UNIT 10
Energy & Light
PHOTOSYNTHESIS
CELLULAR RESPIRATION
Section 6-1 Light Energy
Sun is the source of all energy on earth.
All organisms use energy to function/live.
Organisms that get their energy directly from the Sun are
AUTOTROPHS.
Autotrophs convert light energy from the Sun into chemical energy
they can use.
The biochemical pathway that converts light to chemical energy is
called photosynthesis.
Autotrophs store extra chemical energy as carbohydrates (starch).
Examples: corn, peas, maple trees, some algae and bacteria
Photosynthesis
Chemical equation that sums up all the steps of the
biochemical pathway for photosynthesis:
6 CO2 + 6 H2O
6(carbon dioxide) + 6 (water)
C6H12O6 + 6O2
(light energy)
1 (glucose)
+
6 (oxygen)
The organelle in plant cells where photosynthesis
takes place is the Chloroplast
Light energy from the Sun
Autotrophs convert into
chemical energy in the
chloroplast
Stored as carbohydrates
Eaten by heterotrophs for
energy
Chloroplast Structure
Double membrane around
outside
Disc-shaped thylakoids contain
pigments that absorb light
Stack of thylakoids is called a
granum
Primary pigment=
chlorophyll that absorbs light
energy from the sun
Stages of Photosynthesis
There are three stages in the photosynthesis pathway:
Stage 1 = Light-Dependent Reactions (thylakoids)
light energy is used to split water into
hydrogen ions, electrons and oxygen
Stage 2 = Energy Conversion (stroma)
light energy converted to chemical energy
stored in ATP and NADPH (chemical batteries for energy)
Stage 3 = Calvin Cycle (stroma)
ATP and NADPH stored energy is used to form glucose
in a step known as carbon fixation
Alternative pathways - CAM
plants
CAM plants use another
pathway to fix carbon
CAM plants keep their stoma
closed during the day and only
open them at night (this is the
opposite of what most plants
do)
CAM plants take in CO2 at night
and make sugars during the
day
CELLULAR
RESPIRATION
UNIT 10
LIGHT AND ENERGY
Glycolysis and Fermentation
Cellular Respiration
All plant and animal cells break down complex organic molecules into
simpler molecules and release energy used to make ATP from ADP
and phosphate.
Glycolysis:
takes place in cytosol of the cell
the first chemical pathway
has four steps
produces small amount of ATP
other products can travel either
of two pathways
With Oxygen = Aerobic Respiration
•produces Largest amount of ATP
Without Oxygen = Fermentation
•produces NO ATP
GLYCOLYSIS
Takes place in the cytosol of the cell
4-step process
Uses 2 ATP molecules in Step 1
Produces 4 ATP molecules in Step 3
Net yield of 2 ATP molecules
One molecule of glucose is converted
to two 3-carbon molecules of pyruvic acid
 Most reactions are REDOX – one reactant is oxidized
while one is reduced
AEROBIC OR ANEROBIC RESPIRATION?
If oxygen level is normal 2 pyruvic acid molecules
move to AEROBIC RESPIRATION
If oxygen level is low or absent 2 pyruvic acid molecules move to
ANAEROBIC RESPIRATION (FERMENTATION)
FERMENTATION
Absence of oxygen causes pyruvic acid to be converted
to other organic molecules. ATP IS NOT PRODUCED.
Two types of fermentation:
LACTIC ACID FERMENTATION
ALCOHOLIC FERMENTATION
LACTIC ACID product is lactic acid
produces cheese and yogurt
in muscle cells (burn)
ALCOHOLIC products are alcohol and CO2
produces bread, pizza dough
produces wines, beer
in yeast cells
MEASURING ENERGY
•Energy is Measured in units of kilocalories (kcal).
•One kilocalorie EQUALS 1,000 calories (cal).
•One calorie equals the quantity of thermal energy
required
to raise the temperature of one gram of water 1°C at 15°C.
•Calories are also measurements of how much energy is
available from the foods you eat.
Kcal are used to measure efficiency of glycolysis.
Efficiency = Energy required to make ATP
Energy released by glucose oxidation