CHAPTER 4
Section 1
Do we get energy from food?
 Food contains energy but it has to be broken down in order to
be used. That means that energy comes from food but not
directly.
All cells, including plant cells, use chemical energy carried by ATP
ATP and ADP
ATP = adenosine triphosphate
 ATP is a molecule that transfers energy from the breakdown of
food molecules to cell processes.
 ATP has 3 phosphate groups
 The bond of the 3rd phosphate group is unstable and easily
broken
 All cells, including plant cells, use chemical energy carried by
ATP
 Analogy = just as a wallet carries money, ATP carries chemical
energy
 wallet : money :: ATP : energy
 Energy carried by ATP is released when a phosphate group is
removed from the molecule.
 When the phosphate from ATP is removed, energy is released
and ATP becomes ADP
ADP = adenosine diphosphate
 ADP is a lower energy molecule that can be converted in to ATP
by the addition of a phosphate group.
 If ATP is a wallet filled with money then ADP is a nearly empty
wallet.
 The breakdown of ATP to ADP and the production of ATP from ADP
can be represented by a cycle.
 Adding a phosphate group to ADP to make ATP is not a simple
process.
Foods that you eat do not contain ATP you can use. A process must
take place
 Food must be digested
 Digestion breaks food down into smaller molecules that can be
used to make ATP
 Different foods provide different amounts of ATP.
Different foods have different calories, which are measures of energy.
 A food calorie is the amount of heat energy required to raise
the temperature of one kilogram of water by 1 degree Celsius.
 When a mole of ATP is converted to ADP in a cell, about 7.3
calories (7.3 kilocalories) or energy are released.
The number of ATP molecules produced depends on the type of molecule
that is broken down.
 Carbohydrates are not stored in large amounts in your body,
but they are the molecules most commonly broken down to
make ATP
o The breakdown of the simple sugar glucose makes 36
molecules of ATP
o Carbs do not provide the largest amount of ATP
 Lipids store the most energy
o Fats store about 80% of the energy in your body
o Typical triglyceride can be broken down to make about
146 molecules of ATP
 Proteins store about the same amount of energy as
carbohydrates
o They are less likely to be broken down to make ATP
because they are needed more to make proteins than
energy
Plant cells also need ATP but they do not eat food so the must make their
own food.
 Plants make their own food through photosynthesis
 Plants absorb energy from sunlight and make sugars
 Plant cells break down the sugars made through the process to
produce ATP just as animal cells do
Most organism rely directly or indirectly on sunlight and photosynthesis
as their source of chemical energy. Some organisms do not need or get
sunlight but they still need ATP.
 In the bottom of the ocean, organisms live in very hot water near
cracks called vents which release chemicals such as sulfides that can
serve as an energy source.
 Chemosynthesis a process by which some organisms use chemical
energy instead of light energy to make energy storing carbon based
molecules
 The process of making ATP for these organisms is similar to plants
but the raw materials is what is different.
Section 2 and 3
Producers are organisms that produce the source of chemical energy for
themselves.
 Plants, some bacteria and protists are producers that are the main
source of energy for most organisms on earth.
 Animals that eat only plants obtain their chemical energy directly
form plants
o Wolf eats a rabbit, rabbit eats plants, plants made energy from
sun
Photosynthesis is a process that captures energy from sunlight to make
sugars that store chemical energy.
 Directly or indirectly the energy for almost all organisms begins with
the sunlight
 Sunlight has several types of radiant energy such as ultraviolet
radiation, microwaves, and visible light.
 Visible light appears white but is made up of several colors or
wavelengths of light.
Chlorophyll is a molecule in chloroplasts that absorbs some of the energy
in visible light.
Plants have 2 types of chlorophyll that work together and absorb mostly
red and blue wavelengths of visible light, but neither absorb green.
1. Chlorophyll a
2. Chlorophyll b
 The color of plants comes from the reflection of lights green
wavelengths by chlorophyll
 Color of leaves are made from the same
o Green, orange, yellow, purple, and red
o Brown is not a color of a living leaf, it means a dead leaf
Photosynthesis in plants occurs in chloroplasts.
 Chloroplasts are in leaf cells that are specialized for photosynthesis
 2 parts of a chloroplasts needed for photosynthesis
1. Grana – stacks of coin shaped membrane enclosed
compartments called thylakoids.
 Thylakoids contain chlorophyll (light absorbing molecules)
and proteins
2. Stroma fluid that surrounds the grana inside the chloroplast
Importance of photosynthesis
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Provides the base for almost all food chains
May have been the initial means for evolution
Waste from photosynthesis is oxygen
Leads to increased biodiversity
Stages of Photosynthesis
The whole process doesn't happen all at one time. The process of
photosynthesis is divided into two main parts.
