Transcript Photosynthesis and Cellular Respiration

Photosynthesis and
Cellular Respiration
How do cells obtain organic
compounds for energy?


Heterotrophs: Cannot make their own food
Autotrophs: Can make their own food
–
Photoautotrophs: Use energy from the sun
(photosynthesis) to produce organic compounds
(glucose)

–
Plants, algae and some bacteria
Chemoautotrophs: Use energy stored in inorganic
compounds (chemosynthesis) to produce organic
compounds

Some bacteria found at the hydrothermal vents of the seafloor
Photosynthesis

Method of converting light energy from the sun
into chemical energy that cells can use
–

Divided into the light-dependent and light-independent
reactions
Photosynthesis takes place in chloroplasts
–
The parts of a chloroplast are as follows:
 Thylakoids- disk-shaped structures that contain the
pigment chlorophyll (absorbs the sunlight)
 Grana- A stack of thylakoids
 Stroma- Liquid between grana
Draw a Chloroplast
Overall Photosynthesis Reaction
6CO2 + 6 H2O + light energy → C6H12O6 + 6O2
•On
the left of the arrow are the reactants (the
components that “react” together).
•On the right of the arrow are the products.
•Identify how a plant obtains the reactants.
Light-dependent Reactions

Chlorophyll (in thylakoids) absorbs the light
energy
–



Plants have 2 types: Chlorophyll A and
Chlorophyll B
Water molecules are split apart producing H and
O2
Electrons flow throughout the thylakoid
membrane (electron transport chain)
Energy compounds ATP and NADPH are
produced
Light-independent Reactions (Dark
Reactions)




Occur in the stroma
ATP and NADPH from the light reactions are
used to fuel the break down of CO2 and the
reassembling of the atoms to produce glucose.
This reassembling is called “carbon fixation”.
Carbon fixation occurs in a series of reactions
called the Calvin Cycle.
Harvesting Chemical Energy




So we see how energy enters food chains (via
autotrophs) we can look at how organisms use
that energy to fuel their bodies.
Plants and animals both use products of
photosynthesis (glucose) for metabolic fuel
Heterotrophs: must take in energy from outside
sources, cannot make their own e.g. animals
When we take in glucose (or other carbs),
proteins, and fats-these foods don’t come to
us the way our cells can use them
Cellular Respiration Overview



Transformation of chemical energy in food into
chemical energy cells can use: ATP
These reactions proceed the same way in plants
and animals. Process is called cellular
respiration
Overall Reaction:
–
C6H12O6 + 6O2 → 6CO2 + 6H2O
Cellular Respiration Overview


Breakdown of glucose begins in the cytoplasm:
the liquid matrix inside the cell
At this point life diverges into two forms and two
pathways
–
–
Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration
C.R. Reactions

Glycolysis
–
–
–
–
Series of reactions which break the 6-carbon glucose
molecule down into two 3-carbon molecules called
pyruvate
Process is an ancient one-all organisms from simple
bacteria to humans perform it the same way
Yields 2 ATP molecules for every one glucose
molecule broken down
Yields 2 NADH per glucose molecule
Anaerobic Cellular Respiration

Some organisms thrive in environments with little or no
oxygen
–



Marshes, bogs, gut of animals, sewage treatment ponds
No oxygen used= ‘an’aerobic
Results in no more ATP, final steps in these pathways
serve ONLY to regenerate NAD+ so it can return to pick
up more electrons and hydrogens in glycolysis.
End products such as ethanol and CO2 (single cell fungi
(yeast) in beer/bread) or lactic acid (muscle cells)
Aerobic Cellular Respiration


Oxygen required=aerobic
2 more sets of reactions which occur in a
specialized structure within the cell called the
mitochondria
–
–
1. Kreb’s Cycle
2. Electron Transport Chain
Kreb’s Cycle

Completes the breakdown of glucose
–
–

Takes the pyruvate (3-carbons) and breaks it down,
the carbon and oxygen atoms end up in CO2 and H2O
Hydrogens and electrons are stripped and loaded onto
NAD+ and FAD to produce NADH and FADH2
Production of only 2 more ATP but loads up
the coenzymes with H+ and electrons which
move to the 3rd stage
Electron Transport Chain



Electron carriers loaded with electrons and
protons from the Kreb’s cycle move to this chainlike a series of steps (staircase).
As electrons drop down stairs, energy released
to form a total of 32 ATP
Oxygen waits at bottom of staircase, picks up
electrons and protons and in doing so becomes
water
Energy Tally


36 ATP for aerobic vs. 2 ATP for anaerobic
–
Glycolysis
2 ATP
–
Kreb’s
2 ATP
–
Electron Transport
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon