Station 1: Energy in Cells
MAIN IDEA: Cells need energy to perform the functions essential to life. This energy is produced by
cellular respiration and stored as the molecule ATP.
Energy for Metabolism:
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All organisms require energy to be able to perform the metabolic processes required for them
to function and reproduce.
This energy is obtained by cellular respiration, a set of metabolic reactions which ultimately
convert biochemical energy from “food” into an energy-carrying molecule called adenosine
triphosphate (ATP).
ATP is considered to be a universal energy carrier, transporting chemical energy within the
cell for use in process such as cell division, cell signaling, thermoregulation, cell movement,
and active transport of substances across a membrane.
Adenosine Triphosphate (ATP)
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ATP consists of 3 parts: a purine base (adenine), a 5-carbon sugar (ribose), and 3 phosphate
groups.
ATP acts as a store of energy within the cell. The bonds between the phosphate groups
contain high-energy electrons, and store a large amount of energy that is released during a
chemical reaction.
The removal of one phosphate group from ATP results in the formation of ADP (adenosine
Diphosphate) and the release of energy.
***NOTE*** The phosphate bonds in ATP are often referred to as being high energy bonds. This can
be misleading. The bonds contain high energy electrons (making the bonds themselves very weak). A
small amount of energy is required to break the bonds, but a large amount of energy is released.
The Mitochondrion
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Cellular respiration and ATP production occur in the mitochondria. A mitochondrion is
bound by a double membrane. The outer membrane covers the organelle and contains it like a
skin. The inner membrane folds over many times and creates layered structures called cristae.
The fluid contained in the mitochondria is called the matrix.
Station 2: Photosynthesis
MAIN IDEAS:
1. Photosynthesis is the process of converting sunlight, carbon dioxide, and water into glucose
and oxygen.
2. Photosynthesis occurs in organelles called chloroplasts, which contain the pigment
chlorophyll, which is in charge of capturing light energy.
3. Photosynthesis consists of two phases, the light dependent phase (LDP) and the light
independent phase (LIP)
Chloroplasts
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One leaf cell can contain up to 100 chloroplasts!
The inner structure is characterized by a system of membrane structures called thylakoids
arranged into stacks called grana.
Pigments on these membranes called chlorophylls capture light energy by absorbing light
of specific wavelengths. Chlorophylls reflect green light, giving leaves their green color.
Chloroplasts are usually aligned so that their broad surface runs parallel to the cell wall to
maximize the surface area available for light absorption.
Stages of Photosynthesis
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Light Dependent Phase (LDP):
o Also known as the “light reactions”.
o Light energy is converted to chemical energy (ATP and NADPH). This phase occurs
in the thylakoid membranes of the chloroplast.
Light Independent Phase (LIP):
o Also known as the “dark reactions”.
o The chemical energy from the LDP is used to synthesize carbohydrate (glucose).
This phase occurs in the stroma of the chloroplast.
Photosynthesis Equation
Station 3: Energy Transfer between Systems
MAIN IDEA: The energy from sunlight is stored as glucose, which powers the production of ATP,
which in turn provides the energy for the various chemical reactions in living systems.
Energy in sunlight is used in photosynthesis to make glucose from CO2 and H2O with release of O2.
Other organisms use the O2 and energy in sugar and release CO2 and H2O. Together, these two
processes are responsible for the majority of life on Earth.
Station 4: Glucose
MAIN IDEA: Glucose is an important precursor molecule used to produce a wide range of other
molecules.
Glucose is Versatile:
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It contains the elements carbon, oxygen, and hydrogen which are all used to build many
important molecules produced by both plants and animals.
Plants make their glucose directly from photosynthesis and use it to build all the molecules
they require.
Animals obtain their glucose by consuming plants or other animals (that consumed plants).
Other molecules such as fatty acids and amino acids are also obtained by animals this way.
Glucose has three main fates:
1. immediate use to produce suable energy (as ATP molecules),
2. storage for later energy production,
3. or for use in building other molecules.
How do scientists know so much about glucose?
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Labeling the carbon atoms in a glucose molecule with isotopes shows how glucose is
incorporated into other molecules.
An isotope is an element (ex: Carbon) whose atoms have a particular number of neutrons in
their nucleus. The different number of neutrons allows the isotopes to be identified by their
density (mass= protons + neutrons).