1.The first part is called the light dependent reaction.
o This reaction happens when the light energy is captured from
sunlight and pushed into a chemical called ATP.
o These reactions take place within and across the membranes of
the thylakoids.
o Water and sunlight is needed for this stage
o Used to be called light reactions
o Light dependent reactions are the photo part of photosynthesis
o Main function is to capture light and transfer energy
o This energy is a carrier, not the energy for cellular processes
o The energy carriers are ATP and NADPH
Steps of light dependent reactions
1. Energy is absorbed from sunlight and water molecules are broken
down
2. Hydrogen ions are transported across the thylakoid membrane
3. Energy is absorbed from the sunlight
4. NADPH is produced from the hydrogen (step 2) being added to
NADP
5. Hydrogen ion diffusion across the thylakoid membrane
6. ATP is produced from ADP
2.The second part of the process is called light independent reaction
o This reaction happens when the ATP is used to make glucose.
o These reactions take place in the stroma.
o Carbon dioxide is needed for this stage of photosynthesis.
o This is the synthesis part of photosynthesis
o Known as the Calvin Cycle
o Light independent reactions occur whether there is light
present or not because of where they take place.
o They only depend on the presence of the energy carriers ATP
and NADPH made during the light dependent reactions.
o The purpose of the light independent reactions is to take the
energy from ATP and energized electrons and hydrogen ions
from NADPH and add them to CO2 to make glucose or sugar.
Steps of light independent reactions
1. (Grab) A five-carbon carbon catcher catches one molecule of carbon
dioxide and forms a six-carbon molecule.
2. (Split): the enzyme RuBisCO (with the energy of ATP and NADPH
molecules) breaks the six-carbon molecule into two equal parts.
3. (Leave): A trio of three carbons leave and become sugar. The other
trio moves on to the next step.
4. (Switch): Using ATP and NADPH, the three carbon molecule is
changed into a five carbon molecule.
5. The cycle starts over again.
Section 4 and 5
Plants use photosynthesis to make their own food. Animals eat organisms
for food. Food is not a direct source of energy, instead eukaryotes break
down molecules from food to produce ATP.
Cellular respiration releases chemical energy from sugars and other
carbon based molecules to make ATP when oxygen is present.
 Cellular respiration
o is aerobic
o Aerobic means that it needs oxygen to take place
 takes place in the mitochondria
o mitochondria are called the powerhouse of a cell because
they make most of a cells ATP
Mitochondria cannot directly make ATP from food. Foods need to be
broken down into smaller molecules such as glucose. The glucose is then
broken down.
Steps of Cellular Respiration
1. Glycolysis
 literally means split the sweet
 process that splits glucose into 3 carbon molecules and makes 2
molecules of ATP along with pyruvates
 takes place in the cytoplasm
 is anaerobic
 anaerobic means that it does not need oxygen to take place
Main stages of cellular respiration
2. Krebs Cycle
 Also known as the citric acid cycle
 Process that takes the 3 carbon molecules made in glycolysis
are broken down and 2 molecules of ATP are made
 Takes place in the mitochondria
 Is not considered to be aerobic or anaerobic but could not
happen without the presence of oxygen
 Carbon dioxide is released
3. Electron Transport Chain
 Process that transfers energy down a chain of proteins and 32
molecules of ATP is made along with water and heat
 Takes place in the mitochondria
 Aerobic
 Proteins used here are supplied by NADH and FADH2
Products of all the steps and stages of cellular respiration are
 Carbon dioxide from krebs cycle
 Water from the electron transport chain
 36-38 ATP molecules for every glucose molecule
o 2 from glycolysis
o 2 from krebs cycle
o 34 from electron transport chain
Photosynthesis
Organelles for process Chloroplast
Reactants
Carbon dioxide and
water
Electron transport
Proteins within
chain
thylakoid membrane
Cycle of chemical
reactions
Calvin cycle in stroma
of chloroplasts builds
sugar molecules
Products
Sugars (glucose) and
oxygen
Cellular Respiration
mitochondria
Sugars (glucose) and
oxygen
Proteins within inner
mitochondrial
membrane
Krebs cycle in matrix
of mitochondria
breaks down carbon
based molecules
Carbon dioxide and
water
Section 6
When glycolysis has taken place depending on the presence or lack of
oxygen determines what will happen next.
 If oxygen is present then cellular respiration will begin
 If no oxygen is present then fermentation will take place.
Fermentation does not make ATP, but allows glycolysis to continue.
There are 2 types of fermentation that will take place if there is no
oxygen available for cellular respiration to take place.
1. Lactic Acid Fermentation
2. Alcoholic Fermentation
Lactic Acid Fermentation
 They pyruvic acid from glycolysis is reduced to lactic acid by NADH
 Commonly occurs in muscle cells when they don’t receive the
oxygen they need to perform aerobic respiration
o Occurs when we work them to hard
o The muscle cells still need energy so they perform glycolysis but
cannot perform aerobic respiration
o Muscle cramps will start until oxygen gets to the muscle cells
Alcoholic Fermentation
 They pyruvic acid from glycolysis is reduced to ethyl alcohol
 Commonly occurs in yeast
 Carbon dioxide and alcohol are the by-products of this
fermentation.
o Alcohol remains in the liquid which is great for making an
alcoholic beverage but not for the yeast cells, as the yeast dies
when the alcohol exceeds its tolerance level