Chapter 6 – Biology Reading Guide – pp. 90 – 93
Living organisms need energy to do work – move
things, break things down, build new things……some
processes release energy that can be harnessed to do
other things. ATP is small high energy molecule that all
living organisms as energy currency.
Light energy
Chloroplast
CO2
Chem Energy –
glucose (C6H12O6)
H2O
O2
mitochondria
ATP
Heat energy
This diagram illustrates two basic energy changes that
occur among living systems to sustain life on Earth.
Label both processes where appropriate and identify
the types of energy that are going into and out of the
system.
In the top process, chloroplasts absorb light energy and
convert it to chemical energy in photosynthesis. The
raw materials for this are carbon dioxide and water,
using light energy, bonds are rearranged to make
glucose. Then glucose with the help of oxygen can be
broken back down to carbon dioxide and water to
release energy that may be converted to ATP and heat.
As fairly complex animals, we need as much energy as possible to run our various metabolic reactions.
Some organisms can exist without oxygen (can you think of one that is commonly used to ferment wine
and beer?). We need oxygen as it maximizes the amount of energy we can get from every molecule of
sugar we break down. A by-product of the process is carbon dioxide. In the space below explain how
breathing through your lungs and the flow of blood through your arteries and veins relates to the cells
ability to get energy from food.
Breathing through your lungs brings oxygen to your blood to muscles and brain. Oxygen moves from
your blood to the cell. In the cell, oxygen is taken into the mitochondria where it is used to fully break
down and extract energy from glucose. Using oxygen gives a much greater yield of energy from each
glucose.
Label the diagram above to show how glucose is “burned” by oxygen to produce water, carbon dioxide,
and a usable form of energy for us.
C6H12O6 + 6 O2  6CO2 + 6 H2O + ATP
What do we need ATP for?? Provide examples where you use ATP on a given day.
Everything that needs energy!
We often talk about the carbon bonds storing and providing the chemical energy that is then transferred
to ATP. That is an important bond but more important are the electrons associated with the hydrogen
bonds where hydrogen is bonded to carbon or oxygen in a glucose molecules. The transfer of electrons
from one molecule to another is called a ___Redox______ reaction. The element that loses the
electrons undergoes ___oxidation_____. While the element that gains the electrons undergoes
__reduction______. You cannot have one without the other. As electrons are passed from one atom to
another, a little bit of energy is released. If a series of electron transfers is connected to a process to
make ATP then you have a way to transfer that energy to something we can use in our bodies. This is
essentially what happens both in photosynthesis and cellular respiration.
Define electron-transport chain: The movement of electrons from one carrier to another which
generates some energy – like a battery or a waterfall.
There are 3 main stages to cellular respiration. You need to have a general understanding of what
happens at each stage and where that stage occurs. Briefly outline the location and summary of each
stage below:
Two things have to happen to get energy from an organic molecule – One) the carbon skeleton is
dismantled and ultimately the end product is CO2 and H2O. Two) the electrons that were in the original
carbon skeleton are trapped and used to generate the energy to make ATP.
1. Glycolysis – Initiation of breaking down glucose but it only yields 2 ATP/glucose so if there is no
oxygen and the process stops here, the total yield is 2 ATP. Occurs in the cytoplasm so it also
occurs in bacteria!!! Everything else occurs in the mitochondria.
2. Citric Acid Cycle – Where the glucose carbon skeleton gets fully dismantled to CO2 and the high
energy electrons are picked up to be used in electron transport. In mitochondria.
3. Oxidative Phosphorylation – Final most valuable step where the high electrons from the
breakdown of glucose are used to run the production of ATP – another 34-36 ATP/ glucose can
be made for a total yield of 36 – 38 ATP/glucose. MUST have oxygen to occur. In Mitochondria.
Where is most of the ATP generated?
In the last step of oxidative phosphorylation – in the mitochondria.
What is chemiosmosis?
Making an electron gradient like a battery – all the negative electrons on one side and positive charges
on the other side of a membrane and then letting battery run to make ATP.
Label the diagram:
Summary – big ideas – cellular respiration is the aerobic process where food molecules (like glucose) are
broken ultimately to carbon dioxide and water to release chemical energy that is then trapped in the
chemical energy of ATP. ATP’s energy can be used to do work all over the body.
If there is no oxygen (like in your muscles when you are running a marathon) – the cells can get a little
bit of ATP from each glucose by fermentation – in our muscles the product is lactic acid. In other
organisms the product may be alcohol as in yeast.
Chapter 7 – Read pp. 108-111
Write out the chemical equation for photosynthesis –
6CO2 + 6 H2O C6H12O6 + 6 O2
The energy to drive this process is light energy.
How does it compare to the equation for cellular respiration?
C6H12O6 + 6 O2  6CO2 + 6 H2O + ATP
Why does it make sense that the two reactions are nearly opposite except for the type of energy that
goes in and comes out?
Summarize the process of photosynthesis by using the above diagram:
Just like electrons give off light in a fluorescent light bulb, electrons are used to mediate the energy
transfers in photosynthesis and cellular respiration.
Pigments are special molecules (i.e. chlorophyll) that have “loose” electrons – when light strikes a
pigment, their electrons get energized. These energized electrons are then used to fuel (via ATP) the
building of a carbon molecule like sugar from CO2 and H2O.
Flow of energy (Chloroplasts) in photosynthesis is:
Light electronsATP chemical bonds of organic molecule
Flow of energy (Glycolysis and Mitochondria) in cellular respiration is:
Chemical bonds (sugar) electrons chemical bonds of ATP
The above process is called fermentation in the absence of oxygen –
Purpose of photosynthesis is to trap the only major source of energy coming into Earth (light) and
convert it to chemical energy which is accessible to living organisms.
Purpose of fermentation or cellular respiration is to take the initial form of chemical energy trapped in
photosynthesis and convert it to a more cell-friendly form in ATP.