Photosynthesis and Cellular
Respiration
Objectives Section 1
1. I can explain in detail the flow of energy
through living systems
2. I can compare the chemical processes of
autotrophs and heterotrophs
3. I can describe the role of ATP in
metabolism
4. I can describe how energy is released by
ATP.
Metabolism
Metabolism: all of the chemical reactions
that take place within an organism
• Metabolic pathways alter molecules in a
series of steps.
• Enzymes selectively accelerate each step.
– enzymes are regulated to maintain a balance
of supply and demand.
• Catabolic reactions give off energy by
breaking down complicated molecules to
simpler compounds.
• Anabolic reactions use energy to build
complicated molecules from simpler
compounds.
• The energy released by catabolic
pathways is used to drive anabolic
pathways.
Autotrophs vs Heterotrophs
• Autotrophs make their own food through
anabolic reactions
– Many autotrophs carry out photosynthesis
• Heterotrophs can not make their own food
– Heterotrophs must eat other organisms to
obtain energy from food through catabolic
reactions
– Heterotrophs utilize cellular respiration
ATP
• ATP powers cellular work
• A cell does three main kinds of work:
– Mechanical work, beating of cilia, contraction of
muscle cells, and movement of chromosomes
– Transport work, pumping substances across
membranes against the direction of spontaneous
movement
– Chemical work, driving endergonic reactions such as
the synthesis of polymers from monomers
• ATP (adenosine triphosphate) is a type of
nucleotide consisting of the nitrogenous
base adenine, the sugar ribose, and a chain
of three phosphate groups.
• The bonds between phosphate groups can
be broken by hydrolysis.
So what?
• Energy is stored in these bonds.
• So?
• The breaking of the chemical bond
releases the energy
ATP + H2O→ ADP + P + ENERGY
Cellular Respiration
• The process by which mitochondria break
down glucose to make ATP
• In order for our bodies to use the energy,
the food must be broken down into a
usable form
– What is the usable form of energy?
– What type of process breaks down
molecules?
Objectives Section 3
(yes, we skipped to section 3, for now)
• I can summarize how glucose is broken
down in glycolysis.
• I can describe how ATP is made in cellular
respiration.
• I can identify the role of fermentation in
cellular respiration.
• I can evaluate the importance of oxygen in
aerobic respiration.
Overall Reaction
C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP
• Overall this is a three stage process
1. Glycolysis:
•
•
Occurs in the cytoplasm
Glucose is broken down
2. Krebs Cycle
•
•
Breaks down pyruvate into CO2
Occurs in mitochondrial matrix
3. Electron Transport Chain
•
ATP is synthesized
Glycolysis
• Glyco = glucose
Lysis = break down
• Occurs in the cytoplasm
• This stage occurs in BOTH aerobic and
anaerobic respiration
• Glucose breaks down into 2 pyruvate (2 ATP are
also made)
– Glucose is a 6-carbon sugar
– Pyruvate is a 3-carbon molecule (there are
two of them)
– See diagram on simple explanation handout
Glycolysis Reactants and Products
Reactants
• 1 glucose
• Enzymes are needed
• 2 ATP are needed to
start
Products
• 2 Pyruvates (go to
next step)
• 4 ATP (2 are gained)
• 2 NADH (go to ETC)
Intermediate step
• Pyruvate is converted to acetyl CoA
• Occurs in the cytoplasm
• See diagram on simple explanation
handout
Intermediate step Reactants and products
Reactants
• 2 pyruvate (from
glycolysis)
Products
• 2 Acetyl CoA (go to
next step)
• 2 CO2 (given off as
waste)
• 2 NADH (go to ETC)
Krebs Cycle (Citric Acid Cycle)
• Occurs in the matrix of mitochondria
• A series of reactions occur (this is not just
one step)
• Main purpose is to generate electrons for
use in ETC
• 2 ATP is given off
• See diagram on simple explanation
handout
Krebs Cycle Reactants and Products
Reactants
• 2 Acetyl CoA
•
•
•
•
Products
2 ATP
6 NADH (go to ETC)
2 FADH2 (go to ETC)
4 CO2 (given off as
waste)
Electron Transport Chain
• Occurs in inner membrane of mitochondria
• Series (chain) of coupled redox reactions
(electrons are transported through the
chain)
• Electrons carried to this step by NADH
and FADH2 (produced in previous steps)
• Oxygen is used in this step
• Water is given off
Electron Transport Chain Reactants
and Products
Reactants
• 10 NADH
• 2 FADH2
• Oxygen
Products
• 34 ATP
• H2O
Where do we get 38 ATP?
• 2 ATP made in glycolysis
• 2 ATP made in Krebs Cycle
• 34 ATP made in ETC
– 1 NADH = 3 ATP
o 10 X 3 = 30
– 1 FADH2 = 2 ATP
o2 X 2 = 4
Anaerobic Respiration
(Fermentation)
• Glycolysis
• Yields 2 pyruvate and 2 ATP
• With no oxygen present, cellular
respiration does not occur
• ONLY 2 ATP ARE PRODUCED (compare
to aerobic respiration)
Two Types of Fermentation
Alcoholic Fermentation
• Pyruvate converted to
ethyl alcohol and CO2
• Carried out by yeast
and some bacteria
• Used in producing
alcohol (both
consumable and for
ethanol), and for
baking
Lactic Acid
Fermentation
• Pyruvate converted to
lactic acid
• Carried out by
muscles when
working hard
(muscles need ATP
but can’t get O2 )
• Causes muscle
soreness and cramps
Photosynthesis
• Carried out by most (not all) autotrophs
• 6CO2 + 6H2O + light energy→ C6H12O6 + 6O2
• Basically this reaction is the OPPOSITE of
cellular respiration
• See simple explanation handout and text
Steps of Photosynthesis
1. Light reaction (depends on light)
•
•
•
Traps sunlight
Produces electrons and ATP required to
power the dark reaction
Oxygen given off here
2. Dark reaction, aka Calvin Cycle (does not
directly depend on light)
•
Uses ATP and electrons from light reaction
and CO2 to make glucose
See diagram on simple explanation handout