Chapter 8 Notes
I.
Energy and Life
1. Energy is the ability to do work… nearly every activity depends on some type of
energy
2. Energy is needed for living things and they get it from food
A. Autotrophs & Heterotrophs
1. Autotrophs make own food
a. Plants and some other organisms use light energy from the sun to
produce food in a process called photosynthesis
b. Others use chemical energy rather than the sun in a process called
chemosynthesis (but we won’t be talking about them)
2. Heterotrophs do not make own food
a. Depend on other organisms for food
b. Some eat plants
c. Some eat other animals (that eat plants)
d. Some obtain food by decomposing other organisms (like most fungi)
e. Goal is to get and release the energy in sugars and other compounds
B. Chemical Energy and ATP
1. One of the main chemicals living things use to store energy is ATP
a. It consists of Adenine (a nucleobase), Ribose (a 5-carbon sugar) and
three Phosphate groups
2. Storing Energy
a. ATP looks a lot like a similar compound called ADP, which has only two
phosphate groups
b. Living things can store small amounts of energy by converting ADP to
ATP (which they do by adding a phosphate group to ADP when they
have energy to spare
c. ATP then acts as a fully charged battery, ready to be used
3. Releasing Energy
a. When the chemical bond between the 2nd and 3rd phosphate groups is
broken, a large amount of energy is released
b. So the energy from ATP can be used to power a variety of cellular
activities
(i). Energy from ATP powers important events in the cell, including
the synthesis of proteins and nucleic acids and responses to
chemical signals at the cell surface. The energy from ATP can
even be used to produce light. In fact, the blink of a firefly on a
summer night comes from an enzyme powered by ATP
C. Using Biochemical Energy
1. One way cells use the energy provided by ATP is to carry out active transport.
a. Many cell membranes contain a sodium-potassium pump, a membrane
protein that pumps sodium ion (Na+) out of the cell and potassium ions
(K+) into it. ATP provides the energy that keeps this pump working,
maintaining a carefully regulated balance of ions on both sides of the
cell membrane.
b. ATP produces movement, too, providing the energy for motor proteins
that move organelles throughout the cells.
2. But this energy is very short lived – only a few seconds worth!
a. In fact, most cells have only a small amount of ATP, enough to last them
for a few seconds of activity.
b. Even though ATP is a great molecule for transferring energy, it is not a
good one for storing large amounts of energy over the long term.
(i). A single molecule of the sugar glucose stores more than 90
times the chemical energy of a molecule of ATP.
(ii). Therefore, it is more efficient for cells to keep only a small
supply of ATP on hand.
c. Cells can regenerate ATP from ADP as needed by using the energy in
foods like glucose
Q. Which of the following parts of part of an ADP molecule? ***on test***
Q. Which structures make up an ATP molecule? ***on test***
Q. Between which parts of the molecule must the bonds be broken to form an ADP molecule? ***on
test***
II.
Photosynthesis
A. Investigating Photosynthesis
1. Jan Van Helmont –
a. Devised experiment to find out if plants grew by taking material out of
the soil.
b. Determined the mass of a pot of dry soil and a small seedling. Then he
planted the seedling in the pot of soil. He watered it regularly.
