Download Photosynthesis notes

Chapter 6
“Biochemical Pathways used to
Harvest Energy” in plants
AKA - Photosynthesis
Q: What do you
call this flower?
Pathway 1: Photosynthesis
Main Purpose:
Convert energy in sunlight into stored
organic compounds (mainly sugars)
* Remember: all energy on planet ultimately
comes from sun
Formula for Photosynthesis:
6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2
Q: Why do plants & animals depend on each
other?
Well, look at formula for photosynthesis:
6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2
If you reverse it, it is the formula for cellular
respiration (what animals do), so:
1.Plants need animals for CO2
2. Animals need plants for O2 and food
Q: Do plants undergo cellular respiration or
just photosynthesis?
A: Plants do both.
- They are producers (autotrophs) and
make sugars from CO2 in the atmosphere
- They have to break down the sugar into
ATP (cell fuel) to run cell activities just like
consumers (heterotrophs – organisms that
can't make their own food)
Autotroph or Heterotroph?
Relationship
between
autotrophs
(plants) and
heterotrophs
How does photosynthesis work?
- occurs in chloroplasts
- each chloroplast contains proteins called
pigments that absorb different wavelengths
of light
- Main pigment is chlorophyll
* Chlorophyll absorbs all colors except
green which is reflected (making leaf
look green)
Chlorophyll
in chloroplast
absorbs all
light
wavelengths
except green
Q: Not all leaves are green, why?
A: Leaves have accessory pigments
(like carotenes which are red-orange) that
absorb different wavelengths of light
- In fall, leaves stop producing
chlorophyll because there isn't enough
light or heat for photosynthesis so
accessory pigments show through
(turning leaves red and yellow)
Photosynthesis happens in 2 stages:
Stage 1: Light reactions
- energy is absorbed from sunlight &
converted into chemical energy (ATP and
NADPH)
Stage 2:Calvin Cycle
- CO2 and chemical energy (ATP and
NADPH) are used to make simple sugars
Light reactions and Calvin Cycle in
Chloroplast
Plants use simple sugars to make
complex macromolecules like:
- Carbohydrates
- Lipids
- Proteins
- Nucleic Acid
But all of the carbon ultimately came from
CO2 gas in the atmosphere!
What affects the rate of photosynthesis?
A. Temperature: warmer temps speed
photosynthesis up
B. Light intensity: more intense light
speeds photosynthesis up .... to a point
- if it gets too bright plant can't keep up
& may die
Effect of light and temp on
photosynthesis