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Honors Biology Notes:
Unit 4 BioEnergy
Metabolism and Energy
• chemistry of life is organized into
metabolic pathways
– metabolism: collection of reactions that occur
in organisms; facilitated by enzymes
– two general categories of reactions:
• catabolic: breakdown of macromolecules into
monomers, releasing energy from the broken
• anabolic: building macromolecules from
monomers, using energy to form bonds
• ATP (adenosine triphosphate) powers cellular
– ATP loses one phosphate, producing ADP (adenosine
diphosphate), a phosphate group, and free energy
– Any time bonds are broken; energy is released
– Any time chemical bonds are made, energy is used
A Biochemical Pathway
• Chemical elements essential to life are
recycled in the cells by photosynthesis and
cellular respiration (elements are recycled)
• energy is not recycled
• General
– plants and other autotrophs are producers
• autotroph: organisms that can make their own food
rather than ingesting or absorbing it
• photoautotroph: organisms that use the energy of
the sun to produce carbohydrates from CO2 and
• producer: organisms that are the ultimate source of
organic compounds for heterotrophic organisms
– heterotrophs must ingest or absorb energy from
other organisms
The Action Spectrum for
• Look for the following information in the
• In 1883, Thomas Engelmann devised an
experiment to learn __________________
in carrying out photosynthesis.
• What organism was used?
• The wavelengths that work best for
photosynthesis are ___
• chloroplasts are the site of photosynthesis in
plants and other photoautotrophs
– all green parts of a plant have chloroplasts
– leaves are the major sites of photosynthesis in most
• about ½ million chloroplasts per square millimeter
of leaf surface
– green color comes from the pigment chlorophyll
• chlorophyll absorbs light energy
Source of Reactants
• chloroplasts are found in tissue in the
interior of leaves called mesophyll
• carbon dioxide enters leaf (and oxygen
exits) by pores in the leaf called stomata
• water is absorbed by the roots and moved
through the plant by veins
• Overall (simplified) chemical equation
• 6CO2 + 6H2O + light energy  C6H12O6 + 6O2
• Carbon dioxide plus water, in the presence of
sunlight, produces sugar (glucose,
carbohydrate) and oxygen
Nova Photosynthesis Overview
• MEMORIZE the following diagram!
• For these rather vague diagrams, focus
• What goes in
• What comes out
• Where the process occurs
2 Major Stages of Photosynthesis
• light reactions or photochemical reaction
• the Calvin Cycle or the thermochemical
reaction or dark reactions
Light Reactions General
• require the energy of the sun
– occurs in the thylakoid membrane of the
– rely on two clusters of pigments with different
types of chlorophyll and other pigments
• photosystems I and II (absorb different
wavelengths of light)
Light Reactions of Photosynthesis
Calvin Cycle General
• does not directly require light energy
– occur for only a brief time after sunset,
because the reactions quickly use up the ATP
and NADH produced in the light reactions
• occurs in the stroma of the chloroplast
• 3 “turns” of the Calvin Cycle are required
to produce one molecule of glucose
Calvin Cycle Animations
Factors Affecting Photosynthesis
• Light intensity
– ordinary daily sunlight yields maximum rate of photosynthesis
• CO2
– more CO2 equals a higher rate only if enough light
• 6x CO2 can yield 5x rate of photosynthesis
– atmospheric CO2 has increased 10% in last 200 years; not
enough to cause great increase in photosynthesis
– greenhouse effect- greater impact on length of growing season
than rate of photosynthesis
• H2O- if plant goes dry stomata close, no CO2 taken in.
• Temperature
– primarily via enzyme activity- as temperature increases, rate
goes up (until proteins denature)
– low temperatures (> freezing) influence both enzyme activity and
“fluidity” of chloroplast membrane
– most plants have enzyme systems and membrane structure that
are well matched to the temperature range they experience
Cellular Respiration
• Breakdown of glucose (or other organic
fuel) to produce energy
• Occurs in ALL living organisms (even
those that photosynthesize)
– overall (simplified reaction)
C6H12O6+ 6O2  6H2O + 6CO2 + ATP
MEMORIZE the following diagram!
3 phases
• Glycolysis
• Kreb’s Cycle
• Electron Transport Chain and oxidative
• Glycolysis: glucose, C6H12O6 is broken
– occurs in the cytoplasm of the cell
– products: 2 molecules of pyruvate, C3H3O3
and 2 molecules of ATP and 2 molecules of
Krebs Cycle
• Krebs Cycle: pyruvate is converted to CO2
– occurs in the mitochondrial matrix
– transfers electrons from NAD+ to NADH
– produces: 1ATP and CO2
– aerobic (oxygen requiring) process
Electron Transport chain
• Electron Transport chain and oxidative
– occurs on the cristae of the mitochondria
– produces up to 35 ATP
– aerobic process
• a maximum of 38 molecules ATP are
produced per molecule of glucose during
cellular respiration
• occurs instead of Krebs Cycle and
Electron Transport chain when oxygen is
not present
– anaerobic : (“an” means not or without)
absence of oxygen
• Two types
– Alcoholic fermentation
– Lactic acid fermentation
• MEMORIZE the following diagram!
Alcoholic Fermentation
• pyruvate from glycolysis is converted to
ethanol and 2 ATP
– occurs in yeast (a fungus) and some bacteria
– used to produce breads and alcoholic
Lactic Acid Fermentation
• pyruvate from glycolysis is converted into
lactic acid and 2 ATP
– occurs in some fungi, bacteria, and animal muscle
cells that have depleted stores of oxygen
– used to produce yogurt and cheeses
– in humans, cells must switch from cellular respiration
to lactic acid fermentation when no oxygen is present
• causes muscle fatigue and pain
• lactic acid is gradually carried to liver by blood, and
broken down into pyruvate in the liver