Glenco chapter 8
Energy
The capacity to perform work.
Kinetic energy: The energy that is actually doing the work.
Potential energy: Stored energy with the capacity to do work.
Chemical energy: The potential energy of molecules.
The Laws of Thermodynamics
First Law: Energy can be transformed and transferred, but not created.
Second law: Energy conversion reduces the order in the universe.
Entropy: the amount of disorder in a system.
Obtaining Energy
Autotrophs: Make organic food from inorganic materials (photosynthesis)
Producers
Heterotrophs: Must obtain organic food by absorbtion of ingestion
Consumers
Metabolism
Metabolism: All of the chemical reactions in a cell
Photosynthesis: The process by which plants use light energy to make food
molecules from carbon dioxide and water.
Cellular Respiration: “The aerobic harvesting of energy from food molecules
by cells.”
aerobic: oxygen-containing
anaerobic: oxygen lacking
ATP
Adenosine triphosphate: Almost all energy for cellular work comes from ATP.
Energy coupling: The energy from an exergonic reaction drives an endergonic
reaction
Photosynthesis
The process by which plants use light energy to make food molecules from
carbon dioxide and water.
6 CO2 + 6 H2O
C6H12O6 + 6 O2
Chloroplasts
Site of photosynthesis
Found mainly in the mesophyll
~ ½ million chloroplast per square mm
~ 30-40 chloroplast per mesophyll cell
Chlorophyll: Photosynthetic pigment found in the thylakoid membrane
Where It Happens
Mesophyll: Green tissue in interior of leaf.
Stomata: Small pores on under side of leaf for gas exchange.
Stroma: Thick fluid inside the chloroplast.
Thylakoid: Disklike membranous sacs in the chloroplasts.
Photosynthesis
Occurs in two stages:
The light reactions
The Calvin Cycle
Sun Light
Electromagnetic energy (radiation)
Wavelength: The distance between 2 adjacent waves.
Visible light between 380nm and 750nm
Photosynthetic Pigments
Chlorophyll A: Absorbs mainly blue-violet and red light.
Chlorophyll B: Absorbs mainly blue and orange light.
Carotenoids: Absorbs yellow-orange light.
Chloroplasts absorb light energy and convert it to chemical energy
Photosystems I & II
Photosystem II: Absorbs at 680 nm.
Has a special pair of chlorophyll molecules called P680.
Photosystem I: Absorbs at 700 nm
Has a special pair of chlorophyll molecules called P700.
The Light Reaction
Light energy hits P680 and excites 2 electrons.
The electrons are passed to primary electron acceptor.
Electron passed down electron transport chain providing energy for ATP
synthesis.
Electrons passed to P700.
Light Reaction Part 2
Light at 700 nm excites electrons at P700.
Electrons passed to primary electron acceptor and down the electron transport
chain.
The energy released is used to reduce NAD+ to NADPH
Calvin Cycle
Assembles sugar molecules from CO2 and energy-containing products of the
light reactions. (Carbon fixation)
ATP
NADPH
Alternative Pathways
C4 plants: Fix carbon into a 4 carbon molecule and store it for later use
(corn)
CAM plants: Crassulacean Acid Metabolism, fixes carbon at night (cacti,
pineapple)
Both pathways conserve water
Glucose
A simple sugar
(C6H12O6)
Atoms held together by covalent bonds
Cellular Respiration
The breaking down of glucose to get ATP.
C6H12O6 + 6 O2
6 CO2 + 6 H2O + ATP
Glucose
Oxygen
Carbon
Water
Energy
dioxide
REDOX Reactions
If the substance losses H than it is oxidized.
If the substance gains H than it has been reduced.
C6H12O6 + 6 O2
6 CO2 + 6 H2O + ATP
Metabolic Pathway
Stage 1:
Glycolysis: (exergonic) The breaking down of glucose
Energy-requiring steps (investment)
ATP energy activates glucose and its six-carbon derivatives
Energy-releasing steps (payback)
The products of the first part are split into three-carbon pyruvate molecules
ATP and NADH form
Glycolysis: Net Energy Yield
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Net yield is 2 ATP and 2 NADH
Second Stage Reactions
Preparatory reactions
Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide
NAD+ is reduced
Krebs cycle
The acetyl units are oxidized to carbon dioxide
NAD+ and FAD are reduced
Krebs Cycle
Completes the oxidation of organic fuel
For every glucose molecule:
2 ATP, 6 NADH, 2 FADH2
Stage 3: E.T.C. & Chemiosmosis
Occurs in the mitochondria membrane
Coenzymes deliver electrons to electron transfer chains
Electron transfer sets up H+ ion gradients
Flow of H+ down gradients powers ATP formation
Importance of Oxygen
Electron transport phosphorylation requires the presence of oxygen
Oxygen withdraws spent electrons from the electron transfer chain, then
combines with H+ to form water
Oxygen is the final electron acceptor
Summary of Energy Harvest
(per molecule of glucose)
Glycolysis
2 ATP formed by substrate-level phosphorylation
Krebs cycle and preparatory reactions
2 ATP formed by substrate-level phosphorylation
Electron transport phosphorylation
32 ATP formed
Total of 38 ATP molecules
Fermentation
Alcoholic fermentation: Replenishes NAD+ supply in an anaerobic environment
with ethanol as bi-product.
Lactic acid fermentation: Replenishes NAD+ supply in an anaerobic environment
with lactic acid as a bi-product
Fermentation Pathways
Begin with glycolysis
Do not break glucose down completely to carbon dioxide and water
Yield only the 2 ATP from glycolysis
Steps that follow glycolysis serve only to regenerate NAD+