Some isotopes are radioactive. These radioactive isotopes can be traced using X-ray film or
devices that detect the disintegration of the isotopes.
Isotope experiments with animals:
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Experiments using 13C isotopes to identify the fate of glucose in guinea pigs showed that 25%
of the glucose intake was respired. The rest of the glucose was incorporated into proteins, fats,
and glycogen.
Corals are small sea anemone-like organisms that live in a symbiotic relationship with algae.
The algae transfer sugars to the coral in return for the safe environment provided by the coral.
Experiments with 13C showed that the major molecule being transferred to the coral was
glucose.
Isotope experiments with plants:
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13C
isotopes were used to trace the movement of glucose in plant leaves. It was found that
some glucose is converted to fructose (another monosaccharide with a different shape).
Fructose molecules can be joined together to be stored as fructan in plant vacuoles. Fructose is
also added to glucose to produce sucrose. Sucrose is transported out of the leaf.
Station 5: Cellular Respiration
MAIN IDEA: Cellular respiration is an aerobic process that converts the chemical energy in glucose
into usable energy (in the form of ATP), carbon dioxide, and water.
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Cellular respiration is the process of extracting the energy stored in the chemical bonds in
glucose and storing it in ATP molecules. The process includes many chemical reactions, some
of which produce ATP molecules and some that prepare molecules for further chemical
reactions.
Cellular respiration can be divided into 4 major steps, each with its own set of chemical
reactions. Every step, except the link reaction, produces ATP. The four steps are:
1. Glycolysis
2. Link Reaction (not always considered its own step)
3. Kreb’s Cycle
4. Electron Transport Chain (ETC)
How does Cellular Respiration provide energy?
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A molecule’s energy is contained in the electrons within the molecule’s chemical bonds.
During a chemical reaction, energy (heat) can break the bonds of the reactants.
When the reactants form products, the new bonds within the product will contain electrons
with less energy, making the bond more stable. The difference in energy is usually lost as
heat. However, some of the energy can be captured to do work.
38 ATP molecules can be produced from 1 glucose molecule.
The cell needs small amounts of energy at different times to do different activities.
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Analogy: A mother has a $100 bill (glucose). She takes her three children to the fair and each
wants to do something different. The first wants to play a game, the second wants to buy
cotton candy, and the third wants to ride the ferris wheel. If only the mother had a bunch of
$1 bills (ATP) instead…
Station 6: Fermentation
o All living cells, including the cells in your body and the cells in yeast, need energy for cellular
processes such as pumping molecules into or out of the cell or synthesizing needed molecules.
ATP is a special molecule which provides energy in a form that cells can use for cellular
processes. Each cell in our body and each yeast cell can use the energy stored in organic
molecules in food to make ATP.
o When oxygen is available, cells use aerobic cellular respiration to transfer energy from the
organic molecules in food to ATP. As shown in the figure, aerobic cellular respiration is a
complex process that begins with glycolysis, followed by the Krebs cycle and the electron
transport chain. Aerobic cellular respiration can make up to 38 molecules of ATP per molecule
of glucose. Most of this ATP is produced by the electron transport chain which can only
function if oxygen is available.
o When oxygen is not available, cells can make ATP using glycolysis followed by fermentation.
Glycolysis produces 2 ATP and fermentation restores molecules needed for glycolysis to
continue. Glycolysis followed by fermentation produces much less ATP than aerobic cellular
respiration, but fermentation is very useful when oxygen is not available. In the figure,
fermentation is referred to as anaerobic processes. The "an" in front of aerobic means "not
aerobic". There are two types of anaerobic fermentation:
o Lactic Acid Fermentation (e.g. in muscles when an animal exercises hard)
o Alcohol Fermentation (e.g. in yeast, which can be used to make wine or beer)
Lactic Acid Fermentation:
o Commercially important products of lactic acid fermentation include cheese and yogurt.
o When oxygen is scarce, human muscle cells switch from aerobic respiration to lactic acid
fermentation. Lactate accumulates, but it is gradually carried to the liver where it is converted
back to pyruvate when oxygen becomes available. This is the burning sensation you get when you
exercise too hard!
Alcohol Fermentation:
o Many bacteria and yeast carry out alcohol fermentation under anaerobic conditions.
o This is how wine and beer are made.
o This type of fermentation is used to make bread.