Download Unit Two “Energy Acquisition”

Unit Two
“Energy Acquisition”
“Photosynthesis”
The Sun and Plants
What makes life possible on Earth is the
presence of a medium sized star, the Sun
 Also, just as important is the fact the
Earth is at a near perfect distance from
the sun: “not too hot, and not too cold”
 However, animals like us humans still
could not survive for any length of time
without plants to convert light energy into
biomass, i.e. food for us!

The Sun and Plants
Plants are called producers/autotrophs
because they, in essence, make their own
food by using sunlight and other chemical
compounds found in nature (note: some
algae and bacteria also make their own
food)
 The food they make enables them to grow
(addition of biomass)….. and they do not
ever consume other living organisms in
the process
 Because of this food generating ability,
they are placed at the bottom of the food
chain….all other species depend on them
for survival

Photosynthesis
The process by which plants generate food
(Glucose) for their cells is called
“Photosynthesis”
 There are 3 main stages of
Photosynthesis:
A) Capturing energy from sunlight
B) Using that energy to make ATP and
NADPH (Light Dependent
Reactions)
C) Using ATP and NADPH to make
Carbohydrates (Calvin Cycle)

Chemical Reaction for Photosynthesis
 carbon
dioxide + water + light
energy ---> glucose + oxygen +
water
 CO2
+ H2O + light energy --->
C6H12O6 + O2 + H2O
Photosynthetic Structures
 The
Chloroplast is the light
sequestering organelle, and is also the
site of all three stages of
Photosynthesis
 The Chloroplast is composed of internal
membranes that are organized into
flattened sacs called “Thylakoids”
 These Thylakoids are stacked on top of
each other in columns called “Grana”
 A fluid called the “Stroma” surrounds
the stacks of Thylakoids
Photosynthetic Structures
 The
light sequestering pigment,
Chlorophyll, is located within the
Thylakoids in groups called
“Photosystems”
 The Photosystem is the starting point of
Photosynthesis
 The Chlorophyll captures “Photons”,
tiny packets of energy from sunlight,
which they subsequently transfer to
proteins that assist in the generation of
ATP and NADPH
Sunlight’s Energy
 It
is very fortunate the Chlorophyll
in the Chloroplasts of plants is
perfectly suited to the energy levels
found in visible light that comes from
the sun
 Further, there are many energy
sources like radio waves, gamma
rays, microwaves, but each either
has too little energy or too much
energy to be compatible with plants
energy harnessing system
The Electromagnetic Spectrum
Chlorophyll Absorption



The leaves of plants are usually green due to
the fact Chlorophyll absorbs light in the
violet, blue, and red range of the spectrum
Chlorophyll reflects the green portion of the
visible spectrum, and therefore the leaves
take on a characteristic green appearance
“Carotenoids” are a group of
accessory pigments that capture
violet to blue-green light and
reflect yellow, orange, & red
Photosynthesis: Stage 1
 A)
Capturing energy from sunlight
– A photon of light in the appropriate
wavelength is sequestered by a
chlorophyll molecule and this energy is
passed to another chlorophyll molecule
Photosynthesis: Stage 2
(exergonic)
 B)
Using energy to make ATP and
NADPH (Light Dependent Reactions)
1. the energy from excited electrons
taken from water is used in the
“Electron Transport System” to pump
Hydrogen Ions (protons) across the
Thylakoid membrane
2. Many Hydrogen Ions (protons)
accumulate in the Thylakoid serving as
the energy source to construct ATP
molecules from ADP molecules
Photosynthesis: Stage 2
(exergonic)
3. The electron from water that had its
energy used in the Electron Transport
System is now directed to another
photosystem to be reenergized by the
absorption of another photon of light
4. This electron enters another Electron
Transport System and is transferred to
NADP+
5. NADP+ bonds with a Hydrogen Ion
(proton) to form NADPH, which is
important in stage 3 production of
carbohydrates
Light Dependent Reactions
Photosynthesis: Stage 3
(endergonic)
C) Using ATP and NADPH to make
Carbohydrates (Calvin Cycle)
1. ATP generated in Stage 2 (Light
Dependent Reactions) is used as the
fuel
for the Calvin Cycle
2. NADPH generated in Stage 2
provides the Hydrogens needed to
build Glucose
3. Numerous proteins acting as
enzymes drive the production of
Glucose
Photosynthesis: Stage 3
(endergonic)
4. The Calvin Cycle has to go to
completion six times in order to produce
one Glucose molecule: each cycle
completion adds just one Carbon atom
from CO2 to make the Glucose molecule,
which has 6 Carbon atoms
5. To keep both Stage 2 and Stage 3
functioning, used ADP and NADP+ from
the Calvin Cycle is returned to the
Electron Transport System in the
photosystems
Calvin Cycle
Photorespiration
 During
extreme environmental
conditions (hot and dry), plants close
their “Stomata” to reduce water loss
 Once their stomata are closed they no
longer absorb Carbon Dioxide, and
therefore the Oxygen that is usually
released as a byproduct of
photosynthesis, is incorporated into the
Calvin Cycle causing it to “short circuit”
 Some plants use C4 Photosynthesis
(use of different cells and chemical
reactions) during hot, dry days in order
to continue to photosynthesize
Photosynthesis Overview
 http://vcell.ndsu.nodak.edu/animatio
ns/photosynthesis/movie.htm
 https://www.youtube.com/watch?v=
sQK3Yr4Sc_k