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CLASS NOTES
CHAPTER 8 – PHOTOSYNTHESIS
ENERGY & LIFE
1. Life requires energy.
2. The sun is the source of energy.
3. Energy can change from one form to another.
 Examples: light, heat, electrical, chemical
4. Chlorophyll (chloroplasts) in green plants traps the sun’s energy and
converts it into chemical energy (stored in bonds of glucose
molecules) for use by all living things.
OBTAINING ENERGY
1. autotroph (producer)– an organism that is able to use light energy
from the sun to produce food
 “auto-“ means “self”
 “troph” means “to eat”
example: plants, algae, some bacteria
2. heterotroph (consumer) – an organism that obtains energy from the
other organisms
 “hetero-“ means “other”
example: animals
ENERGY
1. The activities of the cell are powered by chemical fuels.
2. ATP (adenosine triphosphate)
 “energy molecule”
 one of the principal chemical compounds that living
organisms use to store energy
 composed of:
a. adenine – nitrogen containing compound
b. ribose – a sugar with 5 carbon molecules
c. three phosphate groups
3. ADP (adenosine diphosphate)
 has a structure similar to ATP but it only has 2 phosphate
groups
4. Releasing energy from ATP
 Energy is released when the P-P bond is broken
 ATP  ADP + P + energy released
5. Storing energy in ADP
 Energy is stored when an additional P (phosphate group) is
added to ADP
 ADP + P + energy added  ATP
6. Electron transport chain
 Series of protein channels in membranes that pumps out H+
then slowly lets them back in through a protein channel. The
back leak of H+ provides energy to add a phosphate (P) to
ADP to form ATP
 NADPH is the electron carrier used in photosynthesis
7. Using Biochemical energy
 ATP provides energy to move ions across the cell membrane
(active transport)
 ATP provides energy for movement within the cell
 ATP provides energy for the production and processing of
proteins
8. ATP and Glucose
 ATP lasts for only a few seconds so it’s not efficient in
storing large amounts of energy for long periods of time
 Glucose (sugar) stores more than 90 times the chemical
energy as a molecule of ATP
 Therefore, it is more efficient for cells to keep only a small
supply of ATP. Cells can produce ATP from ADP by
breaking down glucose.
PHOTOSYNTHESIS
sunlight
carbon dioxide + water
glucose (sugar) + oxygen
chlorophyll
Chloroplast
 pigment – light absorbing molecule that absorbs the energy from the
sun
 chlorophyll is the main pigment in plants
1. there are 2 types – chlorophyll a and chlorophyll b
 chlorophyll appears green because it reflects the green wavelength
of light
 carotene –plant pigment that appears red and orange
 leaves appear green in the spring and summer because of active
photosynthesis
 during the fall photosynthesis slows down, chlorophyll decreases and
leaves appear red, orange and yellow due to the carotenes
 contains saclike membranes called thylakoids
 thylakoids are arranged in stacks called grana
 stroma – liquid like material found in the space of the chloroplast
Composed of 2 parts:
 Light Reaction
 Calvin Cycle (Light independent Reaction)
Light Reaction
 occurs in thylakoid membrane of chloroplast
 Sunlight is trapped by chlorophyll
 energy from the sun is stored in ATP
 water is split and oxygen is released. Hydrogen is used in the
Calvin Cycle
 Electron transport chain- NADPH is formed. NADPH provides
energy to make sugar in the Calvin cycle
Calvin cycle (Light independent Reaction)
 Does not need light
 Occurs in stroma of chloroplast
 Carbon dioxide enters from the atmosphere
 Carbon from carbon dioxide is “fixed” (turned into) glucose.
 Sugar is released