated through chemiosmosis in a series reactions involving high energy electrons moving through the electron transport chain. Oxygen serves as the final electron acceptor, allowing energy to be released to cells. Each oxygen picks up 2e- and then binds with two H+ to form water.

Energy Totals Glycolysis produces just 2 net ATP molecules per molecule of glucose. Krebs Cycle & ETC produce 34 ATP. The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.

Photosynthesis v. Cellular Respiration Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food