Chapter 5

*Photosynthesis and Cellular Respiration

*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

* Building molecules that store energy

*Metabolism either uses energy to build molecules or break down 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

*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

*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

*PhotosynthesisSection 5-2

* Photosynthetic Organisms Use Sunlight’s Energy

*Plants, algae and some bacteria capture 1% of the energy in the sunlight that reaches Earth

*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+ 6O2Light

*Light Reactions

*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

* 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

*Production of Oxygen

*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 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

*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

*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

*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

*Glycolysis

*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

*Stage 2: More ATP is made

*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

*Krebs Cycle

*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

*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

*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

*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

*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

*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