Department of Cell Biology & Molecular Genetics
Photosynthesis, Respiration, and the Carbon Cycle
I. What is photosynthesis?
A. Photosynthesis:
captured light energy is transformed into chemical energy (stored as sugar).
An energy requiring process.
Net equation:
chlorophyll
6CO2
+ 6H2O +energy as light------------------------------->
C6H12O6 + 6O2
1. Carbon dioxide is the carbon source
2. Light energy is the energy source
3. Releases oxygen
B. Plants,
algae, and cyanobacteria.
II. What is light?
A. Sunlight
is electromagnetic energy, also called radiation.
B. Electromagnetic
spectrum: gamma rays to radio waves
C. Electromagnetic
energy travels through the air in rhythmic waves.
D. When these
waves interact with matter, which is anything that occupies space and has
mass, they behave as particles of energy called
photons.
1. The shorter the wavelength the greater the energy
E. Visible
light = 400 to 700nm. Region used to drive photosynthesis and the
same region humans see.
III. Chloroplasts
A. Sites of
photosynthesis in plants.
B. Found in
mesophyll cells (specifically the palisade mesophyll cells).
C. Chloroplast
structure:
1. Thylakoids and Grana
2. Stroma
D. Pigments
absorb light
1. Only light that is absorbed can produce a biological effect in an object.
2. Pigments: substances that absorb light
3. Two primary pigments in plant chloroplasts:
a) Chlorophyll a
b) Chlorophyll b
4. Minor pigments: carotenoids
5. Absorption spectrum
6. Action spectrum
E. What colors
are the most and least effective for driving photosynthesis?
IV. How photosynthesis actually works
A. It occurs
in two stages:
1. Light reactions: light dependent reactions
2. Dark reactions: light independent reactions or Calvin cycle
B. Light reactions
1. Occurs in the thylakoid membranes
2. Two high energy compounds are made: NADPH and ATP
3. Oxygen is made. (from the splitting of water)
C. Dark reactions
1. occurs in the stroma
2. uses light reaction products and carbon dioxide to make sugar (process
called carbon fixation).
3. reactions are controlled by enzymes.
V. Respiration
A. Respiration:
sugars (chemical energy) are broken down to obtain the energy they contain.
An energy releasing process.
C6H12O6 + 6O2 ----------------------------> 6CO2 + 6H2O + heat + energy (as ATP)
B. Occurs in
the cytosol and mitochondria.
C. All organisms
respire!
VI. Energy is linear
A. Chemical
elements are recycled, but energy is not.
B. Food chains
demonstrate the linear nature of energy.
1. Producers (autotrophic)
2. Primary consumers (heterotrophic)
3. Secondary consumers (heterotrophic)
4. Decomposers (heterotrophic)
VII. Carbon Cycle
A. Carbon
itself is recyclable. CO2 in air converted into organic compounds
by photosynthesis in plants, using light energy. Energy and
carbon in organic compounds passed through food chain to herbivores and
carnivores. Organic compounds converted back to CO2 by
respiration in plants, animals, and microbes in soil.