c. At the end of five years, the seedling, which by then had grown into a
small tree, had gained about 75 kg. The mass of the soil was
unchanged. He concluded that most of the gain in the mass had come
from water, because that was the only thing that he had added
2. Joseph Priestley
a. Devised an experiment to see if air had anything to do with the growth
of plants
b. Put a candle under a bell jar and lit it – candle slowly died out
c. Living things like mice, also could not live without whatever was in the
air that kept the candle lit
d. But a sprig of mint placed in the jar with the candle did not die and after
a few days, he was able to relight the candle
e. So the plant had not needed whatever the candle/mouse did and was
able to produce it
3. Jan Ingenhousz
a. Showed the effect Priestly noticed would only occur in the presence of
light
4. Their work led to other scientists discovering that in the presence of light, plants
transform carbon dioxide and water into carbohydrates and oxygen
B. The Photosynthesis equation
1. It is a series of reactions that uses light energy from the sun to convert water
and CO2 into sugars and oxygen
a. Uses sunlight to convert H2O and CO2 into high energy sugars and O2
b. Plants convert sugar into complex carbohydrates -- starches
2. Usually 6-carbon sugars are produced from photosynthesis
3. 6CO2 + 6H2O C6H12O6 + 6O2
4. Carbon dioxide and water combine in the presence of light to produce a sixcarbon sugar and oxygen
5. Six molecules of carbon dioxide and six molecules of water combine in the
presence of light energy to yield one molecule of glucose and six molecules of
oxygen
6. Plants obtain carbon dioxide from the air or water in which they grow
7. Photosynthesis also requires light and chlorophyll
C. Light and Pigments
1. Plants capture energy from sunlight in light-absorbing pigment molecules
2. Leaves of a plant appear to be green because the leaves absorb wavelengths
other than green and reflect green light
3. The principal pigment in plants is chlorophyll though there are two types
a. Chlorophyll a – absorbs light in blue-violet and red regions of the visible
spectrum
b. Chlorophyll b – absorbs light in blue and red regions of the visible
spectrum
c. Chlorophyll does not absorb light in the green region of the visible
spectrum; that light is reflected back by the leaves therefore plants
appear green
d. In the graph notice how chlorophyll a absorbs light mostly in the blueviolet and red regions of the visible spectrum whereas chlorophyll b
absorbs light in the blue and red regions of the visible spectrum.
4. There are also other pigments in plants (often red and orange) that absorb light
in other regions of the visible spectrum
a. Accessory pigments – transfers the energy to chlorophyll a and initiates
light reactions which produces ATP and NADPH. Chlorophyll b reflects
III.
yellow-green and carotenoids are yellow and orange pigments and gives
fall coloration.
(i). This is why some plants appear to “change colors” in the fall –
the chlorophyll production is decreased and stops as
temperatures and sunlight changes so the chloroplasts “die”
(ii). What you then see are the other pigments in the leaves (light,
temperature and water will also affect how “brilliant” these
pigments appear)
5. How chloroplasts “absorb” light
a. An electron orbiting close to the nucleus has a lower energy than one
orbiting farther from the nucleus. An electron is boosted from a lowerenergy inner orbit to a higher-energy outer orbit when the atom
absorbs a photon.
b. The only photons absorbed are those whose energy is exactly equal to
the energy difference between the ground state and the excited state,
and this energy difference varies from one kind of atom or molecule to
another. Thus, a particular compound absorbs only photons
corresponding to specific wavelengths, which is why each pigment has a
unique absorption spectrum
The Reactions of Photosynthesis
A. Inside a Chloroplast
1. Thylakoid are sac-like membranes in the chloroplast that are photosynthetic
membranes
2. Thylakoids are arranged in stacks called grana (granum)
3. Proteins in the thylakoid membrane organize the pigments into clusters called
photosystems
a. Photosystems collect light
4. Photosynthesis occurs in two parts
a. Light dependent reactions
b. Light-independent reactions AKA The Calvin Cycle
(i). The Calvin Cycle is the synthesis part of P/S. Doesn’t need
sunlight but needs the products of light rx’s, only occurs during
the day
B. Electron Carriers
1. Sunlight excites the electrons in chlorophyll so they gain energy and are called
“high energy electrons”
2. High energy electrons require a special carrier molecule
3. The carrier molecule can accept two high energy electrons and transfer those
electrons and MOST of their energy to another molecule
4. The process of transferring these high energy electrons (and their energy) is
called Electron Transport and the carriers are known as the Electron Transport
Chain
5. A common carrier molecule is NADP+ (nicotinamide adenine dinucleotide
phosphate – no, you don’t need to memorize the full name, just the acronym)
a. NADP+ holds two high energy electrons along with a H+ ion
b. When the H+ ion is added, this converts NADP+ into NADPH
c. This conversion “traps” energy from the sun into chemical energy that
can be used by plants
d. NADPH then carries those electrons to other areas of the cell
C. Light Dependent Reactions
1. Need light
2. Produce oxygen gas (O2) and converts ADP into ATP and NADP+ into NADPH
3. Process of the reactions:
a. Pigments in Photosystem II absorb light, increasing the energy level of
some electrons. Water is broken into H+ ions and O2 gas so that there is
a continuous supply of H+ ions available to the chlorophyll (since it’s lost
some of its original electrons to the electron transport chain). O2 is
released to the atmosphere and H+ ions are released inside the
thylakoid membrane
b. High energy electrons move through the electron transport chain from
photosystem II to photosystem I. Energy from these electrons is used to
transport H+ ions from the stroma to the inner thylakoid space (which is
against the concentration gradient)
c. Pigments in photosystem I use more energy from light to reenergize the
electrons. These electrons are then picked up by NADP+ along with H+
ions to form the molecule NADPH.
