Photosynthesis and Cellular Respiration Chapter 5

Energy and Living Things Section 5-1

Where does energy in food come from? Directly or indirectly, all energy needed for metabolism comes from the SUN Energy enters living systems when plants, algae and bacteria absorb sunlight Some energy from the sun is captured to make organic compounds which are then stored Where does energy in food come from?

Building molecules that store energy Metabolism either uses energy to build molecules or break down molecules that store energy Building molecules that store energy

Building molecules that store energy Photosynthesis is the process by which light energy is converted to chemical energy Autotrophs are organisms that use energy from sunlight or inorganic substances to make organic compounds Most autotrophs like plants are photosynthetic Building molecules that store energy

Breaking down food for energy Chemical energy in organic compounds can transfer to organisms that consume those compounds Heterotrophs are organisms that must get energy from food instead of directly from sunlight or inorganic substances Cellular respiration is a metabolic process where organisms harvest energy from food

Cells Transfer energy from food to ATP Cells burn energy differently than wood burns In cells, stored energy is released in a series of enzyme assisted reactions When cells break down food molecules, some energy is released as heat, most is released as ATP Cells Transfer energy from food to ATP

ATP stores and Releases energy ATP (adenosine triphosphate) is a nucleotide with 2 energy storing phosphate groups Phosphate groups store energy like a spring and releases it when the bonds holding the groups together break ATP ADP + P + Energy ATP stores and Releases energy

Photosynthesis Section 5-2

Photosynthetic Organisms Use Sunlight’s Energy Plants, algae and some bacteria capture 1% of the energy in the sunlight that reaches Earth Photosynthetic Organisms Use Sunlight’s Energy

Photosynthesis Overview Stage 1: Energy is captured from sunlight Stage 2: Light energy is converted to chemical energy; stored as ATP and the energy carrier molecule NADPH Stage 3: Energy from ATP and NADPH powers the formation of organic compounds using carbon dioxide (CO2) 6CO2 +6H2O C6H12O6+ 6O2 Light Photosynthesis Overview

First and second stage of photosynthesis are light stages Without light, these reactions would not occur Light energy is used to make energy storing compounds Light Reactions

Pigments absorb different wavelengths of light Pigments are molecules that absorb certain wavelengths of light and reflect others Chlorophyll is the primary pigment involved in photosynthesis and it absorbs red and blue and reflects green and yellow Carotenoids are pigments that produce yellow and orange fall leaf colors Using both carotenoids and chlorophyll absorbs more light energy, so plants use both Pigments absorb different wavelengths of light

Pigments used in photosynthesis are found in the chloroplast Clusters of pigments are embedded in disk- shaped structures called thylakoids When light strikes a thylakoid, energy is transferred to electrons in pigments and the electrons are excited Production of Oxygen

Production of Oxygen cont… Excited electrons jump from pigment molecules to others and power second stage of photosynthesis The electrons must be replaced so water molecules split, taking electrons from hydrogen, leaving H+ and oxygen O which forms oxygen gas Production of Oxygen cont…

Cellular Respiration Section 5-3

Cellular Respiration Produces ATP Oxygen makes the production of ATP more efficient Some ATP is made without oxygen Metabolic processes that require oxygen are called aerobic Metabolic processes that do not require oxygen are called anaerobic Cellular Respiration Produces ATP

Cellular respiration harnesses the energy in organic compounds C6H12O6 +602  6CO2 + 6H2O + energy Primary fuel for cellular respiration is glucose Glucose is formed when starch or sucrose are broken down Cellular Respiration

Stage 1: Glucose is broken down Glucose (sugar) is broken down in the cytoplasm by the process glycolysis Glycolysis is an enzyme assisted anaerobic process that breaks down one 6-carbon molecule of glucose to two 3-carbon pyruvates Glycolysis uses 2 ATP molecules but produces 4 ATP molecules Stage 1: Glucose is broken down

Step 1: Phosphate groups from 2 ATP molecules are transferred to glucose Step 2: The 6-carbon compound is broken down into two 3-carbon compounds + 1 Phosphate Step 3: Two NADH molecules are made 1 more phosphate group is added Step 4: Each 3 carbon compound is converted to 3-carbon pyruvates, which produces 4 ATP Glycolysis

When oxygen is present, pyruvate from glycolysis enters a mitochondria and is converted to a 2 carbon compound This produces CO2, one NADH and a 2-carbon acetyl group This attaches to an enzyme A (CoA) making acetyl-CoA Acetyl-CoA enters a series of enzyme-assisted reactions called Krebs Cycle Stage 2: More ATP is made

Step 1: Acetyl-CoA combines with a 4-C comp, making a 6-C comp and releasing CoA Step 2: CO2 is released from the 6-C comp forming a 5-C comp. e- transfer making NADH Step 3: CO2 is released from 5-C comp, making a 4-C, ATP and NADH Step 4: 4-C comp is converted to another, and e- transfer to make electron carrier, FADH2 Step 5: 4-C comp is converted to original 4-C comp, NADH is produced and cycle can start over Krebs Cycle

Electron Transport Chain In aerobic respiration, electrons donated by NADH and FADH2 pass through electron transport chains The chain pumps H+ out of the mitochondria which combines with O2 to make H2O ATP is produced as H+ diffuses back into the mitochondria Electron Transport Chain

Fermentation Follows Glycolysis in Absence of Oxygen Without enough oxygen, Electron Transport Chain does not function the same O2 receives electrons and when not present, NADH and NAD+ cannot be recycled So NAD+ undergoes fermentation to recycle it Fermentation Follows Glycolysis in Absence of Oxygen

Lactic Acid Fermentation Lactate is the ion of an organic acid called lactic acid A 3-C pyruvate converts to a 3-C lactate in order to continue glycolysis to produce ATP Lactic Acid Fermentation

Alcoholic Fermentation 3-C pyruvate is broken down to ethanol, a 2-C compound during alcoholic fermentation CO2 is released Electrons transfer from NADH to the 2-C compound producing ethanol NAD+ is recycled to continue glycolysis Alcoholic Fermentation

Comparing Anaerobic with Aerobic The total amount of ATP harvested from each glucose molecule depends on oxygen Cells use energy more efficiently when oxygen is present In stage 1: glucose is broken down by glycolysis (anaerobic) and gains 2 ATP In Stage 2: pyruvate passes thru aerobic respiration or (anaerobic) fermentation In fermentation, small amounts of ATP is produced In respiration, up to 2 ATP are produced by Krebs cycle and 34 through electron transport chains Comparing Anaerobic with Aerobic