Photosynthesis
 The root “photo” means “light” and the root “synthesis” means “to make”
 In photosynthesis, the plant uses sunlight and other materials to make glucose.
 Photosynthesis occurs in the chloroplasts of plant cells.
Structure of chloroplasts:
Chlorophyll is a pigment that captures and absorbs sunlight. It can absorb all colors except for the color green.
H2O + CO2 + sunlight → C6H12O6 + O2
water
Carbon
dioxide
energy
glucose
oxygen
Photosynthesis has two steps or reactions.
 1st – light reaction, also called the light dependent reaction.
o In the light dependent reaction, chlorophyll absorbs the sunlight. The sunlight is converted into a
usable, chemical energy through the electron transport chain and electron carriers. Electron carriers
seen in photosynthesis are ATP and NADPH. The energy created is used to split a water molecule.
o Occurs in the thylakoid of the chloroplast.
 2nd – dark reaction, also called the light independent reaction or Calvin cycle.
o In the dark reaction, the energy that was created in the light reaction is used to break down CO2 so
carbon, hydrogen, and oxygen can come together to form glucose.
o Occurs in the stroma of the chloroplast.
Cellular Respiration
 Process where glucose (sugar) is broken down to create energy in the form of ATP.
 ATP is a usable form of energy and is the cell’s main energy molecule. ATP stands for adenosine triphosphate
(the prefix “tri-“ means that there are 3 phosphate groups attached to
the molecule of adenosine.)
 Cells get energy from ATP by breaking the bond between the last two
phosphate groups. This ends up forming a new molecule, called ADP
(adenosine diphosphate – the prefix “di-“ means “2”)
Does the formula look familiar? It should! The reactants of Cellular Respiration are the products of
photosynthesis.
C6H12O6 + O2 → H2O + CO2 + ATP
oxygen
glucose
Carbon dioxide
water
Reactants (what you begin with)
energy
Products (what you end with)
The reactions/steps of cellular respiration can be classified as either aerobic or anaerobic.
 Aerobic reactions require a sufficient amount of O2 (oxygen) to occur.
 Anaerobic reactions can occur without oxygen being or they occur when O2 supply is low.
Cellular Respiration has 3 steps or stages:
1. Glycolysis
2. Kreb’s cycle (aka the Citric Acid Cycle)
3. Electron Transport Chain (referred to as the ETC from here on)
Glycolysis
 Glyco-“ means glucose
 “-lysis” means to break down or split
 Glycolysis occurs in the cytoplasm of the cell and is an anerobic reaction, meaning it does not require O2 to be
present in order to occur.
 Glycolysis is always the first step of cellular respiration regardless of the amount of O 2 present.
 The cells take one glucose molecules and splits it to form 2 pyruvate molecules through a series of reactions.
In order to do this, the cell must use 2 molecules of ATP.
GLUCOSE
ATP
ATP
PYRUVATE
ATP
ATP
the net ATP gain for glycolysis is 2 ATP
2 molecules were used to create 4 molecules, so (-2)+4 = 2 ATP
PYRUVATE
ATP
ATP
NADH
NADH
NADH is an
electron carrier that
goes to the ETC
The Krebs Cycle aka the Citric Acid Cycle
 The Krebs cycle occurs inside the mitochondrion and is an aerobic process, therefore O2 must be present and
the supply must be sufficient in order for it to occur.
 Before cellular respiration can continue, the pyruvate product from glycolysis must be changed into acetyl
coenzyme, acetyl coA for short.
 The Krebs cycle produces 4 ATP molecules and more electrons carriers (NADH and FADH2)
The Electron Transport Chain
 The ETC produces the most ATP out of all of the steps - ~28-36 ATP molecules
 The ETC occurs inside of the mitochondrion and is an aerobic process.
 To generate ATP, the ETC uses electrons to create a concentration gradient to power an enzyme called ATP
Synthase. This enzyme synthesizes ATP.
 How does it happen?
o A concentration gradient is created using electron carriers like NADH and FADH2 to make one side of
the membrane more negative than the other. Then ions flow from high to low concentration through
ATP synthase. This causes ATP synthase to spin, generating ATP.
Carbon Cycle
 aka the Carbon/Oxygen Cycle
 Carbon and Oxygen cycle through photosynthesis and cellular respiration.
 Carbon dioxide can enter the atmosphere through the burning/combustion of fossil fuels such as coal, oil, and
natural gas.
CO2 in the
atmosphere
Photosynthesis
O2 in the
atmosphere
Cellular Respiration
Cellular Respiration
C6H12O6
(glucose)
Energy Flow through an Ecosystem
 A food chain is a linear model show energy flow from one organism to the next; it is the simplest
representation of energy flow.
 Energy flow is represented by arrows →
 The image to the right is an example of a food
chain.
o The grass is a producer, also known as an
autotroph. This means that they do not
rely on other organisms as an energy
source; they make their own food
(glucose) through photosynthesis.
 This is where carbon enters the food chain/web
o The grasshopper, mouse, and owl are examples of a consumer. Consumers depend on other
organisms to obtain energy/food; they cannot make their own food. Consumers are also known as
heterotrophs.
 We can also classify the organisms based on their
trophic level, which is an organism’s place/ranking in a
food chain/food web/energy pyramid.
o Producer
o Primary consumer (1st, eats the producer)
o Secondary consumer (2nd, eats the primary consumer)
o Tertiary consumer (3rd, eats the secondary consumer)
 A food pyramid is another way to show energy flow and represents the various trophic levels and the energy
transfer between them well.
o The amount of energy passed
10.000 kcal
between trophic levels follows what
10%
12.875 kcal
we call the 10% Rule, meaning that
tertiary consumer
only 10% of energy is passed to the
next trophic level. The other 90% of
100.00 kcal
10%
energy is lost as heat and is
secondary consumer
128.75 kcal
spent/used by the organism during
metabolic processes (essentially, the
1,000.0 kcal
processes performed by the
primary
consumer
10%
cells/organism to stay alive).
1,287.5 kcal
o How do I figure out how much
energy goes to the next level? >
10,000 kcal
producer
multiple by 0.10 OR move the
12,875 kcal
decimal place over one place to the
left.
 A food web is multiple interesting food chains. Food
webs are far more complex and realistic than food
chains because they do not limit an organism to just
one food source. It also shows the biodiversity
(variety of life) within an ecosystem.
Below are examples of how complex food webs can be.