d. As electrons go from the chlorophyll to NADP+, more H+ ions are
pumped across the membrane resulting in a difference in charges across
the membrane (outside negatively charged and inside positively
charged). This difference in charges provides the energy to convert ADP
to ATP
e. H+ can only cross the membrane via a protein called ATP synthase. As
H+ ions pass through this protein, it spins which provides the power for
ADP to be converted into ATP.
D. The Calvin Cycle
1. Needs ATP and NADPH which are produced by the light dependent reactions in
the previous step. Both provide energy but only for a few minutes of time – just
enough so that the plant can build longer lasting, high energy compounds –
sugars!
2. Process of the Calvin Cycle
a. Six CO2 molecules enter the cycle from the atmosphere and combine
with six already existing 5-carbon molecules to form twelve 3-carbon
molecules
(i). CO2 binds to the beginning compound – ribulose biphosphate
(RuBP). This process is called Carbon Fixation. The enzyme used
to catalyze this reaction is the most abundant one found in
plants -- rubisco (aka RuBP carboxylase).
(ii). The product of this reaction, immediately splits in half to form
two molecules of 3-phosphoglycerate.
b. These twelve 3-carbon molecules are then converted into higher energy
forms by the conversion of ATP into ADP and NADPH into NADP+ - they
lose some of their energy to these 3-carbon sugars
c. Two of the twelve 3-carbon sugars are removed from the cycle to
produce sugars, lipids, amino acids, and other compounds needed by
the plant (such as C6H12O6)
(i). Then 3-phosphoglycerate is phosphorylated or converted to
1,3-biphosphoglycerate which is then reduced to
glyceraldehyde 3-phosphate. Glyceraldehyde 3-phosphate
(G3P) is the immediate product of the Calvin cycle. It is a threecarbon sugar.
(ii). Once two G3P molecules are given off, the cell can then convert
them to a molecule of glucose.
d. The remaining ten 3-carbon molecules are converted back into six 5carbon molecules so that the cycle can begin again.
(i). Ribulose biphosphate has to be regenerated so that the cycle
can run again. Remember that six G3P’s are made for three
turns of the cycle. One G3P is the product of
(ii). For every three molecules of CO2 that enters the cycle, one G3P
is produced.
(iii). Nine molecules of ATP and six molecules of NADPH are used for
each G3P produced.
3. One CO2 enters the cycle at a time. However, it takes 3CO2 molecules to
generate one G3P (glyceraldehyde 3-phosphae, the 3-carbon sugar).
4. It takes two G3P’s to make a molecule of sugar
5. The original energy from light is now in the form of glucose
E. Factors Affecting Photosynthesis
1. Shortage of water can slow or stop it
a. Plants in dry areas have a waxy coating or even needles to prevent
water loss
2. Temperature should be between 0°C and 35°C otherwise photosynthetic
enzymes can be damaged
3. Plants have a maximum rate of photosynthesis that varies from species to
species
Know what is inside the thylakoid membrane: electron transport chain, photosystem I and II and ATP
synthase (on test)