High School Biology
Chapter 9 Lecture Notes
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ENERGY IN A CELL
All living things require and use energy.
Examples:
a. active transport of substances across the plasma membrane
b. mitosis (cell division)
c. movement of flagella and cilia
d. production of proteins
e. muscle contraction during movement
f. nerve cells sending signals (action potentials) by the active transport of sodiumpotassium gates in the nerve cell plasma membranes.
b. bioluminescence of fireflies
Adenosine triphosphate is the rechargeable energy storage molecule of the body.
1. It is composed of
a. adenosine—one of the four nitrogenous bases in DNA [A, T, C, G]
(It is composed of a six sided and a five sided carbon ring)
b. ribose sugar—a five carbon cyclic sugar
c. three phosphate groups [–O–PO3– –]
2. Since each of the three phosphate groups had a double negative charge there is a great
deal of energy stored in the bond holding the third phosphate to the second.
3. Energy release:
ATP → ADP + inorganic phosphate group + energy
ADP → AMP + inorganic phosphate group + less energy
4. Cellular respiration provides the energy to recharge ADP → ATP.
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
In Photosynthesis Autotrophs Use the Energy of Sunlight to Make Carbohydrates
1. Photoautotrophs “self feeders” make their own food from the energy of sunlight.
Plants, algae, some Protists (ex. Euglena), some bacteria [Prokaryotes]
Chemoautotrophs—make their own food from the energy of chemical bonds
Certain bacteria—break down hydrogen sulfide
2. Other organisms must eat the food plants produce
Heterotrophs (animals) must eat food
Saphrotrophs (fungi) decompose food outside their bodies and absorb nutrients
3. The basic formula for photosynthesis is
sunlight + 6CO2 + 6H2O → C6H12O6 + 6O2
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4. C. B. van Niel used radioactive isotopes to work out which reactant goes to which
product.
a. There is oxygen atoms in all four compounds in the equation—so which
oxygen goes where.
b. Water is split
i. the oxygen of the water is released into the air for animals to breathe.
ii. the hydrogen of the water joins carbon dioxide to become sugar.
5. The sugar made during photosynthesis is glucose
a. Plants transport sucrose around in the phloem tubes from the leaves to the nonphotosynthesizing trunk & roots.
b. Plants store fructose in fruit
c. Human blood sugar is glucose
Diabetes—is a high blood sugar level (glucose)
6. There are two phases to photosynthesis
a. light-dependant reactions (the light phase)
b. light-independent reactions (dark phase, Calvin cycle)
I. The Light-dependant Reactions
1. Take place in the membranes of the thylakoid discs within the chloroplasts.
2. Chemicals called pigments absorb specific wavelengths of light.
a. Chlorophyll a and chlorophyll b absorb most of the wavelengths of light
i. they peak in the red and blue areas of the spectrum
ii. they reflect green light so leaves look green
b. Other pigments like carotenoids absorb light and give the energy to the
chlorophyll.
In the fall when the chlorophyll breaks down the other pigments turn the
fall leaves beautiful browns, yellows, oranges and reds.
Tannins—brown
Xanthophylls—yellow
Carotenoids—orange
Anthocyanin—red & purple
3. The energy of the absorbed light highly energizes or excites electrons that are
passed from the chlorophyll to an electron transport chain.
An electron transport chain is a series of proteins embedded in the thylakoid
membrane which allow the energized electrons to give off their energy little by
little as they are passed down the chain—instead of all at once in a useless flash.
4. The energy released by the first electron transport chain is used to
a. Phosphorylate ADP → ATP
b. Pump H+ ions into the center of the thylakoid disk creating a proton motive
force (chemical gradient or battery).
5. A second set of pigments absorb sunlight and use the energy to split water into 2 H+
ions, 2 electrons and oxygen (O2).
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2H2O → 4H+ + O2 + 4e–
a. The oxygen is released out of the stoma holes in the bottom of the leaf and
enters the atmosphere for animals to breathe and use in cellular respiration.
b. The electrons are given to the chlorophyll to replace the electrons the
chlorophyll passed on to the electron transport chain in a process called
photolysis.
b. The hydrogen ions join electrons to reduce NADP+ (nicotinamide adenine
dinucleotide phosphate)
6. The electrons then go to the second electron transport chain where the energy they
release is used to join the hydrogen ions from the water and
a. Transform a chemical electron carrier molecule from NADP+ → NADPH
(an electron and a hydrogen ion are added to the NADP)
7. The ATP (an energy source) and NADPH (chemical reducing power) are shipped
from the thylakoid membrane to the stroma of the chloroplast where they will
power the light-independent reactions which generate sugar from carbon dioxide.
II. Light-Independent Reactions (Calvin cycle, dark reactions)
1. Takes place in the stroma of the chloroplasts.
2. Does not require light—therefore is dark reactions or light-independent reactions.
Uses the energy of ATP
3. Involves carbon fixation because it joins carbon dioxide molecules (CO2) to other
organic molecules to make carbohydrates (glucose sugar).
4. This is called the Calvin cycle because it was worked out by Melvin Calvin.
5. It is a cycle because the last molecule formed in the cycle joins the next carbon
dioxide entering the cycle and is regenerated in the last step to join a new carbon
dioxide molecule the next time around.
Steps to the Calvin Cycle
1. Carbon fixation—one carbon from a CO2 molecule enters the Calvin cycle by
joining with the end product of the last turn of the cycle a five carbon molecule
RuBP (ribulose biphosphate)
2. PGA formation—the six carbon sugar from step 1 is an unstable intermediate
and breaks down into two 3 carbon molecules of PGA (phosphoglyceric acid)
3. PGAL formation—in a series of reactions using the ATP (energy source) and
NADPH (chemical reducing power) from the light-dependant reactions PGA is
converted to PGAL (phosphoglyceraldehyde) another 3 carbon molecule.
4. Glucose Sugar formation—one PGAL exits the Calvin cycle each turn of the
cycle and two of them are built up in further reactions into glucose sugar.
5. RuBP replenishing—other PGAL molecules in a series of reactions (involving
ATP as the energy source) are built up into RuBP so the cycle can start over and
another carbon dioxide can be fixed into the cycle.
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